医用高分子材料的致癌性

引言肿瘤是一种常见病,严重威胁着人类健康,肿瘤并非单一的疾病,其种类繁多,原因复杂,致癌因子极其多样化,从目前了解来看,有化学性,物理性及生物因素可直接作用于机体引起肿瘤,也有的因素需经过代谢活化才致癌.当今世界上人们对疾病非常关心的也就是癌症问题,据估计人类肿瘤85%为化学物所引起,有人认为在工业社会中所产生的癌症几乎80%是由于环境因素引起,环境中增加的一些有害化学物可认为是瘤作用的来源.对一部分化学物已作过生物检验,证实对人和动物有致癌性.随着工业用合成高分子材料用于医学的迅速增加,对提出了关于合成高分子材料远期致癌看法的重要问题.在60年代初期,Harris曾通过大量的人体外科植入,讲述了"应用选择的塑料与食品的消费的液体接触,提     

植入用高分子材料表面改性抗细菌粘附的研究进展

以植入材料为中心的感染导致的手术失败，严重限制了临床生物医用材料的应用。本文介绍了有关细菌在材料表面粘附的理论，材料表面自由能与细菌材料表面粘附的关系，并综述了近年来生物医用材料的表面改性的多种方法。     

应用微球柱法探讨高分子材料表面的血小板粘附作用

本文报道用微球柱法检测六种国产高分子材料的血液相容性,以血小板的形态变化与粘附数作指标进行讨论。 实验结果表明:微球柱法与文献及本室的体内留线法结果相符。因而表明微球柱法是体外试验方法中较近于生理状态下的一种实验方法。该法简单、易行,适用于易涂复的或本身可以制成微球状的高分子材料之评价。     

人工心脏用高分子材料的表面形态特征—扫描电镜观察报告

为了制造出表面光滑的高质量人工心脏血泵内表面，获得更好的抗血栓,性能作者对几种目前血泵研制中实验应用和准备应用的高分子材料的表面形态特征作扫描电镜观察，观察对象为PU－BD，Jm80,Pellethane2363-80A，和Pellethane2363-80AE等四种聚氨酯，以及Dow Corning3140硅橡胶和Silastic734硅橡胶，研究结果表明：四种聚氨脂材料表面光滑，但也有少量微缺陷，征的影响不明显，DowCOrning3140硅橡胶表面光滑，很少表面缺陷，但用DowCorning3140其中Pellethane材料更少些，干燥温度对聚氨酯表面形态特稀释溶液涂层的表面上缺陷明显增多，其中30％溶液涂层的表面奶粗糙，缺陷已呈蜂窝状，缺陷直径约2u,SIlastic734硅橡胶表面较粗糙，不宜用于血液接触面材料，本研究结果将对血泵研制的质量控制具有实用价值。     

Biofilm formation by Candida species on the surface of catheter materials in vitro.

A model system for studying Candida biofilms growing on the surface of small discs of catheter material is described. Biofilm formation was determined quantitatively by a colorimetric assay involving reduction of a tetrazolium salt or by [3H]leucine incorporation; both methods gave excellent correlation with biofilm dry weight (r = 0.997 and 0.945, respectively). Growth of Candida albicans biofilms in medium containing 500 mM galactose or 50 mM glucose reached a maximum after 48 h and then declined; however, the cell yield was lower in low-glucose medium. Comparison of biofilm formation by 15 different isolates of C. albicans failed to reveal any correlation with pathogenicity within this group, but there was some correlation with pathogenicity when different Candida species were tested. Isolates of C. parapsilosis (Glasgow), C. pseudotropicalis, and C. glabrata all gave significantly less biofilm growth (P < 0.001) than the more pathogenic C. albicans. Evaluation of various catheter materials showed that biofilm formation by C. albicans was slightly increased on latex or silicone elastomer (P < 0.05), compared with polyvinyl chloride, but substantially decreased on polyurethane or 100% silicone (P < 0.001). Scanning electron microscopy demonstrated that after 48 h, C. albicans biofilms consisted of a dense network of yeasts, germ tubes, pseudohyphae, and hyphae; extracellular polymeric material was visible on the surfaces of some of these morphological forms. Our model system is a simple and convenient method for studying Candida biofilms and could be used for testing the efficacy of antifungal agents against biofilm cells.     

Biofilm formation on surface characterized micro-implants for skeletal anchorage in orthodontics

Micro-implants are increasingly popular in clinical orthodontics to effect skeletal anchorage. However, biofilm formation on their surfaces and subsequent infection of peri-implant tissues can result in either exfoliation or surgical removal of these devices. The present study aimed to assess biofilm formation on five commercially available, surface characterized micro-implant systems in vitro. The elemental surface compositions of as-received and autoclave-sterilized micro-implants were characterized by X-ray photoelectron spectroscopy. High carbon contamination was detected on the oxide surfaces, along with traces of inorganic elements (Ca, Cu, Cr, Pb, Zn, and P) which disappeared after Ar(+) ion sputtering. The mean surface roughnesses (R(a)) were around 182nm for titanium micro-implants, and 69nm for stainless steel micro-implants, as measured by atomic force microscopy. Scanning electron microscopy revealed different surface topographies between manufacturers, varying from typical machined grooves to structural defects like pores and pits. Overnight biofilms were grown on micro-implant surfaces by immersion in pooled human whole saliva. Biofilms on micro-implants treated with chlorhexidine and fluoride mouthrinses contained comparable numbers of viable organisms, but significantly less than did untreated micro-implants. Comparison of different implant systems using multiple linear regression analysis indicated that biofilm formation was governed by roughness of the implant surface and the prevalence of carbon- and oxygen-rich components.     

The surface stability of polymers with adsorbed fibronectin

Linear low-density polyethylene (LLDPE), polypropylene (PP), polystyrene (PS), and polyethylene-co-ethacrylic acid (PE-EAA, 17.5% acid content) films were treated with an aqueous solution of fibronectin. Advancing contact angles of water (straight theta(a)) were used to monitor the change in the surface wettability of these films. With the exception of PE-EAA, all of the samples showed an increase in their wettability by water, indicating that the protein had adsorbed to the polymer surface. The stability of these protein-modified films against a buffered aqueous solution and against air under ambient conditions was monitored over time. The surface wettability of these protein-modified polymers, with the exception of PS, remained unchanged after heating against the buffer solution. In air, however, straight theta(a) increased over a period of 2 months. In addition, the effect of organic solvent extraction on the surface stability of these protein-modified films was investigated. Unmodified samples of LLDPE, PS, and PP were subjected to soxhlet extraction to remove impurities and low-molecular-weight oligomers prior to film preparation and subsequent treatment with fibronectin. These samples were left in air under ambient conditions for 2 months. There was no difference in the magnitude of the change in straight theta(a) for the protein-modified, extracted LLDPE film compared to the protein-modified, nonextracted polymer film. A slight decrease in the rate of thermal reconstruction was observed for the protein-modified extracted PS film compared to the protein-modified nonextracted sample, and a slight increase in the rate of thermal reconstruction was observed for the protein-modified extracted PP film compared to the protein-modified nonextracted sample.Copyright 2000 John Wiley & Sons, Inc.     

Effects of molecular architecture of phospholipid polymers on surface modification of segmented polyurethanes

To modify the surface properties of segmented polyurethane (SPU), effects of the molecular architecture of the 2-methacryloyloxyethyl phosphorylcholine (MPC) polymers on the performance of the SPU/MPC polymer membrane were investigated. We combined the random-type, block-type, and graft-type of the MPC polymers with a typical SPU, Tecoflex^® using double solution casting procedure. The graft-type MPC polymers composed of a poly(MPC) main chain and poly(2-ethylhexyl methacrylate (EHMA)) side chains were synthesized through the combination of two different living radical polymerization techniques to regulate the density and chain length of the side chains. The SPU membranes modified with the MPC polymers were characterized using X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The results revealed that the MPC units were located on the SPU surface. Although the breaking strength of the SPU membranes modified with block-type poly(MPC-block-EHMA) and graft-type poly(MPC-graft-EHMA) was lower than that of SPU membranes modified with random-type poly(MPC-random-EHMA), their breaking strengths were adequate for manufacturing medical devices. On the other hand, better stability was observed in the MPC polymer layer on the SPU membrane after immersion in an aqueous medium, wherein the SPU membrane had been modified with the poly(MPC-graft-EHMA). This was because of the intermixing of the hydrophobic poly(EHMA) segments in the domain of the hard segments in the SPU membrane. After this modification, each SPU/MPC polymer membrane showed hydrophilic nature based on the MPC polymers and a dramatic suppression of protein adsorption. From these results, we concluded that the SPU membrane modified with the poly(MPC-graft-EHMA) was one of the promising polymeric biomaterials for making blood-contacting medical devices.     

Why degradable polymers undergo surface erosion or bulk erosion

A theoretical model was developed that allows to predict the erosion mechanism of water insoluble biodegradable polymer matrices. The model shows that all degradable polymers can undergo surface erosion or bulk erosion. Which way a polymer matrix erodes after all depends on the diffusivity of water inside the matrix, the degradation rate of the polymer's functional groups and the matrix dimensions. From these parameters the model allows to calculate for an individual polymer matrix a dimensionless 'erosion number' epsilon. The value of epsilon indicates the mode of erosion. Based on epsilon, a critical device dimension Lcritical can be calculated. If a matrix is larger than Lcritical it will undergo surface erosion, if not it will be bulk eroding. Lcritical values for polymers were estimated based on literature data. Polyanhydrides were found to be surface eroding down to a size of approximately Lcritical = 10(-4) m while poly(alpha-hydroxy esters) matrices need to be larger than Lcritical = 10(-1) m to lose their bulk erosion properties. To support our theoretical findings it was shown experimentally that poly(alpha-hydroxy ester) matrices, which are considered classical bulk eroding materials, can also undergo surface erosion.     

Control of cell adhesion and detachment on Langmuir-Schaefer surface composed of dodecyl-terminated thermo-responsive polymers

This study used Langmuir-Schaefer (LS) method to produce thermo-responsive poly(N-isopropylacrylamide) (PIPAAm) modified surface. Dodecyl terminated-PIPAAm (PIPAAm-C12) was synthesized by reversible addition-fragmentation chain transfer radical polymerization. PIPAAm-C12 was dropped on an air–water interface and formed Langmuir film by compressing. A surface pressure measurement revealed that PIPAAm-C12 was floated and Langmuir films were formed on the interface. And the Langmuir film was transferred on a hydrophobic substrate to produce PIPAAm-C12 transferred surface (PIPAAm-LS surface). In the results of atomic force microscope, attenuated total reflection Fourier transform infrared spectroscope, and X-ray photoelectron spectroscope measurement, the transference of Langmuir films was demonstrated and densities could be precisely controlled. Ellipsometric measurements of PIPAAm-LS surfaces showed that the thicknesses of the surfaces were less than 10?nm. Cell adhesion and detachment were observed on the PIPAAm-LS surfaces. The amount of adhered cells on all LS surfaces was found to be similar on the control hydrophobic substrate at 37?°C. In regard to cell detachment, adhering cells rapidly detached themselves with higher densities and shorter PIPAAm-C12 molecules. In this method, the effect of densities and molecular weights on cell adhesion and detachment were observed. Our method should be proved novel insights for investigating cell adhesion and detachment on thermo-responsive surfaces.     

Initial adhesion and surface growth of Staphylococcus epidermidis and Pseudomonas aeruginosa on biomedical polymers

The infection risk of biomaterials implants varies between different materials and is determined by an interplay of adhesion and surface growth of the infecting organisms. In this study, we compared initial adhesion and surface growth of Staphylococcus epidermidis HBH(2) 102 and Pseudomonas aeruginosa AK1 on poly(dimethylsiloxane), Teflon, polyethylene, polypropylene, polyurethane, poly(ethylene terephthalate), poly(methyl methacrylate), and glass. Initial adhesion was measured in situ in a parallel plate flow chamber with microorganisms suspended in phosphate-buffered saline, while subsequent surface growth was followed in full and in 20 times diluted growth medium. Initial adhesion of both bacterial strains was similar to all biomaterials. In full growth medium, generation times of surface growing S. epidermidis ranged from 17 to 38 min with no relation to wettability, while in diluted growth medium generation times increased from 44 to 98 min with increasing surface wettability. For P. aeruginosa no influence of surface wettability on generation times was observed, but generation times increased with decreasing desorption rates, maximal generation times being 47 min and minimal values down to 30 min. Generally, generation times of adhering bacteria were shorter than of planktonic bacteria. In conclusion, surface growth of initially adhering bacteria is influenced by biomaterials surface properties to a greater extent than initial adhesion.     

Illustration of surface crosslinking of different polymers treated in argon plasma

The influence of argon plasma on polycarbonate (PC) and poly(propylene) (PP) has been studied in terms of structural changes and reaction mechanisms. In situ UV-visible ellipsometry reveals formation of a surface layer with a higher refractive index than the untreated polymer. The increase in the refractive index is attributed to polymer densification, which is assigned to crosslinking. However, a decrease in the average molecular weight of the PC is also observed and two populations of macromolecules of different size are detected by light scattering measurements, revealing a competition between crosslinking and degradation. The reaction mechanisms were investigated using Nuclear Magnetic Resonance (¹H NMR) and in situ IR ellipsometry. Degradation is caused by carbonate bond breaking, while crosslinking seems to be related to a decrease in methyl groups. The ellipsometry results are correlated with amorphous phase extraction and ¹H NMR analysis of modified PP. The crosslinking mechanism involves the elimination of methyl groups, and also the formation of exomethylenic bonds. Spectroscopic ellipsometry appears to be a valuable tool to study the interaction between a plasma and a polymer, as UV-visible ellipsometry is sensitive to structural changes in the polymer, while IR ellipsometry detects the appearance and disappearance of chemical groups in a surface layer.