Aspects of silicone rubber as encapsulant for neurological prostheses

The paper presents some measurements of the hydrothermal stability of experimental adhesive joints in water at 100°C. The joints are between one adhesive silicone rubber and ten metal or metal-oxide adherends, all combinations of interest to the neurological prosthesis maker. The probable adhesion mechanism is then considered, in the search for some parameter by which the experimental results could have been predicted. Evidence is produced that physical adsorption plays little or no part in the adhesion, but that hydrothermal stability seems to be a function of the adherend ionic charge. In pursuit of this idea, the valency, the Slater potential and the iso-electric point for the surface (IEPS) of the adherend are examined as possible prediction parameters. It is concluded that, at least in neutral and acidified water, the IEPS is a promising predictor, with the benefit that it is experimentally determinable for adherends of unknown composition. The most stable joints seem to occur when the charge density on the adherend has an optimum negative value.     

Aspects of silicone rubber as encapsulant for neurological prostheses Part 4: Two-part rubbers

The durability of the adhesion, in the presence of water, of three two-part silicone rubbers to five adherends of practical interest is examined. The results are contrasted with those obtained, in previous work, from single-part material. It is concluded that two-part rubbers promise outstanding performance in particular circumstances.     

医用硅橡胶的生物相容性缺点及现代改良

硅橡胶具有性能稳定、易于塑形、产品效益可观的优点,已广泛应用于生物医学工程领域和医疗卫生行业.尽管如此,硅橡胶在生物医学领域中的应用仍然受到其自身缺陷的挑战.表面疏水性、自身影像相容性欠佳、长期植入体内后发生钙化乃是医用硅橡胶制品在生物相容性方面亟待克服的缺点.近几年来国内外专家针对以上缺点进行了诸多改良研究,热点主要集中于硅橡胶的表面湿润性增加、X-线阻射功能增强、防钙化预处理等方面.取得了阶段性成果,但尚未使医用硅橡胶的生物相容性达到理想的境界.     

Silicone rubber and natural rubber as biomaterials

The roles of silicone rubber and natural rubber as biomaterials are contrasted, with silicone rubber being widely used and natural rubber having, as yet, found limited application. Relevant properties of both elastomers are described, applications are discussed and possible future developments are considered.     

外科植入硅橡胶材料钙化及抗钙化研究进展

硅橡胶钙化是材料植入体内后其表面或基质内出现病理性矿化的现象,尚无有效防治方法.钙化的重要过程是材料表面的磷酸根离子与钙离子结合启动成核聚集,缓慢增大、融合,逐渐形成较大的羟基磷灰石钙盐堆积.其研究已发展到细胞和基因水平,如基质Gla蛋白质簇是一种硅橡胶假体周围组织钙化的抑制因子.钙化过程中有机模板对无机晶体的调制作用需理论上的突破.硅橡胶自身局部抗钙化性能受到重视.揭示硅橡胶钙化和钙化抑制的机理,可为构建新型抗钙化功能材料提供依据.     

纳米铁显影增强硅橡胶的制备及影像可视性评价

目的 探讨纳米铁微粒作为显影标记物对医用硅橡胶改性的可行性并评价复合材料的影像可视性.方法 硅油与纯铁粉、碳包铁粉混合,按预定的配方比分别与甲基乙烯基硅橡胶共混、密炼、模压、硫化,得到纳米纯铁粉增强硅橡胶（第1组）、纳米碳包铁粉增强硅橡胶（第2组）,空白对照组为医用硅橡胶.CT扫描体外各组材料试件,获取图像并测得CT值,比较组间CT值均值的差异性;将2组材料试件植入犬皮下,获得标准X-线图像;X射线衍射技术分析材料内铁微粒的组分稳定性.结果 分别制备出铁粉显影增强硅橡胶和碳包铁粉显影增强硅橡胶,新材料在体内外的X-线图像清晰可见,复合材料的CT值随金属纳米粉体量和纳米微粒原子量的增加而增加,2组材料的CT值均值、组间配方比相同的材料的CT值均值差异显著（P＜0.001）;材料放置180 d后,单质铁出现衍射峰的位置基本没有变化,分散在硅橡胶中的纳米纯铁微粒、碳包铁微粒较为稳定.结论 金属纳米铁粉、碳包铁粉可作为硅橡胶显影性改良的标记物.     

Superior in vitro biological response and mechanical properties of an implantable nanostructured biomaterial: Nanohydroxyapatite–silicone rubber composite

A potential approach to achieving the objective of favorably modulating the biological response of implantable biopolymers combined with good mechanical properties is to consider compounding the biopolymer with a bioactive nanocrystalline ceramic biomimetic material with high surface area. The processing of silicone rubber (SR)–nanohydroxyapatite (nHA) composite involved uniform dispersion of nHA via shear mixing and ultrasonication, followed by compounding at sub-ambient temperature, and high-pressure solidification when the final curing reaction occurs. The high-pressure solidification approach enabled the elastomer to retain the high elongation of SR even in the presence of the reinforcement material, nHA. The biological response of the nanostructured composite in terms of initial cell attachment, cell viability and proliferation was consistently greater on SR–5 wt.% nHA composite surface compared to pure SR. Furthermore, in the nanocomposite, cell spreading, morphology and density were distinctly different from that of pure SR. Pre-osteoblasts grown on SR–nHA were well spread, flat, large in size with a rough cell surface, and appeared as a group. In contrast, these features were less pronounced in SR (e.g. smooth cell surface, not well spread). Interestingly, an immunofluorescence study illustrated distinct fibronectin expression level, and stronger vinculin focal adhesion contacts associated with abundant actin stress fibers in pre-osteoblasts grown on the nanocomposite compared to SR, implying enhanced cell–substrate interaction. This finding was consistent with the total protein content and SDS–PAGE analysis. The study leads us to believe that further increase in nHA content in the SR matrix beyond 5 wt.% will encourage even greater cellular response. The integration of cellular and molecular biology with materials science and engineering described herein provides a direction for the development of a new generation of nanostructured materials.     

铁质纳米粉体对甲基乙烯基硅橡胶力学性能的影响

目的探讨铁质纳米粉体改性甲基乙烯基硅橡胶的力学性能变化及其在基胶中的分散状态。方法根据国家标准对前期制备出的纳米铁粉增强硅橡胶和碳包铁粉增强硅橡胶复合材料进行邵氏A硬度、拉伸强度、扯断伸长率、扯断永久变形率、撕裂强度等力学性能指标测试,使用热场发射扫描电镜（TFE．SEM）观察复合材料的表面形貌和断口形貌,了解纳米铁在硅橡胶基体的分散状态。结果复合材料试件的邵氏A硬度、拉伸强度、扯断伸长率、扯断永久变形率、撕裂强度的均值随着铁质纳米粉体添加量的增加而增加。当纳米铁在配方中的份数大于17份、碳包铁的份数大于19份时,复合材料的拉伸强度均值不再增加反而呈下降趋势;当铁质纳米粉体的在配方中超过15份时,扯断伸长率、撕裂强度的均值开始下降。铁质纳米微粒在硅橡胶的表面分散均匀,在配方比为85：15的硅橡胶,纳米铁试样的断面及配方比87：13的硅橡胶／碳包铁试件的断面,可观察到粉体的团聚体。结论纳米铁粉体和碳包铁粉体对甲基乙烯基硅橡胶力学性能的补强作用主要取决于纳米粉体的粒径、添加量以及在基胶中的团聚程度。     

Speeding-up the cure of one-part silicone rubber, when encapsulating neurological prostheses: the permeable mould

The Note describes a procedure for encapsulating the implantable microelectronics in an air-curing silicone rubber, by which the shape of the casting is fully defined, and cure is achieved within an acceptable time.     

青蒿琥酯硅橡胶埋植剂的制备与体外释放量的测试

制备青蒿琥酯硅橡胶棒埋植剂,进行体外释放量的测试,为动物(小鼠)试验提供样品及参考依据。用青蒿琥酯原料药与硅橡胶基质混炼均匀,分别加入交联剂和催化剂混匀,于手工挤出机上挤出一定直径的药棒,加热硫化,裁成一定长度的药棒。首先,测定含量,然后测定体外释放量。结果表明青蒿琥酯硅橡胶棒埋植剂平均含量为24.025mg/cm,体外(含药24mg/支)释放量:第一天达860ug,第20天为539ug,第30天仍有305ug的药释放。青蒿琥酯硅橡胶棒埋植剂制剂稳定,体外释放较缓慢稳定。     

Strategies for the prevention of microbial biofilm formation on silicone rubber voice prostheses

Total laryngectomy, a surgical treatment for extensive cancer of larynx, which alters swallowing and respiration in patients, is followed up with a surgical voice restoration procedure comprising tracheoesophageal puncture techniques with insertion of a "voice prosthesis" to improve successful voice rehabilitation. However, microbial colonization is a major drawback of these devices. Antimicrobials are usually used to prevent the colonization of silicone rubber voice prostheses by microorganisms. However, long-term medication induces the development of resistant strains with all associated risks and the development of alternative prophylactic and therapeutic agents, including probiotics and biosurfactants, have been suggested. The inhibition of microbial growth on surfaces can also be achieved by several other techniques involving the modification of physicochemical properties of the biomaterial surface or the covalently binding of antimicrobial agents to the biomaterial surface. An overview of the different approaches investigated to date and future perspectives to reduce the frequent replacements of voice prostheses in laryngectomized patients through microbial biofilm retardation is presented and discussed.     

纳米铁显影增强硅橡胶的制备及影像可视性评价

Objective To explore the feasibility of iron nanoparticles as radiopaque agents for modifying medical silicone rubber and to evaluate image visibility of modified materials.Methods Methyl vinyl silicone elastomer was mixed with iron nanoparticles,carbon-coated ferric nanoparticles,respectively,in accordance with the designed formula ratios.The composites were blended,mixed,molded and vulcanized with.Two groups of new materials,iron nanoparticle enhanced silicone rubber (INESR,Group1) and carbon-coated ferric nanoparticle enhanced silicone rubber(Fe/CESR,Group2),were harvested.Medical silicone rubber was as a negative control group.CT scanning of each group of material samples in vitro was performed,and both CT images and measured CT values were collected.Differences in CT mean values between the groups were compared.Samples of new material groups were implanted subcutaneously in a dog and standardized radiographic images were obtained.X-Ray Diffraction was used to analyze the component stability of iron nanoparticles dispersing in the silicone rubber.Results Two groups of radiographic image enhanced silicone rubber were prepared.The X-ray images of new composites were clearly visible both in vitro and in vivo.CT values were increased with the increase of added metal nanoparticles and metal atomic weight.CT mean values of each group and the materials in Group 1 and Group2 with the same material formulation were significantly different (P＜0.001).After placed for 180 days,the diffraction peak positions of elemental iron in both groups of materials remained essentially unchanged,and it showed that dispersed iron nanoparticles and carbon-coated iron nanopaarticles in silicone rubber were stable.Conclusion The metal nanoparticles of iron and carbon-coated ferrum can be used as radiographic markers for improving quality of X-Ray image of the medical silicone rubber.     

Bronchoalveolar casting using formalin-fixed canine lungs and a low viscosity silicone rubber

A method for creating tough, flexible, bronchoalveolar casts from formalin-fixed canine lung is described. A lung was washed using simple methods and fixed in 10% neutral-buffered formalin. While still wet with formalin, an intact lobe was injected with silicone sealant, Silsastic 734 RTV (Room Temperature Vulcanizing), using a caulk gun. Following digestion with protease and corrosion with potassium hydroxide, a bronchoalveolar cast was recovered giving detail as shown using scanning electron microscopy or conveniently seen by stereo light microscopy. This method should be useful for micro-anatomy studies of normal and diseased lungs. © 1993 Wiley-Liss, Inc.     

Grafting of a synthetic heparinoid polyelectrolyte onto silicone rubber

Using a [3H]-labelled polyelectrolyte as a tracer, the 60Co grafting of a synthetic heparinoid polyelectrolyte onto silicone rubber was studied. The polyelectrolyte was labelled by the coupling of a radioactive amine to carboxylate groups of the polyelectrolyte. The amount of grafted polyelectrolyte was found to be dependent on the radiation dose.     

Experimental modelling of aortic aneurysms: Novel applications of silicone rubbers

A range of silicone rubbers were created based on existing commercially available materials. These silicones were designed to be visually different from one another and have distinct material properties, in particular, ultimate tensile strengths and tear strengths. In total, eleven silicone rubbers were manufactured, with the materials designed to have a range of increasing tensile strengths from approximately 2 to 4 MPa, and increasing tear strengths from approximately 0.45 to 0.7 N/mm. The variations in silicones were detected using a standard colour analysis technique. Calibration curves were then created relating colour intensity to individual material properties. All eleven materials were characterised and a 1st order Ogden strain energy function applied. Material coefficients were determined and examined for effectiveness. Six idealised abdominal aortic aneurysm models were also created using the two base materials of the study, with a further model created using a new mixing technique to create a rubber model with randomly assigned material properties. These models were then examined using videoextensometry and compared to numerical results. Colour analysis revealed a statistically significant linear relationship (p < 0.0009) with both tensile strength and tear strength, allowing material strength to be determined using a non-destructive experimental technique. The effectiveness of this technique was assessed by comparing predicted material properties to experimentally measured methods, with good agreement in the results. Videoextensometry and numerical modelling revealed minor percentage differences, with all results achieving significance (p < 0.0009). This study has successfully designed and developed a range of silicone rubbers that have unique colour intensities and material strengths. Strengths can be readily determined using a non-destructive analysis technique with proven effectiveness. These silicones may further aid towards an improved understanding of the biomechanical behaviour of aneurysms using experimental techniques.     

Combined vascular-bronchoalveolar casting using formalin-fixed canine lungs and a low viscosity silicone rubber

Background: Previous work using unfixed or fixed tissues has shown that casts can be made that demonstrate the three-dimensional structure of tissues such as the bronchoalveolar tree or the vasculature. In this report, a new method for creating a vascular-bronchoalveolar cast is described. Method: Canine lungs were taken from storage in formalin. Silastic 734 RTV (room temperature vulcanizing) with added red or blue pigments was injected into the pulmonary arteries and veins, respectively, using compressed air. This was followed by filling the airway with clear (translucent) Silastic 734 RTV. The lung tissue was then corroded with potassium hydroxide. Results: Vascular-bronchoalveolar casts were recovered giving fine detail as shown using stereo light microscopy or scanning electron microscopy. Conclusions: This method may be useful for not only microvascular anatomy studies of lungs, but also for studying the microvasculature of other normal and diseased tissues. © 1995 Wiley-Liss, Inc.