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.%.

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.

BIORESORBABLE PROPERTIES OF CHITOSAN FIBERS IN ENDOMYSIUM AND PERIMYSIUM MUSCLE TISSUE

Scanning electron microscopy and histologic analysis were used in the comparative in vivo study of resorption of chitosan fibers implanted into endomysium and perimysium of a rat latissimus dorsi muscle. It was demonstrated that the mechanism and rate of chitosan fiber resorption depend on the position of fibers in muscular tissue. After implantation of chitosan fibers into endomysium (when chitosan was in direct contact with muscle fibers), the formation of cross-sectional cracks, fragmentation of implanted fibers and its partial resorption were observed in 14 days. Complete chitosan resorption in endomysium occurred after 30 days only. Chitosan fibers implanted into perimysium preserved integrity for 7 days, and fibrous tissue was formed around implants. After 45 days of exposure, no signs of chitosan fiber destruction were registered in this case. Biocompatibility of chitosan fibers proved by effective adhesion and proliferation of mesenchymal stem cells on their surface.

BIORESORPTION OF POROUS 3D-MATERIALS BASED ON CHITOSAN.

3D-materials with high porosity were prepared by the method of lyophilization of chitosan solution. In vivo investigation of the mechanism and resorption rate of the resulting material in the muscle tissue showed complete resorption occuring in 12 months after implantation in an animal. The formation of scar tissue was not observed; there was no change and damage of the surrounding tissue. Histological analysis showed that chitosan resorption occurred simultaneously with the formation of collagen fibers and blood vessels. This allows us to recommend such porous material based on chitosan as a matrix for tissue engineering.

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.