Abstract:

Objective This study aims to modify the expanded polytetrafluoroethylene (ePTFE) tubular fiber membrane prepared by unidirectional stretching through secondary heating and quenching processes, so as to address the issues of insufficient flexibility and longitudinal elasticity, thereby enhancing the compliance, mechanical properties and antithrombotic performance of artificial blood vessels and providing better materials for clinical vascular transplantation.

Method The ePTFE tubular fiber membranes were prepared by the one-way stretching method. On this basis, secondary heating (at 300 ℃) and water quenching processes were introduced to reshape the structure. The microstructure, crystallinity, mechanical properties, compliance and biocompatibility of the membranes were characterized by electron microscopy scanning, X-ray diffraction, mechanical stretching tests, dynamic vascular compliance tests and cytotoxicity experiments. The in vivo evaluation was conducted through a large dog carotid artery replacement model.

Results After secondary heating and water quenching treatment, the inner wall node spacing of the ePTFE tubular fiber membrane shortened, the pore diameter decreased, and the outer wall fibers were arranged in a wavy pattern, forming a pore structure with a denser inner layer and a sparser outer layer. The inner pore diameter was significantly smaller than the outer pore diameter. XRD analysis showed a decrease in crystallinity of the material and an increase in the proportion of amorphous regions. In terms of mechanical properties, the longitudinal strength was significantly increased (the radial fracture strength did not change much), and the elongation at break remained stable. The stress-strain curve exhibited a typical nonlinear response, and the toe region elongation indicated enhanced flexibility. Vascular compliance tests revealed that the samples after secondary heating treatment had significantly better compliance than the untreated samples, and the wavy fiber structure endowed it with the elastic deformability similar to a spring. Cell toxicity experiments indicated that the cell viability of the extract solution group was higher than 90%, with no significant cytotoxicity and good biocompatibility. Canine carotid artery replacement experiments manifested that the samples after the secondary heating treatment did not form blood clots after the implantation for 6 months. The surface was smooth and endothelial cells grew into the tube wall with well encapsulated connective tissue, and no inflammatory reaction was found, while the primary shaped samples showed blood clotting and inflammatory cell infiltration within 2-3 weeks. The performance improvement was achieved because high compliance reduced blood flow turbulence, smooth and dense inner walls inhibited platelet adhesion, and the microporous structure promoted tissue integration and vascularization.

Conclusion The secondary heating and quenching treatment can effectively optimize the structure and performance of ePTFE tubular fiber membranes, forming a dense inner and sparse outer pore structure and wave-like fiber morphology. The pore structure significantly enhances axial strength, flexibility and elasticity, making them more similar to the mechanical behavior of natural blood vessels. This material has excellent biocompatibility and antithrombotic properties. The animal experiment results, show the material has excellent tissue integration and endothelialization ability, significantly outperforming conventional primary shaped samples. Research indicates that the proposed ePTFE tubular fiber membranes have significant application potential in the field of artificial blood vessels.

Key words: expanded polytetrafluoroethylene tubular fiber membrane, dense inner and sparse outer pore structure, artificial blood vessel, secondary shaping, compliance, medical textiles