The Investigation Of Poly Lactic Acid Polyethylene Glycol (PLA-PEG) Based Composite For Bone Tissue Engineering

ObjectiveTo investigate the affinity for water, biocompatibility and the rate of degradation in vivo of PLA-PEG compared with poly(DL-lactic-co-glycolic acid) (PLGA), then assess the properties of PLA-PEG as a biodegradable scaffold material by means of preparation of PLA-PEG／rhBMP-2 compound, physical examination and animal experiment.Materials and Methods1. Study of the affinity of PLA-PEG for waterWe make membranes of PLA105000-PEG2000 and PLGA100000 with 4:1 copolymer ratio respectively to examine their touching angles with water at room temperature.PLA-PEG and PLGA were fabricated into cylinders with 2mm diameter and 7mm length , then incubated in PBS for one week, and measured the water resorption rate by weighing before and after they were dried.2. Study of biocompatibility and biodegradation rateThe cylinder samples were implanted into the back of rat, then killed in 1w,3w,6w and 12w respectively. And the degradation rate of these samples were measured , the adjacent tissues, liver and kidney were stained by Hematoxylin and Eosin (H & E). 3. Preparation and mechanical test of PLA-PEG/rhBMP-2 multipore compound PLA-PEG(2g)was dissolved, then mixed completely with saccharu(10g), baking soda(1g), and poured the mixture into 20 molds(15×6×5mm), 16 molds among which were added rhBMP－2 powder(100μg),then dried at-70℃. The rest of the mixture was compacted into glass tubes and dried at-70℃ to form samples for mechanical test. Compression intensity and compression module were tested at 20℃ and 25% humidity.4. Reparation of mandibular defect in rabbit with PLA-PEG／rhBMP－2 multipore compound The mandibular defect model ( about 15mm×6mm)in rabbit was made by dental drill, then PLA-PEG／rhBMP－2 was planted into the site of defection, and PLA-PEG without rhBMP－2 as control. The bone specimens were retrieved to make density analysis with X-ray photos following rabbits sacrificed at 2w , 4w, 8w and 16w, then decalcified to make histopathological observation by means of HE stain.Results1. The water resorption rate of PLA-PEG (4.74±0.56%)is slightly higher than that of PLGA (3.23±0.75%),while the touching angle of PLA-PEG (66.333±2.5981)is slightly lower than that of PLGA (74.5±2.5071).2. In the study of biocompatibility, there was slight inflammation reaction around PLA-PEG at 1 week, connective tissue and blood vessels increased while lymphocytes decreased at 3 weeks, fiber membrane around PLA-PEG began to become thin at 6 weeks. In liver and kidney of rat, no abnormal change were observed.The degradation rate of of PLA-PEG was 3.15±0.58%, 3.76±0.38%, 5.24±2.16% and 12.23±1.56% respectively at 1w, 3w,6w and 12w, while the rate of PLGA was 4.62±1.06%, 11.95±1.50%, 20.48±1.10% and 47.89±2.46% respectively(P<0.02,P<0.001).3. The aperture of the compound was 300～500μm, porous rate is 78%, compression intensity was 30.05±3.12Mpa,and compression module was 371.67±12.37Mpa.4. Compared with control group, more marrow-derived mesenchymal stem cells were observed around PLA-PEG／rhBMP－2 compound at 2w ; newly formed bone trabecular were observed inside the compound at 4w; newly formed bone mass was observed adjacent to mandibule at 8w;, the scaffold compound was degraded completely and vast newly formed bone was observed inside the compound at 16w.Through X-ray analysis, we could observe increasingly higher intensity figures of bone inside the scaffold compound gradually. ConclusionAs a kind of biodegradable material, PLA-PGA have better biocompatibility, biodegradation rate and affinity for water than PLGA.The multipore PLA-PEG／rhBMP scaffold compound we obtained maintains the activity of BMP and has ideal aperture and porous rate, which releases BMP gradually and has better mechanical properties suitable for bone defect.