| As a newly developed cure method based on cells, bone repairing material is one of the hotspots of the biomaterial research. It possessed some outstanding advantages rather than autografting, heterogenous grafting, and artificial substitute. In Poly-D,L-latic acid (PDLLA)/β-tricalcium phosphate(β-TCP) bone repairing composite, the acidic product from the degradation of PDLLA can be neutralized by alkalineβ-TCP. Adjustable biodegradation and suitable mechanical properties can be achieved by adjusting the proportion ofβ-TCP and PDLLA, and by using PDLLA with different molecular weight.In order to make a kind of bone repairing composite with favorable biocompatibility, mechanical properties and biodegradability, a process which consisted of an in-situ polymerization stage, an extrusion and compression molding stage had been used to fabricate composites of poly(D,L-lactic acid) (PDLLA) andβ-tricalcium phosphate (β-TCP). The mechanical properties and degradable characteristics of this composite could be controlled by adjusting the components proportion and other parameters.1. With D,L-lactide as raw material, 0.5 wt% SnCl2 as catalyst, ethanol as purifying solvent, a process which consists of a dehydration stage, an oligomerization stage and a depolymerization stage had been used to fabricate high-purity D,L-lactide. The ultimate yield was up to more than 15% and the purity of final product was up to 99.35%. After desiccation in a vacuum for 24h, the high-purity lactide could be used to fabricate PDLLA with its viscosity-average molecular weight up to 1.06×105 and polydispersion coefficient up to 1.89 by ring-opening polymerization. The polymerization patameters were as follows: dosage of Sn(Oct)2 0.1 wt%, temperature 160℃, duration 8h, and vaccum 5kPa.2.β-TCP powder was prepared with CaCO3 and phosphoric acid as raw materials. Firstly, high-purity and ultrafme CaCO3 powder was mixed to slurry with water. Then, CaCO3 slurry was poured rapidly into phosphoric acid solution according to Ca/P=1.50 in ultrasonic agitation to obtain ultrafine and uniform TCP precursor powders. Finally, ultrafineβ-TCP powder was prepared by calcining TCP precursor at 950℃. The surface of TCP particles was activated by treatment with dilute aqueous phosphoric acid. Then in-situ polymerization of lactide in order to graft poly(lactone)s on the surface of TCP was attempted. In a vacuum obturation, in-situ polymerization of lactide in the presence of protonated TCP with 0.1wt% Sn(Oct)2 and without Sn(Oct)2 were respectively at 150℃with a duration of 16h and 4days. The contact angle of modifiedβ-TCP powder for distilled water reached 112°. The particle diameter was about to 5.5μm with smaller particle diameter dispersion. Scanning electron microscope (SEM) observations indicate that: the modified TCP powder had well dispersion and was enwrapped by many slices and blocks; an improved dispersion of the modified TCP embedded in the polymer matrix and a better interracial phase interaction in the composite were clearly visible. FTIR analysis indicated that the chemical bond was formed between the surface of TCP and lactide. TG analysis indicated that when the dosage of lactide was 70wt%, the grafting efficiency was better.3. A process which consisted of an in-situ polymerization stage, an extrusion and compression molding stage had been used to fabricate composites of poly (D,L-lactic acid) (PDLLA) andβ-tricalcium phosphate (β-TCP). With a high vacuum, [160℃-8h], 0.05wt% dosage of Sn(Oct)2 and 30wt% dosage of TCP, as well as 20MPa molding pressure and 1.5min pressure-holding duaration, composite could be fabricated with viscosity-average molecular weight up to more than 1.1×105, and compressive strength and bending strength respectively up to 95MPa and 75MPa. SEM and EDS indicated that TCP had well dispersion in PDLLA matrix and there was no clear interphase what result in better combination between PDLLA andβ-TCP.4. The composites and PDLLA blank sample were immersed in stimulated body fluid (SBF) at 37℃, and sampled after 2,4,6,8 weeks respectively. Mechanical tests indicated that the composites of 15% and 30% TCP appeared higher initial mechanical strength and lower strength decay rate than blank sample. And pH tests indicated a neutual environment could be built during the degradation of composite samples. FTIR and SEM analyses indicated that bone-like apatite could be formed on the surfaces ofβ-TCP/PDLLA composites after 2 weeks and on the cross sections after 4 weeks. Pores and druses were formed within the composite after 6 weeks. Pores increased in size to transfix each other, and the amounts and sizes of druses increased as well after 8 weeks. |
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