The Needle You Never See: Inside the enFuse® System
As more therapies transition from intravenous (IV) infusion to subcutaneous (SC) administration, the conversation around drug delivery continues to evolve. Advances in biologics, formulation science, and wearable drug delivery technologies have expanded what’s possible outside more traditional infusion settings.
No matter how advanced a drug delivery device becomes, one small component still plays an essential role: the needle.
While it may seem like a simple part of the system, the needle is carefully selected based on factors like length, size, insertion mechanism, and how it works with the rest of the device. Each design choice impacts the broader delivery system.
However, for many people, the thought of a needle can bring anxiety before treatment even begins. Research has shown that concerns about needle visibility, anticipated pain, and the injection experience can influence how patients perceive treatment, making thoughtful needle design an important consideration alongside overall device performance. ¹
The enFuse® On-Body Drug Delivery System was designed with this in mind through one of its distinctive features: a hidden, retractable 30-gauge (30G) needle.
Designed to Stay Out of Sight
Unlike a traditional manual syringe or infusion pump, the needle in the enFuse system is never visible to the patient or provider during administration. Once the device is applied to the abdomen, the needle is locked until the safety tab is pulled and the button is pressed to start delivery. Once the injection is complete, the needle retracts back into the device, and the button locks out to prevent re-engaging the needle.
The needle itself is very small. At 30G, it has a much thinner diameter than many needles commonly used for injectable therapies such as a 23-gauge used for manual subcutaneous injections. Research suggests that this difference in size may influence the injection experience.
A study conducted by Præstmarket al. explored the relationship between needle diameter and both penetration force (PF) and subcutaneous bleeding (SBP). The study revealed positive correlations between needle diameter and both PF and SBP, indicating that larger needles require more force for penetration and are associated with higher levels of local tissue trauma. The study also found a positive trend between increasing needle diameter and pain, further supporting the role of needle size in pain perception during subcutaneous administration. ² While needle diameter is one factor that can influence the patient experience, the enFuse system is designed so users interact with the device, not the needle itself, allowing the therapy to be delivered discreetly without requiring users to handle the needle or watch the injection.
By keeping the needle hidden throughout administration and automatically retracting afterward, the enFuse system incorporates design features intended to reduce needle visibility during treatment while also helping minimize the potential for accidental needlestick injuries after use. ¹
Every Detail Has a Purpose
Innovation in wearable drug delivery is often associated with delivering larger volumes of biologics or enabling subcutaneous administration. Equally important are the thoughtful design decisions that shape the patient’s experience.
The hidden, retractable 30G needle is one example of those decisions.
Although it performs one of the most important functions during drug delivery, it remains out of sight throughout the entire administration process. This design allows patients to focus less on the mechanics of the injection and more on their treatment experience.
Clinical evidence highlights the importance of patient experience during device design. In a study evaluating patient experience with an on-body delivery system compared with a manual subcutaneous injection, patients reported less pain and discomfort than they had anticipated during treatment with most preferring the OBDS after experiencing both delivery methods. ² Together, these insights emphasize that thoughtful device design can play an important role in how patients experience treatment.
Sometimes the most innovative part of a drug delivery system is the one that patients never see.
1. Rahman O, Desai M, Candiotti K. Beyond the Point: Navigating the Impact of Needles on Pain, Anxiety and the Patient Experience. ONdrugDelivery. Issue 156. January 17, 2024.
2. Præstmark K, et al., “Pen needle design influences ease of insertion, pain, and skin trauma in subjects with type 2 diabetes”. BMJ Open Diabetes Res Care, 2016, Vol 4(1), Article e000266
3. Parmar G, et al., Patient preference and experience with an on-body delivery system versus manual subcutaneous injection in patients with relapsed/refractory multiple myeloma. Journal of Clinical Oncology. 2026;44(16_suppl):7564. Presented at the 2026 ASCO Annual Meeting.