PVD (Physical Vapor Deposition) and CVD (Chemical Vapor Deposition) are two major thin-film coating technologies. PVD vaporizes materials through physical means (e.g., heating or sputtering), resulting in strong adhesion but slower deposition rates. CVD forms coatings via chemical reactions, off
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PVD and CVD are the most commonly used surface treatment methods for tools and moulds, CVD is based on chemical vapour deposition and PVD is based on physical vapour deposition, as they differ in principle, the final coating results are different and each has its own focus in application.
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PVD stands for Physical Vapour Deposition. PVD coating refers to a thin film deposition technique whereby solid materials are sputtered or evaporated in a vacuum environment and deposited as pure materials or alloy components to form a coating on a substrate.
Views: 41 Author: Site Editor Publish Time: 2022-05-25 Origin: Site
PVD vacuum coating will greatly improve the hardness and adhesion of medical devices. The biocompatibility of the coating is a prerequisite for its use on medical devices.
The biocompatibility of the film layer is certified by a series of tests carried out by an independent medical testing laboratory. These tests are short-term body contact tests on materials according to ISO 10993-1. The results show that TiN, DLC , CrN, TiAlN, AlTiN and other PVD coatings are suitable for use on internal and external medical devices that come into contact with bone, skin tissue and blood.
PVD coatings applied to medical devices have the following advantages.
Increased wear resistance
Reduced friction
Biocompatibility
Decorative colour and aesthetics
Chemical barrier layer
The biocompatibility test contains the following items.
Sensitivity: no significant delayed skin contact sensitivity in the subject.
Cytotoxicity: no cytolysis or toxicity induced
Systemic Acute: no systemic toxic reactions or mortality
Intradermal reactions: no significant irritation or toxicity in rabbits
Genotoxicity: no mutagenicity
USP muscle: no irritation to muscle tissue
Hemolytic: non-hemolytic, compatible with blood
PVD layers on medical devices must also be adapted to the sterilisation process. tiN and CrN are resistant to both steam and chemical autoclaving processes. Components made up of 416 and 304 stainless steel parts are subject to corrosion after autoclaving. The manufacturer tried unsuccessfully to solve this problem with a new grade of stainless steel, TiN and CrN, which were autoclaved in deionised water at 132F and 30MPa and chemically sterilised in vapour phase alcohol. The results showed that both film layers protected the stainless steel substrate against autoclave-induced corrosion.
The use of orthopaedic implants
TiN has been used in clinical orthopaedic implants in North America and Europe for over 9 years. The most common application is joint replacement with Co-Cr-Mo or Ti-6-4 alloy implants. TiN is mainly used for joint implants in the hip, knee, ankle and shoulder areas.
Pappas and Buechel presented four joint simulators tested in 37 degree deionised water subjected to load vibration from 0 to 2200 N. Ti-6-4 femoral joints coated with TiN outperformed uncoated Co-Cr-Mo joints. The TiN film tested was ion plated to a thickness of 9um and the joint was polished to a surface finish of 0.04umRa before and after plating. The results of the tests showed that the TiN coated Ti-6-4 produced half the wear of the uncoated Co-Cr-Mo over a lifetime of 10 million cycles, and that the TiN film prevented this cascading failure mechanism from the outset.
Mobile joints (e.g. hip joints, ankle joints, etc.) are also prone to the formation of wear and tear caused by bone or bone clay third body particles. In the case of artificial knee joints, these wear particles can become trapped between the metal bone joint and the PE tibial joint. The worn down particles can cause breakage of both surfaces. The long-term viability of the implant is not favoured as the scratching of the femoral joint accelerates the wear of the PE material.
TiN is still the only membrane layer in clinical use for orthopaedic implants, but AlTiN,DLC membrane layers are still being tested as an optional material. The main areas of application are hip and knee prostheses, braces, and screws on fractures and spinal fusions.
Micro-movement corrosion is an important issue with PVD coated implants. Micro-movement corrosion occurs when two metal joints are subjected to micro-movements of less than 250um in the presence of a corrosive fluid. The micro-movement removes the inert oxide film from the stainless steel and titanium components, leading to corrosion and the release of ions from the implant. In severe cases, large amounts of metal oxide wear debris are produced.
Titanium is particularly susceptible to micro-movement corrosion. With the widespread use of titanium alloys in spinal implants, there is concern about the long-term outcome of these implants. Black wear debris approaching spinal cord implants has been reported in the clinical literature. The import of Ti-6-4 spinal cord implants is no longer permitted in Japan.
As early as 1991, Mauer suggested that TiN could reduce micro-movement corrosion of Ti-6-4 screws and brackets. The conclusions showed that TiN coated screws would significantly reduce wear on the screw and bracket. When both components are coated, wear is reduced even more. These tests were carried out according to ASTMF897 standards with the fixing screws and brackets immersed in 56 degrees 20ml of 10% calf serum and 0.9% saline for 0 to 10um of micromovement. In addition to the weight loss that needs to be measured, the metal ion concentration in the solution is also tested. Compared to uncoated Ti-6-4, the measurements of metal ion concentration and weight loss are compatible for the various surface treatments.
Due to their corrosion resistance properties, PVD layers have been widely used in orthopaedics and other medical specialities, and TiN, DLC, and CrN have been evaluated for their corrosion resistance on other implants.