|The medical sector is important for plastics, growing at a very healthy rate of 8% pa due to higher income of larger population, long life expectancy and also due to technological advances in the field. Fillers provide specific role in many medical products. Some of the areas where fillers are used where they provide better performance are summarized below:
Fillers are essential in plastics which must be sterilized. Glass fiber in particular is used because it can withstand sterilization and retain mechanical properties. Most medical plastics must be kept scrupulously clean and are handled only in a clean room environment. Static charge built up on these parts will attract contaminants and therefore, it is critical that static charges are dissipated. Fillers perform this function because, unlike organic antistatic additives, they have no tendency to migrate and contaminate the surroundings. Barium sulfate is radio-opaque and it is usually used as a means of imaging the digestive tract. In the application of intravenous catheters, barium sulfate is added to polymers to make catheter inside the blood vessel visible to X ray. Drug delivery patches and implantable or insertable medical devices are methods of releasing a therapeutic agent to a patient. They contain a therapeutic agent, a polymer and filler. Polymer plays a role of binder, and filler has platelet structure which controls the rate and delays drug release. PMMA has a tendency to absorb water which in turn makes its dental products weaker. The use of silane to treat the hydroxyapatite filler in this material reduces water uptake.
Procedures that were previously possible only with surgery, have become Non Invasive because of highly engineered devices. The high precision of the devices now allows access to even smaller areas of the body. For designers of medical devices, the challenge is to create devices with improved feel while continually striving to reduce device size. Design and manufacturing techniques, as well as material modifications play a key role in advances in precision medical devices. An increased spectrum of material options is available through the use of polymer compounds incorporating performance enhancing fillers. Fillers provide properties that are not possible with polymers by themselves. Traditional polymer reinforcing fillers include glass, carbon, and other fibrous materials. However, in today�s medical applications, with catheters and stent delivery balloons, extraordinarily thin walls and smooth surfaces are required. The traditional fillers are far too large in size to provide homogenous compounds suitable for extremely thin sections.
A variety of nanofillers are available for use in nanocomposites, including natural clays, synthetic clays, nano structured silicas, nanotubes, etc. Over time, as the number of larger volume applications increase, leading to improved supplier economies of scale, it will impact the costs of nanofillers. Because the nano filler contains so many individual particles in a small amount of material, it takes very low loading to obtain a high concentration of constrained areas within the polymer. This leads to reinforcing effects at 5% loading equal to about 12-15% glass fiber. The nano filler also creates a torturous path for penetration of gaseous vapors and liquids into the polymer. This, in turn, leads to better resistance to chemicals and moisture. Nanocomposites typically demonstrate unique improvements in material properties, including rigidity, strength and barrier properties, while maintaining a level of transparency and offering potential for recyclability. Nanocomposite polymers offer increased rigidity and stiffness while maintaining a high degree of the elongation inherent in the base polymer. Increased stiffness without brittleness is essential for many catheter applications, where increased torque and push/pull strength is required, without kinking. Also, new dilation balloons are required to withstand higher pressures without tearing, and may also be excellent candidates for improvement in mechanical performance from nanocomposite technology. Low loadings and filler dispersion result in compounded materials that maintain inherent polymer transparency in thin sections. Nanocomposites can be recycled and reprocessed without seriously affecting the physical properties. In the medical field, specific applications under development are highly proprietary. Nevertheless, applications receiving the most notoriety as candidates for nanocomposites are shafts, balloons, catheter luers, and similarly precise device components.
(Reference: Lawrence A. Acquarulo Jr., Charles J. O�Neil, Raymond E. Godaire)