Polymers in Medicine: PMMA Applications and Properties

Polymers in Medicine

• Polymetal Methacrylate (PMMA): a transparent, resistant, lightweight, and highly chemically inert polymer with good impact resistance.
• Applications: used as bone cement, fixation of hip, shoulder, knee, elbow prostheses, and in vertebroplasty and kyphoplasty.
• Requirements: fluid before implantation, solidifies (polymerizes) in situ.

Biomechanical Function of Acrylic Cement

• Load distribution: distributes loads evenly from the metal prosthesis to the surrounding tissue, preventing high stress concentrations.
• Fill and fit: allows for good filling of the bone cavity, promoting good primary fixation due to the proper fit and adjustment of the prosthesis-cement system.

Acrylic Cement Preparation

• Polymerization reaction: begins after mixing the two components, sets after 15 minutes, allowing for introduction into the bone cavity during this time.

Temporal Support

• Gradual transfer of functions: biodegradable implant must be gradually removed as the tissue heals, requiring a synchronized tissue regeneration.

Sutures

• Types: natural (plain catgut, chromic catgut, collagen) and synthetic (polyglycolic acid, polyglycolic acid coated with caprolactone, polygalactin) origin.
• Properties: tensile strength, uniform gauge, flexibility, and elasticity.

Orthopedic Fixation Systems

• PGA screws and plates: used for bone fractures with plates, good for probing, and can be removed after the process ends.
• Mechanical properties: can be enhanced by using reinforcing materials (composites) and ceramic faces.

Temporal Barriers

• Properties: good permeability, non-thrombogenic, easily modifiable, and minimal friction irritation.
• Applications: prevention of adhesion, prevention of particle migration, and controlled release of trapped molecules.

Improvement of Mechanical Properties

• Strategies: improving cross-linking, placing molecules with ceramic materials, and using different types of polymers.

Classification

• Synthetic polymers: acrylic hydrogels, PVA, PEG, PLA, synthesized in the laboratory.
• Natural polymers: collagen, gelatin, fibrin, hyaluronic acid, heparin, alginates, pectins, chitosan, obtained from natural sources.

Passivation vs Corrosion

• Passivation: prevents material surface from continuing to oxidize, acts as an insulator, and prevents material from releasing particles into the environment, ensuring biocompatibility.

Metallic Biomaterials

• Metals that meet requirements: iron, cobalt-chrome, and titanium alloys, used in orthopedics and dentistry.

Stainless Steel

• Properties: corrosion-resistant, magnetic, easy to machine, and good heat treatment.
• Applications: surgical materials, osteosynthesis plates, screws, and nails.

Physical Modifications

• Roughness: increasing roughness improves osteointegration through better micromechanical retention.
• Topography modification: strategy used in commercial implants to improve osteointegration.
• Methods: plasma spraying, grit blasting, acid etching, and electrochemical methods (anodization).