Particular Requirements for Medical Polymer Materials
Because medical polymer materials are directly used for medical purposes, the requirements for materials are relatively high. Material requirements such as mechanical strength and appearance should be met, as well as medical requirements such as controlled release of drugs and promotion of healing of artificial skin. In addition, as a medical polymer material, it must meet the requirements of biology and be able to coexist peacefully with living organisms for a long time.
In order to coexist peacefully with living organisms for a long time, medical polymer materials are generally required to meet the following requirements:
- Blood compatibility
Medical polymer materials, especially implantable materials, must prevent the occurrence of adverse phenomena such as coagulation and hemolysis. Materials with blood compatibility generally have the following surface properties:
- Low interfacial energy: low adsorption capacity of protein, anticoagulant effect.
- Hydrophilic or hydrophobic surfaces: materials with alternating hydrophilic and lipophilic block copolymerization have better blood compatibility.
- Materials with negatively charged interfaces: Such as the introduction of anionic groups into the material can improve the anticoagulant effect.
- A layer of anticoagulant material is attached to the surface of the material, such as heparin adsorption on the surface of the material.
- Histocompatibility
It means that the material does not have inflammation and other rejection reactions, no carcinogenicity and no calcium deposition in the process of contact with the body tissue. To improve the histocompatibility of materials, the following conditions should be met:
- Material purity should be high.
- The chemical stability of the material is good.
- The material has good mechanical strength and smooth surface.
- Biological inert
The so-called biological inertia refers to that the material does not produce harmful chemical reactions and physical damage in the internal environment of the organism itself, nor does it have adverse effects on the organism, that is, it has biocompatibility. High polymer materials with good biocompatibility include polyethylene, polytetrafluoroethylene, silicone rubber, etc. Widely used in artificial organs, artificial joints and other occasions requiring long-term implantation.
- Biodegradability
In some cases, medical polymer materials are required to be biodegradable and can be decomposed and absorbed by organisms after the use period. Degradable polymer materials mainly include modified products of natural polymers and synthetic products with similar natural polymer structures, such as cellulose derivatives, chitin derivatives, collagen, polylactic acid, polyglycolic acid, polyanhydride and so on.
Strategies to improve biocompatibility
One of the most important factors affecting biocompatibility is the surface tension of the material. Since blood is mainly composed of water, the improvement of biocompatibility of polymer materials can also be explored from the perspective of interface energy. Therefore, improving biocompatibility is mainly to change the composition and properties of the material surface, and then adjust the interfacial tension and interfacial energy of the material surface.
- Change the hydrophilic properties of the material surface: for example, by means of grafting, short-chain polyethylene glycol and other hydrophilic polymers are grafted to the surface of common medical polymer polyurethane, which can significantly improve the anticoagulant function of polyurethane resin.
- Block copolymerization with hydrophilic and hydrophobic microphase separation is one of the most studied methods to improve biocompatibility.
- Biocompatible substances such as heparin, urokinase, prostaglandin and albumin are introduced on the surface of the material.
- Negative ions are introduced on the surface of materials, such as carboxylic acid group, sulfonic acid group, sulfa group and so on.
- Pseudo-intima is generated on the surface of the material: that is, a modified layer similar to the inner wall of blood vessels is generated on the surface of the material using the bionic principle.
