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Surgical Instruments: The Plastics Frontier

 In the recent past, prices of surgical instruments have remained under pressure. The trend is likely to continue because of rising sterilization costs on one hand and pressure from insurance companies (especially in Europe and North America) to reduce costs. The increased use of disposable (single use) surgical instruments was precisely for this reason. As the pressure on prices continues, the surgical instrument manufacturers are forced to innovate and look for ways and means to reduce costs. Most of the companies find it difficult to reduce the cost of surgical instruments made or fabricated out of stainless steel. The production processes, cleaning & sterilization and shipment of metal components is expensive. In the current scenario, there is little that can be squeezed out of the equation.

An alternative is to shift from metal to plastics, wherever possible. Thermoset or injection molded plastics offer several advantages over metal components. Not only can the instruments be made at a lower cost, for disposable ones, switching to plastics can even reduce sterilization requirements. Plastic components are light weight and can also be color coded, making packaging more efficient. But the manufacturers of surgical instruments also need to be able to overcome challenges – including material selection, tolerances, design and tooling – these can arise when using plastics for manufacture of life saving instruments.

For those who have already converted, the use of plastics in place of metals has been helpful in maintaining profit margins as costs and competition increases. Some manufacturers have found that the switch also improved products, got them to the market faster, reduced total finished instrument cost and often combined production of many parts into one economical step. Plastics have been competing with metals because they often eliminate expensive secondary processes required on metals and provide greater design flexibility. Plastics also yield past consolidation and reduce total production time. As a result the use of plastics to replace metals has become an essential strategy in the surgical instrument manufacturing industry.
 
Material Selection:
The first decision needed to be taken for switching from metals to plastics is whether to manufacture instruments to be reusable or disposable. The material requirements for each are different. Reusable instruments are most likely going to be steam sterilized. For this type of application, manufacturers should select plastics that can be autoclaved. It is important to note, however, that autoclavable plastics are much more expensive then those that can be used for disposables. Instruments also need to be strong and impact resistant, which further limits the selection of resins. Some resins may be used to form handles. However, handles can benefit from soft touch materials like thermoplastic elastomers or thermoplastic olefins. Disposable instruments have less restrictive resin requirements and are less expensive. After molding, disposable instruments are usually ultrasonically cleaned, blister packaged and gamma irradiated.
 
One additional advantage of plastic resins can be transparency which allows a surgeon to see through the instrument during surgery. But transparent or translucent resins may experience a color shift during Gama sterilization process. So, it is important to work with the material supplier to achieve desired results. Another advantage can be color coding which can be useful with series of instruments that are of different sizes or that are used with other components. Color coding also allows a surgeon or other operating room personnel to quickly identify the appropriate equipment. Material selection (color master batches) is of importance here.
 
Plastic Instrument/ Component Geometry: Strength and Moldability:
The strength properties of metals are generally superior to those of plastics. So, it is important to determine whether a plastic resin is available that meets the requirements of the instruments' intended use. If the instrument is going to be pried with a long lever arm or impacted by a hammer, plastic may not give optimal results. But if the tool/ instrument is simply a cutting guide or a static spacer, then plastics may be suitable. Filled plastic materials provide much more flexural strength then unfilled resins. Certain resins can also be molded in thick sections. Certain additives, such as structural foam, can also yield thicker parts. Plastic moldings have a tendency to warp and sink in certain areas and so these must be designed to overcome these tendencies. Another potential problem is sinking around thick bosses. While working on design of a surgical instrument all these aspects need to be taken care of and the design must cater to overcome potential problems.
 
Prototyping:
The manufacturers switching to plastic resins need to account for extra prototyping time and associated additional costs. Prototyping is important to make sure parts fit up to mating components. This can be done using any of the plastic prototype methods, such as stereo-lithography or selective laser sintering. If the part or tool has snap features, 3D-type printers should be considered. During the process of prototyping, designing of tools (molds) can also be planned.
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