Thermal Shrinkage Temperature Research Articles

Effects of freeze-drying bovine pericardium using a combination of polyethylene glycol and trehalose

The freeze-drying is a technology that preserves biological samples in a dry state, which is beneficial for storage, transportation, and cost saving. In this study, the bovine pericardium was treated with a freeze-drying protectant composed of polyethylene glycol (PEG) and trehalose (Tre), and then freeze-dried. The results demonstrated that the mechanical properties of the pericardium treated with PEG + 10% w/v Tre were superior to those of the pericardium fixed with glutaraldehyde (GA). The wet state water content of the rehydrated pericardium, determined using the Karl Fischer method, was (74.81 ± 1.44)%, which was comparable to that of the GA-fixed pericardium. The dry state water content was significantly reduced to (8.64 ± 1.52)%, indicating effective dehydration during the freeze-drying process. Differential scanning calorimetry (DSC) testing revealed that the thermal shrinkage temperature of the pericardium was (84.96 ± 0.49) ℃, higher than that of the GA-fixed pericardium (83.14 ± 0.11) ℃, indicating greater thermal stability. Fourier transform infrared spectroscopy (FTIR) results showed no damage to the protein structure during freeze-drying. Hematoxylin and eosin (HE) staining demonstrated that the freeze-drying process reduced pore formation, prevented ice crystal growth, and resulted in a tighter arrangement of tissue fibers. The frozen-dried bovine pericardium was subjected to tests for cell viability and hemolysis rate. The results revealed a cell proliferation rate of (77.87 ± 0.49)%, corresponding to a toxicity grade of 1. Additionally, the hemolysis rate was (0.17 ± 0.02)%, which is below the standard of 5%. These findings indicated that the frozen-dried bovine pericardium exhibited satisfactory performance in terms of cytotoxicity and hemolysis, thus meeting the relevant standards. In summary, the performance of the bovine pericardium treated with PEG + 10% w/v Tre and subjected to freeze-drying could meet the required standards.

Role of Heat Release from Inter-Electrode Chemical Crosstalk in Thermal Runaway Propagation Characteristics of Lithium-Ion Battery Modules

While lithium-ion batteries are continually increasing in energy and power density, thermal safety still remains a significant concern. In some thermal abuse scenarios, thermal runaway can be triggered by the exothermic reactions from inter-electrode chemical crosstalk between the cathode and the anode without an internal short circuit. Under these circumstances, the thermal runaway temperature is lower than the separator's thermal shrinkage temperature, implying that the cell's catastrophic thermal runaway occurs without a large-scale short circuit produced by separator failure. These cell failures must be managed such that the neighboring cells in a battery module are not affected, a phenomenon known as thermal runaway propagation. In the present work, we employed a high-resolution cell-level thermal runaway model constructed from the accelerating rate calorimetry data of a commercial Li-ion cell to characterize the cell-to-cell thermal runaway propagation behavior for a basic square arrangement of lithium-ion battery module connected by tabs. We determined safe practices under the effects of different ambient conditions, inter-cell spacing, trigger cell location, and external heating power. Additionally, we have identified the critical pathways for the thermal runaway propagation in the battery module and quantified their statistical distribution in terms of the thermal runaway propagation speed, heat release from exothermic reactions, and heat dissipation to the surroundings. The findings from the study are believed to be of immediate relevance for the safer design of lithium-ion battery packs.

Improved Cytocompatibility and Reduced Calcification of Glutaraldehyde-Crosslinked Bovine Pericardium by Modification With Glutathione

Bioprosthetic heart valves (BHVs) used in clinics are fabricated via glutaraldehyde (GLUT) crosslinking, which results in cytotoxicity and causes eventual valve calcification after implantation into the human body; therefore, the average lifetime and application of BHVs are limited. To address these issues, the most commonly used method is modification with amino acids, such as glycine (GLY), which is proven to effectively reduce toxicity and calcification. In this study, we used the l-glutathione (GSH) in a new modification treatment based on GLUT-crosslinked bovine pericardium (BP) as the GLUT + GSH group, BPs crosslinked with GLUT as GLUT-BP (control group), and GLY modification based on GLUT-BP as the GLUT + GLY group. We evaluated the characteristics of BPs in different treatment groups in terms of biomechanical properties, cell compatibility, aldehyde group content detection, and the calcification content. Aldehyde group detection tests showed that the GSH can completely neutralize the residual aldehyde group of GLUT-BP. Compared with that of GLUT-BP, the endothelial cell proliferation rate of the GLUT + GSH group increased, while its hemolysis rate and the inflammatory response after implantation into the SD rat were reduced. The results show that GSH can effectively improve the cytocompatibility of the GLUT-BP tissue. In addition, the results of the uniaxial tensile test, thermal shrinkage temperature, histological and SEM evaluation, and enzyme digestion experiments proved that GSH did not affect the ECM stability and biomechanics of the GLUT-BP. The calcification level of GLUT-BP modified using GSH technology decreased by 80%, indicating that GSH can improve the anti-calcification performance of GLUT-BP. Compared with GLUT-GLY, GLUT + GSH yielded a higher cell proliferation rate and lower inflammatory response and calcification level. GSH can be used as a new type of anti-calcification agent in GLUT crosslinking biomaterials and is expected to expand the application domain for BHVs in the future.

Achieving superiorly highheat‐dimensionalstability, high strength, and good electrochemical performance for electrospun separators in powerlithium‐ionbattery through building unique condensed structure based on polyimide and poly (m‐phenylene isophthalamide)

AbstractIt is still a challenge for simultaneously achieving high heat resistance, high strength and outstanding electrochemical performance for separators in power lithium‐ion battery (PLB). Herein, new high performance electrospun separators are developed through building unique structure based on polyimide (PI) and poly (m‐phenylene isophthalamide) (PMIA). Orthogonal tests (44) show that the magnitude order of electrospinning factors on the morphology of membrane is concentration>injection rate>receiving distance>voltage. With the optimum factors, the electrospun membrane (PI/PMIA) was prepared, which was further pressed at 100°C for 10 min to get treated membrane (H‐PI/PMIA). Interestingly, the comprehensive performance of PI/PMIA is not a simple combination of those of PI and PMIA; instead, PI/PMIA has much better thermal and mechanical properties than both PI and PMIA, proving that PI/PMIA has a synergistic effect. PI/PMIA and H‐PI/PMIA not only have good ionic conductivity and electrochemical stability, but also have superiorly high properties including dimensional stability (thermal shrinkage temperature>300°C), tensile strengths (24.1 MPa for PI/PMIA, 34.3 MPa for H‐PI/PMIA) and capacity retentions (97.9%, 99.2%) compared with electrospun membranes for PLBs reported in the literature so far (SCI database). The mechanism behind these attractive performances is discussed from condensed structure of membranes.

The study of dry biological valve crosslinked with a combination of carbodiimide and polyphenol.

The glutaraldehyde crosslinked pericardium has been used in bioprosthetic valves for about 50 years. However, problems such as glutaraldehyde residue and calcification still exist in current commercial products. Non-glutaraldehyde crosslinked dry valve is an important strategy to solve those problems. In this study, a non-glutaraldehyde crosslinked dry biological valve material was obtained by the combined crosslinking of carbodiimide (EDC) and polyphenol. The results showed that the comprehensive properties of EDC and curcumin crosslinked pericardium were superior to glutaraldehyde crosslinked pericardium, including unfolding property, anti-calcification, cytotoxicity, anticoagulant properties, mechanical properties, enzyme degradation resistance and thermal shrinkage temperature. EDC and curcumin crosslinked dry pericardium could flatten after being folded at 40°C for 3 days while glutaraldehyde crosslinked pericardium could not. The calcification of pericardium treated with EDC and curcumin was 1.21 ± 0.36 mg/g in rats after 60 days’ subdermal implantation, much lower than that of glutaraldehyde treated control group (22.06 ± 3.17 mg/g).

The penetration and accumulation of hydroxyapatite and the hydrothermal stability of collagen matrix material

Abstract Hydroxyapatite (HAP) has been extensively used in the clinic, for example, for bone tissue repair, because of its outstanding performance. However, whether HAP can be utilized in other fields, such as leather manufacturing, remains unknown. The process of making leather from hide involves a hydrothermal treatment. Thus, in the present work, HAP was synthesized using a hydrothermal method with diammonium hydrogen phosphate and calcium nitrate as phosphorus and calcium precursors, respectively. The condition optimization test results indicated that high-purity HAP can be obtained when the reaction is carried out at 80 °C and pH 11, with surfactant added. To study the effect of HAP on cowhide and to determine whether it can be used as a tanning agent, tests of in vitro and in vivo HAP addition into cowhide were conducted. The cowhide was first subjected to a wet-end leather making process and then cut into samples. Samples were treated using different HAP addition methods, and experimental results obtained under different conditions were compared. Fourier-transform infrared spectroscopy analysis indicated that HAP added by both methods can react with cowhide. Physicochemical properties of cowhide were improved after reaction with HAP, specifically, the thermal stability was enhanced when HAP was synthesized in the skin. The thermal shrinkage temperature of the treated hide was 78 °C, which was higher than 54 °C for the control group samples. The hide tear strength was greatly enhanced because HAP synthesized on hide collagen caused the formation of a rigid module. Therefore, HAP has the potential to be used as a chrome-free tanning agent. This study demonstrated that the modification of cowhide by HAP was feasible and HAP tanning or HAP combination tanning was of practical significance.

Effect of Proteolytic Enzymes and Ginger Extract on Tenderization of M. pectoralis profundus from Holstein Steer.

The effects of proteolytic enzymes (bromelain and bromelain+papain) and a ginger extract were assessed on collagen content and solubility, thermal shrinkage temperature of connective tissue, pH, cooking loss, drip loss, and Warner-Bratzler shear force (WBSF) of M. pectoralis profundus isolated from the beef brisket cut. Both proteolytic enzymes and ginger extract led to a significant increase in cooking loss and collagen solubility compared with untreated controls. On the other hand, the peak (Tp) thermal shrinkage temperature markedly decreased in all treatments compared with those in controls. Samples treated with bromelain, bromelain + papain, and ginger extract showed a significant decrease in WBSF by 36%, 40%, and 37%, respectively, compared with untreated controls. Our findings suggest that ginger extract are useful for postmortem tenderization of meat containing high levels of collagen, compared to control even though, bromelain and bromelain + papain treatments have higher collagen solubility than ginger extract.

Influence of telopeptides on the structural and physical properties of polymeric and monomeric acid-soluble type I collagen

Currently two factors hinder the use of collagen as building block of regenerative devices: the limited mechanical strength in aqueous environment, and potential antigenicity. Polymeric collagen is naturally found in the cross-linked state and is mechanically tougher than the monomeric, acid-soluble collagen ex vivo. The antigenicity of collagen, on the other hand, is mainly ascribed to inter-species variations in amino acid sequences of the non-helical terminal telopeptides. These telopeptides can be removed through enzymatic treatment to produce atelocollagen, although the effect of this cleavage on triple helix organization, amino acidic composition and thermal properties is often disregarded. Here, we compare the structural, chemical and physical properties of polymeric and monomeric type I collagen with and without telopeptides, in an effort to elucidate the influence of either mature covalent crosslinks or telopeptides. Circular dichroism (CD) was used to examine the triple helical conformation and quantify the denaturation temperature (Td) of both monomeric collagen (36.5°C) and monomeric atelocollagen (35.5°C). CD measurements were combined with differential scanning calorimetry (DSC) in order to gain insight into the triple helix-to-coil thermal transition and shrinkage temperature (Ts) of polymeric atelo collagen (44.8°C), polymeric collagen (62.7°C), monomeric atelo collagen (51.4°C) and monomeric collagen (66.5°C). Structural and thermal analysis was combined with high pressure liquid chromatography (HPLC) to determine the content of specific collagen amino acidic residues used as markers for the presence of telopeptides and mature crosslinks. Hydroxylamine was used as the marker for polymeric collagen, and had a total content of 9.66% for both polymeric and polymeric atelo collagen; tyrosine was used as the marker for telopeptide cleavage, was expressed as 0.526% of the content of polymeric collagen and the partially-reduced content of 0.39% for atelocollagen.

Chromium recovery from tannery sludge by bioleaching and its reuse in tanning process

Bioleaching has been demonstrated as a feasible and effective technology for removing Cr(III) from tannery sludge, but the recovery of bioleachate derived from tannery sludge by bioleaching is rarely reported. The purpose of this study was therefore to figure out the components of bioleachate and develop a chromium-iron tanning agent using the bioleachate and reuse it in tanning process. Component analysis indicated that the bioleachate contained high concentrations of Cr and Fe, as well as small quantities of other elements. The dissolved organic matter in the bioleachate was detected to be less than 1000 mg/L, which was mainly composed of polysaccharide, aliphatic or aromatic carboxylic acid compounds. A chromium-iron tanning agent was then prepared using the bioleachate, iron and chromium salts in a suitable ligand environment, and reused for tanning. In the tanning experiments, the pickled pigskins were tanned with this prepared tanning agent and the results indicated that chromium-iron tanned crust leather presented comparable physical and mechanical properties as well as air permeability when compared with conventional chromium tanned crust leather, but the thermal shrinkage temperature was about 4 °C lower than that of the chromium tanned crust leather. Therefore, this study provides not only a reuse route for tannery sludge bioleachate but also a clean tanning agent for leather processing.

Acoustic radiation force for noninvasive evaluation of corneal biomechanical changes induced by cross-linking therapy.

To noninvasively measure changes in corneal biomechanical properties induced by ultraviolet-activated riboflavin cross-linking therapy using acoustic radiation force (ARF). Cross-linking was performed on the right eyes of 6 rabbits, with the left eyes serving as controls. Acoustic radiation force was used to assess corneal stiffness before treatment and weekly for 4 weeks after treatment. Acoustic power levels were within US Food and Drug Administration guidelines for ophthalmic safety. Strain, determined from ARF-induced displacement of the front and back surfaces of the cornea, was fit to the Kelvin-Voigt model to determine the elastic modulus (E) and coefficient of viscosity (η). The stiffness factor, the ratio of E after treatment to E before treatment, was calculated for treated and control eyes. At the end of 4 weeks, ex vivo thermal shrinkage temperature analysis was performed for comparison with in vivo stiffness measurements. One-way analysis of variance and Student t tests were performed to test for differences in E, η, the stiffness factor, and corneal thickness. Biomechanical stiffening was immediately evident in cross-linking-treated corneas. At 4 weeks after treatment, treated corneas were 1.3 times stiffer and showed significant changes in E (P= .006) and η (P= .007), with no significant effect in controls. Corneal thickness increased immediately after treatment but did not differ significantly from the pretreatment value at 4 weeks. Our findings demonstrate a statistically significant increase in stiffness in cross-linking-treated rabbit corneas based on in vivo axial stress/strain measurements obtained using ARF. The capacity to noninvasively monitor corneal stiffness offers the potential for clinical monitoring of cross-linking therapy.

Collagen crosslinking of porcine sclera using genipin

To evaluate the effect of collagen cross-linking induced by genipin in porcine sclera. Porcine cadaver eyes were treated with genipin at concentrations (by w/v) of 0.01%, 0.03%, 0.1%, 0.3%, 1.0% for 15 and 30 min. Riboflavin/ultraviolet A(UVA)-treated and untreated samples were used as controls. After treatment, scleral strips of 4.0 × 10.0 mm were cut. Twenty-four hours later, the stress-strain parameters of the strips were measured using a biomaterial microtester. The stress and Young's modulus at 8% strain were evaluated. Compared with untreated groups, after treatment with genipin for 15 min, the stress was increased by 66-246%, depending on the concentration of genipin. As for the 30-min groups, the stress was 171-444% higher than that of the control. The difference of the Young's modulus between genipin 15-min groups, except the 0.01% groups (p = 0.095), also had statistical significance (p < 0.05). The Young's modulus had significant difference between the untreated group and the genipin 30-min groups (all p < 0.05). Of 0.3% genipin for 15 min or 0.01% genipin for 30 min had a similar stress-strain curve with those of eyes treated with the riboflavin/UVA group. The sclera exhibited a bluish colour which became deeper with increase concentration and cross-linking time. Collagen cross-linking induced by genipin could increase the biomechanical strength in porcine sclera. The effect depends on the concentration and treatment time of genipin.

Assessment of physical properties of fibres from thermoplastic polymers by means of tensiometric tests

Several properties of fibres and monofilaments made from polymers such as polyamide 6 (PA), poly(ethylene terephthalate) (PET), polypropylene (PP), aliphatic polyester of butanediol, succinic and adipic acids (PBSA), aliphatic-aromatic polyester of butanediol, terephthalic and adipic acids (PBTA) have been studied. Wettability of monofilaments has been tested by dynamic contact angle method, so surface free energy of synthetic fibres could be calculated. A tensiometer was used for testing the fibre-to-fibre friction coefficient, Young's modulus and bending modulus. It was found that the surface properties of fibres from synthetic polymers such as surface free energy, moisture absorption, and friction coefficient are related to the physical as well as physical–chemical properties, elasticity, elongation, thermal shrinkage and glass transition temperature. The good coherence of the tests performed with the theoretical relationship between Young's modulus of fibres and glass transition temperature of fibre-forming polymers clearly and definitely verifies the experimental results.

Aliphatic β-Nitroalcohols for Therapeutic Corneoscleral Cross-linking: Chemical Mechanisms and Higher Order Nitroalcohols

The recent tissue cross-linking studies indicate that aliphatic beta-nitroalcohols (BNAs) may be useful as pharmacologic corneoscleral cross-linking agents. The present study was performed to identify the specific chemistry involved under physiologic conditions, with the intent of identifying more effective agents. The mechanism of chemical cross-linking at pH 7.4 and 37 degrees C was studied using three techniques. The colorimetric Griess assay was used to follow the release of nitrite from three mono-nitroalcohols (2-nitroethanol [2ne], 2-nitro-1-propanol [2nprop]), and 3-nitro-2-pentanol [3n2pent]). Second, the evolution of 2nprop in 0.2 M NaH(2)PO(4)/Na(2)HPO(4)/D(2)O was studied using (1)H-NMR. Third, thermal shrinkage temperature analysis (T(s)), a measure of tissue cross-linking, was used to support information from (1)the H-NMR studies. A time-dependent release of nitrite was observed for all three mono-nitroalcohols studied. The maximum levels were comparable using either 2ne or 2nprop (approximately 30%). However, much less (approximately 10%) was observed from 3n2pent. Using (1)H-NMR, 2nprop evolved into a unique splitting pattern. No match was observed with reference spectra from three possible products of denitration. In contrast, 2-methyl-2-nitro-1,3-propanediol (MNPD), a nitro-diol, was identified, implying the formation of formaldehyde from a retro-nitroaldol (i.e., reverse Henry) reaction. In support of this mechanism, T(s) shifts induced by the nitro-triol 2-hydroxymethyl-2-nitro-1,3-propanediol (HNPD) were superior to the nitro-diol MNPD which were superior to the mono nitroalcohol 2nprop. BNAs function as both formaldehyde and nitrite donors under physiologic conditions to cross-link collagenous tissue. Higher order BNAs are more effective than mono nitroalcohols, raising the possibility of using these agents for therapeutic corneoscleral cross-linking.

Initial Studies Using Aliphatic β-Nitro Alcohols for Therapeutic Corneal Cross-Linking

Corneal collagen cross-linking through UVA-riboflavin photochemistry (UVAR) has been shown to be an effective treatment for keratoconus and related keratectasias. In recent studies using sclera, the authors observed that short-chain aliphatic beta-nitro alcohols can cross-link collagenous tissue under physiologic conditions. Thus, this study was undertaken to evaluate these agents as potential pharmacologic alternatives to UVAR. Porcine corneal strips (8 x 4 mm) and corneoscleral complexes were cross-linked using 1 to 100 mM 2-nitroethanol (2ne), 2-nitro-1-propanol (2nprop), and 3-nitro-2-pentanol (3n2pent) at pH 7.4, 34 degrees C. Cross-linking by UVAR was carried out for comparison. Thermal shrinkage temperature analysis was used to evaluate cross-linking effects, and changes in corneal light transmission were determined with a fiber-optic spectrophotometer. At 10 and 100 mM for 96 hours, initial shrinkage temperature (T(i)) was shifted by 3.3 degrees C (P < 0.001) and 9.8 degrees C (P < 0.001) for 2ne, 2.9 degrees C (P = 0.008) and 4.9 degrees C (P < 0.001) for 2nprop, and 3.8 degrees C (P = 0.003) and 4.9 degrees C (P < 0.001) for 3n2pent. Reacting at 1 mM through daily exchange of fluid over 7 days shifted T(i) by 3.8 degrees C (P < 0.001), 4.4 degrees C (P = 0.002), and 3.2 degrees C (P = 0.005), for 2ne, 2nprop, and 3n2pent, respectively. These shifts were greater than cross-linking using UVAR (T(i) = 1.9 degrees C; P = 0.012). In the blue light region (400-500 nm), transmission was decreased by 5.6% (P = 0.003), 2.1% (P = 0.260), and 0% (P = 0.428) for 2ne, 2nprop, and 3n2pent, respectively. beta-Nitro alcohols can induce corneal cross-linking in vitro better than the UVAR technique and can induce negligible effects on light transmission. These early results suggest that such compounds could be used as topical stiffening agents for keratoconus and related disorders.

Aliphatic β-nitro alcohols for non-enzymatic collagen cross-linking of scleral tissue

The success of riboflavin photochemical cross-linking of the cornea in treating keratoconus and post-surgical keratectasia has prompted interest in cross-linking scleral tissue with a potential application to stabilize myopic progression. Applying an UVA light source to the sclera is difficult, particularly in the posterior region. An alternate pharmacologic approach to scleral cross-linking may be possible. The present study was undertaken in order to identify nitrite related compounds capable of inducing scleral tissue cross-linking and to gain information regarding the possible chemical mechanisms involved. 8 × 4 mm strips of porcine and human sclera were incubated in various concentrations of nitrite related agents (1–100 mM) at 37 °C. pH 7.4 was used for all experiments except those involving NaNO 2. Following a 24–96 h incubation period, the samples were tested for cross-linking effects using thermal shrinkage temperature ( T s) analysis. Several compounds were studied including NaNO 2, 2-nitroethanol, 2-nitro-1-propanol, 3-nitro-2-pentanol, 2-nitrophenol, 2-nitroethane, 2-aminoethanol, isopentyl nitrite, DPTA/NO, DETA/NO, and urea, a nitrous acid trap. The results indicate that short chain aliphatic β-nitro alcohols (2-nitroethanol, 2-nitro-1-propanol, and 3-nitro-2-pentanol) are particularly effective cross-linking agents at pH 7.4, showing both time and concentration dependent effects. Furthermore, nitrosation does not appear to induce tissue cross-linking. In conclusion, aliphatic β-nitro alcohols can cross-link scleral tissue at physiologic pH and temperature. Since β-nitro alcohols are known to have reasonable toxicity profiles, these agents could find utility as pharmacologic cross-linking agents for scleral thinning disease.

Thermal stability of connective tissue from porcine muscles

Connective tissue of three porcine muscles ( M. infraspinatus, IS; M. longissimus dorsi, LD; M. semimembranosus, SM) from 27 animals [populations A ( n = 13, reared in Ireland) and B ( n = 14, reared in Finland)] was studied by measuring the collagen content, collagen solubility and thermal shrinkage temperature of the connective tissue. Colour and pH were also determined. Collagen solubility was highest in IS ( p < 0.05) and lowest in SM ( p < 0.05) although no difference between LD and SM was found in population B. The onset and peak temperatures of thermal shrinkage ( T o and T p) were highest in IS ( p < 0.05). The lowest T o and T p were found in SM from population B whereas no differences were seen between LD and SM muscles in population A. It was concluded that the thermal stability of the connective tissue in the three porcine muscles differ. IS, as a dark muscle has high thermal shrinkage temperatures and high collagen solubilities in comparison to the lighter LD and SM muscles which have lower thermal shrinkage temperatures and collagen solubilities. Collagen contents were highest in IS and lowest in LD.

Microwave thermal keratoplasty for myopia: keratoscopic evaluation in porcine eyes.

Microwave thermal keratoplasty applies microwave energy to elevate the temperature of the paracentral stroma of the cornea to its thermal shrinkage temperature of about 60 degrees C. A suitable pattern of shrinkage in the paracentral cornea can flatten the central cornea. A surface cooling system preserves the epithelium during the procedure. Fourteen enucleated porcine eyes were treated with a prototype microwave thermal keratoplasty applicator that heated in a ring pattern with inner diameter of 3.2 mm and width of 0.7 mm. The change in corneal power was quantified by a videokeratoscope. Slit-lamp microscope examinations and histological assessments were made. The 3-mm simulated keratometry reading showed an average of 6.60+/-6.00 D (standard deviation) of flattening. The region of opacity associated with shrinkage extended to 62% (+/-26%) of the corneal thickness. The epithelium was intact in all eyes. Microwave thermal keratoplasty applied in the paracentral cornea may flatten the central cornea.

Novel acrylic resins for dental applications

A heat-cured resin based on a copolymer of bis-phenol-A glycidyl methacrylate (bis-GMA) and tetrahydrofurfuryl methacrylate (THFM) was investigated. Workable pastes were made by adding 90 10 w/w bis-GMA/THFM copolymer powder to a 70 30 w/w monomer of the same composition. The organic filler content was 60–64% w/w. Young's modulus, flexural strength, impact strength, hardness, water absorption and desorption, linear thermal expansion, polymerization shrinkage and glass transition temperature were determined. The materials studied showed high elastic modulus, hardness and glass transition temperature. A relatively low linear thermal expansion was obtained but poor impact strength and low flexural strength, indicating brittleness. Acceptable values were obtained for water absorption.

Relationship between pyridinoline concentration and thermal stability of bovine intramuscular collagen

Semimembranosus muscle samples were obtained from 49 Holstein beef animals representing different USDA maturities. Intramuscular collagen (IMC) was isolated in the frozen state and evaluated for heat-labile collagen solubility (% Sol), thermal shrinkage temperature (Ts), enthalpy (Hs) changes, and mature crosslink (pyridinoline) content. These measures were obtained to elucidate a relationship between pyridinoline content of IMC and beef maturity level and to relate IMC thermal stability (% Sol, Ts, and Hs) to pyridinoline content. With increasing maturity, % Sol decreased (P less than .01) and Ts increased (P less than .01), whereas Hs showed no change (P greater than .05). Thus, IMC melted at increasing temperatures, but the amount of energy required to induce this endothermic change remained constant throughout maturation. The pyridinoline content of IMC increased (P less than .01) linearly with maturity, indicating that this heat-stable, mature crosslink enhances thermal stability of IMC as beef muscle matures. Significant correlations between pyridinoline content and maturity (r = .56; P less than .001) and Ts (r = .34; P less than .05) support this contention.

Intramuscular collagen and serum hydroxyproline as related to implanted testosterone, dihydrotestosterone and estradiol-17 β in growing wethers

Relationships of implanted testosterone, dihydrotestosterone and estradiol-17 beta to collagen degradation and intramuscular collagen concentration and stability were determined. Intramuscular collagen content, solubility and shrinkage temperature and serum hydroxyproline were analyzed in groups of six rams, wethers, and wethers implanted with various levels of testosterone or dihydrotestosterone and groups of 10 rams, wethers and wethers implanted with estradiol-17 beta, dihydrotestosterone or a combination of these two steroids. Intramuscular collagen content in both experiments was higher (P less than .05) in muscles of rams than in muscles of wethers. Administration of the highest level of testosterone to wethers raised (P less than .05) total and insoluble intramuscular collagen to concentrations noted in rams. Administration of the testosterone metabolite, dihydrotestosterone, to wethers had no effect on intramuscular collagen. Administration of estradiol-17 beta to wethers tended to raise concentrations of intramuscular collagen so that they were no longer lower (P less than .05) than those in rams. Collagen stability as measured by solubility and thermal shrinkage temperature did not differ among rams, wethers or implanted wethers (P greater than .05). Increases in collagen accretion due to hormone administration were observed to be the result of increases in the insoluble portion of the intramuscular collagen (P less than .05).