Biomedical Industry
The biomedical industry demands high – performance surface modifications for various medical devices and implants to meet the requirements of biocompatibility, wear resistance, corrosion resistance, and other specific functions. Thermal spray technology has emerged as a valuable technique to address these needs.
thermal spray technologies applicable to the biomedical industry
Plasma Spraying
Characteristics:
Plasma spraying is a method that uses a plasma arc to heat the spraying materials to a molten or semi-molten state and then sprays them at high speed onto the surface of the substrate to form a coating. It can generate a high-temperature, high-speed plasma flame flow, enabling the spraying materials to obtain relatively high kinetic energy and thermal energy, thus forming coatings with high bonding strength and good compactness.
Applications:
Preparation of Bioactive Coatings:
It can be used to spray bioactive ceramic coatings such as hydroxyapatite on the surface of metal implants to improve the biocompatibility and bone bonding ability of the implants. For example, spraying a hydroxyapatite coating on the surfaces of implants like artificial hip joints and knee joints can promote the growth and attachment of bone tissue on the implant surface and accelerate the recovery process of patients.
Preparation of Antibacterial Coatings:
By adding antibacterial components such as silver ions and using plasma spraying technology to prepare antibacterial coatings together with other materials, the risk of implant infection can be effectively reduced and the success rate of implantation surgery can be improved.
High-Velocity Oxygen-Fuel (HVOF) Spraying
Characteristics:
High-Velocity Oxygen-Fuel spraying adopts specially designed combustion chambers and nozzles. It uses high-pressure oxygen to support combustion and drives a large flow of fuel to generate a supersonic combustion flame flow. The coatings prepared by this technology have relatively high density, hardness and bonding strength, with low porosity and less impurity content.
Applications:
Preparation of Wear-Resistant Coatings:
It is suitable for preparing wear-resistant coatings in biomedical instruments, such as the friction surfaces of artificial joints and the necks of dental implants. Using hard alloys such as tungsten carbide-cobalt (WC-Co) as spraying materials, the wear-resistant coatings prepared by High-Velocity Oxygen-Fuel spraying can significantly improve the wear resistance and service life of components, reduce the generation of wear particles and lower the potential harm to human tissues.
Improvement of Biocompatible Coatings:
After some biocompatible materials are treated by High-Velocity Oxygen-Fuel spraying, the performance of their coatings can be further optimized. For example, when common biomedical materials such as titanium alloys are treated by High-Velocity Oxygen-Fuel spraying, the surface roughness and hardness can be improved, enhancing the attachment and proliferation ability of cells and thus strengthening their biocompatibility.
Suspension Plasma Spraying
Characteristics:
Suspension plasma spraying is a new type of thermal spraying technology. It makes the spraying materials in the form of a suspension, and then uses plasma spraying equipment to heat, accelerate and deposit the particles in the suspension onto the surface of the substrate to form a coating. This technology can prepare nanostructured coatings with the advantages of being thin, having high crystallinity and strong adhesion.
Applications:
Surface Modification of Bone Implants:
It can be used to spray a nanostructured biomaterial layer on the surface of 3D-printed titanium implants, such as a composite coating composed of hydroxyapatite, silver and graphene. This kind of coating can not only improve the biocompatibility and bone bonding ability of the implants but also has antibacterial properties, which helps to prevent infections and promotes the rapid formation and repair of bone tissue.
Preparation of Coatings for Cardiovascular Stents:
Coatings with good blood compatibility and drug slow-release functions can be prepared on the surface of cardiovascular stents. Through suspension plasma spraying technology, the suspension made of drugs and biocompatible materials can be sprayed onto the surface of the stents to form a uniform and stable coating, realizing the slow release of drugs, inhibiting the excessive proliferation of vascular smooth muscle cells and reducing the incidence of in-stent restenosis.
Electrothermal Explosion Spraying
Characteristics:
Electrothermal explosion spraying applies an instantaneous direct current high voltage along the axial direction of a metal conductor, causing a powerful current to be generated inside the metal and then an explosion occurs. The shock wave generated sprays metal particles at an extremely high speed onto the surface of the substrate to form a coating. This technology can achieve metallurgical bonding between the coating and the substrate, greatly improving the bonding strength of the coating.
Applications:
Strengthening of Orthopedic Implants:
For some orthopedic implants that bear relatively large loads, such as spinal fusion cages and bone screws, electrothermal explosion spraying technology can be used to prepare a high-strength metal coating, such as a titanium alloy coating, on their surfaces to enhance the mechanical properties of the implants, improve their stability and reliability inside the human body and reduce the risk of surgical failure caused by implant loosening or fracture.
Coatings for Dental Restorations:
Coatings with special properties, such as those that can improve hardness, wear resistance and corrosion resistance, as well as those with antibacterial and whitening functions, can be sprayed on the surfaces of dental restorations like porcelain-fused-to-metal crowns and all-ceramic crowns to improve the performance and aesthetic effect of the restorations and extend their service lives.
The Specific Applications of Thermal Spay to Biomedical Industry
Orthopedic Implants
Enhanced Bone – Implant Integration:
Plasma spraying is widely used to deposit hydroxyapatite (HA) coatings on the surface of orthopedic implants such as hip and knee prostheses. HA is a bioactive ceramic that closely mimics the mineral component of natural bone. The plasma – sprayed HA coating provides a favorable surface for osteoblasts (bone – forming cells) to adhere, proliferate, and differentiate. This promotes osseointegration, which is crucial for the long – term stability and success of the implant. For example, in a clinical study, implants with plasma – sprayed HA coatings showed significantly better bone – on – growth compared to non – coated implants, leading to reduced implant loosening and better patient outcomes.
Wear – Resistant Coatings:
High – Velocity Oxygen – Fuel (HVOF) spraying of carbide – based materials like tungsten carbide – cobalt (WC – Co) is applied to the articulating surfaces of joint implants. The high hardness and excellent wear – resistance of these coatings minimize the generation of wear debris, which can cause osteolysis (bone resorption) and implant failure. In vitro wear tests have demonstrated that HVOF – sprayed WC – Co coatings can reduce wear rates by up to 90% compared to uncoated metal surfaces, significantly prolonging the lifespan of the implant.
Dental Applications
Dental Implants:
Similar to orthopedic implants, the surface of dental implants can be treated with thermal spray. Plasma spraying of titanium or titanium alloy coatings can improve the osseointegration of dental implants. Additionally, for the exposed part of the implant (above the gum line), a ceramic coating can be applied to enhance aesthetics and corrosion resistance. In a dental practice, patients with plasma – sprayed titanium – coated dental implants have shown better initial stability and long – term success rates, with reduced risks of peri – implantitis (inflammation around the implant).
Dental Restorations:
Thermal spray can be used to apply wear – resistant and esthetic coatings on dental restorations such as crowns and bridges. For example, a zirconia – based coating can be sprayed onto porcelain restorations to improve their hardness and wear resistance, while also maintaining a natural – looking appearance. This helps to extend the service life of the restorations and reduces the need for frequent replacements.
Cardiovascular Devices
Stents:
Suspension plasma spraying is used to coat cardiovascular stents with biocompatible polymers and drugs. The coatings can control the release of anti – proliferative drugs to prevent restenosis (re – narrowing of the blood vessel after stent implantation). The nanostructured coatings prepared by this method have a high surface area – to – volume ratio, allowing for more efficient drug loading and release. Clinical trials have shown that stents with well – designed plasma – sprayed drug – eluting coatings can significantly reduce the incidence of restenosis and improve patient survival rates.
Artificial Heart Valves:
Thermal spray can be used to apply coatings to artificial heart valves to improve their hemocompatibility (compatibility with blood). For example, a coating of pyrolytic carbon can be deposited to reduce the risk of blood clot formation and improve the long – term performance of the valve.
Advantages of Thermal Spray in Biomedical Applications
Customizable Coatings
Thermal spray allows for the combination of different materials to create coatings with multiple functions. For example, a composite coating of HA and an antibacterial agent can be prepared to provide both bone – promoting and infection – preventing properties. The composition and structure of the coating can be adjusted according to the specific requirements of different medical applications.
Minimal Substrate Alteration
The thermal spray process generally has a relatively low impact on the substrate material. The temperature rise during spraying is usually limited, which is beneficial for heat – sensitive medical materials such as polymers and some bioactive substances. This ensures that the mechanical and biological properties of the substrate are maintained, while only the surface properties are modified.
Versatile Shapes and Sizes
Thermal spray can be applied to medical devices of various shapes and sizes. Whether it’s a small – diameter stent or a large – sized orthopedic implant, the technology can provide a uniform coating. This versatility makes it suitable for a wide range of biomedical products.