A contraceptive implant, a slender and flexible rod, is inserted under the skin, releasing contraceptive medication into the body for several years. As one of the most effective forms of contraception, it eliminates the need for daily pill-taking. However, its requirement for minor surgery can limit accessibility. To improve this, researchers are developing a self-assembling contraceptive implant that can be administered via a single injection by the user herself.

A research team has developed technology for self-injectable contraceptive shots that function similarly to traditional contraceptive implants. According to a study published in the journal Nature Chemical Engineering, these shots would provide a highly effective and long-term contraceptive method, increasing accessibility for women with limited access to medical facilities. Additionally, the design could be used for administering long-term medications, such as those for HIV.

The new method uses “Self-assembling Long-acting Injectable Microcrystals” (SLIM) to deliver the contraceptive hormone levonorgestrel. Once injected, the tiny crystals assemble into an implant, or a drug “depot,” which releases levonorgestrel as it erodes over several months or years.

“Our goal is to provide women with easy-to-administer, compatible, and flexible contraceptive options that can be used in various settings and have differing durations of action,” Vivian Feig, a mechanical engineer at Stanford University and co-author of the study, stated in a Massachusetts Institute of Technology (MIT) statement.

Conventional birth control shots exist and are more accessible than implants since they can be self-administered without a hospital visit. However, they are less effective and have a shorter duration, requiring administration every three months.

The new contraceptive design combines the accessibility of self-administered shots with the long-term efficacy of an implant. A challenge with self-administering similar technologies, such as SLIM, has been the need for large, painful needles. In contrast, the team’s formula, consisting of tiny crystals and a solvent (benzyl benzoate), allows for the use of smaller needles.

“The size of the needle and liquid viscosity are crucial for the commercial translation of injectables,” said Giovanni Traverso, senior author of the study and a gastroenterologist at MIT and Brigham and Women’s Hospital, in a Mass General Brigham statement. “Our engineering challenge was to maximize patient comfort by using smaller needles, reducing bruising and bleeding, and making the viscosity low enough for easy application with a syringe by hand.”

Traverso and his colleagues can modify the mixture to “regulate the drug release rate, extending its duration while maintaining injectability,” MIT graduate student Sanghyun Park explained in the MIT statement. “This demonstrates the adaptability of our system, which can be engineered to accommodate a broader range of contraceptive needs and tailored dosing regimens for other therapeutic applications.”

While SLIM has not undergone clinical trials, its development in preclinical models paves the way for more convenient and effective long-term medications in the future.