到目前為止，使用聚乳酸植體最大的限制仍是其強度不足，故多用於海綿骨骨折之固定，製備時可 以緩慢降溫方式來提高聚乳酸結晶度，增加聚乳酸的強度，但缺少此種聚乳酸的組織學研究，且有 關聚乳酸之研究多為長期觀察，缺乏對於聚乳酸植體在海綿骨骨折癒合關鍵的前五週時期之組織學 及物理性質變化的探討。所以本研究的目的在探討以緩慢降溫方式所製備之聚乳酸 poly (L-lactide) 在體內 35 天期間的組織反應及物理性質變化。使用日本島津公司重量分子量 21 萬之聚乳酸，以 22 0 ℃ 熱熔法，在氮氣中自 220 ℃ 緩慢降溫產生結晶度 43 % 的聚乳酸，並切割成 2 x 6 x 25 mm3 試 樣，經環氧乙烯滅菌後，植入在 Sprague Dawley 大鼠背部皮下組織，經 1 天、 3 天、 7 天、 21 天
、 35 天五個試驗期間，以石臘及樹脂標本之組織學觀察，評估其組織反應並以三點彎曲強度、黏 度及熱性質檢測，評估其物理性質變化。滅菌前聚乳酸植體試樣三點彎曲強度為 120 MPa 左右，結 晶度為 43 % 左右，經 55 ℃ 、 2.5 小時環氧乙烯滅菌後，發現滅菌前後之物理性質沒有差異。就聚 乳酸植體試樣組織癒合過程而言，可分為止血期、發炎期、增生期及重塑期四個時期。術後第一至 三天為止血期、發炎期，是手術外傷所造成之發炎反應，炎症細胞以中性白血球為主，術後第三天
，炎症細胞以單核球細胞為主，可見纖維母細胞分布。術後第七天為增生期，炎症細胞分布範圍變 小，可見單核球細胞數目減少，此時可見含有許多增生纖維母細胞及血管的纖維包膜形成，由樹脂 磨片標本可見纖維包膜與聚乳酸植體緊密接觸。植入後第 21 天為重塑期，可見纖維包膜的厚度比 第 7 天薄，包膜內之纖維母細胞變較細長，血管數目減少。植入後第 35 天亦屬重塑期，纖維包膜 厚度比第 21 天薄，包膜內之纖維母細胞及血管數目減少。所以此聚乳酸植體試樣之組織反應是以 單核球細胞為主要的炎症細胞反應，植入後第七天形成纖維包膜，且隨植入時增加，纖維包膜愈成 熟，在植入 35 天期間未見多核吞噬細胞。就聚乳酸植體試樣物理性質變化而言，經 35 天試驗期間 其分子量沒有明顯差異，故沒有明顯降解反應發生，能維持一穩定之三點彎曲強度、黏度及熱性質
，所以植入周圍組織對此聚乳酸植體試樣反應溫和，纖維包膜隨植入時間增長而愈成熟。這可能是 因為具有足夠高之初始分子量且在製備時置於氮氣中緩慢降溫，聚乳酸主鏈未受製備過程產生大幅 熱降解而製備時不予施壓致使材料具有適當之結晶度，雖然進一步長期降解研究是必須的，此種製 備方式所得之聚乳酸植體為一可維持五週機械強度之生物鈍性材料。
聚乳酸在活體內的組織反應與物理性質之變化
So far the greatest limitation of using polylactide implant is insufficient strength, so it is used in fixation of sponge bone fracture mostly. To increase th e crystallinity and strength of polylactide by gradually cooling from the melting temperature to room temperature, but lacking of relating histological s tudy. Most study of polylactide were done for long term study, there were few study about histological and physical change of polylactide during the d ecisively initial 5 weeks of healing period of spongy bone fracture. The purpose of this study was to investigate the tissue response and physical chang e of annealing poly (L-lactide) during initial 35 d in vivo test.
PLLA (Mw = 210000 Da.) was obtained from Shimazu chemicals, Inc. (Japan). 2 x 6 x 25 mm3 tested plates were cut from samples prepared from he ating the PLLA powder at 220 oC under vacuum without pressure and gradually cooled from 220 oC until room temperature in a pot vented with nitro gen for one night. The crystallinity value of resultant samples was 43 %. These tested plates were implanted in the dorsal subcutis of S.D. rat after steri lization with ethylene oxide and removed at 1 d 、 3 d 、 7 d 、 21 d and 35 d intervals. These specimens were examined histologically with paraffin embedding section and resin embedding grounding section by light microscopy to evaluate tissue response. Three points bending test, viscosity and th ermal properties were also examined. The bending strength and crystallinity values of samples were 120 MPa and 43 %before sterilization. There was no significant change in physical properties after 55 oC, 2.5 h ethylene oxide sterilization. As for healing progress of PLLA implantation, there were h emostatic 、 inflammatory 、 proliferating and remodeling stages. The initial three days were defined as hemostatic and inflammatory stages, caused b y surgical trauma. Inflammatory cells were neutrophils predominately. The third day after implantation was inflammatory stage with mononuclear cell s predominately. Fibroblasts were also noticed. The seventh day was proliferating stage, the inflammatory infiltration area and number of mononuclear cells decreased. Fibrous capsule with proliferating fibroblasts and blood vessels was found. Close contact between PLLA implant and fibrous capsule was noticed by resin grounding section. 21 d after implantation was remodeling stage, the thickness of fibrous capsule was reduced and fibroblasts bec ame more slender. The number of blood vessels of fibrous capsule was reduced. 35 d after implantation was remodeling stage, the thickness and numb ers of blood vessels and fibroblasts of fibrous capsule were reduced further. Histologically, the inflammatory cells in tissue response of PLLA implant was mononuclear cells predominately. A fibrous tissue layer was formed around the PLLA plate from 1 wk. This became more mature over time. Duri ng the experimental period, there were no multi-nuclear phagocytes.
As for physical change of PLLA implant through 35 days, there was no significant difference in molecular weight and no obvious degradation occurre d. Tested samples can maintain stable three points bending strength, viscosity and thermal properties. So tissue response of tested PLLA implant was mild and fibrous capsule became more mature over time. These may result from sample with enough initial molecular weight annealed under nitrogen without large degree of thermal degradation during processing and proper crystallinity by processing without pressure. Although further long term stu dies for degradation are needed, the PLLA implants processed by this method have promising mechanical strength and are bioinnert materials during t he five weeks periods.
Tissue response and physical change of poly-L- Lactide
