Experimental Studies On Three-Dimensional Porous Poly-DL-Lactide/Hydroxyaptite Composites

Experimental Studies on Three-Dimensional PorousPoly-DL-Lactide/ Hydroxyapatite compositesShaoxiong Mi Anmin JinCentre of Orthopadics of PLA, Zhujiang Hospital, The First MilitaryMedical University, Guangzhou 510282AbstractObjective:A preliminary study was carried out to investigate the basic behavior of three-dimensional porous poly-DL-lactide (PDLLA) , and to sift a basic valuble scaffold or carrier. In order to improve the properties of PDLLA, hydroxyapatite (HA) particles were added to PDLLA. To investigate the effect of different weight HA for PDLLA/HA composites in vitro degradation and to evaluate the effects on bone formation of PDLLA/HA composites. Try to find the mechanisms of optimizing composites, and to provide an experimental reference for improving the constitution of composites. A preliminary study was also carried out to discuss the osteoinductive ability of composites consisting of basic fibroblast growth factor (bFGF) and PDLLA or PDLLA/HA, and to evaluate the prospect in orthopaedic use, and to develop a new kind of absorbable osteosynthesis material.Methods:High-porosity foams of PDLLA and PDLLA/HA were fabricated by a solvent-casting particulate-leaching technique with Nacl as the leachable component. Successive studies were done in such ways:1.Foams of PDLLA with three different pore sizes (70~50 ii m, 1 50?00 i?m and 400?00 ii m) were implanted into bilateral 1.0cm radial diaphyseal defects with complete resection of periosteum of 31 New Zealand white rabbits. The specimens were harvested in 2,4,8,12 weeks. The samples were-5-examined by X-ray, histology and scanning electronic microscope (SEM) toevaluate the effectiveness of defect repair2. Every kind of fOams of PDLLA/HA (5%Wt), PDLLA/HA (20%wt) andPDLLA/HA (35%Wt) with the same pore size in range of l50~300 ll m wasimmersed in the distilIed wateL Different methods such as PH, mass lost,viscosity-average molecular weight and compressive strength were employedto study the degradation in vitro.3. Each of l.0cm radial diaphyseal defects with complete resection ofperiosteum of New Zea1and white rabbits was implanted with various fOamswith the same pore size in range of l50~300 ll m of PDLLA, PDLLA/bFGF,PDLLA/HA '20%wt) and PDLLA/HA/ bFGF. The specimens were harvestedin 2,4,8,l2 weeks. The samples were examined by X-ray, histology andscanning electronic microscope (SEM) to evaluate the effectiveness of defectrepair At 8, l2 weeks after implantation of grafts, the biomechanical testing(bending strengh) was employed to study the quality of bone fOrmation.Rcsults: l. White porous biodegradable fOams were manufactured using acombined soIvent casting, extrusion, and saIt Ieaching technique as decribed.SEM photomicrographs of the foams revealed extensive pores which wereroughly spherical in shaPe a-nd evenly distributed throughout. The poresappeared connected to each othef, forming an interconnected network.Results obtained from measurement indicated a porosity of about 80%, and acontrollable pore size in range of 70~700 ll m.2. The results obtained from radiograPhic bone fOrmation, histologicanalysis and SEM indicated the materials having different pore sizesstimulated different bone formations. The PDLLA having pore sizes in therange of 70--l50 or l50~300 ll m stimulated more bone fOrmation than thematerial with pore size in the range of 400~700 ll m a-nd control group. Theformer two experiment groups were significantly higher compared with thelatter two groups in every stage ofpost-implantaiion.3. There were statistically differences in PH, mass lost, viscosity-averagemoIecular weight and compressive strength between the PDLLA/HA (20%wt)-6-composite group and the other groups at 12th week after implantation (P<0.05). It was concluded that a PDLLAIHA composite has higher viscosity-average molecular weight, lower mass lost, and better compressive strength than the other foams. The PH indicator of unfilled PDLLA...