Studies On The Application Of Poly(Propylene Fumarate)-based Composite Materials In The Repairing Of Mandibular Bone Defects

Bone is second only to blood as a material most often implanted in the body. It is very important that to archive the favorable bone substitute materials to fulfill the bone defects or to be the networking materials in bone tissue engineering. Autograft bone , transferred from one site in the patient's body to anther, is limited by the amount of donor bone available. Moreover, its use creates an additional surgical site for the patient, increasing the incidence of further pain and infection. Allografts from human banked bone or synthetic products, including coral or bovine-collagen-based materials, have demonstrated an association with increased risk of viral infection, contamination and long-term complications. Some synthesized materials, PMMA and metal materials, can cause inflammation or stress shield, leading to the absorption of the bone and a second surgery to get them out. Bioresorbable bone void fillers could provide a viable alternative to autografts and allografts used in current bone graft procedures to repair defects caused by surgery, tumors, trauma, implant revision and infections, and also for joint-fusion. But currently approved synthetic products have significant drawbacks, including a lack of resorbability and poor handling characteristics. With the emergence of the field of tissue engineering, the use of synthetic, biodegradable polymers has gained renowned focus. Biodegradable poly(α-hydroxy esters), such as poly(L-lactic acid), poly(glycolic acid), and poly(DL-lactic-co-glycolic acid)(PLGA), were assayed for osteoblast attachment, proliferation, and migration. Although PLA, PGA or PLGA foams provide an excellent scaffold for three-dimensional(3-D) osteoblast culture, they possess mechanical properties inferior to trabecular bone and may not be used at load-bearing sites. Ideally, a bioresorbable bone graft substitute should be biocompatible and display minimal inflammatory response. It should act as bone filling grout that initially provides space filling with dimensional stability and appropriate porosity in a bony defect. It should then provide an osteoconductive network that degrades at a rate commensurate with bone recovery. Poly(propylene fumarate), PPF, is an unsaturated linear polyester that can be crosslinked through its fumarate double bonds using a vinyl monomer(N-vinyl pyrrolidone) and an initiator (benzoyl peroxide). Composite formulations can be produced incorporating an osteoconductive matrix (β-tricalcium phosphate) and a porogen(sodium chloride), creating an injectable paste capable of filling defects of any shape or size. This material can be polymerized in situ, and can create a porous composite material possessing mechanical properties sufficient for the replacement of human trabecular bone for 3-D osteoblast culture. Moreover, by altering the composite formulation, we were able to modulate the handling characteristics of the injectable paste, creating a mixture that hardens within a several minutes time span, cures at body temperature, and agrees with the mechanical properties of human trabecular bone. Along with the development of physics and chemistry, researchers had made great achievements in the bone defects repairing materials field. But there were some disadvantages, such as infirmness and the low mineral degree. Although the researchers compounded the growth factors in the materials to fulfill the bone defects, but the purifying of the growth factors is complicated and expensive, and the sources are limited. PRP are derived from self-blood, and is rich in several high density cell growth factors. Because of the simple purifying progress and low cost, PRP is used gradually in clinic and does work. This paper investigated the synthesis of poly(propylene fumarate), the mechanical properties of PPF-based composite materials, the biocompatibility, and degradation in vivo. The study compared the ability of porous PPF/β-TCP and porous PLA in repairing the defects of rabbit's mandibular. The research fulfilled the dog's mandibular bone defects with PPF/β-TCP compounded with PRP to detect the effects of PRP in vivo used with the composite material. At last, we did some jobs on the effects of PRP in the culture of rat's MSCs in vitro. 一,The research of synthesis of PPF The first step involves forming a short chain oligomer from fumaryl chloride and propylene glycol in the presence of potassium carbonate. The following is a transesterification step. After a 18-h transesterification , we got the finalproduct, PPF. The polymeric backbone was investigated through the use of FTIR and NMR. GPC was used to determine polymer molecular weight and distribution.The final product, PPF, was an unsaturated polyester. 二,Mechanical properties of PPF-based composite materials Different amounts of NaCL andβ-TCP was added into the PPF materials. After it crosslinked, we got the samples being used in the compressive test. The mean compressive strength ranged from 12.57Mpa(SD3.19) to 40.37Mpa(SD3.07), while the mean modulus in compression were in the range of 73.77Mpa(SD17.98) to 543.67Mpa(SD7.02). The difference in the mechanical properties tested in this study was found to be statistically significant based on a two-factor ANOVA. So we should alter the amounts of β-TCP and NaCL in the same time to get the appropriate strength and moduli of elasticity. The different content of NaCl made the porous PPF/β-TCP composite material have different pore content and size of the pore. They ranged from 52.3% to 85.7% and 86.7μm to 158.6μm, respectively. With the dosage of NaCl increasing, both of them increased; The mean compressive strength ranged from 13.64MPa(SD2.35MPa) to 2.68MPa (SD0.22MPa), while the mean modulus in compression were in the range of 87.54MPa(SD15.22MPa) to 26.93MPa(5.89MPa). With the dosage of NaCl increasing, both of them decreased. 三,Biocompatibility and degradation of PPF/β-TCP composite material in vivo Through a period of 12 weeks being planted under the back skin with PPF/β-TCP composite material, all of the rats were in good condition with no obvious inflammation and there were no changes in the livers and kidneys. The study confirmed that the material had an excellent compatibility. The loss ratio of weight postoperatively is 49%, 50.35%, 51.15%, 51.5%, 57.5%, respectively. So we concluded that the degradation of it in vivo is mainly through self-acceleration and/or the effect of the enzyme in body, but not through the effect of the macrophage. 四,The comparison of porous PPF/β-TCP composite material and porous PLA in repairing the mandibular bone defects of rabbit Using porous PPF/β-TCP composite material and porous PLA to fulfill thebone defects of rabbit's mandibular and analyzing the results with radiography, light density and histopathology method, we drew the conclusion that porous PPF/β-TCP composite material have excellent degradation ratio and compatibility in vivo. The results of radiography and analysis of light density confirmed PPF/β-TCP composite material was much better than porous PLA. Addition, we discussed the mechanism of new bone formation to put forward that the component ofβ-TCP in the material had great advantages in the progress of bone formation and minerization. 五,Study on the effects of PRP in the culture of rat's MSCs in vitro We estimated the effects of PRP in vitro using the culture medium contenting 1%PRP to induce the rat's MSCs. Using the MTT method to evaluate the proliferation of MSCs, ALP staining and calcium nodule staining, we confirmed that PRP did have great effects on the proliferation and differentiation of MSCs. The research revealed that the cell growth factors in PRP had obvious effects on the cells in the bone defects. 六,Study on fulfilling the dog's mandibular bone defects with PPF/β-TCP composite material compounded with PRP PRP is a product of self blood, containing many cell growth factors. It was studied and applied popularly in the clinical research since 1997. The study repaired mandibular bone defects of dog with PPF/β-TCP composite material compounded with PRP and pure PPF/β-TCP composite material as the controlled group. We found that there were lots of vascular and small bone nodules formation at the defect area in the early time, and a large quantity of MSCs and osteoblasts around them. In PRP group, they could be found much more than in the controlled group. In addition, there were areas in which the fibroblasts formed the new bone in the PRP group. We could conclude that the application of PRP in vivo could accelerate the proliferation and differentiation of MSCs and fibroblasts to form new bones. PRP made the progress of bone repairing start on a higher level. Through a series of studies, we could conclude that PPF was an excellent biodegradable material. PPF had the appreciating degradation ratio and biocompatibility. PPF/β-TCP composite material had excellent biomechanical properties and was suitable for repairing the bone defects. PPF/β-TCP composite material had good osteoconductivity and accelerated the progress of bone minerization. PRP had distinct effects on the MSCs'proliferation and...