Abstract: Metal materials are the earliest applications in biomedical materials. Made of high strength and toughness, it is suitable for repairing or changing the hard tissues of the human body. It has been used for precious metal implants more than 100 years ago. With the corrosion-resistant stainless steel, elastic modulus and bone structure close to copper-iron alloy, as well as new biomedical metal materials such as memory alloy materials and composite materials, the application range is also expanding.
Key words: titanium alloy material, surface coating treatment, surface modification
(1) Treatment of medical metal and alloy surface coating
The biological activity, wear and corrosion of metals and their alloys in the living body have not been solved, and the surface needs to be modified. Surface modification not only inhibits the dissolution of harmful metal ions, but also promotes the regeneration of tissues and strengthens the bonding of materials to tissues.
The surface modification technology of bio-titanium alloy materials can be mainly divided into:
(1) Physical and chemical methods (2) Morphological methods (3) Biochemical methods.
1 Physical and chemical methods - the main method to improve the surface properties of metal biomaterials
(1) Thermal spraying
Thermal spraying is to use a flame of a heat source to heat and melt the powdered metal or non-metal spray material and soften it, and atomize it with the power of the heat source or a high-speed air stream to spray the droplets of the spray material at a certain speed. A process for treating a clean substrate surface, relying on physical changes and chemical reactions of the spray material to form a bond layer with the substrate. Can be divided into arc spraying, plasma spraying, flame spraying, explosive spraying and so on.
(2) Pulsed laser fusion
It is a method of melting a coating material on a surface of a substrate under irradiation of a pulsed laser with a low output power and a high scanning speed.
(3) Ion sputtering
Ion sputtering bombards the target with high-speed ions, causing the coating material particles to be sputtered and deposited on the metal substrate
(4) Sandblasting method
The coating material powder is directly sprayed onto the surface of the substrate by a sand blasting machine at a high speed.
(5) Electrochemical method
The electrochemical method is an electrochemical method for controlling the preparation of a reaction by adjusting the concentration, pH, reaction temperature, electric field strength, current, etc. of the electrolyte.
(6) Ion implantation method
Ion implantation modification is to vaporize the required elements in the ion gasification chamber, ionize them by high-frequency discharge, and extract, bunch and accelerate the electric field to form a high-energy fine ion beam. The surface of the solid material as a target, thereby achieving a method of changing the surface properties of the material. The non-thermal equilibrium process is not limited by the laws of metallurgy, and any elemental atom can be accelerated into the powder box material; the ion implantation process is a low temperature process, which does not cause changes in the internal structure, composition and external shape of the metal target material; Injection technology is also a highly controllable technique that accurately controls the injection concentration, gradient, and depth of implantation of the target material by controlling the implantation energy and implant dose.
2 Morphological methods:
The metal substrate is directly implanted into the living body without changing the chemical composition of the surface layer of the metal substrate, thereby achieving an important influence on the adhesion, growth and adhesion strength of the living tissue. This method does not produce a strengthening layer or an additional coating on the surface of the substrate, but rather achieves the best implant effect by improving the surface topography of the implant. The morphological surface modification process generally improves the bonding strength and generally does not detract from the biocompatibility of the material. It is a relatively simple and effective surface modification method. The specific methods include: plasma spray, supersonic oscillation, laser beam spot melting and electrochemical grain boundary corrosion.
3 Biochemical methods
The organic polymer substance such as macromolecular protein or enzyme is introduced into the surface of the substrate to have more excellent biological activity, and thus has more direct and more effective characteristics. Such materials can promote healing of the wound at the implant, accelerate the bonding of the implant to the surrounding tissue, and also improve the safety and longevity of the implant.
Most metal surfaces have an oxide film that, under certain conditions, acts with [H] or H+ to form an -OH hydroxyl group attached to the surface of the substrate. In this case, the substrate is silanized with (APS), and some proteins or enzyme molecules such as trypsin are chemically bonded to the surface of the substrate by the action of glutaraldehyde. This method was proposed by the American scientist David A. Puleo, which can immobilize living biomolecules on the surface of inorganic, non-porous, non-loose biomaterials, thereby greatly increasing the surface activity of the material.
(2) Improve the surface modification of titanium metal
1 Improve the biological activity of titanium alloy surface modification
In order to improve the biological activity of medical titanium alloy and improve its blood compatibility, a bioactive ceramic coating is usually prepared on the surface of titanium alloy. At present, the preparation methods of bioceramic coating mainly include: plasma spraying method, electrophoretic deposition method, ion beam sputtering method, dip coating method, radio frequency magnetron sputtering method, ion beam dynamic mixing method, excimer laser deposition method, sol - a gel method, a biomimetic solution growth method, an integration-sintering method, and a dip coating-sintering method.
2 Surface modification of titanium alloy to improve wear resistance
Titanium alloy implants should have good wear resistance and will not cause prosthetic loosening due to frequent wear. Although the currently applied medical titanium alloy has excellent corrosion resistance and specific strength, but the wear resistance is poor, in order to improve the wear resistance of the titanium alloy, a surface treatment process is usually used to form a wear-resistant coating on the surface of the titanium alloy. Floor. Commonly used wear-resistant surface coatings are diamond-like carbon (DLC) films, titanium nitride (TiN) coatings, and the like.
(1) Diamond-like coating
Diamond-like carbon films have advanced properties such as high hardness, chemical inertness, low friction coefficient, high impedance, good thermal conductivity and excellent optical permeability. Therefore, it can be widely used as a wear-resistant protective layer for medical orthopedic bodies.
(2) TiN coating
TiN has high hardness, excellent friction and wear properties, good chemical inertness and unique color. These extraordinary characteristics make it widely used in wear-resistant and corrosion-resistant surface coatings. In addition, because its biocompatibility has been recognized by the medical community, it has laid a foundation for its application in the clinical medicine field.
3 Surface modification of titanium alloy to improve corrosion resistance
Corrosion mechanism
Essentially electrochemical corrosion. The principle of corrosion is similar to that of the primary battery.
Corrosion classification: (1) general corrosion (2) local corrosion: 1 pitting; 2 intergranular corrosion; 3 crevice corrosion (3) abrasion (4) stress corrosion (5) fatigue corrosion (6) galvanic corrosion
Ways to improve the corrosion resistance of metals: (1) Form a protective layer on the surface of the material - bioceramics (2) Improve the surface finish of the material
Prospect of titanium alloy biomaterials
With the improvement of people's living standards and higher requirements for health, the demand for biomedical materials is growing rapidly. Although in recent years people have used surface engineering methods to improve the performance (bioactivity and compatibility, wear resistance and corrosion resistance) of medical titanium alloy materials, and have made great progress, but the interface between the coating and the titanium alloy matrix The lower strength is still a bottleneck problem that plagues the clinical application of titanium alloy implants.
Therefore, from the perspective of bionic principle, tissue engineering principle and matrix control mineralization, considering the high wear resistance, excellent corrosion resistance and biocompatibility of the coating, the multi-functional surface coating system suitable for the characteristics of titanium alloy is studied. The development of a new coating preparation process using the new coating formation principle is an important development direction for the surface modification of medical titanium alloys in the future.
