Medical devices used for minimally invasive surgery (MIS) are small, complex multi-component assemblies. These involve highly skilled labor as most devices are a compilation of several machined components assembled under a microscope and use secondary manufacturing operations such as bonding and welding. Years were spent to develop and perfect products to ensure quality compliance, reduce risk and lower costs. Micro molding can permit these machined components to be replaced, combined or insert molded, as well as eliminate bonding and welding, thereby reducing the number of components, overall size, assembly complexity and time required to start-up and assemble the device. Micro molding is commonly defined as anything less than 1 mg in weight. However, technically, micro molding can refer to the micro sized parts themselves or to larger parts that have miniscule features. Medical device designers and makers have realized the need for this technology that has become well entrenched in the manufacturing of medical devices over the last few years.
Demand for increasingly smaller devices is driven by the enormous growth in the number of noninvasive procedures and day surgeries. This requires tools and implantable devices that can transverse orifices and tiny blood vessel. The medical field is traversing toward implants and devices made from bioresorbable polymers that can be absorbed by the body weeks or months after they have served their purpose, and the tissue has healed. Also, screws and other devices made of metal can break or can cause adverse reactions. Micro molding and bioresorbable materials work well together, because micro sized parts do not consume a great deal of the highly expensive bioresorbable polymers that can cost between US$6000-40000/kg. Though demand for micro molded devices from resorbable polymers is expected to increase, the conversion is expected to be slow. Better technologies and lower price of resorbable polymers will help in the growth.
A trend in micro molding is the development of new techniques to provide tighter tolerances and better quality control and surface finishes. Micro molded parts must have tight tolerances, ranging from �0.001 to �0.0001 inches and lower as per devicelink. Product and mold designs for micro parts have been going through a learning curve over the years. Specialized micro molding machines have also improved significantly over the past several years to offer integrated part removal, packaging and vision inspection.
Since smaller parts have less shrinkage and lower transfer forces, release from the cavity side can be affected significantly by the surface finish. With conventionally sized parts, the machine cavity finish can be stoned and polished, which is not possible for a part with micro features. Hence improved surface finishes of micromolded parts is becoming vital. An emerging technique to finish micro molded parts is stereo lithography. Parts from the gates are being removed with ultrasonic energy. Developments with hot runner and cold runner systems also have helped to improve the precision and output of micro molded parts. Validating the micro part is yet another challenge. A promising technology uses ultrasonic waves to characterize the micro molding process. Atomic force microscopy and nanoindentation are techniques being developed to derive relationships between the process variables and product characteristic. Another trend in micro molding is the increased speed at of part turn around.
One challenge faced is that micro molding can change the properties of a polymer as it is gets squeezed into a miniscule area. The material has to be forgiving, and the manufacturing process must be designed so that there is little, if any, waste from the process. Growth of micro molded parts will be slow, as the medical field, used to metals for its devices for the last century may take a long time to adapt to better, newer, cheaper technology to eliminate the element of risk, until they continue to prove themselves.
Improved technologies as well as reduced price will increase demand for micromolding with bioresorbable polymers.
Micromolders see the demand for microsized medical device parts only continuing to grow with the development of new technologies, new materials and new processes. Micro molding is still in its infancy, and therefore can be called a �disruptive� technology. Medical device designers and manufacturers are just beginning to realize that there is a need for this technology and are looking to fill this technology gap. Micro molding coupled with the trend toward miniaturization of medical device and less invasive procedures will provide ample opportunity to develop new and innovative products. Micro molding overcomes the limitations of established technologies, facilitating smaller components, incorporating complex features, reducing the number of components, and eliminating archaic processes which results in reducing the number of processes performed under the microscope.