Preparation Of The Biomimetic Bone Scaffold Based On Polymer Templates By Electrodeposition

Bone defect caused by fractures, tumors and other diseases, is a common disease in clinical medicine. To date, autologous bone grafts, allogous bone grafts and artificial substitutes are the most common therapeutic approachs, but several inherent limitations, such as limited supply, immune rejection and so on, dramatically constricted their application for bone repair. Alternatively, bone tissue engineering has brought new perspective for the repair of bone defects. Since the native bone is a biomineralization system mainly composed of collagen fibers and hydroxyapatite(HA) crystals and owns the unique organic/inorganic hierarchical structure, the bone tissue engineering scaffold should mimic the formation mechanism, the main component as well as the special structure of the native bone. Recently, electrodeposition begins to show the infinite charm in biomedical field, especially in the fabrication of bone scaffold, from the fabrication of coating on the metal to the polymer substrate. The coating of apatite and other particles on a number of substrates can be obtained by one-step electrodeposition. Compared with other techniques, electrodeposition shows several advantages: simple apparatus, easy operation, cost-effective, the fast deposition rate and the uniform coating. So if the bone mineral could be deposited on the polymer substrate to prepare organic/inorganic composite scaffold which is similar with the native bone in structure and function, this will supply the theoretical value for the development of the biomimetic bone grafts.Based on the above-mentioned advantageous, with the aim to prepare the biomimetic bone grafts, we fabricated organic/inorganic composite scaffolds by electrodeposition technology with the polymer as the template, and studied their physical and chemical properties, and in vitro and in vivo osteogenesis ability. The major contents are listed as follows:At first, some factors were studied which could be having an influence on the deposition of the bone mineral on the polymer substrate by electrodeposition. Briefly, three kinds of typical electrospun nanofibers including poly(L-lactic acid)(PLLA), collagen, and chitosan were selected as deposition substrates, and four kinds of metal electrodes including copper(Cu), nickel(Ni), titanium(Ti) and stainless steel(SS) as the working electrode. The results demonstrated that the minerals showed different morphologies on the different polymer substrates.The component of all the minerals was mainly HA. Besides, different metal electrodes also had influences on the morphologies and component of the minerals. Moreover, the effects of deposition parameters(deposition time, deposition voltage and deposition temperature) on the formation of the minerals were also studied. It was found that the morphologies and component were changed with different deposition conditions, and the uniform mineral coating was deposited under the appropriate deposition voltage, time and temperature. According to the analysis of the deposition mechanism, it indicated that the parameters could affect the nucleation and growth of the mineral crystals.The fabrication of the mineral coating on the three-dimensional(3-D) scaffold by electrodeposition was further studied. First of all, the 3-D porous PLLA/poly(ε–caprolactone)(PLLA/PCL) scaffold with nanofibrous structure was fabricated via thermally induced phase separation(TIPS) technology. Then the mineralized PLLA/PCL scaffold was obtained by electrodeposition. By studying the effects of the deposition voltage and the deposition time on the mineralization, it was found that the relatively pure HA crystals were deposited on the scaffold under the appropriate condition, and the prepared mineralized scaffold could maintain the porous structure. Finally, BMSCs were seeded and cultured on the mineralized PLLA/PCL and PLLA/PCL scaffold, indicating that the mineralized PLLA/PCL could not only enhance the adhesion and alkaline phosphatase(ALP) activity of cells, but also promote the formation of the minerals matrix. After the scaffold implanted to the calvarial defect site of the SD rat for 12 W, it found that the mineralized scaffold could accelerate the calvarial healing. In summary, the mineralized scaffolds based on the biodegradable polymer substrate and the inorganic component offer great potential to to mimic the native biochemistry of bone: interpenetrating collagenous matrix and mineral content. More importantly, the 3-D scaffold showed the porous and nanofibrous structure, which is similar to the structure of native bone extracellular matrix(ECM). Therefore, the prepared 3-D mineralized scaffolds are promising scaffold biomaterials for bone tissue engineering.In order to explore the effects of the additive on the deposited calcium phosphate and the behavior of BMSCs, strontium(Sr) was introduced into the electrolyte. Firstly, PLLA nanofibers were prepared by electrospinning and used as the deposition template. Then strontium nitrate(Sr(NO3)2) with different contents was added into the electrolyte. The mineralized PLLA mats were fabricated by electrodeposition and the influence of Sr on the deposited minerals was tested by several methods. SEM images indicated that the morphologies of the minerals were flower-like structure, and then gradually turned to flake-like and ball-like with the increasing of Sr content. In addition, the dispersibility of the crystals was improved due to the incorporation of Sr, and the crystal form was changed from polycrystalline to single crystal morphology. From the ion release curves, it was found that the release of the Ca2+ and PO43+ were accelerated from the composite nanofibers due to the introduction of Sr. Moreover, using BMSCs as an in vitro cell model, the mineralized PLLA mats containing Sr showed higher bioactivities in terms of the cell proliferation, ALP activity, the deposition of calcium nodules and the expression of osteocalcin(OCN). In a certain range of Sr content, the role of promoting the cell proliferation and differentiation was more obvious with the higher content of Sr.The feasibility of the introduction of the osseous microcarrier on the materials surface was also studied, and thus the functional bone repair scaffolds was fabricated via electrodeposition. Mesoporous silica nanoparticles(MSNs) were prepared and modified with amine groups(-NH2), which were subsequently used as the microcarrier to load a kind of bone related small molecules-dexamethasone(DEX), marked as DEX@MSNs-NH2. DEX@MSNs-NH2 nanoparticles were then deposited onto the PLLA/PCL scaffold by electrodeposition. The results indicated that DEX@MSNs-NH2 could be uniformly deposited on the PLLA/PCL scaffold and the composite scaffolds remained the 3-D porous and nanofibrous structure when the deposition voltage was 3 V. In addition, the in vitro and in vivo biocompatibility and bioactivity of DEX@MSNs-NH2/PLLA/PCL composite scaffold were evaluated. The in vitro experiments showed that DEX@MSNs-NH2/PLLA/PCL scaffold exhibited good biocompatibility and could support adhesion, growth and migration of the cells. Moreover, compared with PLLA/PCL and MSNs-NH2/PLLA/PCL scaffold, BMSCs cultured on DEX@MSNs-NH2/PLLA/PCL scaffold exhibited higher activities of osteogenic differentiation in terms of ALP activity, alizarin red S(ARS) staining and OCN staining. Furthermore, the in vivo results demonstrated the DEX@MSNs-NH2/PLLA/PCL scaffold could significantly promote the calvarial defect to heal compared with PLLA/PCL scaffold after implantation. Therefore, our results demonstrated that the prepared DEX@MSNs-NH2/PLLA/PCL composite scaffold is a promising alternative for bone repair.