What is the special significance of surface treatment for medical implants?

1. Improve biocompatibility and lessen rejection reactions.
Biocompatibility is an important need for medical implants. It means that materials should not produce bad reactions like toxicity, sensitization, inflammation, or thrombosis when they come into touch with human tissue. Surface treatment improves the surface qualities of implants using physical or chemical approaches. This makes them much more biocompatible.
By applying methods like sandblasting, acid etching, and laser processing, micro- or nano-scale rough structures are made on the implant's surface. This increases the surface area and tissue contact area, which helps cells stick to the implant and grow. For instance, after being sandblasted and acid etched, the surface roughness (Sa value) of dental implants can be kept between 1 and 2 μm, which can greatly increase the strength of the bone bond and speed up the healing process.
Chemical modification: Adding bioactive groups like hydroxyl and amino groups to the surface of implants, or adding minerals that help bones grow, such strontium and calcium, to improve the chemical interaction between materials and tissues. After anodizing, a thick oxide film forms on the surface of titanium alloy. Electrochemical methods are then used to embed calcium and phosphorus elements to mimic the composition of natural bone and encourage bone cell development.
Biocoating technology: Bioceramics (like hydroxyapatite) or bioactive glass coatings are put on the surface of implants using technologies like plasma spraying and electrochemical deposition. These coatings are directly involved in the mechanisms that make bones work. Studies indicate that the osseointegration rate of hydroxyapatite-coated implants exceeds that of untreated implants by over 40%.
2. Improve resistance to corrosion and lengthen service life
Medical implants must endure prolonged exposure to human bodily fluids, which can be readily eroded by corrosive agents such as chloride ions and proteins. This corrosion results in the dissolution of metal ions and the detachment of coatings, potentially causing inflammatory responses or implant failure. By creating a thick protective layer, surface treatment greatly increases the corrosion resistance of implants.
Passivation treatment: After being treated with nitric acid, a chromium oxide passivation film forms on the surface of stainless steel implants. This film stops metal ions from seeping out and lowers the corrosion rate to less than 0.001mm/year, which is what is needed for long-term implantation.
Micro arc oxidation technology: A high-voltage electric field is used to excite micro arc discharge on the surface of titanium alloy. This makes a ceramic oxide film that contains titanium, oxygen, and phosphorus. It can get harder than 1000HV, and it is three times more resistant to wear than regular anodic oxide films. It works well for situations with a lot of weight, like joint prosthesis.
Using physical vapor deposition (PVD) or chemical vapor deposition (CVD) technology, nano scale TiN, TiAlN, and other hard coatings can be applied to the surface of implants with a thickness of only 1–5 μm. This can improve corrosion resistance by more than 50%, lower the friction coefficient, and cut down on the amount of wear particles that are made.
3. Give it antibacterial properties and lower the chance of getting sick
Infections that happen after surgery are one of the main reasons why medical implants fail. For example, infections in orthopedic, cardiovascular, and other implants can happen in 1% to 5% of cases. Surface treatment works well to stop bacteria from sticking to surfaces and forming biofilms by making surfaces that kill bacteria or adding antibacterial chemicals.
Surface grafting of antibacterial groups: Antibacterial groups like quaternary ammonium salts and fluorides are added to the surface of the implant using plasma treatment or chemical grafting. This changes the structure of the bacterial cell membrane and has long-lasting antibacterial effects. For instance, an antibacterial coating that contains silver can kill 99% of Staphylococcus aureus and stay effective for more than 30 days.
Light-responsive intelligent coating: This involves putting photosensitizers (such porphyrin compounds) on the surface of implants and using light of a certain wavelength to make reactive oxygen species (ROS) that destroy germs without hurting host cells. This method has been used to disinfect the surfaces of equipment that might easily spread infections, like endoscopes and catheters.
Antibacterial coating and drug release work together: Antibiotics like vancomycin and gentamicin are added to the bioceramic coating to control how quickly the coating breaks down, which releases the drugs. The concentration of the medicine in the area can be more than 1000 times higher than the concentration of the drug in the blood, which stops infections after surgery.
4. Improve the ability of osseointegration and the rate of clinical success.
For orthopedic, dental, and other implants, the capacity to osseointegrate is a significant aspect in clinical success. Surface treatment speeds up the process of bone integration by controlling the shape, chemical makeup, and biological activity of the surface, which helps bone cells stick, grow, and change.
Double acid etching treatment technology: By using two acids (like HCl+H ₂ SO ₄ mixed acid and HNO 3 solution) in a two-step process, a multi-level pore structure is created on the surface of the implant. This structure has micrometer-level roughness that provides mechanical interlocking force and nanometer-level pores that increase biological activity, making the bond between the implant and bone stronger by more than 30%.
3D printing of porous structures: Using selective laser melting (SLM) technology to make porous titanium alloy implants that are 60% to 80% porous and have pores that are 200 to 500 μm wide. This simulates the natural bone trabecular structure, encourages the growth of blood vessels and bone tissue, and achieves "biological fixation." Clinical evidence indicates that the osseointegration duration of porous structure implants is 50% less than that of solid structures.
Changing bioactive molecules: Putting bioactive molecules like bone morphogenetic protein (BMP) and collagen on the surface of implants to start signaling pathways that help bone cells differentiate. For instance, implants that have been changed with BMP-2 can cut the time it takes for osseointegration from 3 months to 6 weeks and raise the success rate of implantation to more than 98%.