Long-Acting Contraceptive Implant Developed with Tiny Needles

Mass General Brigham and MIT investigators have developed a long-acting contraceptive implant that can be delivered through tiny needles to minimize patient discomfort and increase the likelihood of medication use. 

Their findings in preclinical models provide the technological basis to develop self-administrable contraceptive shots that could mimic the long-term drug release of surgically implanted devices. 

The new approach, which would reduce how often patients need to inject themselves and prove valuable for patients with less access to hospitals and other medical care providers, is described in Nature Chemical Engineering.

“Needle size and liquid viscosity are crucial considerations for commercial translation of injectables,” said senior author Giovanni Traverso, MB, PhD, MBBCH, of the Division of Gastroenterology in the Department of Medicine at Brigham and Women’s Hospital, a founding member of the Mass General Brigham healthcare system. “Our engineering challenge was finding a way to maximize comfort for patients by using smaller needles, which cause less bruising or bleeding, and to make the viscosity low enough for easy application with the syringe by hand.”

Traditional contraceptive implants are small, flexible rods that are surgically inserted under the skin to slowly deliver drugs over time, removing the hassle of remembering to take a pill. But the surgery required for implants makes them less accessible to some patients.  

Traverso’s team developed a new approach to deliver the contraceptive drug levonorgestrel (LNG) through Self-assembling Long-acting Injectable Microcrystals (SLIM). SLIM act like tiny puzzle pieces that, once injected inside the body, undergo solvent exchange to assemble into a single solid implant that slowly releases the drug as the surface erodes. Unlike similar self-administering technologies, the solvent exchange assembly enables delivery by much smaller needles. 
 
The researchers will continue their work to optimize the dosing, duration, and injectability of the SLIM system, including understanding how it performs in the human body. The design could also be applied to other hydrophobic drugs, which make up most new pharmaceuticals. The researchers plan to investigate how different drug properties impact the SLIM system’s effectiveness. 

“We anticipate that SLIM could be a new addition to the current suite of family planning options available to women, especially for people in low-resource settings where options for contraception and health care facilities are limited,” said Traverso. 

Reference: Feig VR, Park S, Rivano PG, et al. Self-aggregating long-acting injectable microcrystals. Nat Chem Eng. 2025;2(3):209-219. doi: 10.1038/s44286-025-00194-x

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