Tissue response to polyglycolide, polydioxanone, polylevolactide, and metallic pins in cancellous bone: An experimental study on rabbits.

The purpose of this study was to investigate, qualitatively and histoquantitatively, the tissue response of rabbit femur cancellous bone to polyglycolide (PGA), polydioxanone (PDS), polylevolactide (PLLA), and stainless steel pins under identical conditions. Eighty knees in 50 rabbits were operated on by inserting bioabsorbable pins (PGA, PDS, or PLLA) together with metallic Kirschner wire in 60, and two metallic Kirschner wires alone in 20 knees, while 20 knees served as intact controls. Follow-up times were 3, 6, 12, 24, and 52 weeks. Cancellous bone tissue response to implants was studied using histological, histomorphometrical, microradiographical, and oxytetracycline fluorescence methods. Residual fragments of PGA and PDS were seen at 24 weeks. Complete degradation of these polymers had taken place before 52 weeks. No signs of degradation of the PLLA pins were observed within the entire follow-up period. The osteoid formation surfaces at tissue implant-interface were statistically larger in all test groups as compared to intact controls. The number of macrophages at tissue implant-interfaces increased in all bioabsorbable implant specimens until 6 weeks, and with PGA until 12 weeks. No differences in the osseous response emerged when comparing groups of bioabsorbable implants with each other or with stainless steel group. Bioabsorbable pins and metallic Kirschner wires evoked an osteoconductive response in the cancellous bone surrounding implant, but the response intensity between implants displayed no differences. This suggests a simple, nonspecific walling-off new-bone front type of response. Consequently, the polymers possessed no specific osteostimulatory or osteoinhibitory properties. Within the follow-up, no significant differences in biocompatibility between the implants appeared, and no frank inflammatory foreign-body reactions occurred. The small-volume pins obviously did not exceed the local tissue tolerance and clearing capacity of the bone.     

可吸收内固定材料L/DL-聚乳酸的体外降解特性

背景：目前以左旋聚乳酸为代表的可吸收骨折内固定物已应用于临床,这种人工合成的高分子聚合物充分展示了其优越性,但同时也存在不足,限制了其广泛应用。目的：评价可吸收内固定材料L/DL-聚乳酸的体外降解情况。方法：将L/DL-聚乳酸试件置于37 ℃恒温的磷酸盐缓冲液中,在2,4,8,12,20,28周时间点取材,进行大体观察、扫描电镜观察、三点弯曲强度测定、重均分子质量检测并计算其降解率。另将相同试件置于蒸馏水中,于不同时间点测其pH值变化。结果与结论：降解早期试件重均分子质量和机械强度下降较快,8周时重均分子质量降解了74.29%,机械强度衰减了60.99%,随后趋于平缓;对试件降解过程中抗弯强度衰减率和重均分子质量降解率进行双变量相关性分析,结果表明两者呈正相关性(r=0.958,P < 0.05);pH值在20周后有较明显下降;L/DL-聚乳酸的降解腐蚀在其表面和内部几乎同时发生。提示L/DL-聚乳酸符合骨折内固定物的生物降解性和机械性能要求,有望在颌面外科领域应用。     

The efficacy of a double-layer collagen membrane technique for overlaying block grafts in a rabbit calvarium model

Objectives: To analyze the outcomes of a single- and a double-layered collagen membrane on the efficacy of onlay block grafts in terms of bone resorption and augmentation.
Material and methods: A total of 36 New Zealand white rabbits were used in this study. Calvarial bone blocks were obtained from one side of the parietal bone and fixed on the contaralateral side. The onlay grafts were covered with either no (C group), one (M1 group), or two (M2 group) layers of a non-cross-linked collagen membrane (BioGide^®). After 2, 4, and 6 months of healing, rabbits were sacrificed and explanted specimens were prepared for histologic and histomorphometric analysis. At each period, the overall pattern of graft bone resorption and membrane biodegradation were examined histologically, and the sustained external form of grafted bone (%) and the remaining mineralized bone volume (%) were measured histomorphometrically.
Results: The M1 and M2 groups exhibited decreased bone resorption compared with the C group at all periods. The M2 group had less graft resorption and a higher bone density of the grafted bone than the M1 group. In the M1 group, the collagen membrane was degraded partially or completely by 4 months and was absent at 6 months. Conversely, for the M2 group, the membrane body was retained up to 6 months.
Conclusions: Our results demonstrated that the collagen membrane used here can reduce graft bone resorption. Furthermore, the double-layer technique using non-cross-linked collagen membranes (BioGide^®) can enhance the efficacy of the onlay block bone graft technique in terms of both bone resorption and augmentation compared with a single-layer collagen membrane.     

Structure-property relationships for the design of polyiminocarbonates

Structure-property relationships for the design of new polyiminocarbonates were established, based on the investigation of thermal stability and processibility, morphology, tensile strength, hydrolytic degradation and drug release profiles of 15 different polyiminocarbonates. The results indicated that some polyiminocarbonates were among the mechanically strongest, bioerodible polymers currently available. The iminocarbonate bond was highly unstable under physiological conditions, facilitating the design of rapidly degrading devices. The drug-release profiles of certain polyiminocarbonates exhibited lag periods, facilitating the design of pulsed-release or delayed-release devices. Possible limitations of the practical applicability of polyiminocarbonates as biomaterials were the low thermal stability of the iminocarbonate linkage and the complicated, two-phase degradation mechanism that led to the formation of slowly degrading residues of low molecular weight. To identify non-toxic diphenols as monomers for the synthesis of polyiminocarbonates, derivatives of tyrosine dipeptide were systematically explored. Using structure-property relationships as design guidelines, desaminotyrosyl-tyrosine hexyl ester was identified as a promising, tyrosine-derived diphenol. The corresponding poly(desaminotyrosyl-tyrosine hexyl ester iminocarbonate) formed amorphous, transparent films and was mouldable at about 70°C. It had a tensile strength of 400 kg/cm² and a tensile modulus of 16 300 kg/cm². Under physiological conditions in vitro, a thin film made of high molecular weight poly(desaminotyrosyl-tyrosine hexyl ester iminocarbonate) degraded to low molecular weight oligomers within 5 d. The results indicated that polyiminocarbonates and in particular poly (desaminotyrosyl-tyrosine hexyl ester iminocarbonate) might be of interest in a variety of biomedical applications.     

生物可降解分子印迹聚合物的制备及评价

背景：交联剂是支撑分子印迹聚合物骨架的主要单元,分子印迹聚合物是否生物友好与交联剂的性能密不可分,但目前常用交联剂的生物相容性和生物降解性还不明确。 目的：制备新型生物可降解分子印迹聚合物,分析其吸附性能和可降解性能。 方法：以丙烯酰化的聚ε-己内酯为交联剂,以丙烯酸为功能单体,采用紫外光引发聚合法制备茶碱分子印迹聚合物,通过等温吸附、Scatchard分析和动力学曲线研究其吸附能力,在模拟人体生理环境体系中进行体外降解实验。 结果与结论：等温吸附曲线表明茶碱分子印迹聚合物和非分子印迹聚合物对模板分子茶碱均有吸附能力,但茶碱分子印迹聚合物的吸附量显著高于非分子印迹聚合物。茶碱分子印迹聚合物对茶碱的载药量为1.54%,包封率为12.48%,茶碱分子印迹聚合物和聚ε-己内酯二醇在观察时间内的体外降解率分别为6.60%和1.33%。制备的分子印迹聚合物不仅对目标分子有特异的吸附性能,而且具有良好的生物降解性能,可在模拟人体环境中进行降解。     

可吸收胶原蛋白线与丝线编织非吸收线在口腔种植中的应用

背景：胶原蛋白线由动物的胶原蛋白制备而成,由于其具备可降解、无排异、易于制备、使用方便等优点,现在已开始大量使用于临床。 目的：比较胶原蛋白线与丝线编织线对口腔种植手术切口愈合的影响。 方法：100例种植手术患者随机等分为可吸收胶原蛋白线组和丝线编织非吸收性缝线组,分别使用2-0带圆针可吸收胶原蛋白缝合线与4-0带圆针丝线编织非吸收性缝线对伤口进行间断无张力缝合。植入后3,5,7 d观察缝线及伤口愈合情况,植入后第7天拆线,植入后14 d复诊。 结果与结论：可吸收胶原蛋白线组患者切口甲级愈合率明显多于丝线编织非吸收性缝线组(P < 0.05)。可吸收胶原蛋白线组患者口腔切口中的2-0带圆针可吸收胶原蛋白缝合线在治疗7 d时大多数被吸收,而丝线编织非吸收线组患者口腔切口中4-0带圆针丝线编织非吸收性缝线未见吸收。且使用2-0可吸收胶原蛋白线的患者口内缝线未见污物附着,线体清洁。而使用4-0丝线编织非吸收线缝合的患者口内可见线体周围有软垢附着。提示胶原蛋白线比丝线编织线更适合口腔种植手术切口的无张力缝合,能够获得更好的愈合效果,且时间能够与伤口愈合时间匹配,并能维持更好的口腔卫生。中国组织工程研究杂志出版内容重点：生物材料;骨生物材料; 口腔生物材料; 纳米材料; 缓释材料; 材料相容性;组织工程全文链接：     

假单胞菌降解药厂含酚废水动力学及复合固定化

目的通过研究假单胞菌对药厂不同质量浓度含酚废水的生物降解作用,并对降解过程进行动力学分析,为实际应用提供理论依据。方法采用复合固定化的方法制作固定化细胞,使菌株更适用于工业废水处理的需要。结果从药厂废水中分离出的菌株Pseudomonas stutzeri JFL2008能够以苯酚为唯一碳源生长。降酚实验的结果表明当苯酚初始质量浓度小于1 200 mg.L-1时,其生物降解过程遵循Monod方程;当苯酚初始质量浓度大于1 200 mg.L-1时,其生物降解过程遵循Hal-dane方程。结论固定化菌株在处理含酚废水时有很好的应用前景。     

Effects of platelet factors on biodegradation and osteogenesis in metaphyseal defects filled with nanoparticular hydroxyapatite—an experimental study in minipigs

There are no studies on the cellular activity in the early phase of biodegradation and bone healing of bone substitutes loaded with platelet factors (PLF). The purpose of this study was to evaluate the cellular effects of PLF in combination with nanoparticulate hydroxyapatite (HA) on the biodegradation and bone formation after 20 days. Autogenous PLFs were obtained by centrifugation of miniature pig blood samples and subsequent degranulation of platelets by calcium and thrombin. A cylindrical bone defect with a diameter of 8.9 mm was created in the distal femoral condyle of 20 miniature pigs. Four of the defects were left empty, 8 were filled with HA with loading and 8 with HA loaded with PLF. The distal femur was harvested after 20 days and TRAP-staining, cathepsin-K and CD44 staining and scanning electron microscopy were performed for cellular assessment of biodegradation was done. Histomorphometry of new bone formation and of biodegradation of HA material was performed. PLF loading of HA led to statistically significant more TRAP-positive cells with enhanced biodegradation of the nanoparticulate HA but no statistically enhanced new bone formation compared to unloaded HA. Furthermore, there was a higher number of CD44 and cathepsin-K positive cells by PLF-loading. In summary, PLF led to stimulation of the cellular process of the biodegradation of HA.     

Commercial polyurethanes: The potential influence of auxiliary chemicals on the biodegradation process

This investigation elucidates some aspects of auxiliary chemicals on the biodegradation of two commercial polyurethanes (Pellethane® and Corethane®). The materials were incubated for 28 days with cholesterol esterase and/or with phosphatidylcholine. Extraction studies were carried out on the two materials, using different solvents, chosen on the basis of solvent polarity. FT-IR spectra for the extracted materials indicated the presence of poly(methylene)_n oxide moities, silicone oil, bis-ethylene-stearamide, aromatic moities, and alkyd-urea compounds in Pellethane®. Corethane® materials were shown to contain some fatty acids, hydrocarbon waxes, ester-based species, and chlorinated compounds. Analysis of incubation solutions by high performance liquid chromatography failed to isolate methylene dianiline (MDA) or any of its derivatives from the various polymer incubation solutions. However, a methanol extract of Corethane® samples that were incubated for 28 days in cholesterol esterase did show the presence of MDA. The absence of MDA in the Pellethane methanol extracted samples may reflect the differences in surface additives found for this material versus the Corethane. FT-IR/ATR analysis of polymer surfaces exposed to cholesterol esterase/phospholipids mixture showed that there was an increase in the uptake of phospholipids over samples that were incubated in phospholipid dispersion alone. The results of this study show that some of the auxiliary chemicals found in commercial polyurethanes may hinder the specific release of hydrolytic degradation products and delay polymer degradation. However, it should be recognized that the surface layer containing these compounds is susceptible to change following the interaction between the polyurethane-based devices and elements of the host environment (i.e. lipids, enzymes, etc.). Hence, recognition and identification of these changes will ultimately be important in assessing a commercial polymer's blood compatibility characteristics.     

Rifampicin-carrying poly(D,L-Iactide) microspheres: Loading and release

—Rifampicin-loaded poly(D,L-lactide) (PDLLA) microspheres in the size range of 0.8-8.0μm were prepared by a modified solvent evaporation method. Rifampicin loading was changed by using different types of solvents (i.e. methylene chloride, chloroform, and carbon tetrachloride) with different solvent/polymer ratios and different emulsifiers (i.e. methyl cellulose, gelatin, and Tween-20), and by changing the initial drug/polymer ratio. These rifampicin-loaded PDLLA microspheres degraded much faster in the medium at basic pH (9.8) and at high temperatures (55°C). Rifampicin release was also high under these conditions. It was concluded that rifampicin release was both degradation- and diffusion-controlled.