Biopolymers for medical applications

For many biomedical applications, the slow production rate and web structure are not major disadvantages. This is especially true when the porosity and surface area properties are being exploited. Improvements in biomedical materials (implants, prosthetics, tissue replacement, and drug delivery devices) are continually in demand. Much of the current research is focused on natural materials for improved biocompatibility. Various physical and chemical properties define the potential biomedical use of a material. First, chemical reactions such as adsorption/recognition processes at the interface of the biomaterial influence biocompatibility. Also, physical properties, such as modulus of elasticity, need to match that of the neighboring tissue. Ideally, the device is truly integrated into the body's natural environment at a rate exactly equal to its being replaced by healthy tissue without causing an adverse reaction. In reality, distinction has to be made between those materials that are bioinert or cause no host response and no property changes over time, and those that biodegrade or bioresorb during which the implant decomposes in a natural, controlled manner with the degradation products being removed and replaced by the body in normal metabolic processes.

The physical compatibility of biomaterials includes variables such as structural integrity, strength, deformation resistance, fatigue properties, and modulus of elasticity. For prosthetic devices, carefully engineered metallic or ceramic biomaterials have adequate mechanical properties, wear, and corrosion resistance. However, metals and ceramics do not match both modulus and resiliency of living bone. Bone is continually undergoing fracture and repair processes whereas current synthetic materials do not have this property. Attempts to overcome this challenge have included making the surface or the entire material porous or biodegradable. Porous materials are used to encourage tissue growth into the prosthetic. Biodegradable materials are chosen so that the prosthetic will gradually disappear and be replaced by living tissue. To date, neither approach has been highly successful.

Biopolymers are better suited for applications that require flexibility, elasticity, and shapeability. Examples for biopolymer stets include wound dressings, drug release devices, soft tissue replacements, cardiovascular grafts, and sutures. Research in biodegradable polymers has increased dramatically over the past decade and good reviews are available in the literature (see e.g., Refs. [15, 10]).

Materials with high surface area and extended pores have a built-in scaffold for cell adhesion and cell in-growth. Porous coatings and modifications that render the implant surface rough and irregular encourage cell adhesion and favorable interactions with biological tissue. Examples for surface modifications include plasma treatments and grafting of either charged molecules, hydrophobic side-chains, or peptides to enhance cell attachment [16]. Electrospinning offers a method to produce high surface-to-volume ratio materials with extended porous systems easily. Besides the scaffolding itself being made from electrospun fibers, an interphase in the form of electrospun coatings that could adhere to a prosthetic device could be made as a transition region to the host tissue [2]. In the following sections a few more specific examples of potential biomedical applications of the electrospinning technology will be introduced.

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