Preparation Of Polypyrrole/poly(l-lactide) Conductive Composite Nanofibers For Bone Regeneration Via Electrical Stimulation

The purpose of tissue engineering is to create a functional tissue substitute by combining the use of biomaterials, cells and/or growth factors. Recent studies have found that the electrical stimulation can modulate cell adhesion, migration, protein secretion and DNA synthesis, and thus promotes tissue regeneration. As a newly-developing bone tissue engineering material, conducting polypyrrole(PPy) is the most studied conductive polymer, which can be developed as a potential biomaterial for bone repair.Chemical oxidation and electrodeposition are common synthetic methods for PPy. The monomers can be polymerized and then deposited onto the substrates by electrodeposition with an external electric field. Compared with chemical oxidation, electrodeposition shows several advantages such as simple apparatus, easy operation, cost-effective, the fast deposition rate and the uniform coating, etc. In this study, conducting PPy was firstly electrodeposited on the prepared polylactic acid(PLLA) nanofibers, which were subsequently used as scaffolds for growth of bone marrow mesenchymal stem cells(BMSCs) under electrical stimulation. The main contents are divided into two parts:(1) PLLA nanofibers were fabricated by electrospinning and used as deposition substrate for PPy deposition, and PPy was then polymerized on the PLLA nanofibrous mats by electrodeposition to obtain the conductive PPy/PLLA composite nanofibers. The different cyclic voltages, working electrodes and dopants were used for electrodeposion to determine the optimum deposition conditions. PPy could be uniformly and continuously deposited on the suface of PLLA nanofibers, which was conducted under the cyclic voltages ranging from-0.8 V to 0.8 V. The conductivity of the prepared composite mats were measured, and the results indicated that the conductivity of the composite mats prepared by using stainless steel electrode as working electrode was higher than those prepared by using titanium and porous stainless steel electrodes. Furthermore, the composite mats doped by benzene sulfonate showed higher conductivity than those doped by camphor sulfonic acid. The composition, structure and properties of composite nanofibers were characterized by infrared spectrum, X-ray photoelectron spectroscopy and contact angle test, tensile mechanical test and conductivity test methods. The results showed that PPy was successfully deposited on PLLA surface by electrochemical method, and the prepared composite mats possessed the increased hydrophilicity, improved mechanical performance and conductivity.(2) We further evaluated the in vitro biocompatibility of the PPy/PLLA composite fibers. The biocompatibility and osteoconduction of the composite nanofibers were studied by seeding and culturing the BMSCs on the composite films. The MTT and SEM results showed that PPy/PLLA composite flims could promote cell proliferation and differentiation. Under intensity of 100 mV/cm, 5 day rountie electrical stimulation(ES), conductive composite films can promote the adhesion proliferation of BMSCs, activity of alkaline phosphatase and expression of osteocalcin, compared with the PPy/PLLA nanofibers without ES. Therefore, the developed conducting PPy/PLLA composite nanofibers could promote osteogenic differentiation, which has the potential to serve as a scaffold for bone tissue engineering.