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Dear Readers, Welcome to the latest issue of Micr
Biomedical engineering of silicone breast implants allows for a range of complex designs to be utilized in medical devices for long-term, implantable use. The convergence of science, engineering and technology enabled the development of sophisticated raw materials and methods to manufacture advanced medical devices.
While a number of factors influence the in-use performance of a medical device (e.g. the skill of the surgeon and the raw materials used in the device), ongoing regulation and oversight of the medical devices is also critical.
Silicone breast implants are made of medical-grade polydimethylsiloxane (MMS), also known as PDMS. PDMS is a Siloxane-based elastomer which consists of long, repeating backbones with methyl side groups.
Unlike organic polymers, PDMS retains its mechanical properties over a broad range of temperatures and is resistant to environmental stress cracking and degradation.
Its biocompatibility and relatively low toxicity allow PDMS to be used in a number of biomedical applications. In addition, high purity fumed silica is used in PDMS-based breast implants to enhance mechanical properties and impart resistance to failure, and a platinum-based addition curing system is used to further improve purity of the implant.
Current-generation silicone breast implants have a multilayer elastomer shell structure with a filled gel or saline core. Most high-end implants have a core of highly cohesive gel, also known as “form stable” or “gummy bear” gel.
High cross-linking of the gel enhances shape and stability of the implant and minimizes gel dispersal in the event the implant shell ruptures. Cross-linking is balanced with other variables to achieve the desired stiffness and stability of the implant.
High purity, medical grade silicone is compounded and sterilized in controlled clean room conditions (ISO Class 7 or better). The shell is formed by dip-molding with an aluminum mandrel. Each layer of the shell is cured prior to the next layer being deposited. This allows the shell to be controlled within +/- tolerances.
The surface of the shell may be textured or left smooth based on the clinical indication. Texturing is produced by a variety of methods including salt-loss molding.
Smooth implant shells have gained market predominance due to the increased incidence of Breast Implant Associated Anaplastic Large Cell Lymphoma (BIA-ALCL) with textured implants. After filling the shell with silicone gel, the fill port is vacuum-oded to expel any trapped air and gel is held under partial vacuum to ensure complete filling.
The fill port is then sealed with silicone elastomer and a secondary cure is performed. The implants are washed to remove impurities, and then sterilized using ethylene oxide to provide a safe and secure product for end-use.
Quality control is performed at all stages of manufacturing and final product testing. The raw materials are evaluated to determine conformance to medical device standards, and the manufacturing processes are validated to comply with cGMP. Statistical process control and risk management are implemented to reduce process variation.
In addition to the physical and chemical testing mentioned in the previous chapters, implants also undergo microbiological and biological testing.
Representation of the intended use of the implant (long-term) is accomplished by performing durability tests on the implant shell, and analyses of the silicone gel to determine the coefficients of adhesion of the gel to the shell.
It is also necessary to test the implant shell to determine the tensile strength, elongation at break, and resistance to tearing. Fatigue testing is performed to assess the durability of the implant to withstand millions of load cycles. The shell may also be tested to determine burst pressure and resistance to compression.
In addition to the mechanical and chemical testing described above, many of the biological tests performed on implants are mandated by the International Organization for Standardization (ISO) to determine the safety of a medical device.
Biological testing of medical devices may also include genotoxicity testing. Clinical studies of medical devices may also be mandated.
Manufacturers of medical devices are also obligated to perform post-market studies of implantable devices to assess device performance and determine the occurrence of infrequent, adverse events.
Breast implants are considered to be one of the highest risk, Class III, medical devices in the U.S. As such, they are required to undergo premarket approval by the Food and Drug Administration.
In addition to the testing and reports specified in the Quality System (21 CFR 820) regulation and guidance, the FDA also requires breast implant manufacturers to validate the manufacturing processes and perform clinical studies for a period in excess of 5 years.
The use of breast implants can bring several clinical benefits. High-cohesive gel implants, for example, have improved shape and volume retention by reducing gel mobilization when compared to other implant types.
Implant design can take into consideration the shape and proportions of the human body in order to provide aesthetic outcomes in reconstructive and cosmetic surgery.
Other clinical benefits include improved tactile qualities of the implant, biocompatibility, resistance to fatigue and chemistry.
As with all prosthetic devices, complications can occur. Capsular contracture, rupture and infection are common. MRI and Ultrasound may be necessary to evaluate a possibly ruptured implant. It has been reported that textured implants can be associated with BIA-ALCL.
Considering the benefits and disadvantages of current breast implant technologies, further research and advancements in breast implant reliability and safety is expected.
Authored By: Priyabrata Pattnaik
Chief Executive Officer (CEO) Ami Polymer
[email protected]
