Polymethyl methacrylate, or PMMA, is a synthetic polymer that has become a staple in both consumer products and medical applications. It is a transparent thermoplastic material, commonly known by trade names such as Plexiglas or Lucite, which is valued for its durability, lightness, and shatter-resistance. This acrylic glass is formed from methyl methacrylate monomers and possesses a high degree of biocompatibility, allowing it to be safely introduced into the human body. While it serves widespread industrial purposes as a glass substitute, its unique properties have led to its extensive use in the medical field. Its medical applications range from structural components in orthopedic surgery to injectable materials for cosmetic enhancement.
PMMA in Medical Devices and Procedures
In a non-injectable, solid form, PMMA has a long history of use in various medical devices. One of its most common and longest-standing applications is as a bone cement in orthopedic surgery. During total joint replacement procedures, such as hip or knee replacements, PMMA is mixed on-site to create a putty-like substance. This material functions as a grout to mechanically interlock the artificial joint component to the surrounding bone, providing immediate fixation and stability.
PMMA has also been used for decades in ophthalmology to manufacture intraocular lenses (IOLs). These lenses are implanted into the eye, typically after cataract surgery, to replace the eye’s natural lens. The material is favored for its optical clarity and stability, although rigid PMMA IOLs have largely been replaced by newer, foldable acrylic materials to allow for smaller surgical incisions. PMMA is utilized in dentistry for creating durable dental prosthetics, including denture bases, artificial teeth, and orthodontic retainers, due to its ease of processing and aesthetic qualities.
PMMA as a Permanent Dermal Filler
The use of PMMA as an injectable dermal filler represents a distinct application compared to its structural uses. In this context, PMMA is formulated as microscopic, non-absorbable polymer beads, or microspheres, suspended in a liquid carrier. The carrier solution is often a purified bovine collagen gel, which also typically includes a local anesthetic like lidocaine. Once injected beneath the skin, the collagen gel provides immediate volume correction, filling in wrinkles, folds, or depressed scars.
Over the next few months, the body gradually absorbs the collagen carrier component of the filler. However, the PMMA microspheres themselves are too large to be absorbed by the body’s cells and remain in place. These stable microspheres serve as a scaffold, stimulating the surrounding tissue to produce new, native collagen around each sphere. This process of new collagen formation, or neocollagenesis, encapsulates the PMMA particles, providing the long-term, permanent volume correction. PMMA fillers are considered permanent, offering a lasting solution for concerns like nasolabial folds and atrophic acne scars.
Safety Profile and Regulatory Status
PMMA dermal fillers are regulated by the Food and Drug Administration (FDA) as a medical device, and specific formulations are approved for use in the United States. The only FDA-approved non-biodegradable permanent filler is a PMMA-based product, which received approval for the correction of nasolabial folds and later for certain types of acne scars. Before treatment, a skin test is often recommended, especially with formulations containing bovine collagen, to check for potential hypersensitivity.
Despite the material’s general biocompatibility, the permanent nature of PMMA fillers presents unique safety considerations and risks. Potential long-term local complications include the formation of palpable nodules or granulomas, which are inflammatory reactions to the foreign material. These complications can sometimes manifest years after the initial injection, and the permanent nature of the PMMA microspheres means that surgical removal of the material may be difficult or impossible. The FDA continues to monitor postmarket data for permanent fillers, acknowledging the need for long-term safety studies given the durability of the material.