The rundown on dip manufacturing for medical devices

June 1, 2023 By MDO Contributors Network Leave a Comment

By Dan Sanchez, Trelleborg Healthcare & Medical

Dip-coated surgical blades [Photo courtesy of Trelleborg]

These methods can contribute to the success of a medical device project when correctly specified for an application. Component and contract manufacturers that understand customer requirements and align their manufacturing capabilities to them will have the greatest success with these dipping techniques.

Dip molding involves submerging a mandrel, or a geometric form, into silicone. The silicone then cures to a solid before the mandrel and silicone shell are separated. The mandrel is used again for the next batch and the silicone shell is used in a finished medical device.

Applications include balloons, breather bags, probe covers, tissue expanders and syringe covers.

Dip-molded breast implant shells [Photo courtesy of Trelleborg]

Many variables can be controlled during dip molding, including the number of dip coats, heating and movement of the mandrel, component thickness and mechanical properties, depending on material choice. By focusing on these factors, manufacturers can create an engineered solution to meet a customer's specific requirements.

Dip molding provides excellent flexibility as it allows for a wide variety of shapes, sizes and wall thicknesses. Additionally, it enables quick prototyping of mandrils and prototypes resulting in short lead times. The prototyping process is cost effective due to a relatively simple setup.

Achieving tight tolerances can be difficult with dip molding. Even though varying wall thicknesses offer flexibility, thin-walled dip molded shells make ensuring accurate measurements complicated, especially when separating the shell from the mandrel.

Designs for dip molding must consider how the shell will be removed from the mandrel without tearing or distorting it, and how the hollow shell will be trimmed or covered in secondary processes.

Finally, even though dip molding can be quick to prototype, it can be relatively time consuming and expensive compared to other production processes, so it is best used when the advantages outweigh any disadvantages.

Dip coating involves immersing a component substrate into a liquid silicone, which adheres to the substrate as it cures.

To illustrate this, consider the dip coating process of a metal electrode scalpel used for electrosurgery. The silicone acts as a nonstick coating, and its flexibility allows the surgeon to manipulate the electrode to the preferred shape. Biocompatibility of the silicone is crucial for the safety of the patient in this invasive procedure. Other fluorinated coatings have been used on electrosurgical scalpels, but such coatings are outperformed by silicone because they are not flexible and have poor biocompatibility.

Dip coating usually requires an adhesive bond between the coating and the substrate, which must be completely clean. Material selection of the coating plays an important role in adhesion. For example, some silicones can be formulated to bond with specific substrates while others may require better adhesion through surface preparation of the substrate. Silicone dispersions are typically solvent-based, so a solvent evaporation step is often needed before a component is cured in an oven.

After cooling, several secondary operations can be performed to the dipped part to get it ready for the finished device. For example, electrode scalpels might receive an additional layer for electrical insulation on the undipped portion. In addition, a contract manufacturing partner can kit, package, or assemble dip-coated parts to a customer's specifications.

The application of dip coating offers several advantages. For instance, when applied to electrosurgical scalpels, it reduces sticking and the accumulation of charred tissue, facilitating easier cleaning. This leads to a reduced frequency of blade changes and shorter surgery times. Dip coating also plays a significant role in enhancing patient comfort by minimizing friction and pain during procedures involving hypodermic needles and scalpels.

Dip coating can improve the grip on surgical instrument handles and jaws while also providing enhanced biocompatibility when encapsulating sensors. Another benefit is that dip coating can be efficiently scaled up for high-volume production, depending on the size and complexity of the instruments. Finally, quick production of dip-coated prototypes can contribute to shorter development lead times.

The disadvantages of dip coating include challenges in achieving uniform thickness on complex substrates, the need for secondary processes for inaccessible areas, and the careful management of volatile solvents for environmental and safety concerns.

Achieving a uniform thickness by dip coating is impractical for component substrates that include geometric features like pockets, corners, and edges. Gripping of a substrate to control dipping can restrict coverage, requiring a secondary process for uncoated areas.

Finally, polymers used for dipping are often mixed with high concentrations of volatile solvents that must be controlled to ensure environmental health and safety.

Dip molding and dip coating are two processes that offer unique advantages and considerations for medical device production.

Successful implementation relies on effective collaboration between original equipment manufacturers and their component and contract manufacturing partners. By seeking knowledgeable partners who comprehend unique requirements and possess suitable capabilities, custom-engineered solutions can achieve optimal results in medical device manufacturing.

Dan Sanchez is a product manager at Trelleborg Healthcare & Medical. [Photo courtesy of Trelleborg]

The opinions expressed in this blog post are the author's only and do not necessarily reflect those of Medical Design & Outsourcing or its employees.