Influence of chitin nanofibrils ultrasonic treatment on structure and properties of chitosan-based composite materials.

The influence of ultrasonic treatment parameters of chitin nanofibrils aqueous suspension on structure, strength and deformation properties of chitosan-based composite films and fibers was investigated. Model calculations of ultrasound-induced cavitation parameters in the aqueous suspension of the chitin nanofibrils showed that an increase in the field power up to 630 W led to destruction of the cavity, to an increase in the temperature in the vicinity of cavitation area (up to 507 °C) and, as a consequence, to destruction of chitin glycoside ring (which is confirmed by the IR data). The results of light scattering, IR spectroscopy, and electron microscopy investigations indicated that the optimal duration of ultrasonic treatment of the chitin nanofibrils aqueous solution was 4-10 min (depending on oriented state of the scaffold). Tensile strength of the composites was 130 ± 11 MPa (films), 226 ± 4.8 MPa (fibers); deformation at break was 43 ± 7.5% (films), 10 ± 0.6% (fibers).

Influence of surface morphology of chitosan films modified by chitin nanofibrils on their biological properties.

The paper is devoted to the study of influence of chitin nanofibrils on the structure, surface morphology, mechanical properties, and electrical conductivity of chitosan-based composite films intended for use in biomedical technologies. It was demonstrated that the optimal concentration of chitin nanofibrils in the composite film is 5 wt.%. For the films of this composition, we observed orientation of structural elements on film surface, enhanced mechanical properties as well as an increase in both specific conductivity and proliferative activity of skin fibroblasts on film surface. These results are related to the appearance of oriented structure in nanocomposites and to self-organization of chitosan macromolecules on the surface of chitin nanofibrils. It was revealed that increase in surface energy and surface hydrophilicity did not facilitate effective adhesion, viability and proliferative activity of cells during cultivation on the surface of composite films.

Thermodynamics of interaction between water and the composite films based on chitosan and chitin nanofibrils.

Interaction between water and composite films based on chitosan and chitin nanofibrils was studied. Isotherms of water vapor sorption by composite films were used to calculate partial values of entropy and enthalpy of sorbate; dependences of entropy and enthalpy on water sorption value were obtained. It was demonstrated that introducing chitin nanofibrils into chitosan matrix leads to decrease in sorption capacity of composite films. Apparently, this phenomenon is caused by formation of ordered structures consisting of chitosan macromolecules on the surface of chitin nanofibrils. The hypothesis was confirmed by calculations of thermodynamic parameters of the chitosan/chitin/water system. The calculations led to the conclusion that thermodynamically stable chitosan/chitin system is formed in composite films; in addition, it was revealed that the strongest chitosan-chitin interaction arises in the composite containing 1-5 wt.% of chitin nanofibrils. In this concentration range, Gibbs energy, entropy and enthalpy of mixing pass through a minimum; this result indicates that the highest affinity between chitosan and chitin exists when concentration of chitin nanofibrils varies from 1 to 5 wt.%.

[Development and assessment of efficacy of L-polylactide matrix for creation of a tissue-engineered vascular graft]. / Razrabotka i otsenka éffektivnosti matritsy iz L-polilaktida dlia sozdaniia tkaneinzhenernogo sosudistogo implantata.

In order to create a tissue-engineered vascular graft we elaborated a matrix consisting of nanofibres of biodegradable polymer L-polylactide. We worked out the methodology of crystallization of the matrix on a rod, making it possible to manufacture specimens possessing strength and deformity characteristics superior to those of native vessels. This was followed by a series of chronic experiments on implanting the elaborated matrix into the abdominal aorta of rats for the duration of up to 16 months. We obtained satisfactory parameters of the patency of the matrices (71%). According to the findings of histological examination, in the course of time there occurred biodegradation of the matrix and formation of a new vascular wall, with no evidence of either inflammation or neointimal hyperplasia in the zone of the anastomoses. Resorption of the polymeric fibres commenced 12 weeks after exposure and completely terminated after 64 weeks. By that time, both neointima and neoadventitia were formed, whose composition and structure were close to those of the native vessel. Insufficiently high mechanical properties of the zone of reconstruction turned out to be the cause of the formation of aneurysms.

Tissue-Engineered Vascular Graft of Small Diameter Based on Electrospun Polylactide Microfibers.

Tubular vascular grafts 1.1 mm in diameter based on poly(L-lactide) microfibers were obtained by electrospinning. X-ray diffraction and scanning electron microscopy data demonstrated that the samples treated at T = 70°C for 1 h in the fixed state on a cylindrical mandrel possessed dense fibrous structure; their degree of crystallinity was approximately 44%. Strength and deformation stability of these samples were higher than those of the native blood vessels; thus, it was possible to use them in tissue engineering as bioresorbable vascular grafts. The experiments on including implantation into rat abdominal aorta demonstrated that the obtained vascular grafts did not cause pathological reactions in the rats; in four weeks, inner side of the grafts became completely covered with endothelial cells, and fibroblasts grew throughout the wall. After exposure for 12 weeks, resorption of PLLA fibers started, and this process was completed in 64 weeks. Resorbed synthetic fibers were replaced by collagen and fibroblasts. At that time, the blood vessel was formed; its neointima and neoadventitia were close to those of the native vessel in structure and composition.

Vascular Prostheses Based on Nanofibers from Aliphatic Copolyamide.

Tubular grafts based on nanofibers of copolymer of ε-caprolactam and hexamethylendiaminadipate were obtained by the electrospinning method. The strength of materials based on the dry nanofibers was 6.2 MPa with elongation at break of 133%, or 7.5 MPa and 299% in saline, respectively. The pressure value at which liquid started seeping through the tube wall was P = 10 kPa. Absence of cytotoxicity was proved, as well as adhesion and proliferation of mesenchymal stem cells on the surface. Tubes with inner diameter of 1 mm were tested in vivo in rat abdominal aorta. A layer of endothelial cells was shown to form on the inner side of the prosthesis after 30 days. There was no evidence of stenosis or dilatation of the prosthesis after 14 months with observation of endothelial and subendothelial layers.

Structure and properties of porous films based on aliphatic copolyamide developed for cellular technologies.

The effect of concentration and viscosity of the copolyamide (copolymer of ε-caprolactam and hexamethylendiaminadipate) solutions in aqueous/alcoholic solvents on its phase state was studied. The films obtained by the coagulation method were characterized by monodisperse pore distribution with an average pore size of 1.3 µm. The films processed by electrospinning from copolyamide solutions were characterized by a bimodal distribution of macropores with one peak of pore radius at 2.0 µm and second peak of pore radius at 20 µm. The adhesion and proliferation of mesenchymal adhesion stem cells (ASCs) stem cells to copolyamide matrix were studied. With the help of scanning electron microscopy it was shown that both tapes porous films were characterized by good adhesion of mesenchymal ASCs stem cells. It was shown that the porous structure, transport and mechanical properties of these copolyamide films allow their use as two-dimensional matrices for cellular technology.

[Composite materials based on chitosan and montmorillonite: prospects for use as a matrix for stem and regenerative cell cultivation].

This paper examines the structural and mechanical properties of composite materials based on chitosan and micro- and nanoparticles of Na-montmorillonite and possibility of application for cultivation and targeted delivery of mesenchymal stem cells and regenerative cells. It's have been shown by addition of Na-montmorillonite biomaterial acquires stability of structural and mechanical properties in the sterilization process the handling of liquid media in cell culture. In vitro studies using dermal fibroblasts and adipose tissue mesenchymal stem cells demonstrated that this material has a set of properties to ensure matrix biocompatibility.