Modern science has allowed surgeons to fix the human body amazingly fast yet leave behind only small traces where repairs were performed. One of the more commonly used methods to achieve this is by a minimally invasive technique called laparoscopic surgery, where small incisions are made into a patient's skin, a laparoscope is inserted to provide a magnified view of the patient's organs, the procedure is performed, and the incision is closed by stitching or surgical staples. You can have your gallbladder removed before breakfast and be binge-watching Netflix from the comfort of your couch by dinner.
Typically, the small openings created during laparoscopic surgery are closed in one of two ways: manually stitching sub-cutaneously (beneath the skin) with a bio-absorbable, thread-like material and a curved needle that moves from one side of the hole to the other to close it tight, or with a surgical stapler that inserts metal staples into the skin to close the wound. The first technique is more time consuming but leaves less surgical evidence. The latter method is faster but can cause scarring and infection.
Development Challenge: Combining Methods
Chuck Rogers, PhD, and Kenneth Danielson, MD, of Massachusetts-based Opus KSD, have spent the past several years developing and eventually launching to market, with help from Protolabs, a surgical tool that combines the best of both worlds: the ease of a stapler with proprietary bioabsorbable subcutaneous fasteners.
“General surgeons are finding themselves under pressure because the user-friendly metal staplers that became very popular in the 1990s are not cost-effective,” explains Rogers, CEO of Opus and a biomedical engineer. “When people really began doing cost analysis, the five minutes that a surgeon saved in the operating room did not compensate for the fact that the patient still had to come back to have the staples removed.”
Danielson, a Harvard physician with more than 30 years of surgical experience, approached Rogers with a concept for a new stapler and shortly thereafter the two began development on the SubQ It! skin closure system — a disposable, handheld surgical stapler that delivers bioabsorbable fasteners beneath the skin with one click of the device.
The first step in development was to design, build, and test the tiny fastener, since that would ultimately guide the design of the actual device. Rogers and Danielson worked on refining the fastener, including elements such as its distinctive shape, the length required to suture properly, the number of barbs it would need, and other critical features.
Due to the extremely small size of the SubQ It! fastener with a mass of only 0.0064 g, it was 3D printed by both the extrusion process of fused deposition modeling (FDM) and by the laser-curing method of stereolithography (SL; see the Sidebar, “How Does Stereolithography Work?”).
How Does Stereolithography Work?
Stereolithography (SLA) is an industrial 3D printing process used to create concept models, cosmetic prototypes, and complex parts with intricate geometries in as fast as one day. A wide selection of materials, extremely high feature resolutions, and quality surface finishes are possible with SLA.
The SLA machine begins drawing the layers of the support structures, followed by the part itself, with an ultraviolet laser aimed onto the surface of a liquid thermoset resin. After a layer is imaged on the resin surface, the build platform shifts down, and a recoating bar moves across the platform to apply the next layer of resin. The process is repeated layer by layer until the build is complete.
Newly built parts are taken out of machine and into a lab where solvents are used to remove any additional resins. When the parts are completely clean, the support structures are manually removed. From there, parts undergo a UV-curing cycle to fully solidify the outer surface of the part. The final step in the SLA process is the application of any custom or customer-specified finishing. Parts built in SLA should be used with minimal UV and humidity exposure, so that they don't degrade.
Solution: Machining and Molding
After Rogers and his team knew what the fastener itself would look like, development of the multipart device began. “Like the fasteners, we initially used FDM and SL on the delivery device in order to inexpensively modify the parts as the device evolved,” Rogers says. The SubQ It! stapler is composed of nine plastic parts, including two exterior shell halves, a plunger operated by the user, and internal parts that feed the fasteners. The contract manufacturer creates all of the parts through injection molding.
However, before a shift from additive to injection molding was made, Opus had each part milled through the contract manufacturer's CNC machining service. The milled parts were designed as if they were being molded, with proper draft built in, so the form, fit, and function of the device could be studied before tooling up for molding. “Once we put the prototypes together, we could test to make sure the fasteners were feeding correctly, and if the sliding action of the plunger was operating smoothly without jamming. If there were any problems, we would modify the part and have another one machined,” Rogers says. “Once everything was working, we made molds.”
Although the design remained consistent from machining to molding, the material employed did not. In the stapler's first iteration, the material used for the machined parts closely resembled the resin that would be used to mold it, but they discovered that surface finishes between processes varied. In subsequent iterations, they switched to machined acetals like Delrin, for example, even though final parts would be molded in an FDA-approved Lustran ABS, which provides more structural rigidity and can handle gamma sterilization.
“Most of the parts were only modified one or two times, and we were really pleased with being able to match the performance of the mold to what we achieved in the machined parts,” Rogers notes.
Outcome: Market Launch, Rising Demand
The last few years have been busy for Opus, getting trademark approval for SubQ It! fastener, gaining additional patent protection, and eventually garnering FDA approval for use in “abdominal, thoracic, gynecologic, orthopedic, plastic, and reconstructive surgery” — all while scaling up for manufacturing in parallel. Now on the market, production is currently being increased to meet the rising demand for the product.
Additionally, Opus plans to expand SubQ It! to the veterinarian field. Rogers says that even if pet owners don't care if scarring is visible on their pet's skin, the benefit to vet and pet owner is the time and money saved from not having to return to the clinic to have the staples removed since they will have dissolved. Also, because SubQ It! fasteners are underneath the pet's skin, the potential for biting or scratching them is reduced, which may in turn reduce the chances of having to don the unflattering cone of shame.
The SubQ It! system is designed to make life easier for surgeons and better for their patients, whether human or animal.
This article was written by Annie Cashman, Global Segmentation Manager — Medical, at Protolabs, Maple Plain, MN. For more information, visit here.