On Demand Additive Manufacturing of a Basic Surgical Kit

Treatment of battlefield trauma presents a unique set of challenges, among which is the logistical challenge of providing sterile surgical instruments to surgeons. Transport and supply constraints limit the quantity and variety of surgical instruments available in the field and sterilization equipment is often not available to support the instruments on hand. Furthermore, it is difficult to predict and supply the exact type and quantity of instruments needed by a surgeon in the field.New manufacturing technology offers a compelling solution to overcome the logistical challenge. Durable, biocompatible plastic resins can be formed into any shape using commercially available additive manufacturing devices. This technology is already having an impact on healthcare with the production of custom shaped prostheses and implants [1]. A 2009 SBIR/STTR grant solicitation from the National Institutes of Health, suggested that additive manufacturing technologies could be employed for on demand production of medical instruments in remote sites [2]. This concept was recently explored by the Defense Advanced Research Projects Agency (DARPA) as a 90 day technology evaluation project by the Third Quarter 2012 DARPA Service Chiefs Fellowship Program. The DARPA Fellows assembled a team from the Naval Postgraduate Dental School (Bethesda, MD), US Army Edgewood Chemical Biological Center, (Aberdeen Proving Grounds, MD), and Stratasys (Eden Prairie, MN) to conduct a rapid demonstration of additive manufacturing of surgical instruments in a field hospital setting. The goal of the demonstration was to show that on demand, remote site fabrication of a variety of sterile surgical instruments is a real possibility with the current technology.Over a period of less than three months the team developed and demonstrated the ability to produce sterile surgical instruments in a field setting using a material extrusion 3D printer. The instruments were printed in a modified ABS plastic resin, extruded in layers to form the instrument shapes. High processing temperatures of the ABS resin produced sterile parts, directly out of the printer. Rapid trials and iterations of the instrument designs resulted in a functional surgical kit which could be printed in a single build on the 3D printer. At the conclusion of the project, the 3D printer and surgical instrument kit were demonstrated in a mock field surgery. A team of military surgeons used the printed instruments to perform a laparotomy procedure on a model wearing a ‘Cut Suit' training simulator (Strategic Operations, San Diego, CA).Digital models of the instruments comprising basic surgical kit (a partial laparotomy instrument set) were produced in SolidWorks 2012 Computer Aided Design (CAD) software (Dassault Systemes SolidWorks Corp., Waltham, MA), running on a Microsoft Windows 7 based workstation. The following instruments were modeled: Kelly hemostat, needle driver, tissue forceps, retractor, scalpel handle, and Metzenbaum scissors. A parameterized 3D CAD model was created for each instrument based on adaptations of commonly available stainless steel instruments. Key dimensions were identified and then defined as driving dimensions for the CAD geometry. Driving dimensions were modified to generate unique digital versions of the instruments; these were exported, and saved, in the additive manufacturing standard.STL file format.Instruments were printed in an ABS thermoplastic; thus, it was necessary to modify these instrument designs to replicate the mechanical performance of standard instruments (usually fabricated from stainless steel). In particular, cutting instruments were designed with ABS bodies accepting standard scalpel blades.The team elected to pursue an evolutionary design approach due to time constraints. Candidate instrument designs were created digitally, fabricated, evaluated and modified, as necessary, to overcome identified deficiencies in weight, balance, stiffness, and tactile control.Instruments were fabricated directly from digital files using a Dimension uPrint Plus SE desktop material extrusion 3D printer (Stratasys, Eden Prairie, MN). Digital.STL models were prepared for fabrication using CatalystEX 4.3 (Stratasys, Eden Prairie, MN) 3D printing software. Preparation consisted of importing and orienting the. STL model within the build envelope of the 3D printer, incorporation of support structures necessary to affix the part during fabrication, sectioning of the part and supports into layers, then generation of toolpaths to guide material deposition.To form parts, the 3D printer deposited strands of molten thermoplastic material (300–311 °C) into a controlled temperature environment (77 °C), where the material rapidly solidified. Material was deposited on a flat 203 mm square platform in a layered build-up. First, multiple layers of support material were deposited to form a fixture substrate on the platform. Next, 0.254 mm thick layers of structural ABS were deposited from the bottom of the parts upward.Instruments were printed in ABSi-Ag, an engineered ABS plastic resin with silver loading under development by Stratasys. Support structures were printed in Stratasys' P400-SR and SR30-XL; these materials were designed to provide structural support of the part during fabrication, while minimizing interface bonds with the ABS for easy removal.Sample instruments were printed on identical equipment at Naval Postgraduate Dental School (NPDS) and Edgewood Chemical Biological Center (ECBC). Sterility of the instruments printed at both locations was evaluated at ECBC. Samples were tested for sterility by immersing them in 20 mL of autoclaved microbial growth promoting culture media, tryptic-soy broth. The devices were cultured overnight at 37 °C in an orbital shaker (at 170 rpm) to promote microbial growth. Turbidity was observed to assess bacterial growth; lack of turbidity in the culture media indicated a lack of microbial load on the instrument samples.Functional tests of the instruments were performed at NPDS. Instrument function, mechanical strength and durability were initially tested by dissecting and suturing fryer chickens obtained from a local grocery.A basic surgical kit was arrayed on a single 203 mm square platform in the 3D printer. Upon completion of printing, the entire platform was placed in a sterile bag for storage. Before use, instruments were separated from the platform manually. Two part instruments, such as the hemostats or needle drivers, were manually assembled after removal from the platform.A mock field hospital was set-up on the grounds of Walter Reed National Military Medical Center, Bethesda, MD, for a field demonstration. A 3D printer, laptop computer, and a portable generator were set-up alongside the mock field hospital tent. A simulated laparotomy surgery was performed on a ‘Cut Suit' human-worn surgical simulator, worn by a volunteer model, using a kit of printed instruments. An additional hemostat was printed in the field hospital during the simulated surgery.Surgical instrument printing in ABS plastic by material extrusion 3D printing was demonstrated in the lab and, to a limited extent, in a mock field setting. Basic surgical instruments were digitally designed, printed, tested and refined. Dissection and suturing was successfully performed on fryer chicken parts, then in a later demonstration on a human surgical simulator. With the exception of the Metzenbaum scissors, all instruments performed adequately to dissect and suture on the surgical simulator without failure. Scalpel blades were used for cutting blades of the scissors, but these often did not engage, failing to cut tissue in many instances.A printed minor surgery/laparotomy kit consisting of: 3 scalpel handles, a retractor, a needle driver, a hemostat, and one tissue forceps, is shown in Fig. 1. This surgical kit took just over 6 hours to print. Single instrument print times ranged from 1 to 3 hours, with printing time depending on the number of layers required to form the instrument. Instruments were manually separated from the build platform and support substrate by twisting the platform from opposing corners. Once the parts were partially separated from the support substrate, they could be manually removed by gloved fingers. 90% of the instruments sampled, directly out of the 3D printer, were determined to be sterile.Fabrication of a useable surgical instrument kit by material extrusion 3D printing was successfully demonstrated using commercially available equipment and software. Biological testing of laboratory printed samples showed that the sterility was high; however, to achieve 100% sterility of all instruments more research on process control is necessary.Additive manufacturing of surgical instruments equipment was demonstrated in a simulated field environment. Electrical power, digital instrument files, and ABS material(s) were all that was necessary to print instruments on demand. Conceivably, a catalog of thousands of open-source instrument designs, or even custom tailored instruments, can be stored on digital media or remotely accessed from the internet for printing in the field.Print times with currently available "general-purpose" 3D printers are too long for real time, on demand printing of instruments during a surgical procedure. However, a 3D printer could replenish depleted supplies of sterile instruments in a matter of hours to keep a necessary inventory of commonly used instruments continuously available. A printer optimized for this specific application, addressing instrument sterility and print speed concerns, is conceivable, but further research and development is needed. This successful pilot study indicates that such technology is feasible.The views expressed in this article are those of the authors and do not necessarily reflect the official policy, position, or endorsement of the Department of the Navy, Army, Department of Defense, nor the U.S. Government.