The effect the thickness of a cartilage plate has on its laser reshaping is studied. The dynamics of heating during laser irradiation is recorded by means of IR radiometry, along with the dynamics of IR laser radiation passed through the cartilage plate. Variation in the cartilage plate’s shape is traced using still and video photography. It is shown that the time needed to attain a stable curvature and the final radius of the cartilage grow along with the cartilage plate thickness.

A systematic study of changes in the physicochemical characteristics of scleral collagen in the course of glycosylation by threose, including their dependence on the time changes of transverse cross-linking, was performed. Glycosylation by threose leads to a significant increase in heat, proteolytic, and biomechanical stability of collagen in the scleral tissue and has been shown to be a useful approach for stabilizing scleral collagen. It was found that a fraction of collagen with a reduced denaturation temperature is, apparently, an intermediate in the reaction of glycosylation by threose. The most likely reason for its occurrence is the elongation of the side chains of amino acid residues of the protein in the early stages.

Проведено систематическое изучение изменений физико-химических характеристик коллагена склеры в ходе гликозилирования треозой, включая зависимость их изменения от времени поперечного сшивания. Показано, что гликозилирование треозой приводит к значительному увеличению термической, протеолитической и биомеханической стабильности коллагена в тканях склеры. Установлено, что этот подход может быть использован для стабилизации склерального коллагена. Обнаруженная фракция коллагена с пониженной температурой денатурации, является, по-видимому, интермедиатом в ходе реакции гликозилирования треозой. Сделан вывод, что наиболее вероятной причиной ее возникновения является удлинение боковых цепей аминокислотных остатков в белке на начальных стадиях.

A technique for simultaneous measurements of the thermal diffusivity, specific heat, and effective absorbtion coefficient was developed. The technique is based on local heating of a sample by laser radiation and thermal imager measurement of the temperature field dynamics in the surface layer in both the heating and cooling stages. The technique includes a program for calculating the laser-induced temperature field in the sample volume and the determination of three parameters by the Levenberg-Marquardt algorithm to provide the best fit of calculations to experimental results. The statistical error of thermal diffusivity, specific heat, and effective absorbtion coefficient measurements was 5–6%. The technique efficiency was demonstrated by the example of the development of a thermal and optical equivalent of cartilage tissue, based on polyacrylamide hydrogel.

The concentrations of hydroxyproline (an amino acid specific of collagen) in a number of connective tissues were determined. Two procedures were compared. In one of them, amino acids were preseparated by chromatography and then determined on a standard amino acid analyzer. In the other procedure, hydroxyproline was selectively oxidized without amino acid separation and determined by a spectrophotometric reaction with Ehrlich’s reagent. Data obtained for purified collagen preparations in accordance with the two procedures were consistent with each other. The results can be somewhat different in unpurified preparations and tissues because of the presence of polysaccharide components in the 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.

Определено содержание гидроксипролина – аминокислоты, специфичной для коллагена, в ряде соединительных тканей. Сравнивали две методики. По первой – аминокислоты предварительно разделяли хроматографически, а затем определяли на стандартном аминокислотном анализаторе, по второй – без разделения аминокислот селективно окисляли гидроксипролин и определяли его по спектрофотометрической реакции с реактивом Эрлиха. Для препаратов очищенного коллагена данные, полученные по двум методикам, находятся в хорошем согласии. В неочищенных препаратах и тканях результаты могут несколько различаться из-за наличия в тканях полисахаридных компонентов.

The thermal stability of the scleral and corneal tissues after in vitro treatment with ribose, threose, and glyceraldehyde was investigated. The thermal transition temperature and the enthalpy of collagen fiber crosslinking were determined by differential scanning calorimetry (DSC). The resistance of the tissues toward trypsin was also determined after heating tissue samples in the DSC furnace. It was shown that the denaturation temperature of scleral and corneal samples treated by crosslinking agents increased, but the enthalpy of denaturation decreased. It is suggested that crosslinking in the collagen matrix of the cornea and sclera prevents complete collagen denaturation if the temperature does not rise up to 110 °C.

The thermal stability of collagen II in various cartilaginous tissues was studied. It was found that heating a tissue of nucleus pulposus results in collagen II melting within a temperature range of 60–70°C; an intact tissue of hyaline cartilage (of nasal septum and cartilage endplates) is a thermally stable system, where collagen II is not denatured completely up to 100°C. It was found that partial destruction of glycosaminoglycans in hyaline cartilage leads to an increase in the degree of denaturation of collagen II upon heating, although a significant fraction remains unchanged. It was shown that electrostatic interactions of proteoglycans and collagen only slightly affect the thermal stability of collagen II in the tissues. Evidently, proteoglycan aggregates play a key role: they create topological hindrances for moving polypeptide chains, thereby reducing the configurational entropy of collagen macromolecules in the state of a random coil.