PLGA/TCP/Mg Composite Porous Scaffold Manufactured By Low-temperature Deposition 3D Printing For Bone Repair

Steroid- associated osteonecrosis(SAON) is a common orthopaedic problem caused by the frequently treatment of excessive steroids in certain conditions, such as severe acute respiratory syndrome and acquired immune deficiency syndrome. The incidence of steroid-induced osteonecrosis increased continuously in recent years, ranking first in non-traumatic osteonecrosis. Core decompression is usually performed in the early stages of SAON to reduce intraosseous pressure and provide blood supply for subchondral bone, as so to enhance bone repair. A key step of preventing subchondral collapse is to reinforce the surgically bone defect resulted from core decompression. The autologous bone grafts are used as excellent substitutes, but the limitations in clinical application include the insufficient supply, secondary damage and complications. In the recent years, with the development of tissue engineering, tissue engineering scaffolds for bone repair are under extensive exploration in musculoskeletal research.Tissue engineering is a new field applying principles of biology to engineering in order to develop functional substitutes for damaged tissue. An ideal scaffold for bone repair should have the following properties:(i) three-dimensional and porous structure that enables nutrients supply, cell migration and growth, and vascular invasion;(ii) good biocompatibility and antibacterial ability with non-toxic degradation products;(iii) a balance between the rate of bone remodeling and rate of degradation;(iv) enough mechanical properties during the process of bone regeneration;(v) good osteogenic and osteoinducive ability. Currently bone tissue engineering scaffold materials includes inorganic materials, natural polymer, synthetic polymer and composite materials. Composite material is made from two or more constituent materials which combined with certain percentage, with characteristics combining the individual components.Poly lactide-co-glycolide(PLGA) is a FDA-approved biomaterial with good biocompatibility and biodegradability, processing good toughness and ductility. The main disadvantages of PLGA are related to its poor cell adhesion performance, low mechanical strength and acidic degradation products. Beta-tricalcium phosphate(?-TCP) is a commercial osteoconductive biomaterial which can be incorporated and remodeled into new bone, but with low mechanical strength. Magnesium is considered to be a promising metal for bone regeneration because its mechanical strength is similar to that of human cancellous bone, and it is a biodegradable metal with good biocompatibility. The shortcomings of Mg are related to its fast degradation rate and alkaline degradation products. PLGA/TCP/Mg composite scaffold is an ideal combination which avoids the drawbacks of the individual components however process characteristics such as good biocompatibility, excellent mechanical strength and suitable degradation rate. Low-temperature rapid prototyping manufacturing is a recently developed process with excellent accuracy and reproducibility, which can preserve bioactivities of scaffold materials. In this study, we use this process to create 3D PLGA/TCP/Mg composite scaffold with specific geometries for bone repair.The main content of this thesis is divided into the following three parts:Part I: preparation and characterization studies of PLGA/TCP/Mg composite scaffold. Using low-temperature rapid prototyping 3D printing technology, we have successfully created PLGA/TCP/Mg composite scaffold with a desired porosity(?80%), pore size(300-500 microns), pore connectivity(100%), mechanical strength(Young's modulus?114MPa, compressive strength?3.2MPa). Mechanical strength of scaffolds with 15% magnesium is similar to that of cancellous bone(Young's modulus?20-500 MPa, compressive strength?4-12MPa). These results indicate that PLGA/TCP/Mg composite scaffold meet the needs of bone tissue engineering materials.Part II: in vitro cell toxicity evaluation of PLGA/TCP/Mg composite scaffold extract. Results show that 800 ppm is the cell toxicity threshold of MC3T3-E1. The cell toxicity test result of PLGA/TCP/Mg composite scaffold extract is within safety level in different time point. These results indicate good in vitro biosafety performance of PLGA/TCP/Mg composite scaffold.Part II: in vivo efficacy studies of PLGA/TCP/Mg composite scaffold in steroidassociated osteonecrosis rabbit bone defect model. At 12 weeks post surgery, significant higher BV/TV(p<0.05, n=8), Tb.N(1/mm)(p<0.05, n=8), Conn.Dn(1/mm^3)(p<0.05, n=8) but lower Tb.Sp(1/mm)(p<0.0015, n=8) were found in PLGA/TCP/Mg group compared with that in control group(p<0.05, n=8). At 4 weeks post implantation, PLGA/TCP/Mg group performed good blood perfusion and showed significantly higher ?maximum enhancement? than the PLGA/TCP group and control group(p<0.05, n=3). Magnesium concentrations in PTM group and PT group are within reference range meanwhile no significant difference was found between the two groups. Liver function and kidney function were normal in both groups.In conclusion, we successfully designed and manufactured an innovative bioactive porous scaffold composed of PLGA, TCP and Mg with physical structure that meet the needs of bone tissue repair. Further studies indicate that the PLGA/TCP/Mg scaffolds have good in vitro biosafety performance, significant osteogenetic and angiogenic ability. All in all, our studies demonstrate that PLGA/TCP/Mg scaffold is a promising biomaterial for bone regeneration.