Collagen Melting Research Articles

Sutureless Femtosecond Laser-Assisted Anterior Lamellar Keratoplasty Using a Bioengineered Cornea as a Viable Alternative to Human Donor Transplantation for Superficial Corneal Opacities.

To evaluate the safety and efficacy of a bioengineered corneal implant using femtosecond laser-assisted anterior lamellar keratoplasty for superficial corneal opacities. Six eyes of 6 consecutive patients with superficial corneal stromal opacities involving <220 μm owing to various pathologies were included in the study. Preoperatively, all patients underwent anterior segment optical coherence tomography (Visante; Carl Zeiss Meditec AG) to evaluate the depth of the corneal opacity. All patients underwent sutureless femtosecond laser-assisted anterior lamellar keratoplasty using a bioengineered collagen corneal implant (linkcor). Visual indices, refraction, and keratometry were evaluated preoperatively and 12 months postoperatively. Corrected distance visual acuity improved significantly in all patients (P = 0.02). A significant decrease was seen in refractive astigmatism postoperatively (P = 0.04). Flat keratometry reduced significantly 12 months after the intervention (P = 0.04). No intraoperative or early postoperative complications were noticed. All implants were fully covered by healthy epithelium within a month after the surgery and remained clear at follow-up visits. The results of this procedure remained stable throughout the follow-up period. In 1 patient, mild inferior collagen melting and epithelial defect formation occurred at 1-year follow-up. Despite frequent topical corticosteroid therapy the melting progressed, the collagen tissue was removed and the patient was treated accordingly with good visual outcomes. Femtosecond laser-assisted anterior lamellar keratoplasty with bioengineered corneal (linkcor) implantation is an effective treatment for improving vision quality in anterior stromal opacities. This procedure reduces the need for human donor tissue and avoids human donor-related and suturing complications.

Effect of Brahman genetics on myofibrillar protein degradation, collagen crosslinking, and tenderness of the longissimus lumborum.

The objective of this study was to examine the effect of percent Brahman genetics on Warner-Bratzler shear force (WBSF), desmin and troponin-T (TnT) degradation, hydroxylysyl pyridinoline (HP) crosslink content, and perimysial collagen melting temperature. Steers ( = 131) produced in 2012 and 2013 were harvested at 1.27 cm of visual s.c. back fat thickness. Steers were divided into 4 genetic categories consisting of steers that contained 6/32 or less Brahman genetics, 12/32 Brahman genetics, 14/32 to 18/32 Brahman genetics, and 23/32 to 32/32 Brahman genetics. Twenty-four hours after harvest, a 7.62-cm piece of the longissimus lumborum beginning at the 13th rib was collected and aged for 14 d. Following aging, three 2.54-cm steaks were cut for WBSF, trained sensory panel, and laboratory analyses. Laboratory analyses steaks were used to determine protein degradation, HP crosslink analysis, and perimysial collagen melting temperature. Data were analyzed using a polynomial regression for unequally spaced treatments. As the percent Brahman genetics increased, WBSF increased (linear, = 0.01). As percent Brahman genetics increased, tenderness score decreased (less tender) and connective tissue score increased (more connective tissue; linear, = 0.01). As the percentage of Brahman genetics increased, the amount of degraded desmin (38 kDa) and TnT (34 and 30 kDa) decreased (linear, < 0.03) whereas the amount of immunoreactive 36 kDa TnT increased (linear, = 0.04). Percent Brahman genetics had no effect ( = 0.14) on HP crosslink content but did tend to increase ( = 0.07) perimysial collagen melting temperature as the percent Brahman increased. The percentage of Brahman genetic influence was positively correlated to WBSF ( = 0.25), 36 kDa immunoreactive TnT ( = 0.26), and perimysial collagen melting temperature ( = 0.25, = 0.01). Sensory panel tenderness ( = -0.44), juiciness ( = -0.26), and connective tissue scores ( = -0.63); 38 kDa degraded desmin ( = -0.34), 34 ( = -0.36) and 30 kDa degraded TnT ( = -0.29); and HP collagen crosslinks ( = -0.20) were negatively correlated to percent Brahman genetic influence ( < 0.03). Increasing Brahman genetic influence in steers negatively affects tenderness, partially through a reduction in degradation of desmin and TnT. Although HP collagen crosslinks are unaffected by Brahman genetics, a tendency for increased perimysium melting temperature indicates that other collagen-stabilizing crosslinks may be affected.

Performance of a universal adhesive on etched and non-etched surfaces: Do the results match the expectations?

A universal adhesive was applied to human dentin in both the etched and rinsed state and the normal non etched state, to compare the resulting properties and detect any significant differences. The study focused on observations of the hybrid layer by scanning electron microscopy and on fluid permeation measurements as a function of time. Spectroscopic characterizations included infrared and differential calorimetric curves of the samples. The results obtained show non-statistically significant fluid permeability between the two sample types. Both the etched and rinsed samples and the non-etched ones showed similar homogeneous hybrid layers that reduced the fluid flow, and corresponded to well spread polymer coatings. The infrared results illustrated the spectra obtained on going from the outside adhesive layer to the inside portion of the dentin-polymer interface and did not reveal any intermediate zone resembling demineralized collagen that would be water saturated and not infiltrated with adhesive. The Differential Scanning Calorimetry (DSC) curves corresponded to the curves obtained with ethanol wet bonding in that free water (melting at 0°C) was removed by the universal adhesive, and that no collagen melting was observed for the non-etched samples. The Diffusion-Ordered Spectroscopy Nuclear Magnetic Resonance (DOSY NMR) spectrum of the virgin adhesive showed the presence of water and ethanol solvents and indicated that several monomer or prepolymer molecules were present with multiple acrylic functional groups with diffusion coefficients related to molecular weights.Overall, the results show that universal adhesive can be used in the milder self-etch mode and that more aggressive etch and rinse procedure can be reserved for the occasions with sclerotic dentin or enamel regions more difficult to treat.

Protective Effects of Deswelling on Stromal Collagen Denaturation After a Corneal Femtosecond Laser Cut

To evaluate the effect of corneal deswelling prior to a microkeratome and femtosecond (fs) laser cut and the impact of the fs laser energy settings on the tissue surface and collagen quality. Porcine and human corneas were incubated in THIN-C (deswelled) or EUSOL-C (control) at 4°C for 4 hours. Porcine corneas were cut using a microkeratome or an Intralase fs laser 150 Hz and 0.75 μJ energy. Human corneas were cut using the laser at different energy settings. The tissue thickness was measured using Visante OCT and the endothelial cell density (ECD) was evaluated by an Eye Bank KeratoAnalyzer or trypan blue staining. The tissue was analyzed using scanning electron microscopy (SEM). In porcine corneas, tissue deswelling resulted in a reduction of 14% in the central corneal thickness (CCT), a regular surface, and increased tissue stiffness without affecting ECD. After fs laser cutting, the control corneas showed superficial collagen denaturation that was absent in the deswelled corneas. The deswelled human corneas showed a CCT reduction of 20%, better surface smoothness, preserved collagen, and increased stiffness after fs laser cutting at 1.0 to 1.2 μJ, compared with controls. Surface smoothness decreased and collagen fibers showed a melted-like aspect both in deswelled and control corneas at greater than 1.4 μJ. Fs laser cutting parameters can reduce corneal surface smoothness and increase collagen melting damage. The use of a deswelling medium resulted in tissues for Descemet stripping automated endothelial keratoplasty (DSAEK) with increased stiffness, smooth surfaces, and no thermal damage to the collagen matrix.

Ocular rigidity and ocular response analyzer

Abstract Purpose To study ocular rigidity and sclera crosslinking level at diferent stages of primary open angle glaucoma (POAG). Methods Biomechanical parameters of the eye especially corneal hysteresis (CH, mm Hg) were measured in 238 patients (311 eyes) aged 40‐84 (median age 67.4 yrs) at various stages of compensated primary open‐angle glaucoma using Reichert Ocular Response Analyzer (ORA). Besides, scleral samples obtained during sinus trabeculectomy combined with sclera trephination in the inferio‐exterior quadrant of 28 patients (28 eyes) with various stages of POAG were studied using differential scanning calorimetry (Mettler TA 4000 with DSC20 cell). Results Average value (median) of CH gradually decreased from 10.1 mm Hg in the initial glaucoma stage (I) to 9.1 mm Hg in the developed (II) and 8.6 mm Hg in the advanced (III) glaucoma stage. The decrease of this clinical parameter is caused by structural and biochemical damage of the corneoscleral coat. In stage I, endothermic scleral collagen transition occurred at the median thermal peak Tm=60.3 grad.C, while in stages II and III the median peaks of scleral collagen melting emerge at higher temperatures: Tm=62.0 grad.C and Tm=64.5 grad.C, respectively (p&lt;0,05). This testifies to a significant increase of scleral cross‐linking and ocular rigidity during glaucoma development. Conclusion Biomechanical and biochemical disorders of glaucomatous sclera may cause clinical changes of ocular rigidity of eyes with POAG. This may be an important link of POAG pathogenesis requiring special therapy.

Transmission Electron Microscopic Examination of the Interface Between a Resin-Modified Glass-Ionomer and Er:YAG Laser-Irradiated Dentin

The aim of this study was to analyze the ultrastructural characteristics of the interface between a resin-modified glass ionomer (RMGI) and Er:YAG laser-irradiated dentin. The Er:YAG laser has been considered as a possible alternative for cavity preparation, but the interaction between glass ionomers and Er:YAG-lased dentin still needs further investigation. Five dentin surfaces were prepared by diamond bur (120,000 rpm) as controls or for Er:YAG laser irradiation (31.45 J/cm(2), 200 mJ, 10 Hz, 100 micros). The RMGI Fuji II LC (GC) was then applied to their surfaces, which were previously conditioned with a 20% polyalkenoic acid conditioner. The samples were sealed with an unfilled resin, stored in distilled water for 1 wk at 37 degrees C, and then processed for transmission electron microscopic (TEM) examination. When applied to bur-cut dentin (controls), Fuji II LC was able to partially demineralize the dentin surface, resulting in the formation of a hybrid layer, on top of which a sub-micron gel-phase was observed. In the laser-irradiated samples, the RMGI was in close contact with the irregular dentin substrate, but no hybrid layer or gel-phase formation could be detected, nor were there signs of dentin demineralization or collagen melting. Horizontal cracks were clearly seen in the sub-surface layer of dentin. Although presenting horizontal micro-cracks in its sub-surface, the irregular laser-irradiated dentin showed close contact with the RMGI. However, no hybrid layer or gel-phase could be detected, and there were no signs of dentin demineralization and collagen melting.

Structural Heterogeneity of Type I Collagen Triple Helix and Its Role in Osteogenesis Imperfecta

We investigated regions of different helical stability within human type I collagen and discussed their role in intermolecular interactions and osteogenesis imperfecta (OI). By differential scanning calorimetry and circular dichroism, we measured and mapped changes in the collagen melting temperature (DeltaTm) for 41 different Gly substitutions from 47 OI patients. In contrast to peptides, we found no correlations of DeltaTm with the identity of the substituting residue. Instead, we observed regular variations in DeltaTm with the substitution location in different triple helix regions. To relate the DeltaTm map to peptide-based stability predictions, we extracted the activation energy of local helix unfolding (DeltaG) from the reported peptide data. We constructed the DeltaG map and tested it by measuring the H-D exchange rate for glycine NH residues involved in interchain hydrogen bonds. Based on the DeltaTm and DeltaG maps, we delineated regional variations in the collagen triple helix stability. Two large, flexible regions deduced from the DeltaTm map aligned with the regions important for collagen fibril assembly and ligand binding. One of these regions also aligned with a lethal region for Gly substitutions in the alpha1(I) chain.

Thermal stability of collagen in intervertebral disc tissues

The thermal stability of collagen in intervertebral disc tissues was studied using differential scanning calorimetry. It was found that the melting of collagen in a native tissue was complete at 62–75°C (ΔH = 62.4 J/g) under heating excised annulus fibrosus and nucleus pulposus samples. On heating an intact structure up to 80°C, the denaturation of collagen did not occur. It was shown that the degradation of a proteoglycan component in the test tissues had no effect on the thermal stability of collagen.

The effect of γ-irradiation on the temperature dependence of D.C. electrical conductivity of dry bone

The effect of γ-irradiation with doses from 10 to 500 kGy on the electrical conductivity ( g) of dry bone was studied. Temperature measurement of electrical conductivity were made from 393 to 533 K. The dependence obtained indicates the increase in g with temperature. An increase in irradiation dose resulted in a decreased g value for each dose up to temperature 462 K. Temperature 462 K was interpreted as the temperature of collagen melting point in dry bone. Above 462 K, g values were dose independent. A dose of 500 kGy shifted the melting point to lower temperature. In addition, the activation energy for the charge conduction process was calculated. Obtained values for electrical conductivity and activation energy were typical for dielectrics and indicated degradation of the organic component of bone.

The order-disorder transitions in fibrillar proteins. Stress-temperature dependence of hydrothermal contraction of the native collagen fibers.

The melting of collagen in rat tail tendons tanned by p-benzoquinone has been investigated. It was shown that the degree of tannage if it is not too high does not influence the tension-temperature dependence. Our data indicate that the isometric tens

The effect of extraction, animal age and post mortem storage on tendon collagen. A differential scanning calorimetric study

SummaryDifferential scanning calorimetry was used to study the collagen → denatured collagen transition in tendon collagen. It was found that purification of collagen by salt (KCI) and trypsin caused a slight, but significant, decrease in the transition temperature, but no significant change in the enthalpy, ΔHD, of the transition.Animal age (0‐6 years) had no significant effect on either ΔHD (mean value = 1293 ± 72 cal. amino acid residue−1) or the extrapolated onset temperature, T0, (334.2 ± 0.3°K) of the transition in untreated tendon. However, the amount of collagen melting after 340°K increased markedly with age (from 0 to about 250 mg/g of tendon) although the amount melting before 340°K was approximately constant, 138 ± 17 mg/g tendon.Upon storage at 1 ± 1°C for 2 weeks 7 out of 16 tendons became less stable as judged by decreases in T0 and increases in the amount of collagen melting before 340°K. Two of the tendons became more stable as judged by increases in T0 and decreases in the amount melting before 340°K. These results are briefly discussed.

The Effect of Aqueous Salt Solutions on the Melting of Collagen and the Viscosity of Gelatin

Abstract Measurements of shrinkage temperatures (TS) for fibrous collagen, of equilibrium degree of swelling (v−1) for the same in the amorphous state, and of intrinsic viscosity ([η]) for randomly coiled gelatin are reported. The data were obtained for a large variety of salts which are typical representatives of lyotropic series. The order of anions and cations for decreasing TS and increasing both v−1 and [η] (generally, for increasing salting in) is F− < SO2- 4 < acetate < Cl− < Br− < NO− 3 < I− < SCN− and K+ < Mg2+ < Na+ < Cs+ < Li+ < Ca2+. For salts of ions at the extreme left of the series (salting-out agents) the shrinkage temperature in solutions of different salt concentration (CS) is controlled by the amount of diluent in equilibrium swelling with the molten network, and the shape of TS vs. CS curves can be represented by conventional theories valid for binary polymer diluent systems based on a lattice model with a single interaction parameter. In such cases the salt-water solution behaves as a...