Ptolemy

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Ptolemy 

Ptolemy
Κλαύδιος Πτολεμαῖος
Ptolemy "the Alexandrian", as depicted in a 16th-century engraving.
Born	c. 100 AD Egypt, Roman Empire
Died	c. 170 (aged 69–70) AD Alexandria, Egypt, Roman Empire
Citizenship	Roman; ethnicity: Greco-Egyptian
Known for	Ptolemaic universe Ptolemy's world map Ptolemy's intense diatonic scale Ptolemy's table of chords Ptolemy's inequality Ptolemy's theorem Equant Evection Quadrant
Scientific career
Fields	Astronomy, Geography, Astrology, Optics
Influences	Aristotle Hipparchus
Influenced	Theon of Alexandria Abu Ma'shar Nicolaus Copernicus

Claudius Ptolemy (/ˈtɒləmi/; Greek: Πτολεμαῖος, Ptolemaios; Latin: Claudius Ptolemaeus; c. 100 – c. 170 AD) was a mathematician, astronomer, astrologer, geographer, and music theorist, who wrote about a dozen scientific treatises, three of which were of importance to later Byzantine, Islamic, and Western European science. The first is the astronomical treatise now known as the Almagest, although it was originally entitled the Mathēmatikē Syntaxis or Mathematical Treatise, and later known as The Greatest Treatise. The second is the Geography, which is a thorough discussion on maps and the geographic knowledge of the Greco-Roman world. The third is the astrological treatise in which he attempted to adapt horoscopic astrology to the Aristotelian natural philosophy of his day. This is sometimes known as the Apotelesmatika (lit. "On the Effects") but more commonly known as the Tetrábiblos, from the Koine Greek meaning "Four Books", or by its Latin equivalent Quadripartite.

Unlike most ancient Greek mathematicians, Ptolemy's writings (foremost the Almagest) never ceased to be copied or commented upon, both in Late Antiquity and in the Middle Ages. However, it is likely that only a few truly mastered the mathematics necessary to understand his works, as evidenced particularly by the many abridged and watered-down introductions to Ptolemy's astronomy that were popular among the Arabs and Byzantines alike.

Biography

Ptolemy lived in or around the city of Alexandria, in the Roman province of Egypt under Roman rule, had a Latin name (which several historians have taken to imply he was also a Roman citizen), cited Greek philosophers, and used Babylonian observations and Babylonian lunar theory. In half of his extant works, Ptolemy addresses a certain Syrus, a figure of whom almost nothing is known but who likely shared some of Ptolemy's astronomical interests.

The 14th-century astronomer Theodore Meliteniotes gave his birthplace as the prominent Greek city Ptolemais Hermiou (Πτολεμαΐς Ἑρμείου) in the Thebaid (Θηβᾱΐς). This attestation is quite late, however, and there is no evidence to support it. Ptolemy died in Alexandria around 168.

Naming and nationality

Engraving of a crowned Ptolemy being guided by Urania, from Margarita Philosophica by Gregor Reisch (1508), showing an early confluence between his person and the rulers of Ptolemaic Egypt.

Ptolemy's Greek name, Ptolemaeus (Πτολεμαῖος, Ptolemaîos), is an ancient Greek personal name. It occurs once in Greek mythology and is of Homeric form. It was common among the Macedonian upper class at the time of Alexander the Great and there were several of this name among Alexander's army, one of whom made himself pharaoh in 323 BC: Ptolemy I Soter, the first pharaoh of the Ptolemaic Kingdom. Almost all subsequent pharaohs of Egypt, with a few exceptions, were named Ptolemies until Egypt became a Roman province in 30 BC, ending the Macedonian family's rule.

The name Claudius is a Roman name, belonging to the gens Claudia; the peculiar multipart form of the whole name Claudius Ptolemaeus is a Roman custom, characteristic of Roman citizens. Several historians have made the deduction that this indicates that Ptolemy would have been a Roman citizen. Gerald Toomer, the translator of Ptolemy's Almagest into English, suggests that citizenship was probably granted to one of Ptolemy's ancestors by either the emperor Claudius or the emperor Nero.

The 9th century Persian astronomer Abu Ma'shar al-Balkhi mistakenly presents Ptolemy as a member of Ptolemaic Egypt's royal lineage, stating that the descendants of the Alexandrine general and Pharaoh Ptolemy I Soter were wise "and included Ptolemy the Wise, who composed the book of the Almagest". Abu Ma'shar recorded a belief that a different member of this royal line "composed the book on astrology and attributed it to Ptolemy". We can infer historical confusion on this point from Abu Ma'shar's subsequent remark: "It is sometimes said that the very learned man who wrote the book of astrology also wrote the book of the Almagest. The correct answer is not known." Not much positive evidence is known on the subject of Ptolemy's ancestry, apart from what can be drawn from the details of his name, although modern scholars have concluded that Abu Ma'shar's account is erroneous. It is no longer doubted that the astronomer who wrote the Almagest also wrote the Tetrabiblos as its astrological counterpart. In later Arabic sources, he was often known as "the Upper Egyptian", suggesting he may have had origins in southern Egypt. Arabic astronomers, geographers and physicists referred to his name in Arabic as Baṭlumyus (Arabic: بَطْلُمْيوس).

Ptolemy wrote in ancient Greek and can be shown to have utilized Babylonian astronomical data. He might have been a Roman citizen, but was ethnically either a Greek or at least a Hellenized Egyptian.

Astronomy

Astronomy was the subject to which Ptolemy devoted the most time and effort; about half of all the works that survived deal with astronomical matters, and even others such as the Geography and the Tetrabiblos have significant references to astronomy.

Mathēmatikē Syntaxis

Further information: Almagest

 

Pages from the Almagest in Arabic translation showing astronomical tables.

Ptolemy's Mathēmatikē Syntaxis (Ancient Greek: Μαθηματικὴ Σύνταξις, lit. "Mathematical Systematic Treatise"), better known as the Almagest, is the only surviving comprehensive ancient treatise on astronomy. Although Babylonian astronomers had developed arithmetical techniques for calculating and predicting astronomical phenomena, these were not based on any underlying model of the heavens; early Greek astronomers, on the other hand, provided qualitative geometrical models to "save the appearances" of celestial phenomena without the ability to make any predictions.

The earliest person that attempted to merge these two approaches was Hipparchus, who produced geometric models that not only reflected the arrangement of the planets and stars but could be used to calculate celestial motions. Ptolemy, following Hipparchus, derived each of his geometrical models for the Sun, Moon, and the planets from selected astronomical observations done in the spanning of more than 800 years; however, many astronomers have for centuries suspected that some of his models' parameters were adopted independently of observations.

Ptolemy presented his astronomical models alongside convenient tables, which could be used to compute the future or past position of the planets. The Almagest also contains a star catalogue, which is a version of a catalogue created by Hipparchus. Its list of forty-eight constellations is ancestral to the modern system of constellations but, unlike the modern system, they did not cover the whole sky (only what could be seen with the naked eye). For over a thousand years, the Almagest was the authoritative text on astronomy across Europe, the Middle East, and North Africa, and its author soon became an almost legendary figure: Ptolemy, King of Alexandria.

The Almagest was preserved, like many extant Greek scientific works, in Arabic manuscripts; the modern title is thought to be an Arabic corruption of the Greek name Hē Megistē Syntaxis (lit. "The greatest treatise"), as the work was presumably known in Late Antiquity. Because of its reputation, it was widely sought and translated twice into Latin in the 12th century, once in Sicily and again in Spain. Ptolemy's planetary models, like those of the majority of his predecessors, were geocentric and almost universally accepted until the reappearance of heliocentric models during the scientific revolution.

Handy Tables

The Handy Tables (Ancient Greek: Πρόχειροι κανόνες) are a set of astronomical tables, together with canons for their use. To facilitate astronomical calculations, Ptolemy tabulated all the data needed to compute the positions of the Sun, Moon and planets, the rising and setting of the stars, and eclipses of the Sun and Moon, making it a useful tool for astronomers and astrologers. The tables themselves are known through Theon of Alexandria’s version. Although Ptolemy's Handy Tables do not survive as such in Arabic or in Latin, they represent the prototype of most Arabic and Latin astronomical tables or zījes.

Additionally, the introduction to the Handy Tables survived separately from the tables themselves (apparently part of a gathering of some of Ptolemy's shorter writings) under the title Arrangement and Calculation of the Handy Tables.

Planetary Hypotheses

A depiction of the Ptolemaic Universe as described in the Planetary Hypotheses by Bartolomeu Velho (1568).

The Planetary Hypotheses (Ancient Greek: Ὑποθέσεις τῶν πλανωμένων, lit. "Hypotheses of the Planets") is a cosmological work, probably one of the last written by Ptolemy, in two books dealing with the structure of the universe and the laws that govern celestial motion. Ptolemy goes beyond the mathematical models of the Almagest to present a physical realization of the universe as a set of nested spheres, in which he used the epicycles of his planetary model to compute the dimensions of the universe. He estimated the Sun was at an average distance of 1,210 Earth radii (now known to actually be ~23,450 radii), while the radius of the sphere of the fixed stars was 20,000 times the radius of the Earth.

The work is also notable for having descriptions on how to build instruments to depict the planets and their movements from a geocentric perspective, much like an orrery would have done for a heliocentric one, presumably for didactic purposes.

Other works

The Analemma is a short treatise where Ptolemy provides a method for specifying the location of the sun in three pairs of locally orientated coordinate arcs as a function of the declination of the sun, the terrestrial latitude, and the hour. The key to the approach is to represent the solid configuration in a plane diagram that Ptolemy calls the analemma.

In another work, the Phaseis (Risings of the Fixed Stars), Ptolemy gave a parapegma, a star calendar or almanac, based on the appearances and disappearances of stars over the course of the solar year.

The Planisphaerium (Ancient Greek: Ἅπλωσις ἐπιφανείας σφαίρας, lit. 'Simplification of the Sphere') contains 16 propositions dealing with the projection of the celestial circles onto a plane. The text is lost in Greek (except for a fragment) and survives in Arabic and Latin only.

Ptolemy also erected an inscription in a temple at Canopus, around 146–147 AD, known as the Canobic Inscription. Although the inscription has not survived, someone in the sixth century transcribed it and manuscript copies preserved it through the Middle Ages. It begins: "To the saviour god, Claudius Ptolemy (dedicates) the first principles and models of astronomy," following by a catalogue of numbers that define a system of celestial mechanics governing the motions of the sun, moon, planets, and stars.

Cartography

Main article: Geography (Ptolemy)

Further information: Ptolemy's world map

 

A printed map from the 15th century depicting Ptolemy's description of the Ecumene by Johannes Schnitzer (1482).

Ptolemy's second most well-known work is his Geographike Hyphegesis (Ancient Greek: Γεωγραφικὴ Ὑφήγησις; lit. "Guide to Drawing the Earth"), known as the Geography, a handbook on how to draw maps using geographical coordinates for parts of the Roman world known at the time. He relied on previous work by an earlier geographer, Marinus of Tyre, as well as on gazetteers of the Roman and ancient Persian Empire. He also acknowledged ancient astronomer Hipparchus for having provided the elevation of the north celestial pole for a few cities. Although maps based on scientific principles had been made since the time of Eratosthenes (c. 276–195 BC), Ptolemy improved on map projections.

The first part of the Geography is a discussion of the data and of the methods he used. Ptolemy notes the supremacy of astronomical data over land measurements or travelers' reports, though he possessed these data for only a handful of places. Ptolemy's real innovation, however, occurs in the second part of the book, where he provides a catalogue of 8,000 localities he collected from Marinus and others, the biggest such database from antiquity. About 6,300 of these places and geographic features have assigned coordinates so that they can be placed in a grid that spanned the globe. Latitude was measured from the equator, as it is today, but Ptolemy preferred to express it as climata, the length of the longest day rather than degrees of arc: the length of the midsummer day increases from 12h to 24h as one goes from the equator to the polar circle. One of the places Ptolemy noted specific coordinates for was the now-lost Stone Tower which marked the midpoint on the ancient Silk Road, and which scholars have been trying to locate ever since.

In the third part of the Geography, Ptolemy gives instructions on how to create maps both of the whole inhabited world (oikoumenē) and of the Roman provinces, including the necessary topographic lists, and captions for the maps. His oikoumenē spanned 180 degrees of longitude from the Blessed Islands in the Atlantic Ocean to the middle of China, and about 80 degrees of latitude from Shetland to anti-Meroe (east coast of Africa); Ptolemy was well aware that he knew about only a quarter of the globe, and an erroneous extension of China southward suggests his sources did not reach all the way to the Pacific Ocean.

It seems likely that the topographical tables in the second part of the work (Books 2–7) are cumulative texts, which were altered as new knowledge became available in the centuries after Ptolemy. This means that information contained in different parts of the Geography is likely to be of different dates, in addition to containing many scribal errors. However, although the regional and world maps in surviving manuscripts date from c. 1300 AD (after the text was rediscovered by Maximus Planudes), there are some scholars who think that such maps go back to Ptolemy himself.

Astrology

Main article: Tetrabiblos

 

A copy of the Quadripartitum (1622)

Ptolemy wrote an astrological treatise, in four parts, known by the Greek term Tetrabiblos (lit. "Four Books") or by its Latin equivalent Quadripartitum. Its original title is unknown, but may have been a term found in some Greek manuscripts, Apotelesmatiká (biblía), roughly meaning "(books) on the Effects" or "Outcomes", or "Prognostics". As a source of reference, the Tetrabiblos is said to have "enjoyed almost the authority of a Bible among the astrological writers of a thousand years or more". It was first translated from Arabic into Latin by Plato of Tivoli (Tiburtinus) in 1138, while he was in Spain.

Much of the content of the Tetrabiblos was collected from earlier sources; Ptolemy's achievement was to order his material in a systematic way, showing how the subject could, in his view, be rationalized. It is, indeed, presented as the second part of the study of astronomy of which the Almagest was the first, concerned with the influences of the celestial bodies in the sublunary sphere. Thus explanations of a sort are provided for the astrological effects of the planets, based upon their combined effects of heating, cooling, moistening, and drying. Ptolemy dismisses other astrological practices, such as considering the numerological significance of names, that he believed to be without sound basis, and leaves out popular topics, such as electional astrology (interpreting astrological charts to determine courses of action) and medical astrology, for similar reasons.

The great popularity that the Tetrabiblos did possess might be attributed to its nature as an exposition of the art of astrology, and as a compendium of astrological lore, rather than as a manual. It speaks in general terms, avoiding illustrations and details of practice.

A collection of one hundred aphorisms about astrology called the Centiloquium, ascribed to Ptolemy, was widely reproduced and commented on by Arabic, Latin, and Hebrew scholars, and often bound together in medieval manuscripts after the Tetrabiblos as a kind of summation. It is now believed to be a much later pseudepigraphical composition. The identity and date of the actual author of the work, referred to now as Pseudo-Ptolemy, remains the subject of conjecture.

Music

A diagram showing Pythagorean tuning

 

See also: Ptolemy's intense diatonic scale

Ptolemy wrote an earlier work entitled Harmonikon (Ancient Greek: Ἁρμονικόν), known as the Harmonics, on music theory and the mathematics behind musical scales in three books. It begins with a definition of harmonic theory, with a long exposition on the relationship between reason and sense perception in corroborating theoretical assumptions. After criticizing the approaches of his predecessors, Ptolemy argues for basing musical intervals on mathematical ratios (in contrast to the followers of Aristoxenus), backed up by empirical observation (in contrast to the overly theoretical approach of the Pythagoreans).

Ptolemy introduces the harmonic canon, an experimental apparatus that would be used for the demonstrations in the next chapters, then proceeds to discuss Pythagorean tuning. Pythagoreans believed that the mathematics of music should be based on the specific ratio of 3:2, whereas Ptolemy merely believed that it should just generally involve tetrachords and octaves. He presented his own divisions of the tetrachord and the octave, which he derived with the help of a monochord. The book ends with a more speculative exposition of the relationships between harmony, the soul (psyche), and the planets (harmony of the spheres).

Although Ptolemy's Harmonics never had the influence of his Almagest or Geography, it is nonetheless a well-structured treatise and contains more methodological reflections than any other of his writings. During the Renaissance, Ptolemy's ideas inspired Kepler in his own musings on the harmony of the world (Harmonice Mundi, Appendix to Book V).

Optics

Main article: Optics (Ptolemy)

The Optica (Ancient Greek: Ὀπτικά), known as the Optics, is a work that survives only in a somewhat poor Latin version, which, in turn, was translated from a lost Arabic version by Eugenius of Palermo (c. 1154). In it, Ptolemy writes about properties of sight (not light), including reflection, refraction, and colour. The work is a significant part of the early history of optics and influenced the more famous and superior 11th-century Book of Optics by Ibn al-Haytham. Ptolemy offered explanations for many phenomena concerning illumination and colour, size, shape, movement, and binocular vision. He also divided illusions into those caused by physical or optical factors and those caused by judgmental factors. He offered an obscure explanation of the sun or moon illusion (the enlarged apparent size on the horizon) based on the difficulty of looking upwards.

The work is divided into three major sections. The first section (Book II) deals with direct vision from first principles and ends with a discussion of binocular vision. The second section (Books III-IV) treats reflection in plane, convex, concave, and compound mirrors. The last section (Book V) deals with refraction and includes the earliest surviving table of refraction from air to water, for which the values (with the exception of the 60° angle of incidence) show signs of being obtained from an arithmetic progression. However, according to Mark Smith, Ptolemy's table was based in part on real experiments.

Ptolemy's theory of vision consisted of rays (or flux) coming from the eye forming a cone, the vertex being within the eye, and the base defining the visual field. The rays were sensitive, and conveyed information back to the observer's intellect about the distance and orientation of surfaces. Size and shape were determined by the visual angle subtended at the eye combined with perceived distance and orientation. This was one of the early statements of size-distance invariance as a cause of perceptual size and shape constancy, a view supported by the Stoics.

Philosophy

Although mainly known for his contributions to astronomy and other scientific subjects, Ptolemy also engaged in epistemological and psychological discussions across his corpus. He wrote a short essay entitled On the Criterion and Hegemonikon (Ancient Greek: Περὶ Κριτηρίου καὶ Ἡγεμονικοῡ), which may have been one of his earliest works. Ptolemy deals specifically with how humans obtain scientific knowledge (i.e., the "criterion" of truth), as well as with the nature and structure of the human psyche or soul, particularly its ruling faculty (i.e., the hegemonikon). Ptolemy argues that, to arrive at the truth, one should use both reason and sense perception in ways that complement each other. On the Criterion is also noteworthy for being the only one of Ptolemy's works that is devoid of mathematics.

Elsewhere, Ptolemy affirms the supremacy of mathematical knowledge over other forms of knowledge. Like Aristotle before him, Ptolemy classifies mathematics as a type of theoretical philosophy; however, Ptolemy believes mathematics to be superior to theology or metaphysics because the latter are conjectural while only the former can secure certain knowledge. This view is contrary to the Platonic and Aristotelian traditions, where theology or metaphysics occupied the highest honour. Despite being a minority position among ancient philosophers, Ptolemy's views were shared by other mathematicians such as Hero of Alexandria.

Named after Ptolemy

There are several characters or items named after Ptolemy, including:

• The crater Ptolemaeus on the Moon
• The crater Ptolemaeus on Mars
• The asteroid 4001 Ptolemaeus
• Messier 7, sometimes known as the Ptolemy Cluster, an open cluster of stars in the constellation of Scorpius
• The Ptolemy stone used in the mathematics courses at both St. John's College campuses in the U.S.
• Ptolemy's theorem on distances in a cyclic quadrilateral, and its generalization, Ptolemy's inequality, to non-cyclic quadrilaterals
• Ptolemaic graphs, the graphs whose distances obey Ptolemy's inequality
• Ptolemy Project, a project at University of California, Berkeley, aimed at modeling, simulating and designing concurrent, real-time, embedded systems
• Ptolemy Slocum, actor

Works

• Quadripartitum (in Latin). Venezia: Ottaviano Scoto (1.) eredi & C. 1519.
• [Opere] (in Latin). Basel: Heinrich Petri. 1541.
• In Claudii Ptolemaei Quadripartitum (in Latin). Basel: Heinrich Petri. 1559.
• Quadripartitum (in Latin). Frankfurt am Main: Johann Bringer. 1622.
• Quadripartitum (in Latin). Padova: Paolo Frambotto. 1658.
• De iudicandi facultate et animi principatu (in Latin). Paris: Sebastian Cramoisy (1.) & Sebastian Mabre-Cramoisy. 1663.
• De iudicandi facultate et animi principatu (in Latin). Den Haag: Adriaen Vlacq. 1663.
• Harmonicorum libri (in Latin). Oxford: Theatrum Sheldonianum. 1682.
• Planisphaerium, medieval Arabic translations and an English translation thereof, https://www.sciamvs.org/files/SCIAMVS_08_037-139_Sidoli_Berggren.pdf

Nanogel

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Nanogel 

A nanogel is a polymer-based, crosslinked hydrogel particle on the sub-micron scale. These complex networks of polymers present a unique opportunity in the field of drug delivery at the intersection of nanoparticles and hydrogel synthesis. Nanogels can be natural, synthetic, or a combination of the two and have a high degree of tunability in terms of their size, shape, surface functionalization, and degradation mechanisms. Given these inherent characteristics in addition to their biocompatibility and capacity to encapsulate small drugs and molecules, nanogels are a promising strategy to treat disease and dysfunction by serving as delivery vehicles capable of navigating across challenging physiological barriers within the body.

Nanogels are not to be confused with Nanogel aerogel, a lightweight thermal insulator, or with nanocomposite hydrogels (NC gels), which are nanomaterial-filled, hydrated, polymeric networks that exhibit higher elasticity and strength relative to traditionally made hydrogels.

Synthesis

The synthesis of nanogels can be achieved using a vast array of different methods. However, two critical steps typically included in each method are polymerization and crosslinking, with physical and chemical crosslinking the most common. These steps can be completed concomitantly or in sequential order depending on the synthesis method and eventual nanogel application. Here, several different synthesis mechanisms are described briefly.

Graphical representation of seven different methods of synthesizing polymeric nanogels. Created with BioRender.

Desolvation/Coacervation and Precipitation 

In desolvation or coacervation, a non-solvent is added to a homogeneous polymer solution to produce individual, nanosized polymer complexes dispersed in the same solution. These complexes then undergo crosslinking to form nanogels with surface functionalization an optional next step.

In precipitation, initiators and crosslinking agents are added to a homogenous monomer solution to induce a polymerization reaction. When the polymer chain reaches the desired length, the reaction is halted and a polymer colloidal suspension is formed. Surfactants are the final addition to produce nanosized polymers.

Electrostatic and Hydrophobic Interactions

Electrostatic interactions can form nanogels through the combination of anionic and cationic polymers in an aqueous solution.  The size and surface charge of the resulting nanogels can be modulated by changing the molecular weight or the charge ratio of the two different polymers. Ionotropic gelation can also leverage electrostatic interactions between multivalent anions and cations to form nanogels.

Hydrophobic interactions rely heavily on physical crosslinking to form nanogels. In this method, hydrophobic groups are added to hydrophilic polymers in an aqueous solution to induce their self-assembly into nanogels.

Inverse-emulsion

Inverse-emulsion, or reverse miniemulsion, requires an organic solvent and a surfactant or emulsifying agent. Nanosized droplets are produced when an aqueous monomer solution is dispersed in the organic solvent in the presence of the surfactant or emulsifying agent. Upon removal of the organic solvent and further chemical and physical crosslinking of the droplets, nanogels are formed. The size of nanogels synthesized using this method can vary greatly depending on the type of surfactant and reaction medium used. Purifying nanogels produced using an emulsifying agent may also pose a challenge.

Microtemplate Polymerization

The addition of a monomer precursor solution and crosslinking agent to a microtemplate, or mold-type device, can initiate polymerization and the formation of nanogels. This method can be used to create nanogels in specific shapes and load them with various small molecules. Lithographic microtemplate polymerization is a similar process that uses a photoinitiator and light to trigger the formation of nanogels. Lithographic microtemplate polymerization can produce smaller nanogels on a length scale of <200 nm, which has a higher resolution compared to microtemplate polymerization that does not require a photoinitiator.

Cross-linking Micelles

Polymer-based micelles that undergo crosslinking reactions can induce the formation of nanogels. Crosslinking either the core or the shell of a preexisting micelles can synthesize nanogels with a “high degree of spatial organization”.

Composition and Structure

Materials

Six different types of nanogels. Created with BioRender.

Since biodegradability is an important characteristic of nanogels, these hydrogels are typically composed of natural or degradable synthetic polymers. Polysaccharides and proteins largely dominate the natural forms of polymers used to synthesize nanogels. Advantages of natural polymer-based nanogels include biocompatibility and degradability by cellular mechanisms in vivo. Natural polymers also tend to be nontoxic and bioactive in which they are more likely to induce biological cues that govern various aspects of cellular behavior.  However, natural-based polymers can still cause an immune response and possess other disadvantages such as variable degradation rates and heterogeneous structures. Conversely, synthetic-based polymers have more defined structures, increased stability, and controlled degradation rates. In comparison to natural-based polymers, synthetic polymers lack biological cues that may be necessary for specific therapeutic applications. Given that natural and synthetic polymers are defined by their own set of advantages and disadvantages, an ongoing area of research aims to create composite hydrogels for nanogel synthesis that combines synthetic and natural polymers to leverage the benefits of both in one nanogel formulation. 

Various types of natural and synthetic biomaterials used to synthesize nanogels.

Structure

The structure of a nanogel is dependent upon the synthesis mechanism and its application. Simple or traditional nanogels are nanoparticle-sized crosslinked polymer networks that swell in water. Hollow nanogels consisting only of an outer shell can increase the amount of cargo loaded into the platform. In other nanogel structures, the inner core and outer shell can be made of two different materials, such as a hydrophobic inner core to surround drugs or other small molecules and a hydrophilic outer shell that interacts with the external environment. The addition of a second linear monomer crosslinked to a nanogel is deemed a “hairy nanogel”. Different nanogel synthesis methods can be completed in sequential order to create multilayered nanogels, such as starting with ionotropic gelation and then combining anionic and cationic polymers in an aqueous solution. Functionalized nanogels, in which targeting ligands or stimuli-sensitive functional groups are conjugated to the outer shell of a nanogel, are also important for certain nanogel applications.

Stimuli-responsive Nanogels

Nanogels can be designed to respond to various stimuli including changes in pH and temperature or the presence of redox and light cues. Thoughtfully designed stimuli-responsive nanogels can be leveraged to transport and release different types of cargo to specific tissues within the body with increasing spatiotemporal resolution.

Stimuli-responsive nanogels with different examples of stimuli and two potential release mechanisms. Created with BioRender.

pH-responsive Nanogels

pH responsive nanogels are an attractive form of nanogel technology due to the different pH levels found within the body. Healthy tissues exhibit a pH of 7.4 whereas tumors can be as low as 6.5 and the stomach as low as 1.0. The protonation or deprotonation of certain functional groups can change the swelling rate and stability of a nanogel, thus resulting in the release of encapsulated cargo when exposed to different pH ranges. For example, anionic nanogels with carboxylic acid groups will collapse upon exposure to a pH that is smaller than the pKa of the nanogel polymer. Similarly, cationic nanogels with terminal amino groups will become protonated if the pH of the environment is less than the pKa of the hydrogel. In this case, the swelling rate of the nanogel will change and it will become more hydrophilic. Other groups have also previously cross-linked pH-responsive hydrazone linkages to polysaccharide-based nanogels that released a payload in an acidic environment.

Temperature-responsive Nanogels

The usage of thermoresponsive polymers in nanogel synthesis allows these systems to respond to changes in temperature. Depending on the chemical groups present, thermoresponsive polymers can either respond to a decrease in temperature or an increase in temperature. Both hydrophobic and hydrophilic groups are typically present in thermoresponsive polymer nanogels that react to temperature decreases, whereas nanogels that respond to temperature increases often have to be prepared by a hydrogen-bonded layering technique. Temperature-responsive nanogels are a potential strategy when a therapeutic is targeting the skin, which has a natural temperature gradient, or a region experiencing inflammation.

Redox-responsive Nanogels

Redox-responsive nanogels generally contain crosslinks formed by disulfide bonds or specific crosslinking agents such as cystamine. Nanogels made of bioreducible and bifunctional monomers have also been responsive to redox cues6. In the presence of redox agents such as thioredoxin and peroxiredoxin, these nanogels respond by releasing their cargo. Given that these two redox agents and several others are found in larger concentrations inside cells compared to their external environment, redox-responsive nanogels are a promising strategy for targeted intracellular delivery.

Light-responsive Nanogels

Light-responsive nanogels can be triggered to release their cargo with exposure to light at a certain wavelength. These nanogels are synthesized to contain specific acrylic or coumarin-based bonds that cleave during a photoreaction. With the tunability of the wavelength of light, energy, and time of irradiation, light-responsive nanogels can be triggered to degrade with an increased control over crosslinking density. For example, both the swelling and size of light-responsive nanogels with vinyl groups were found to decrease and produce a sustained release of drugs after irradiation with UV light.

Physiological Responses to Nanogels

Example of an endocytosis process for a drug-loaded nanogel. Created with BioRender.

Biocompatibility, Biodegradability, and Biodistribution

One major concern with any form of drug delivery system, including nanogels, is potential side effects and damage to healthy tissue in addition to causing a negative immune response with the introduction of a foreign substance. This has to be balanced with the need for nanogels to remain within circulation for an adequate period to deliver cargo and produce a therapeutic effect. To combat a significant immune response, degradable nanogels are the typical default since they are considered less toxic compared to non degradable nanogels. The compliance and small size of degradable nanogels also allows them to travel through blood vessels and reach their target area before consumption by immune cells or filtration by the liver and spleen.

Cellular Uptake Mechanisms

After nanogels exit the vasculature, they diffuse through the interstitial space into their target tissue. At the cellular level, nanogels can be internalized by a large number of different types of endocytosis that depend on the particle’s size, shape, and surface properties. Endocytosis is the most common mechanism that starts with the nanogels engulfed by the cellular membrane. The nanogels are transported in intracellular vesicles for delivery to endosomes that eventually combine with lysosomes. Once lysosomes are released into the cytosol of a cell, they deliver their cargo immediately or move to the appropriate cellular compartment.

Applications

Potential applications of nanogels include drug delivery agents, contrast agents for medical imaging or ¹⁹F MRI tracers, nanoactuators, and sensors.

Drug Delivery

Cancer Therapeutics

In 2022, over 1.9 million new cancer cases are projected in the U.S. alone. Nanogels are an attractive drug delivery solution for increasing both the efficacy of cancer therapeutics and their localization to cancer cells. Nanogels are currently being investigated for the treatment of different types of cancer, of which a few examples are listed here.

In one study, chitosan-based nanogels loaded with doxorubicin, a chemotherapeutic, with a positive surface charge demonstrated a lower colorectal cancer cell viability compared to control groups and a similarly loaded nanogel with a negative surface charge. Another group conjugated folic acid to nanogels loaded with cisplatin or doxorubicin and delivered these therapeutics to ovarian cancer cells, which overexpress the folate receptor that binds with folic acid. These conjugated nanogels produced a significant decrease in tumor growth in a mouse model compared to vehicle controls and showed a site-specific delivery model for nanogels that may be effective for other types of cancer with upregulated folate receptors. Interestingly, gelatin-based nanogels loaded with cisplatin and conjugated to epidermal growth factor receptor (EGFR) ligands have been reported to successfully target lung cancer cells both in vitro and in vivo, with additional work confirming the effectiveness of these nanogels when transformed into aerosol particles.

Example of using a therapeutic nanoparticle for targeted drug delivery to cancer cells. Created with BioRender.

Nucleic Acid-based Molecules

Nanogels are advantageous carriers of small, nucleic-acid based molecules that can be employed to treat a variety of diseases. Examples of three different types of molecules that fall into this category, oligonucleotides, miRNA, and nucleoside analogs, are discussed here.

In one study, cationic synthetic nanogels modified with insulin and transferrin were synthesized to transport oligonucleotides, a possible therapeutic and diagnostic tool for neurodegenerative disorders, to the brain. These nanogels successfully localized through an in vitro model of the blood-brain barrier and accumulated in the brain in a mouse model. With the treatment of cardiovascular diseases in mind, polysaccharide-based nanogels have been functionalized with fucoidan to target overexpressed P-selectin receptors on platelets and endothelial cells. After loading with miRNA, these nanogels bound to platelets and became internalized by an endothelial cell line. Nanogels have also been used to encapsulate phosphorylated nucleoside analogs, or active forms of anticancer therapeutics. In one study, nanogels loaded with nucleoside 5’-triphosphates underwent surface modifications and successfully bound to overexpressed folate receptors on breast cancer cells. These nanogels were then internalized by the cells and produced a significant increase in cytotoxicity compared to control groups.

Stimuli-responsive Nanogels for Drug Delivery

Nanogels that respond to various stimuli including changes in pH and temperature or the presence of redox and light cues have proven to be useful tools for drug delivery. One such responsive nanogel was designed to switch from a surface negative charge to a surface positive charge upon exposure to decrease in pH once inside a tumor. When loaded with a  chemotherapeutic agent, this technology induced a lower viability in 3D tumor spheroids compared to control groups. Another type of nanogel loaded with osteoarthritis anti-inflammatory drugs was found to significantly increase the amount of drug transported after topical application to the skin and exposure to its natural elevated temperature. One group reported a method to control the release rate of an antiplatelet medication from a nanogel by using UV light to alter the crosslinking density of the polymer and subsequently change the swelling rate. Additionally, other nanogels have been synthesized to include disulfide cleavable polymers that respond to reductive cues in the surrounding environment. One such nanogel was loaded with a chemotherapeutic agent and demonstrated a decrease in cell viability compared to a free version of the same agent.

Imaging and Diagnostics

In addition to drug delivery applications, nanogels have been utilized as a type of imaging modality as they can encapsulate small dyes and other reporter molecules.

An example of pH-responsive nanogels to increase MRI sensitivity. Created with BioRender.

MRI Imaging

Typical MRI contrast agents that contain gadolinium and manganese are quickly excreted from the body and carry risks of increased toxicity. Nanogels aim to circumvent these limitations by encapsulating these agents and increasing their relaxivity, or sensitivity. One study encapsulated gadolinium-III within a nanogel and observed a significant enhancement in relaxivity compared to a clinically available formulation of gadolinium-III. Another group developed pH-responsive nanogels containing both manganese oxide and superparamagnetic iron oxide nanoparticles that successfully imaged small tumors, where the pH was more acidic compared to the surrounding healthy tissues. Fluorine-containing nanogels can also be used as tracers for ¹⁹F MRI, because their aggregation and tissue binding has only minor effect on their ¹⁹F MRI signal. Furthermore, they can carry drugs and their physico-chemical properties of the polymers can be highly modulated.

PET Imaging

Similar to MRI imaging, metal radionuclides can be loaded into nanogels and crosslinked to obtain PET radiotracers for imaging. Nanogels containing copper isotopes commonly used for PET imaging demonstrated overall stability and accumulation in tumors, which produced  a higher signal in comparison to nearby tissue. Other studies have explored similar technologies with redox-responsive nanogels loaded with an isotope of gallium and other trivalent metals for PET imaging. Nanogels composed of dextran have also been developed for imaging tumor-associated macrophages with radionuclides and targeting the bone.

Other Optical Imaging

For in vivo fluorescence-based optical imaging, dyes that emit NIR wavelengths >700 nm are most effective, such as indocyanine green, but encounter limitations with reduced circulation time and nonspecific interactions with other biological factors that affect the fluorescence. pH-sensitive nanogels with functionalized surface receptors to target cancer cells were loaded with a fluorescent dye that was only released upon endocytosis. These nanogels successfully generated a fluorescent signal from within the cancer cells and many other groups have developed similar technologies.

Regenerative Medicine

Various applications of nanogels in regenerative medicine contexts including as injectable delivery vehicles and as components of  implantable polymeric scaffolds. Created with BioRender.

Wound Healing

Nanogels are a promising technology being explored to aid in the wound healing process. Given their ability to encapsulate various types of cargo, nanogels can strategically deliver anti-inflammatory agents, antimicrobial drugs, and necessary growth factors to facilitate new tissue growth and blood vessel formation. Chitosan-based nanogels have demonstrated an improved wound healing effect in previous studies. Chitosan-based nanogels encapsulating interleukin-2 were successfully used to stimulate the immune system and advance the wound healing process. Additionally, chitosan-based nanogels carrying an antibiotic, silver sulfadiazine, were found to decrease the size of second-degree burns in one in vivo study. In another study, silver-loaded nanogels were synthesized in a natural polymer-based solution containing aloe vera, and the presence of aloe vera led to increased healing and a decrease in wound size. With the goal of preventing infection and accelerating the healing process, one group has also published a new nanogel design consisting of an encapsulating core and a functionalized outer surface capable of targeting bacteria present in wounds.

Tissue Regeneration

To repair and regenerate damaged tissue, nanogels have been explored to not only encapsulate drugs and growth factors for local administration, but also to serve as porous scaffolds at a tissue implantation site. Boron-containing temperature-responsive nanogels formed a solid scaffold upon injection into a critical bone defect and continued to induce the production of new osteoblast cells. To treat the effects of myocardial infarction, one in vivo study loaded temperature-responsive nanogels with cardiac stem cells and observed improved cardiac function through an increase in left ventricular ejection. Blood vessels have been successfully regenerated in an in vivo model of ischemia using nanogels to encapsulate vascular endothelial growth factors. Heparin-based nanogels loaded with growth factors have also been tested in the regeneration of the urethral muscle that causes urinary incontinence.

Other Applications

Sensors

A fluorescent nanogel thermometer was developed to measure temperatures to within 0.5 °C (0.90 °F) in living cells. The cell absorbs water when colder and squeezes the water out as its internal temperature rises; the relative quantity of water masks or exposes the fluorescence of the nanogel.

Resurrection

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Resurrection 

Plaque depicting saints rising from the dead

Resurrection or anastasis is the concept of coming back to life after death. In a number of religions, a dying-and-rising god is a deity which dies and is resurrected. Reincarnation is a similar process hypothesized by other religions, which involves the same person or deity coming back to live in a different body, rather than the same one.

The resurrection of the dead is a standard eschatological belief in the Abrahamic religions. As a religious concept, it is used in two distinct respects: a belief in the resurrection of individual souls that is current and ongoing (Christian idealism, realized eschatology), or else a belief in a singular resurrection of the dead at the end of the world. Some believe the soul is the actual vehicle by which people are resurrected.

The death and resurrection of Jesus is a central focus of Christianity. Christian theological debate ensues with regard to what kind of resurrection is factual – either a spiritual resurrection with a spirit body into Heaven, or a material resurrection with a restored human body. While most Christians believe Jesus' resurrection from the dead and ascension to Heaven was in a material body, some believe it was spiritual.

Like the Abrahamic religions, Hinduism also has a core belief in resurrection and reincarnation. This is known as saṃsāra.

Etymology

Resurrection, from the Latin noun resurrectio -onis, from the verb rego, "to make straight, rule" + preposition sub, "under", altered to subrigo and contracted to surgo, surrexi, surrectum ("to rise", "get up", "stand up") + preposition re-, "again", thus literally "a straightening from under again".

Religion

Ancient religions in the Near East

See also: Dying-and-rising god

The concept of resurrection is found in the writings of some ancient non-Abrahamic religions in the Middle East. A few extant Egyptian and Canaanite writings allude to dying and rising gods such as Osiris and Baal. Sir James Frazer in his book The Golden Bough relates to these dying and rising gods, but many of his examples, according to various scholars, distort the sources. Taking a more positive position, Tryggve Mettinger argues in his recent book that the category of rise and return to life is significant for Ugaritic Baal, Melqart, Adonis, Eshmun, Osiris and Dumuzi.

Ancient Greek religion

In ancient Greek religion a number of men and women became physically immortal as they were resurrected from the dead. Asclepius was killed by Zeus, only to be resurrected and transformed into a major deity. Achilles, after being killed, was snatched from his funeral pyre by his divine mother Thetis and resurrected, brought to an immortal existence in either Leuce, the Elysian plains or the Islands of the Blessed. Memnon, who was killed by Achilles, seems to have received a similar fate. Alcmene, Castor, Heracles, and Melicertes, were also among the figures sometimes considered to have been resurrected to physical immortality. According to Herodotus's Histories, the seventh century BC sage Aristeas of Proconnesus was first found dead, after which his body disappeared from a locked room. Later he found not only to have been resurrected but to have gained immortality.

Many other figures, like a great part of those who fought in the Trojan and Theban wars, Menelaus, and the historical pugilist Cleomedes of Astupalaea, were also believed to have been made physically immortal, but without having died in the first place. Indeed, in Greek religion, immortality originally always included an eternal union of body and soul. As may be witnessed even into the Christian era, not least by the complaints of various philosophers over popular beliefs, traditional Greek believers maintained the conviction that certain individuals were resurrected from the dead and made physically immortal and that for the rest of us, we could only look forward to an existence as disembodied and dead souls.

Greek philosophers generally denied this traditional religious belief in physical immortality. Writing his Lives of Illustrious Men (Parallel Lives) in the first century, the Middle Platonic philosopher Plutarch in his chapter on Romulus gave an account of the mysterious disappearance and subsequent deification of this first king of Rome, comparing it to traditional Greek beliefs such as the resurrection and physical immortalization of Alcmene and Aristeas the Proconnesian, "for they say Aristeas died in a fuller's work-shop, and his friends coming to look for him, found his body vanished; and that some presently after, coming from abroad, said they met him traveling towards Croton". Plutarch openly scorned such beliefs held in traditional ancient Greek religion, writing, "many such improbabilities do your fabulous writers relate, deifying creatures naturally mortal."

Alcestis undergoes resurrection over a three-day period of time, but without achieving immortality.

The parallel between these traditional beliefs and the later resurrection of Jesus was not lost on the early Christians, as Justin Martyr argued: "when we say ... Jesus Christ, our teacher, was crucified and died, and rose again, and ascended into heaven, we propose nothing different from what you believe regarding those whom you consider sons of Zeus." (1 Apol. 21).

Buddhism

Further information: Rebirth (Buddhism)

There are stories in Buddhism where the power of resurrection was allegedly demonstrated in Chan or Zen tradition. One is the legend of Bodhidharma, the Indian master who brought the Ekayana school of India that subsequently became Chan Buddhism to China.

The other is the passing of Chinese Chan master Puhua (Japanese:Jinshu Fuke) and is recounted in the Record of Linji (Japanese: Rinzai Gigen). Puhua was known for his unusual behavior and teaching style so it is no wonder that he is associated with an event that breaks the usual prohibition on displaying such powers. Here is the account from Irmgard Schloegl's "The Zen Teaching of Rinzai".

"One day at the street market Fuke was begging all and sundry to give him a robe. Everybody offered him one, but he did not want any of them. The master [Linji] made the superior buy a coffin, and when Fuke returned, said to him: "There, I had this robe made for you." Fuke shouldered the coffin, and went back to the street market, calling loudly: "Rinzai had this robe made for me! I am off to the East Gate to enter transformation" (to die)." The people of the market crowded after him, eager to look. Fuke said: "No, not today. Tomorrow, I shall go to the South Gate to enter transformation." And so for three days. Nobody believed it any longer. On the fourth day, and now without any spectators, Fuke went alone outside the city walls, and laid himself into the coffin. He asked a traveler who chanced by to nail down the lid.

The news spread at once, and the people of the market rushed there. On opening the coffin, they found that the body had vanished, but from high up in the sky they heard the ring of his hand bell."

Christianity

In Christianity, resurrection most critically concerns the resurrection of Jesus, but also includes the resurrection of Judgment Day known as the resurrection of the dead by those Christians who subscribe to the Nicene Creed (which is the majority or mainstream Christianity), as well as the resurrection miracles done by Jesus and the prophets of the Old Testament.

Resurrection miracles

The Resurrection of Lazarus, painting by Leon Bonnat, France, 1857.

 

Main article: Miracles of Jesus § Resurrection of the dead

In the New Testament, Jesus is said to have raised several persons from death. These resurrections included the daughter of Jairus shortly after death, a young man in the midst of his own funeral procession, and Lazarus of Bethany, who had been buried for four days.

During the Ministry of Jesus on earth, before his death, Jesus commissioned his Twelve Apostles to, among other things, raise the dead.

Similar resurrections are credited to the apostles and Catholic saints. In the Acts of the Apostles, Saint Peter raised a woman named Dorcas (also called Tabitha), and Paul the Apostle revived a man named Eutychus who had fallen asleep and fell from a window to his death. According to the Gospel of Matthew, after Jesus's resurrection, many of those previously dead came out of their tombs and entered Jerusalem, where they appeared to many. Following the Apostolic Age, many saints were said to resurrect the dead, as recorded in Orthodox Christian hagiographies. St Columba supposedly raised a boy from the dead in the land of Picts.

Resurrection of Jesus

Main articles: Life-death-rebirth deity, Resurrection of Jesus, Easter, and Resurrection appearances of Jesus

 

Resurrection of Jesus

Christians regard the resurrection of Jesus as the central doctrine in Christianity. Others take the incarnation of Jesus to be more central; however, it is the miracles – and particularly his resurrection – which provide validation of his incarnation. According to Paul, the entire Christian faith hinges upon the centrality of the resurrection of Jesus and the hope for a life after death. The Apostle Paul wrote in his first letter to the Corinthians:

If only for this life we have hope in Christ, we are to be pitied more than all men. But Christ has indeed been raised from the dead, the first fruits of those who have fallen asleep.

Resurrection of the dead

Main articles: Universal resurrection § Christianity, and Christian eschatology § Resurrection of the dead

Christianity started as a religious movement within 1st-century Judaism (late Second Temple Judaism), and it retains what the New Testament itself claims was the Pharisaic belief in the afterlife and resurrection of the dead. Whereas this belief was only one of many beliefs held about the world to come in Second Temple Judaism, and was notably rejected by the Sadducees, but accepted by the Pharisees (cf. Acts 23:6-8). Belief in the resurrection became dominant within Early Christianity and already in the Gospels of Luke and John, included an insistence on the resurrection of the flesh. Most modern Christian churches continue to uphold the belief that there will be a final resurrection of the dead and world to come.

Belief in the resurrection of the dead, and Jesus' role as judge, is codified in the Apostles' Creed, which is the fundamental creed of Christian baptismal faith. The Book of Revelation also makes many references about the Day of Judgment when the dead will be raised.

The emphasis on the literal resurrection of the flesh remained strong in the medieval ages, and still remains so in Orthodox churches. In modern Western Christianity, especially "from the 17th to the 19th century, the language of popular piety no longer evoked the resurrection of the soul but everlasting life. Although theological textbooks still mentioned resurrection, they dealt with it as a speculative question more than as an existential problem."

Difference from Platonic philosophy

In Platonic philosophy and other Greek philosophical thought, at death the soul was said to leave the inferior body behind. The idea that Jesus was resurrected spiritually rather than physically even gained popularity among some Christian teachers, whom the author of 1 John declared to be antichrists. Similar beliefs appeared in the early church as Gnosticism. However, in Luke 24:39, the resurrected Jesus expressly states "behold my hands and my feet, that it is I myself. Handle me and see, for a spirit does not have flesh and bones as you see, I have."

Hinduism

Further information: Reincarnation

There are folklore, stories, and extractions from certain holy texts that refer to resurrections. One major folklore is that of Savitri saving her husband's life from Yamraj. In the Ramayana, after Ravana was slain by Rama in a great battle between good and evil, Rama requests the king of Devas, Indra, to restore the lives of all the monkeys who died in the great battle. Mahavatar Babaji and Lahiri Mahasaya are also believed to have resurrected themselves.

Islam

Main article: Islamic eschatology

Belief in the Day of Resurrection (yawm al-qiyāmah) is also crucial for Muslims. They believe the time of Qiyāmah is preordained by God but unknown to man. The trials and tribulations preceding and during the Qiyāmah are described in the Quran and the hadith, and also in the commentaries of scholars. The Quran emphasizes bodily resurrection, a break from the pre-Islamic Arabian understanding of death.

According to Nasir Khusraw (d. after 1070), an Ismaili thinker of the Fatimid era, the Resurrection (Qiyāma) will be ushered by the Lord of the Resurrection (Qāʾim al-Qiyāma), an individual symbolizing the purpose and pinnacle of creation from among the progeny of Muhammad and his Imams. Through this individual, the world will come out of darkness and ignorance and “into the light of her Lord” (Quran 39:69). His era, unlike that of the enunciators of the divine revelation (nāṭiqs) before him, is not one where God prescribes the people to work but instead one where God rewards them. Preceding the Lord of the Resurrection (Qāʾim) is his proof (ḥujjat). The Qur’anic verse stating that “the night of power (laylat al-qadr) is better than a thousand months” (Quran 97:3) is said to refer to this proof, whose knowledge is superior to that of a thousand Imams, though their rank, collectively, is one. Hakim Nasir also recognizes the successors of the Lord of the Resurrection to be his deputies (khulafāʾ).

Judaism

Main article: Jewish eschatology

There are three explicit examples in the Hebrew Bible of people being resurrected from the dead:

• The prophet Elijah prays and God raises a young boy from death (1 Kings 17:17-24)
• Elisha raises the son of the Woman of Shunem (2 Kings 4:32-37) whose birth he previously foretold (2 Kings 4:8-16)
• A dead man's body that was thrown into the dead Elisha's tomb is resurrected when the body touches Elisha's bones (2 Kings 13:21)

According to Herbert C. Brichto, writing in Reform Judaism's Hebrew Union College Annual, the family tomb is the central concept in understanding biblical views of the afterlife. Brichto states that it is "not mere sentimental respect for the physical remains that is...the motivation for the practice, but rather an assumed connection between proper sepulture and the condition of happiness of the deceased in the afterlife".

According to Brichto, the early Israelites apparently believed that the graves of family, or tribe, united into one, and that this unified collectivity is to what the Biblical Hebrew term Sheol refers, the common grave of humans. Although not well defined in the Tanakh, Sheol in this view was a subterranean underworld where the souls of the dead went after the body died. The Babylonians had a similar underworld called Aralu, and the ancient Greeks had one known as Hades. According to Brichto, other biblical names for Sheol were Abaddon "ruin", found in Psalm 88:11, Job 28:22 and Proverbs 15:11; Bor "pit", found in Isaiah 14:15, 24:22, Ezekiel 26:20; and Shakhat "corruption", found in Isaiah 38:17, Ezekiel 28:8.

During the Second Temple period, there developed a diversity of beliefs concerning the resurrection. The concept of resurrection of the physical body is found in 2 Maccabees, according to which it will happen through re-creation of the flesh. Resurrection of the dead also appears in detail in the extra-canonical Book of Enoch, 2 Baruch, and 2 Esdras. According to the British scholar in ancient Judaism Philip R. Davies, there is “little or no clear reference … either to immortality or to resurrection from the dead” in the texts of the Dead Sea Scrolls. C.D. Elledge, however, argues that some form of resurrection may be referred to in the Dead Sea texts 4Q521, Pseudo-Ezekiel, and 4QInstruction.

Both Josephus and the New Testament record that the Sadducees did not believe in an afterlife, but the sources vary on the beliefs of the Pharisees. The New Testament claims that the Pharisees believed in the resurrection, but does not specify whether this included the flesh or not. According to Josephus, who himself was a Pharisee, the Pharisees held that only the soul was immortal and the souls of good people will “pass into other bodies,” while “the souls of the wicked will suffer eternal punishment.” Paul the Apostle, who also was a Pharisee, said that at the resurrection what is "sown as a natural body is raised a spiritual body." The Book of Jubilees seems to refer to the resurrection of the soul only, or to a more general idea of an immortal soul.

Anastasis in contemporary philosophy

Anastasis or Ana-stasis is a concept in contemporary philosophy emerging from the works of Jean-Luc Nancy, Divya Dwivedi and Shaj Mohan. Nancy developed the concept through his interpretation of paintings depicting the resurrection of Jesus Christ. Dwivedi and Mohan, referring to Nancy, defined Ana-stasis as coming over stasis, which is a method for philosophy to overcome its end as Martin Heidegger defined. This concept is noted to be linked in the works of Nancy, Dwivedi and Mohan to have a relation to Heidegger's “other beginning of philosophy”. The use of the phrase “anastasis of philosophy” indicates such other beginning.

Technological resurrection

Cryonics is the low-temperature freezing (usually at −196 °C or −320.8 °F or 77.1 K) of a human corpse or severed head, with the speculative hope that resurrection may be possible in the future. Cryonics is regarded with skepticism within the mainstream scientic community. It is generally viewed as a pseudoscience, and has been characterized as quackery.

Russian cosmist Nikolai Fyodorovich Fyodorov advocated resurrection of the dead using scientific methods. Fedorov tried to plan specific actions for scientific research of the possibility of restoring life and making it infinite. His first project is connected with collecting and synthesizing decayed remains of dead based on "knowledge and control over all atoms and molecules of the world". The second method described by Fedorov is genetic-hereditary. The revival could be done successively in the ancestral line: sons and daughters restore their fathers and mothers, they in turn restore their parents and so on. This means restoring the ancestors using the hereditary information that they passed on to their children. Using this genetic method it is only possible to create a genetic twin of the dead person. It is necessary to give back the revived person his old mind, his personality. Fedorov speculates about the idea of "radial images" that may contain the personalities of the people and survive after death. Nevertheless, Fedorov noted that even if a soul is destroyed after death, Man will learn to restore it whole by mastering the forces of decay and fragmentation.

In his 1994 book The Physics of Immortality, American physicist Frank J. Tipler, an expert on the general theory of relativity, presented his Omega Point Theory which outlines how a resurrection of the dead could take place at the end of the cosmos. He posits that humans will evolve into robots which will turn the entire cosmos into a supercomputer which will, shortly before the Big Crunch, perform the resurrection within its cyberspace, reconstructing formerly dead humans (from information captured by the supercomputer from the past light cone of the cosmos) as avatars within its metaverse.

David Deutsch, British physicist and pioneer in the field of quantum computing, formerly agreed with Tipler's Omega Point cosmology and the idea of resurrecting deceased people with the help of quantum computers but he is critical of Tipler's theological views.

Italian physicist and computer scientist Giulio Prisco presents the idea of "quantum archaeology", "reconstructing the life, thoughts, memories, and feelings of any person in the past, up to any desired level of detail, and thus resurrecting the original person via 'copying to the future'".

In his book Mind Children, roboticist Hans Moravec proposed that a future supercomputer might be able to resurrect long-dead minds from the information that still survived. For example, this information can be in the form of memories, filmstrips, medical records, and DNA.

Ray Kurzweil, American inventor and futurist, believes that when his concept of singularity comes to pass, it will be possible to resurrect the dead by digital recreation.

In their science fiction novel The Light of Other Days, Sir Arthur Clarke and Stephen Baxter imagine a future civilization resurrecting the dead of past ages by reaching into the past, through micro wormholes and with nanorobots, to download full snapshots of brain states and memories.

Both the Church of Perpetual Life and the Terasem Movement consider themselves transreligions and advocate for the use of technology to indefinitely extend the human lifespan.

Zombies

Main article: Zombie

A zombie (Haitian French: zombi, Haitian Creole: zonbi) is a fictional undead being created through the reanimation of a human corpse. Zombies are most commonly found in horror and fantasy genre works. The term comes from Haitian folklore, where a zombie is a dead body reanimated through various methods, most commonly magic.

Disappearances (as distinct from resurrection)

See also: Entering heaven alive

As knowledge of different religions has grown, so have claims of bodily disappearance of some religious and mythological figures. In ancient Greek religion, this was a way the gods made some physically immortal, including such figures as Cleitus, Ganymede, Menelaus, and Tithonus. After his death, Cycnus was changed into a swan and vanished. In his chapter on Romulus from Parallel Lives, Plutarch criticises the continuous belief in such disappearances, referring to the allegedly miraculous disappearance of the historical figures Romulus, Cleomedes of Astypalaea, and Croesus. In ancient times, Greek and Roman pagan similarities were explained by the early Christian writers, such as Justin Martyr, as the work of demons, with the intention of leading Christians astray.

In the Buddhist Epic of King Gesar, also spelled as Geser or Kesar, at the end, chants on a mountain top and his clothes fall empty to the ground. The body of the first Guru of the Sikhs, Guru Nanak Dev, is said to have disappeared and flowers left in place of his dead body.

Lord Raglan's Hero Pattern lists many religious figures whose bodies disappear, or have more than one sepulchre. B. Traven, author of The Treasure of the Sierra Madre, wrote that the Inca Virococha arrived at Cusco (in modern-day Peru) and the Pacific seacoast where he walked across the water and vanished. It has been thought that teachings regarding the purity and incorruptibility of the hero's human body are linked to this phenomenon. Perhaps, this is also to deter the practice of disturbing and collecting the hero's remains. They are safely protected if they have disappeared.

The first such case mentioned in the Bible is that of Enoch (son of Jared, great-grandfather of Noah, and father of Methuselah). Enoch is said to have lived a life where he "walked with God", after which "he was not, for God took him" (Genesis 5:1–18). In Deuteronomy (34:6) Moses is secretly buried. Elijah vanishes in a whirlwind 2 Kings (2:11). In the Synoptic Gospels, after hundreds of years these two earlier Biblical heroes suddenly reappear, and are reportedly seen walking with Jesus, then again vanish.^[65] In the Gospel of Luke, the last time Jesus is seen (24:51) he leaves his disciples by ascending into the sky. This ascension of Jesus was a “disappearance” of sorts as recorded by Luke but was after the physical resurrection occurring several days before.