Injection molding, a manufacturing method used for making everything from car parts to kids’ toys, is also utilized to make life-saving medical devices, including those inserted or implanted into patients’ bodies. Catheters, balloons, and feeding tubes are all made possible and affordable when biocompatible materials combine with injection molding.
As we have discussed before in an earlier article, the material of choice for implantable medical devices is often medical grade silicone. Its range of available durometers, extreme chemical inertness and biocompatibility, excellent tear and heat resistance make it ideal for parts that need to remain in the human body for extended periods of time.
Furthermore, the low viscosity of liquid silicone rubber (LSR) make that elastomer ideal for injection molding (and therefore mass producing) implantable medical devices, making life-saving advances in medical technology more affordable for patients.
Polymers Delivering Doses: Drug-Eluting Implantable Devices
But those advances don’t stop with opening up arteries or providing ports into and out of the body. Increasingly, injection molded implantable medical devices are being used to deliver steady, long-term doses of hormones, cancer drugs and other active pharmaceutical agents (APIs). Injection molding of medical devices is extending its impact into drug delivery.
Drug-eluting medical implants offer several advantages over both pills and injections when it comes to drug delivery. Perhaps the most important clinical benefit is the larger amount of time the API dose is within therapeutic window—the range of concentrations within the body low enough not to be toxic, but high enough to be effective. Both pills and injections produce API concentrations that rapidly rise and then exponentially decay as the body dilutes, metabolizes, and/or excretes the pharmaceutical compounds. By contrast, drug-eluting implants can slowly and steadily release the API at a controllable, optimal rate within the therapeutic window.
These implants are able to do so because the matrix of the device is loaded with the API before they are molded. Silicones, because of the relatively low temperatures at which they can be injection molded and vulcanized and their ability to be compounded with various APIs, are optimal for this application because the injection molding process is less likely to degrade the drug.
Molded medical implants can also provide site specific administration of a drug, and therefore achieve local concentrations of an API that would be above the therapeutic window if present systematically. This enables lower total doses, reduces side effects, and has a greater therapeutic effect.
A third benefit of drug delivery via an implantable device is much greater patient compliance. Since the implant can continually release the drug within the body for several months, there are no daily doses for the patient to forget.
Peering Beyond Silicone
Even as medical grade silicone finds wide use in drug-eluting implantable devices, an exciting new frontier is opening up: expanding beyond silicone into synthetic biodegradable polymers. Such polymers open the door to drug-eluting implants which slowly and safely dissolve away inside the patient’s body, releasing the loaded therapeutic as they do so. These implants don’t need to be removed at the end of the treatment period. Another benefit is the potential to slowly release difficult to deliver API’s, because the therapeutic is released as the polymer encasing the API particles dissolves away, much like an oral pill. This results in steady release rate over time even for these difficult molecules.
Although this new breed of drug-eluting implants won’t be made with silicone, they in all likelihood will still be made via injection molding. Although technical questions still remain—like which polymers in this class have low enough melting points to be molded without significantly degrading any compounded API—injection molding’s ability to produce high volumes at low price per part while at the same time maintaining tight dimensional tolerances, will surely play a key role in this new drug delivery technology.
