History of Breast Implants

Silicone polymers may be produced in a variety of forms including oil, gels, or elastomers (rubber). The physical state is determined by the degree of chemical cross-linking. Cross-linking occurs between vinyl and hydrogen groups on silicon atoms. Silicone oils are straight chains of PDMS without cross-linking and are insoluble in water. PDMS will remain in liquid form indefinitely. Silicone gels consist of cross-linked (of various degree) PDMS chains together with variable amounts of PDMS liquid. It is important to keep in mind that the majority of silicone gel is silicone oil within the confines set by the PDMS gel matrix. The ratio of silicone liquid to gel is controlled by manufactures to control the viscosity of the gel. Elastomers of silicone have high degrees of cross-linking and almost no PDMS oil. Breast implant shells, both silicone and saline filled, consist of a vulcanized silicone elastomer that is reinforced with silica for increased strength.1 In an effort to reduce gel bleed from silicone filled devices, phenyl or triflouropropyl groups are bonded to the shell to decrease the shell permeability to PDMS oil.2,3 These "low bleed" implant shells with "barrier coating" are characteristic of current 3rd ,4th and 5th generation implants (discussed later).

Manufacturing and Materials

Prior to the development of prosthetic breast implants numerous materials were trialed for the purpose of augmenting the female breast. Up until the 1950's materials included autogenous fat and dermal grafts, fat injections, paraffin injections, insertion of glass balls, ivory, rubber, and terylene wool.4,5 These materials frequently led to infection, tissue necrosis and firmness of the breast. The autogenous materials were uniformily troubled by resorption. The 1950-1960's saw the use of many other products. Free injections of hydrocarbons, petroleum jelly, silicone oils, vegetable oils and bees wax were tried and led to many problems including infection, granulomas, fistulas and breast firmness.4,5 During this same time many different types of sponges were developed hoping that soft tissue ingrowth would improve the biocompatibility of these products. Polyvinyl and polyether were the most common sponge materials (figure 2) others included silastic and Teflon. Unfortunately these products were complicated by many of the same problems and were discontinued.

The development of the silicone gel prosthesis in 1962 marked a very important new era in breast surgery. Since Cronin and Gerow6 first reported its use very few other materials have been used for breast augmentation. This is partly due to the success of silicone devices and also by the subsequent FDA regulation of medical devices that was started shortly after the development of silicone gel devices.

Fewer materials has not equated to fewer devices. It has been reported that more than 200 different types of silicone breast implants and expanders have been manufactured in the United States.7 Since the original Silastic gel implant was produced many modifications have been made to the design of these devices. The evolution in design and manufacturing of breast implants has focused on four major areas: characteristics of the shell, characteristics of the filler, shape, and surface configuration.

Any device can be expected to perform different from its counterparts based on its physical and structural properties, and therefore presents a significant challenge when we attempt to retrospectively review the outcomes of breast implant surgery over the last 40 years. To assist in this review, attempt has been made to classify breast implants into generations based on the time period of their development.8-11 This classification system recognizes the evolution and variations in the design that have occurred over time; however, it does not provide the ability to compare outcomes of breast implant surgery based on the time period the surgery was performed. Large overlaps of the periods of manufacturing of a particular device and the continued clinical use of those devices into the period of the next generation of manufacturing prevents this concept from having clinical applicability.