Design And Development Of SF/PLLA Nanofiber Yarn-based Textiles For Tendon Tissue Engineering Application

With the interactive development of multiple disciplines,novel nanofibrous textiles made from a combination of nanotechnology and traditional textile technology have gained attractive interest in the fields of tissue engineering and regenerative medicine most recently.From the perspective of traditional textile technology,we know that the yarns constructed with fibers are the primary processing unit for braided,woven and knitted,as well other textiles pattens.Once the nanofibers are collected in the form of yarn-like shape,it can widely expand the application of nanofibers in biomedical textiles.Although both domestic and foreign scholars have carried out a lot of research work on nanofiber yarn forming technology,how to improve the orientation,crystallinity,mechanical properties and biological activity of obtained nanofiber yarns still remains big challenge.In this thesis,a combination of self-designed electrospun nanofiber yarn-forming technology and thermal drafting process was adopted to prepare silk fibroin(SF)/ poly(L-lactic-acid)(PLLA)nanofiber yarns.The fiber orientation degree,crystallinity,mechanical and biological properties of SF/PLLA nanofiber yarns were expected to be improved by optimizing the polymer components and yarn structure.Regulating the textile-forming capacity and stability of nanofiber yarns was expected to better biomimetic the structure and properties of natural tendon tissues.Eventually,the optimized SF/PLLA nanofiber yarn woven fabrics were employed as a new-type tendon patch to reconstruct and repair the largely injured Achilles tendons in rat animal models.Firstly,a series of PLLA nanofiber yarns were manufactured through a combination of self-designed electrospun nanofiber yarn-forming device and subsequent thermal drafting process,and the influence of different thermal drafting ratios on the yarn structure and performance was systematically explored.The results showed that the orientation degree,crystallinity and the mechanical strength of PLLA nanofiber yarns can be improved after the thermal drafting treatment.Importantly,the hot stretched PLLA nanofiber yarns were demonstrated to significantly promote the attachment,alignment,proliferation and tenogenic differentiation of human adipose-derived mesenchymal stem cells(HADMSCs).For example,compared with the PLLA nanofiber yarns without thermal drafting,the fiber orientation degree of the PLLA nanofiber yarns with 3-fold thermal-draft increased by 51%,the breaking strength increased by 544%,and the Young’s modulus increased by 932%.In the cell culture process,the orientation degree of HADMSCs increased by 43%,and the tenocyte-related m RNA markers including SCX,TNC,COL1,COL3 and TNMD,were found to be significantly upregulated in HADMSCs seeded on hot stretched PLLA nanofiber yarns in comparison with those cultured on unstretched PLLA nanofiber yarns.Secondly,the self-extracted SF was employed to blend with PLLA,four different kinds of SF/PLLA nanofiber yarns with diverse mass ratios(0:100,20:80,35:65 and 50:50)were prepared by using the above-mentioned yarn forming and thermal drafting device.The effect of SF content on the structure and properties of nanofiber yarns was widely investigated.The results showed that,with the increase of SF content,the mean nanofiber diameter and mechanical properties of as-prepared yarn presented a decreased trend,but the degradability and cytocompatibility significantly increased.Compared with the pure PLLA nanofiber yarns,the mean nanofiber diameter of 20:80,35:65 and 50:50 SF/PLLA nanofiber yarns decreased by 20%,21% and 32%,respectively.The breaking stress reduced by 19%,51%,and 60%,respectively.It should be noticed that,the 35:65 and 50:50 SF/PLL nanofiber yarns began to degrade on week 3,and with the increase of SF content,the degradation capacity enhanced.Moreover,the nanofiber yarns with high SF content were demonstrated to effectively promote adhesion and proliferation of HADMSCs in vitro,and significantly reduce the inflammation response in vivo.Finally,the optimized PLLA nanofiber yarns,SF/PLLA nanofiber yarns,and commercial PLLA microfiber yarns were utilized to pass through the PLLA microfiber yarns to generate three different tendon patches with same textile woven structure,and the three different tendon patches were utilized to repair the large-scale injured Achilles tendons in rat models.At six months after surgery,H&E staining showed the regenerated tendon tissues presented highly aligned structure in both PLLA nanofiber yarn and SF/PLLA nanofiber yarn contained tendon patch group compared with PLLA microfiber yarn-contained tendon patch group.Immunohistochemical staining indicated that the regenerated tendon tissues in both PLLA and SF/PLLA nanofiber yarn contained tendon patch groups expressed higher COL1,COL3 and TNMD contents.Transmission electron microscopy(TEM)observation displayed that the regenerated tendon tissues in both PLLA and SF/PLLA nanofiber yarn combined tendon patch groups presented higher collagen fiber diameters,and the regenerated tendon tissue in SF/PLLA nanofiber yarn contained patch group was basically mature at this time,and the mean diameter of as-formed collagen fibers was 101.96±19.84 μm,and the breaking strength of the regenerated tissue is23.11±2.35 N/mm,which was comparable to the breaking strength of native tendon tissues(21.17±2.08 N/mm).