Elastomeric Force Research Articles

Chlorhexidine hexametaphosphate as a coating for elastomeric ligatures with sustained antimicrobial properties: A laboratory study

White spot lesions are a common side effect of orthodontic treatment. This laboratory study aimed to explore the suitability of chlorhexidine hexametaphosphate (CHX-HMP) as a coating for orthodontic elastomeric ligatures to provide sustained chlorhexidine (CHX) release. Dissolution kinetics of CHX-HMP were firstly explored using spectroscopy and a colorimetric phosphate assay. Elastomeric ligatures were categorized into 3 groups-acetone-conditioned, ethanol-conditioned, and as received-and were then immersed in 5mM CHX-HMP suspension or 5mM chlorhexidine digluconate solution and rinsed. CHX release was measured over 8weeks, and the effects of conditioning and immersion on elastomeric force and extension at rupture and surface topography were investigated. CHX-HMP exhibited a gradual equilibration that had not reached equilibrium within 8weeks, releasing soluble CHX and a mixture of polyphosphate and orthophosphate. CHX digluconate-treated ligatures showed no CHX release, whereas CHX-HMP-treated ligatures showed varying degrees of release. As received, CHX-HMP-treated ligatures showed a modest release of CHX up to 7days. Acetone conditioning did not enhance CHX-HMP uptake or subsequent CHX release and caused a deterioration in mechanical properties. Ethanol conditioning enhanced CHX-HMP uptake (6×) and led to a sustained CHX release over 8weeks without affecting mechanical properties. Within the inherent limitations of this in-vitro study, CHX-HMP led to a sustained release of CHX from orthodontic elastomeric ligatures after ethanol conditioning. Conditioned and coated elastomeric ligatures may ultimately find application in the prevention of white spot lesions in orthodontic patients.

Embedded piezoresistive pressure sensitive pillars from piezoresistive carbon black composites towards a soft large-strain compressive load sensor

Soft robotics is a rapidly expanding field that aims at replacing rigid robotic components in a wide range of applications with more compliant, organic and functional components. The limited availability actuator-compatible sensors that can provide real-time feedback limits large scale implementation of these soft robots. A secondary sensing layer that encompasses the soft actuator or a sensor embedded soft actuator would enhance the suitability of soft robots in a wider range of applications. This article describes the design, fabrication and characterization of a carbon composite elastomeric force sensor, which aims to be a free standing film than can be cut into desired shape and embedded into soft robots while manufacturing for imparting self-sensing capabilities. Various concentrations of carbon black in the elastomer composite have been studied and the ideal concentration is derived. Carbon composite pillars as soft sensors with conductive tracks on top and bottom were fabricated and embedded in a soft elastomer matrix for analysing the sensor response under physical loading. The sensitivity of these sensors were identified and characterised, and were found to be capable of detecting forces as small as 0.1 N. The thin-film free-standing architecture of sensing element allows embedding the fabricated sensing element into any elastomer matrix improves the applicability of these sensors in a wide range of soft robotic applications.

Correlation between in vitro Elastomeric Force Degradation and Glass Transition Temperature determined by Dynamic Mechanical Analysis

Correlation between in vitro Elastomeric Force Degradation and Glass Transition Temperature determined by Dynamic Mechanical Analysis

Correlation between in vitro Elastomeric Force Degradation and Glass Transition Temperature determined by Dynamic Mechanical Analysis

Objective: To determine the relation between force degradation of elastomeric chains and its glass transition temperature (Tg) by dynamic mechanical analysis (DMA). Materials and methods: Elastomeric products from two different manufacturers (Groups A and B) were compared for their force decay in an in vitro experiment for 4 weeks. Force values (F) were measured at 0 hour, 1 hour, 24 hours, 1, 2, 3 and 4 weeks. Samples were subjected to DMA for its corresponding Tg. Mean force and Tg were compared with one-way analysis of variance (ANOVA) and post-hoc Duncan multiple range test. Two-way ANOVA was used to assess the effects between Groups and different time periods. Relationship between force and Tg were studied with regression analysis. Results: Force values decreased by 48% within 1 hour and then showed a continuous decrease to cease with only 24.5 and 20.2% for Groups A and B respectively. Tg also paralleled a decrease (Group A: –19.21 ± 1.73 to –26.10 ± 1.72 and Group B: –21.09 ± 2.14 to –27.30 ± 1.82). Beta and gamma subtransitions other than main alpha transitions (Tg) were noted. Loss of rigidity and deformation of samples were thus attributed to the structural changes in polymer. A strong relationship was noticed for force values and Tg (r = 0.89 for Group A and 0.86 for Group B). Conclusion: Tg can be considered as a dependable parameter in envisaging the force properties of an elastomeric chain. Clinically, it suggested

On the inverse temperature transition and development of an entropic elastomeric force of the elastin mimetic peptide [LGGVG](3, 7).

We report on a molecular dynamics simulation based study of the thermal and mechanical properties of the elastin mimetic peptide [LGGVG](n) (n = 3, 7). Our findings indicate that this peptide undergoes an inverse temperature transition as the temperature is raised from ~20 °C to 42 °C. The thermal behavior is similar to what has been observed in other well studied short mimetic peptides of elastin. Both [LGGVG](n) (n = 3, 7) peptides exhibit an increase in the number of side chain contacts and peptide-peptide hydrogen bonds when the temperature is raised from ~20 °C to 42 °C. These observations are accompanied by a decrease in the number of proximal water molecules and number of peptide-water hydrogen bonds. This work also reports on a comparison of the thermal and mechanical properties of [LGGVG](3) and [VPGVG](3) and quantifies the interaction with surrounding waters of hydration under mechanically strained conditions. It is demonstrated, via a quasi-harmonic approach, that both model peptides exhibit a reduction in the population of low-frequency modes and an increase in population of high-frequency modes upon elongation. The shift in population of frequency modes causes the peptide entropy to decrease upon elongation and is responsible for the development of an entropic force that gives rise to elasticity. These observations are in disagreement with a previously published notion that model elastin peptides, such as [VPGVG](18), increase in entropy upon elongation.

Motion-Based-Design of Elastic Material for Passive Assistive Device Using Musculoskeletal Model

We are developing a passive power assist device, “Smart Suit Lite.” Smart Suit Lite is a compact, lightweight power assist device that utilizes the elastomeric force of elastic materials. We have developed a “motion-based assist method” in order to design Smart Suit Lite for particular motions. We have also developed an extended musculoskeletal model which has “Skin segments” that aid in analyzing assistive force. In this paper, we target the movements of caregivers. From three-dimensional motion data and an extended musculoskeletal model, we analyze human muscle forces and assistive forces. We then design the arrangement and properties of the elastic materials, based on the motion-based assist method. Finally, we verify its assistance effect through basic experiments.

NMR studies of localized water and protein backbone dynamics in mechanically strained elastin.

We report on measurements of the dynamics of localized waters of hydration and the protein backbone of elastin, a remarkable resilient protein found in vertebrate tissues, as a function of the applied external strain. Using deuterium 2D T(1)-T(2) NMR, we separate four reservoirs in the elastin-water system characterized by water with distinguishable mobilities. The measured correlation times corresponding to random tumbling of water localized to the protein is observed to decrease with increasing strain and is interpreted as an increase in its orientational entropy. The NMR T(1) and T(1ρ) relaxation times of the carbonyl and aliphatic carbons of the protein backbone are measured and indicate a reduction in the correlation time as the elastomer strain is increased. It is argued, and supported by MD simulation of a short model elastin peptide [VPGVG](3), that the observed changes in the backbone dynamics give rise to the development of an entropic elastomeric force that is responsible for elastins' remarkable elasticity.

2A1-E07 筋骨格モデルに基づく介護用スマートスーツ・ライトの開発と実フィールド評価(ウェアラブルロボティクス)

We are developing a passive power assist supporter "Smart Suit Light". The smart suit light is a compact and lightweight power assist device utilizing elastomeric force of elastic materials. We constructed Motion-based-assist method to design the smart suit light for particular motions. Moreover, we developed an extended musculoskeletal model which has skin segments for analyzing assist force. In this paper, we deal with care motions as target movement. From three-dimensional motion data and the extended musculoskeletal model, we analyzed human muscle forces and assist forces. Then we designed arrangement and property of the elastic materials based on Motion-based-assist method. Furthermore, its assist effect was verified by basic experiments.

Porous PDMS force sensitive resistors

Here we present an elastomeric force sensitive resistor (FSR) made from a porous matrix of polydimethylsiloxane (PDMS) filled with carbon black. The fabrication process is based on the use of a low cost sacrificial sugar cube scaffold which leads to a highly porous and compressible material. By filling this porous matrix with carbon black we can achieve typical resistance changes from 20 kΩ to 100 Ω for an applied 95% compressive strain. This material is suitable for a wide variety of sensing applications which include tactile artificial skin for robotics and solvent detection.

On the source of entropic elastomeric force in polypeptides and proteins: Backbone configurational vs. side-chain solvational entropy

At physiological temperature In water, the relaxed state of the protein, elastin, and model elastomeric sequential polypeptides derived from this biological elastomer is the result of an inverse temperature transition. At lower temperatures, say at 20°C. the hydrophobic side chams of the elastomers are hydrated with a low-entropy net of water. On raising the temperature, the more ordered waters of hydrophobic hydration are converted to less ordered bulk water as the polypeptide chains fold increasing intra- and intermolecular hydrophobic contacts. Following Flory and colleagues, thermoelasticity studies suggests that these polypeptide elastomers are dominantly entropic elastomers above the temperature of the inverse temperature transition. A central question becomes the source of the entropic elastomeric force. On stretching, hydrophobic side chains become exposed to water, resulting in an exothermic reaction of hydrophobic hydration. The issue addressed by the present report is whether this decrease in solvent entropy on stretching might make a major contribution to the entropic elastomeric restoring force. It has previously been argued that the free energy of solvation can be made very small by a 30% ethylene glycol (EG):70% water solvent mixture. This is demonstrated here using the repeating pentapeptide sequence of elastin (Val '-Pro2-Gly'-Va14-Gly '). or poly( VPGVG) and its 7-irradiation cross-linked elastomeric matrix. Differential scanning calorimetry of the inverse temperature transition of poly( VPGVG) shows the endothermic heat of the transition to become very small in EG/HZO when compared with H20 alone, which also indicates a very small entropy change for the transition on exposure of the hydrophobic side chains to the EG/H20 solvent mixture. A similar result is found for the crosslinked elastomeric matrix. Significantly, however, in spite of the lower heats for hydrophobic solvation. the elastic modulus and the entropic elastomeric forces generated are greater in EG/H2O. Thus, even though the heat of the transition and the entropy change on solvation are markedly reduced, the entropic elastomeric force is increased. Accordingly, it is argued that the entropy change due to hydrophobic sidechain solvation on extension is considered not to be a primary source of the entropic elastomeric force.

Elastin: a representative ideal protein elastomer.

During the last half century, identification of an ideal (predominantly entropic) protein elastomer was generally thought to require that the ideal protein elastomer be a random chain network. Here, we report two new sets of data and review previous data. The first set of new data utilizes atomic force microscopy to report single-chain force-extension curves for (GVGVP)(251) and (GVGIP)(260), and provides evidence for single-chain ideal elasticity. The second class of new data provides a direct contrast between low-frequency sound absorption (0.1-10 kHz) exhibited by random-chain network elastomers and by elastin protein-based polymers. Earlier composition, dielectric relaxation (1-1000 MHz), thermoelasticity, molecular mechanics and dynamics calculations and thermodynamic and statistical mechanical analyses are presented, that combine with the new data to contrast with random-chain network rubbers and to detail the presence of regular non-random structural elements of the elastin-based systems that lose entropic elastomeric force upon thermal denaturation. The data and analyses affirm an earlier contrary argument that components of elastin, the elastic protein of the mammalian elastic fibre, and purified elastin fibre itself contain dynamic, non-random, regularly repeating structures that exhibit dominantly entropic elasticity by means of a damping of internal chain dynamics on extension.

Wheat seed proteins exhibit a complex mechanism of protein elasticity

Elastomeric proteins are found in a number of animal tissues (elastin, abductin and resilin), where they have evolved to fulfil a range of biological functions. All exhibit rubber-like elasticity, undergoing deformation without rupture, storing the energy involved in deformation, and then recovering to their initial state when the stress is removed. The second part of the process is passive, entropy decreasing when the proteins are deformed, with the higher entropy of the relaxed state providing the driving force for recoil. In plants there is only one well-documented elastomeric protein system, the alcohol-soluble seed storage proteins (gluten) of wheat. The elastic properties of these proteins have no known biological role, the proteins acting as a store for the germinating seed. Here we show that the modulus of elasticity of a group of wheat gluten subunits, when cross-linked by γ-radiation, is similar to that of the cross-linked polypentapeptide of elastin. However, thermoelasticity studies indicate that the mechanism of elastic recoil is different from elastin and other characterized protein elastomers. Elastomeric force, f, has two components, an internal energy component, f e, and an entropic component, f s. The ratio f e/ f can be determined experimentally; if this ratio is less than 0.5 the elastomeric force is predominantly entropic in origin. The ratio was determined as 5.6 for the cross-linked high M r subunits of wheat glutenin and near zero for the cross-linked polypentapeptide of elastin. Tensile stress must be entropic or energetic in origin, the results would suggest that elastic recoil in the wheat gluten subunits, in part, may be associated with extensive hydrogen bonding within and between subunits and that entropic and energetic mechanisms contribute to the observed elasticity.

?-Spiral conformations of the elastomeric polytetrapeptides, (VPGG)n and (IPGG)n, by 2DNMR and molecular mechanics studies

The synthetic polytetrapeptide using the repeating sequence VPGG found in the fibrous protein, elastin, exhibits a reversible inverse temperature transition, i.e., the molecular order increases on raising the temperature of the polypeptide in aqueous solutions. The matrices formed from the coacervate by γ-irradiation-induced cross-linking exhibit an elastic modulus and temperature dependence of elastomeric force with similarity to that of fibrous elastin. As demonstrated on poly(VPGVG), which forms a β-spiral structure with recurring Type II β-turns, the molecular structure of the elastin-based polypeptides is fundamental to an understanding of the mechanism of elasticity. It was found previously that the repeating unit VPGG in the polytetrapeptide forms a Type II β-turn with a hydrogen bond between Val1 CO and Gly4 NH. This secondary structural feature is confirmed in this report by 2D NMR data as indicated by specific NOE cross-peaks, particularly, dNN(3,4), dαN(2,3), dαN(2,4), and dγN(1,4). The same secondary structural feature is found in the 2D NMR data for its analog polypeptide, poly(IPGG). The NMR data provide conclusive evidence for the Type II β-turn secondary structure. Molecular mechanics computations were performed to develop a more detailed tertiary structure for the polytetrapeptides. The ECEPP/2 potential field and build-up strategy were employed in mapping conformational space of VPGG and its high polymer. In addition, helical structures are sought using the Go–Scheraga condition, on the assumption that the repeated sequence would preferentially adopt a helical or nearhelical conformation on optimization of intramolecular hydrophobic contacts. A number of structures with helically recurring β-turns was obtained and can be used as starting structures in future studies that are to include hydration. The structures were also evaluated in terms of potential energy using the CHARMm force field.

Mechanochemical coupling in synthetic polypeptides by modulation of an inverse temperature transition.

For the polypentapeptide of elastin, (L-Val-L-Pro-Gly-L-Val-Gly)n, and appropriate analogs when suitably cross-linked, it has been previously demonstrated that development of elastomeric force at fixed length and length changes at fixed load occur as the result of an inverse temperature transition, with the temperature of the transition being inversely dependent on the hydrophobicity of the polypeptide. This suggests that at fixed temperature a chemical means of reversibly changing the hydrophobicity could be used for mechanochemical coupling. Evidence for this mechanism of mechanochemical coupling is given here with a 4%-Glu-polypentapeptide, in which the valine in position 4 is replaced in 1 out of 5 pentamers by a glutamic acid residue. Before cross-linking, the temperature for aggregation of 4%-Glu-polypentapeptide is remarkably sensitive to pH, shifting from 25 degrees C at pH 2 to 70 degrees C at pH 7.4 in phosphate-buffered saline (PBS). At 37 degrees C, the cross-linked 4%-Glu-polypentapeptide matrix in PBS undergoes a pH-modulated contraction and relaxation with a change from pH 4.3 to 3.3 and back. The mean distance between carboxylates at pH 4.3 in the elastomeric matrix is greater than 40 A, twice the mean distance between negatively charged species in PBS. Accordingly, charge-charge repulsion is expected to make little or no contribution to the coupling. Mechanochemical coupling is demonstrated at fixed load by monitoring pH dependence of length and at constant length by monitoring pH dependence of force. To our knowledge, this is the first demonstration of mechanochemical coupling in a synthetic polypeptide and the first system to provide a test of the recent proposal that chemical modulation of an inverse temperature transition can be a mechanism for mechanochemical coupling. It is suggested that phosphorylation and dephosphorylation may modulate structure and forces in proteins by locally shifting the temperatures of inverse temperature transitions.

Entropic elastic processes in protein mechanisms. II. Simple (passive) and coupled (active) development of elastic forces.

The first part of this review on entropic elastic processes in protein mechanisms (Urry, 1988) demonstrated with the polypentapeptide of elastin (Val1-Pro2-Gly3-Val4-Gly5)n that elastic structure develops as the result of an inverse temperature transition and that entropic elasticity is due to internal chain dynamics in a regular nonrandom structure. This demonstration is contrary to the pervasive perspective of entropic protein elasticity of the past three decades wherein a network of random chains has been considered the necessary structural consequence of the occurrence of dominantly entropic elastomeric force. That this is not the case provides a new opportunity for understanding the occurrence and role of entropic elastic processes in protein mechanisms. Entropic elastic processes are considered in two classes: passive and active. The development of elastomeric force on deformation is class I (passive) and the development of elastomeric force as the result of a chemical process shifting the temperature of a transition is class II (active). Examples of class I are elastin, the elastic filament of muscle, elastic force changes in enzyme catalysis resulting from binding processes and resulting in the straining of a scissile bond, and in the turning on and off of channels due to changes in transmembrane potential. Demonstration of the consequences of elastomeric force developing as the result of an inverse temperature transition are seen in elastin, where elastic recoil is lost on oxidation, i.e., on decreasing the hydrophobicity of the chain and shifting the temperature for the development of elastomeric force to temperatures greater than physiological. This is relevant in general to loss of elasticity on aging and more specifically to the development of pulmonary emphysema. Since random chain networks are not the products of inverse temperature transitions and the temperature at which an inverse temperature transition occurs depends on the hydrophobicity of the polypeptide chain, it now becomes possible to consider chemical processes for turning elastomeric force on and off by reversibly changing the hydrophobicity of the polypeptide chain. This is herein called mechanochemical coupling of the first kind; this is the chemical modulation of the temperature for the transition from a less-ordered less elastic state to a more-ordered more elastic state. In the usual considerations to date, development of elastomeric force is the result of a standard transition from a more-ordered less elastic state to a less-ordered more elastic state.(ABSTRACT TRUNCATED AT 400 WORDS)

Entropic elastic processes in protein mechanisms. I. Elastic structure due to an inverse temperature transition and elasticity due to internal chain dynamics.

Numerous physical characterizations clearly demonstrate that the polypentapeptide of elastin (Val1-Pro2-Gly3-Val4-Gly5)n in water undergoes an inverse temperature transition. Increase in order occurs both intermolecularly and intramolecularly on raising the temperature from 20 to 40 degrees C. The physical characterizations used to demonstrate the inverse temperature transition include microscopy, light scattering, circular dichroism, the nuclear Overhauser effect, temperature dependence of composition, nuclear magnetic resonance (NMR) relaxation, dielectric relaxation, and temperature dependence of elastomer length. At fixed extension of the cross-linked polypentapeptide elastomer, the development of elastomeric force is seen to correlate with increase in intramolecular order, that is, with the inverse temperature transition. Reversible thermal denaturation of the ordered polypentapeptide is observed with composition and circular dichroism studies, and thermal denaturation of the crosslinked elastomer is also observed with loss of elastomeric force and elastic modulus. Thus, elastomeric force is lost when the polypeptide chains are randomized due to heating at high temperature. Clearly, elastomeric force is due to nonrandom polypeptide structure. In spite of this, elastomeric force is demonstrated to be dominantly entropic in origin. The source of the entropic elastomeric force is demonstrated to be the result of internal chain dynamics, and the mechanism is called the librational entropy mechanism of elasticity. There is significant application to the finding that elastomeric force develops due to an inverse temperature transition. By changing the hydrophobicity of the polypeptide, the temperature range for the inverse temperature transition can be changed in a predictable way, and the temperature range for the development of elastomeric force follows. Thus, elastomers have been prepared where the development of elastomeric force is shifted over a 40 degrees C temperature range from a midpoint temperature of 30 degrees C for the polypentapeptide to 10 degrees C by increasing hydrophobicity with addition of a single CH2 moiety per pentamer and to 50 degrees C by decreasing hydrophobicity.(ABSTRACT TRUNCATED AT 400 WORDS)

Entropic elastomeric force in protein structure/function

Briefly noting earlier studies on the polypentapeptide of elastin, (Val1-Pro2-Gly3-Val4-Gly5)n, and on elastin, it is emphasized that entropic elastomeric force can be exhibited by nonrandom, anisotropic polypeptide systems and therefore that entropic elastomeric force does not necessarily result from isotropic random chain networks as required by the classical theory of rubber elasticity, nor does it result from solvent entropy effects as deduced from the slow loss of elastomeric force on thermal denaturation. Instead entropic protein elasticity can be the result of internal chain dynamics, specifically of librational processes that become damped on chain extension. This new mechanism of entropic protein elasticity allows for an understanding not only of elastin but also of the passive tension of striated muscle, of the voltage-dependent interconversion between open and closed conductance states in the sodium channel of squid nerve, and of protein elastic forces producing strain in a substrate bond during enzyme catalysis. Because entropic elastomeric force develops as a result of an inverse temperature transition, it becomes possible to shift the temperature of the transition to higher or lower temperatures by decreasing or increasing, respectively, the hydrophobicity of the elastomeric polypeptide chain. In warm-blooded animals this allows for biochemical modulation of the relaxation or development of entropic elastomeric force by an enzymatically modulated decrease or increase of the hydrophobicity, as for example, by phosphorylation or dephosphorylation of the elastomeric polypeptide chain. This understanding provides a mechanism for modulating protein function, whether for example enzymatic or channel, a mechanism for the remarkable reversible structural processes that attend parturition, and a mechanism for the connective tissue anomalies of wound repair and enviromentally induced lung disease.

Polytetrapeptide of elastin

High molecular weight polytetrapeptide of elastin, (L.Val1-L.Pro2-Gly3-Gly4)n, was synthesized using activation of the (GGVP) permutation for polymerization. The temperature-dependence of aggregation was characterized as a function of concentration and the circular dichroism spectra were obtained in the 20 degrees to 70 degrees C temperature range. The latter showed an inverse temperature transition centered near 50 degrees C in which polypeptide order increased on raising the temperature. A concentration of 0.6 g of polytetrapeptide in 1 g of water was gamma irradiation cross-linked (20 Mrad) to form an elastomeric matrix. A study of the temperature-dependence of elastomeric force demonstrated a transition toward increased force on raising the temperature with a midpoint of the transition near 50 degrees C. Thus, there is a correlation between increase in intramolecular order and elastomeric force development. These results are compared to previous results on the polypentapeptide of elastin, (VPGVG)n and on an analog, (IPGVG)n, to demonstrate that the temperature of the transition is proportional to the hydrophobicity of the repeating unit. The point is noted that the elastomeric force development correlates better with intramolecular ordering than with intermolecular processes.

Temperature-correlated force and structure development in elastomeric polypeptides: the Ile1 analog of the polypentapeptide of elastin.

AbstractThe Ile1 analog of the polypentapeptide of elastin, (L · Ile1‐L · Pro2‐Gly3‐L · Val4‐Gly5)n, abbreviated as Ile1‐PPP, was synthesized with n > 100 to determine the effect of the increased hydrophobicity of the pentamer resulting from Val1 replacement by Ile1 on the previously characterized inverse temperature transition of the polypentapeptide of elastin (PPP). Ile1‐PPP, dissolved in water at 4°C, was found to aggregate, forming a viscoelastic coacervate on raising the temperature. The onset of aggregation was 8°C for Ile1‐PPP, as compared to 24°C for PPP. Characterization by CD demonstrated an increase in intramolecular order on raising the temperature from 8°C to 25°C, and demonstrated similar conformations for PPP and Ile1‐PPP before and after their respective transitions. The CD‐characterized transition also occurred at a temperature some 15°C lower than that of PPP. By means of 20‐Mrad γ‐irradiation cross‐linking of the Ile1‐PPP coacervate, an elastomeric matrix was formed with an elastic modulus, similar to that of 20‐Mrad cross‐linked PPP. The temperature dependence of elastomeric force of cross‐linked Ile1‐PPP showed an abrupt increase from essentially zero at 8°C to three‐quarters of full force at 10°C and essentially full force by 20–25°C. This development of elastomeric force for the more hydrophobic Ile1‐PPP matrix, which parallels the increase in intramolecular order characterized by the CD studies, also occurs at a temperature some 15°C lower than that for the PPP matrix. Thus, in these elastomeric polypeptides, development of elastomeric force is coupled to an inverse temperature transition, the temperature of which depends inversely on the hydrophobicity of the constituent pentamer. It appears that a series of elastomeric polypeptide biomaterials are possible in which the temperature over which elastomeric force develops can be varied.

Carbon-13 NMR relaxation studies demonstrate an inverse temperature transition in the elastin polypentapeptide.

Carbon-13 NMR longitudinal relaxation time and line-width studies are reported on the coacervate concentration (about 60% water by weight) of singly carbonyl carbon enriched polypentapeptides of elastin: specifically, (L-Val1-L-[1-13C]Pro2-Gly3-L-Val4-Gly5)n and (L-Val1-L-Pro2-Gly3-L-Val4-[1-13C]Gly5)n. On raising the temperature from 10 to 25 degrees C and from 40 to 70 degrees C, carbonyl mobility increases, but over the temperature interval from 25 to 40 degrees C, the mobility decreases. The results characterize an inverse temperature transition in the most fundamental sense of temperature being a measure of molecular motion. This transition in the state of the polypentapeptide indicates an increase in order of polypeptide on raising the temperature from 25 degrees C to physiological temperature. This fundamental NMR characterization corresponds with the results of numerous other physical methods, e.g., circular dichroism, dielectric relaxation, and electron microscopy, that correspondingly indicate an increase in order of the polypentapeptide both intramolecularly and intermolecularly for the same temperature increase from 25 to 40 degrees C. Significantly with respect to elastomeric function, thermoelasticity studies on gamma-irradiation cross-linked polypentapeptide coacervate show a dramatic increase in elastomeric force over the same interval that is here characterized by NMR as an inverse temperature transition. The temperature dependence of mobility above 40 degrees C indicates an activation energy of the order of 1.2 kcal/mol, which is the magnitude of barrier expected for elasticity.