Research and development of metals for medical devices based on clinical needs

Abstract

The current research and development of metallic materials used for medicine and dentistry is reviewed. First, the general properties required of metals used in medical devices are summarized, followed by the needs for the development of α + β type Ti alloys with large elongation and β type Ti alloys with a low Young's modulus. In addition, nickel-free Ni–Ti alloys and austenitic stainless steels are described. As new topics, we review metals that are bioabsorbable and compatible with magnetic resonance imaging. Surface treatment and modification techniques to improve biofunctions and biocompatibility are categorized, and the related problems are presented at the end of this review. The metal surface may be biofunctionalized by various techniques, such as dry and wet processes. These techniques make it possible to apply metals to scaffolds in tissue engineering.     

Rapid synthesis of thermally stable hydroxyapaptite

We have optimized the wet precipitation synthesis of hydroxyapaptite to obtain thermally stable powder in the short time span of 3 min. Exposure of the reaction mixture to 1000 W microwave for 3 min furnished hydroxyapatite, which was thermally stable at temperatures up to 1200 °C. Powders were analyzed for phase purity using X-ray crystallography; chemical composition was studied using Fourier transform infrared spectroscopy while particle morphology was analyzed using scanning electron microscopy.     

Tribological behaviour of AISI 316L stainless steel for biomedical applications

Abstract

The aim of this research is to study the tribological behaviour of AISI 316L stainless steel for surgical implants (total hip prosthesis). The tribological behaviour is evaluated by wear tests, using tribometers ball on disc and sphere on plane. These tests consisted of measuring the weight loss and the friction coefficient of stainless steel (SS) AISI 316L. The oscillating friction and wear tests have been carried out in ambient air with an oscillating tribotester in accord with standards ISO 7148, ASTM G99-95a and ASTM G133-95 under different conditions of normal applied load (3, 6 and 10 N) and sliding speed (1, 15 and 25 mm s^?1). A ball of 100Cr 6, 10 mm in diameter, is used as counter pairs. These tribological results are compared with those carried out with a tribometer type pin on disc under different conditions of normal load applied P (19·43, 28 and 44 N) and sliding speed (600 and 1020 rev min^?1). The behaviour observed for both samples suggests that the wear and friction mechanism during the tests is the same, and to increase the resistance to wear and friction of biomedical SS AISI 316L alloy used in total hip prosthesis (femoral stems), surface coating and treatment are necessary.     

氧化铝瓷表面施加生物玻璃涂层的研究

本文探索了氧化铝瓷基板上涂二层生物玻璃的工艺,以保证生物活性。用上述工艺制备的样品植入家兔的骨和肌肉,发现无排异迹象并与骨组织紧密结合。     

骨水泥生物材料研究与开发进展

本文概述了骨水泥生物材料的开发和研究。重点介绍了和骨组织结构相似、多为惰性材料的第一代骨水泥材料聚甲基丙烯酸甲酯(PMMA)和可吸收性、可被再生组织取代第二代骨水泥材料羟基磷灰石(HA)的发展,阐述了HA和生物降解材料的复合。展望了骨水泥材料的广阔应用前景。     

Development and characterization of photopolymerizable biodegradable materials from PEG-PLA-PEG block macromonomers

As tissue engineering and drug delivery applications increase in both number and complexity, the demand for new synthetic biocompatible polymers with precisely tailored properties grows accordingly. Block copolymers are a particularly promising biomaterial as the physical and physiological properties of these polymers can be closely controlled through manipulation of the type and organization of the blocks in the polymer's backbone. In this work, poly(ethylene glycol) (PEG) and poly(lactic acid) (PLA) were incorporated into PEG-PLA-PEG block macromonomers with (meth)acrylate functionality to form photopolymerizable, highly cross-linked polymers for potential use in a variety of biomedical applications. Simply by directing the PLA:PEG ratio in these macromonomers, the hydrophobicity, physical behavior, degradation, and biocompatibility of the resulting polymer were controlled. Specifically, it was found that by increasing the PLA:PEG ratio, the degree of water uptake and the mechanical strength of the material is significantly decreased, while the glass transition temperature and degradation of the PEG-PLA polymers are delayed. Additionally, the biocompatibility of the PEG-PLA polymers is significantly influenced by the chemical composition of the material as increased PLA generally yields greater cell compatibility. By demonstrating the versatility of the photopolymerizable PEG-PLA polymers, the results of this study indicate that these materials have the potential to serve as a synthetic biomaterial platform, in which the properties of the polymer can be tailored to a variety of tissue engineering or drug delivery applications.     

Initiated chemical vapor deposition of a siloxane coating for insulation of neural probes

Recent advances in the field of neuroprosthetics have brought the possibility of human utilization into the near term. However, current implant coating chemistries require thicknesses of ~ 25 μm in order to provide the required electrical insulation, significantly increasing the diameter of the neural probe shanks and resulting surgical damage upon implantation. In this work, a novel biopassivation coating is created through initiated chemical vapor deposition (iCVD) of trivinyl-trimethyl-cyclotrisiloxane. The resulting material is a highly crosslinked organosilicon polymer matrix which is synthesized directly on the surface of the substrate. This material possesses an electrical resistivity which allows for a coating thickness on the order of only 5 μm. The material has also been demonstrated to retain its electrical properties in a simulated biological environment for over 3 years.     

TiO2 nanotubes from stirred glycerol/NH4F electrolyte: Roughness, wetting behavior and adhesion for implant applications

Titanium oxide (TiO₂) was anodically formed on titanium from non-aqueous electrolyte containing glycerol and 0.5 wt.% ammonium fluoride (NH₄F). Oxidation was carried out for 30, 60, 120 and 240 min at potentiostatic 30 V with the bath being stirred using magnetic pellet. All the conditions produced amorphous nanotubes. They had an average diameter of 50–130 nm and length in the range of 1.2–1.9 μm. The porosity was in the range of 70–80%. Stirring of the glycerol-based electrolyte has proved to be advantageous in retaining the tubular structure and providing smooth tubes even at 30 V condition.The coatings had surface roughness Ra lower than 0.5 μm, water wetting angles in the range of 58–84°. Increasing pore diameters increased the water wetting angles. All the coatings invariably showed poor tensile pull-off adhesion strengths. This poor adhesion is attributed to the stirring of the electrolyte.     

A Micro Peristaltic Pump Using an Optically Controllable Bioactuator

Peristalsis is widely seen in nature, as this pumping action is important in digestive systems for conveying sustenance to every corner of the body. In this paper, we propose a muscle-powered tubular micro pump that provides peristaltic transport. We utilized Drosophila melanogaster larvae that express channelrhodopsin-2 (ChR2) on the cell membrane of skeletal muscles to obtain light-responsive muscle tissues. The larvae were forced to contract with blue light stimulation. While changing the speed of the propagating light stimulation, we observed displacement on the surface of the contractile muscle tissues. We obtained peristaltic pumps from the larvae by dissecting them into tubular structures. The average inner diameter of the tubular structures was about 400 μm and the average outer diameter was about 750 μm. Contractions of this tubular structure could be controlled with the same blue light stimulation. To make the inner flow visible, we placed microbeads into the peristaltic pump, and thus determined that the pump could transport microbeads at a speed of 120 μm·s⁻¹.