An evaluation of the usability and durability of 3D printed versus standard suture materials

The capability to produce suture material using three‐dimensional (3D) printing technology may have applications in remote health facilities where rapid restocking of supplies is not an option. This is a feasibility study evaluating the usability of 3D‐printed sutures in the repair of a laceration wound when compared with standard suture material. The 3D‐printed suture material was manufactured using a fused deposition modelling 3D printer and nylon 3D printing filament. Study participants were tasked with performing laceration repairs on the pigs' feet, first with 3‐0 WeGo nylon suture material, followed by the 3D‐printed nylon suture material. Twenty‐six participants were enrolled in the study. Survey data demonstrated statistical significance with how well the 3D suture material performed with knot tying, 8.9 versus 7.5 (p = 0.0018). Statistical significance was observed in the 3D‐printed suture's ultimate tensile strength when compared to the 3‐0 Novafil suture (274.8 vs. 199.8 MPa, p = 0.0096). The 3D‐printed suture also demonstrated statistical significance in ultimate extension when compared to commercial 3‐0 WeGo nylon suture (49% vs. 37%, p = 0.0215). This study was successful in using 3D printing technology to manufacture suture material and provided insight into its usability when compared to standard suture material.

7.5 (p = 0.0018).Statistical significance was observed in the 3D-printed suture's ultimate tensile strength when compared to the 3-0 Novafil suture (274.8 vs. 199.8MPa, p = 0.0096).The 3D-printed suture also demonstrated statistical significance in ultimate extension when compared to commercial 3-0 WeGo nylon suture (49% vs. 37%, p = 0.0215).This study was successful in using 3D printing technology to manufacture suture material and provided insight into its usability when compared to standard suture material.

| INTRODUCTION
Using suture material to repair wounds is the primary method of laceration repair.Although there are other methods to repair a laceration such as skin glue and steri-strips, the use of sutures affords clinicians with the agency to repair a wide range of wound presentations.Having the capability to produce suture material on an ad hoc basis may have applications in remote health facilities where rapid restocking of supplies is not an option.The use of three-dimensional (3D) printing technology to produce medical equipment such as forceps and needle drivers has been described in the literature with overall positive Abbreviations: EO, ethylene oxide; FDM, fused deposition modelling; MPa, megapascal; PGY, postgraduate year; SEM, scanning electron microscopy.2][3][4] A single study was identified demonstrating the successful use of 3D printing technology to fabricate suture material with nylon filament. 5In our study, we will evaluate the usability of 3D-printed sutures in the repair of a laceration wound when compared with a standard suture material.

| OBJECTIVES
The study objectives are: (1) To develop a process of using 3D printing technology to manufacture suture material and (2) To compare the usability of 3D-printed nylon suture material with commercially available nylon suture material.

| METHODS
This is an exempt study approved by the Institutional Review Board of a level-1 trauma centre in the Midwest USA.A convenience sampling of emergency medicine residents and faculty was conducted to enrol the study participants.

| Suture fabrication
The 3D-printed suture material was manufactured using an Ultimaker S3 fused deposition modelling (FDM) 3D printer and Ultimaker nylon 3D printing filament.The nylon filament was extruded through a 0.4 mm hot-end nozzle at 245-250 C using the 3D printer's load function.The extruded filament was further compressed by stretching it to increase its tensile strength and to match the thread's diameter to the thickness of 3-0 WeGo nylon suture material.The stretching procedure was accomplished by having the investigator manually pinch each end of the extruded filament with their fingers and pull outward until maximal compression is achieved, as indicated by a positive stop.The 3D-printed suture material was then cut to a length of 450 mm to match the 3-0 WeGo nylon suture material.A digital calliper was used to ensure uniform material thickness of the compressed 3D suture material.
The 3D suture material was attached to the suture needle by wrapping it around the proximal end of a curved needle and secured in place with cyanoacrylate adhesive glue.

| Laceration repair procedure
Each participant was presented with two pigs' feet, each with a 25 mm laceration involving the subcutaneous tissue.The participants were tasked with performing two laceration repairs using their suture technique of choice on the pigs' feet.The first repair was performed with standard 3-0 WeGo nylon suture material, followed by the 3D-printed nylon suture material.The participants were asked to complete a seven-question post-study survey (Table 1), rating their experience with each suture material.Paired t-tests were used to compare the functionality of the suture materials at the p < 0.05 level.

| Tensile strength testing
Tensile strength for the 3D suture material, along with multiple two commercially available suture materials (3-0 Novafil and 3-0 WeGo nylon), were tested using an Intron 5944 Universal testing system with an attached strain transducer.Two commonly used suture brands of 3-0 size were tested along with the 3D-printed suture material.The suture materials were secured to the testing system using pneumatic clamps, and the material thickness was measured using a digital calliper.Accounting for the clamp depth, approximately 55 mm of length was tested.Each suture material was tested six times with the tensile strength reported in units of megapascal (MPa).The strain rate for all test runs was 254 mm/min.Young's modulus was calculated as the slope from 0% to 5% strain for all samples.Analysis of variance was used to compare the mean measures of ultimate tensile (MPa), ultimate extension (%), and Young's modulus (MPa) between the suture material groups.If the overall p value was significant, pairwise comparisons were adjusted using Tukey's test.Tensile strength data is presented in Figure 1.

| Scanning electron microscopy
All suture materials underwent scanning electron microscopy (SEM) imaging.Materials were cut to 6 mm lengths and attached to aluminium SEM stubs with double-sided carbon tape.The following day, samples were coated with 50 nm gold-palladium alloy in a Hummer VI Sputter Coater (Anatech USA) and imaged at 25 kV in an FEI Quanta 200 SEM operating in high vacuum mode.

| RESULTS
A total of 26 participants were enrolled in the study.Twenty-five of the participants were residents, with one participant being an emergency medicine faculty.Eleven participants were at the postgraduate year (PGY)-1 level, 9 were at the PGY-2 level, and 5 were at the PGY-3 level.Eighteen (69.2%) participants had performed >40 laceration repairs previously, with 7 (26.9%)having completed 21-40 and 1 (3.8%) having completed 1-20.All participants performed simple interrupted suture techniques with 3-0 WeGo nylon and 3D-printed suture materials.Based on the survey data, traditional suture had a mean value of 8.7, 7.5 and 8.3, respectively, when evaluated for how well the material pulled through the tissue, tied knots and the user's confidence in ability to maintain wound adhesion.The 3D-printed suture material had mean values of 7.1, 8.9 and 8.7, respectively, when evaluated for the same three parameters.There is no statistical significance between the two suture materials with regard to pull through tissue and confidence in ability to maintain wound adhesion.
There is a statistically significant difference in the rating of how well the suture material performed with knot tying between 3D-printed and standard sutures ( p = 0.0018).On average, the 3D-printed suture was rated 1.4 points higher than the standard suture.When comparing usability between the 3D-printed suture and the traditional suture, 16 participants (61.5%) rated it as the same.Five participants (19.2%) found it to be more usable and another 5 (19.2%) participants found it to be less usable.User comments are presented in Table 1.
The 3D-printed suture material was found to have a higher ultimate tensile strength when compared to 3-0 Novafil, which was statistically significant (274.82 vs. 199.79MPa, p = 0.0096).Using SEM imagery, the 3D-printed suture material was observed to be slightly thicker in diameter than 3-0 WeGo nylon (8.3%) and 3-0 Novafil (14.4%) suture materials.SEM images and material thickness data are presented in Figure 2.
No significance was observed between the 3D-printed suture and 3-0 WeGo nylon on this metric.Alternatively, the 3D-printed suture demonstrated statistical significance in the measure of ultimate extension when compared to 3-0 WeGo nylon (49%-37%, p = 0.0215).There is also a statistically significant difference in the  Q3a/5a: Rate suture knot tying 7.5 (SD 1.9) vs. 8.9 (SD 1.5) Q4/6: Rate confidence in ability to maintain wound adhesion 8.3 (SD 1.9) vs. 8.7 (SD 1.3) Q7: Rate usability of 3D suture when compared to standard suture Less: 5, Same: 16, More: 5 Survey comments regarding 3D-printed suture material More usable with knot tying.Less usable with difficulty getting needle through the skin Difficult to push needle through skin.Ties better + holds knot better than non-3D The suture material was easier to tie and appeared to form a better knot, but my first needle could not get through the skin at all (at the attachment), second one the suture material came off the needle

| DISCUSSION
This study was successful in using FDM 3D printing technology to manufacture suture material and provided insight into its usability when compared to commercial suture material.The use of 3D printing technology to manufacture ad hoc medical equipment has the potential for a paradigm shift in the medical supply chain.These benefits would be most apparent in healthcare facilities that lack the ability to rapidly restock their supply stock, such as rural or developing regions, war zones or even space exploration scenarios.A standard spool of 3D printing filament contains 1 kg of printable material and depending on the size of the printed part, 1 kg of filament can produce hundreds to thousands of parts.Based on procurement costs at our institution, a single pack of 3-0 Novafil and 3-0 Ethicon nylon sutures cost approximately $17.76 and $14.52, respectively.Not considering capital or overhead costs such as the 3D printer, labour, or utilities, a similar length (450 mm) of 3D-printed nylon suture costs approximately $0.004 to produce.
As inferred by the survey data, the method of wrapping the 3D-printed suture material around the needle resulted in difficulties pulling the suture through tissue, potentially contributing to the 3D-printed suture's lower rating for this variable.The investigators are developing a follow-up study to blind the participants to each suture material by utilising bare suture needles with eye holes to facilitate the loading of the suture material.Nevertheless, statistical significance was observed when assessing the materials' ability to tie knots, with most users commenting on the 3D-printed suture's ease of knot tying, smoothness, and tensile strength.The higher Young's modulus rating for the 3D-printed suture material may have contributed to its higher rating with knot tying.
As demonstrated by the SEM images, the 3D-printed suture material was thicker in diameter when compared to equivalent standard size 3-0 suture materials, also potentially contributing to its higher rating with knot tying.The investigators did not anticipate 3D-printed suture materials would exhibit a similar smoothness to their surface texture when compared to standard Novafil and nylon suture materials.3D-printed products usually have a coarseness to their surface, which is a byproduct of the 3D printing process.The investigators postulate this coarseness was not observed in the 3D-printed suture materials because it was extruded in a single layer as opposed to the multilayered extrusion of traditional 3D-printed products.
The 3D-printed suture was equivalent to 3-0 Novafil in its ability to stretch but demonstrated statistical significance when compared to similar-sized nylon sutures.The stretchability of suture materials is felt to minimise tissue hypertrophy and scarring as it allows for more tissue oedema while maintaining wound adhesion. 6,7This aspect of the 3D-printed suture warranted further investigation with in vitro studies.
Although most 3D printing materials can withstand high temperatures, the question of product integrity after heat sterilisation F I G U R E 2 Scanning electron microscopy (SEM) images of commonly used emergency department suture materials with material thickness measured in microns.
techniques such as autoclaving needs to be evaluated.In a current wound repair study using an animal model, the investigators used ethylene oxide (EO) sterilisation to sterilise the 3D-printed suture material with no apparent detrimental effects.EO sterilisation may be an ideal sterilisation method for 3D-printed medical equipment because it is low cost and does not require the use of heat or chemical baths, which may degrade 3D printing materials.
Data from this study is encouraging, but the investigators feel further studies are warranted to explore additional variables such as a larger sample size, long-term wound adhesion, infection rates, and the potential for tissue toxicity.

| CONCLUSIONS
As demonstrated during the COVID-19 pandemic, the global supply chain is a delicate infrastructure that, once disrupted, can have prolonged adverse rippling effects.It is critical that the healthcare community continue to explore alternative manufacturing processes, such as 3D printing technology, to supplement traditional manufacturing channels.As demonstrated in this study, 3D printing technology was capable of manufacturing suture material that, in some respects, was superior to commercially available suture materials.This feasibility study provided valuable insight into this concept, and the investigators intend to further explore this research stream.

F I G U R E 1
Mean ultimate tensile strength (MPa) of 3-0 Novafil, 3-0 WeGo Nylon, and 3D nylon suture materials as compared to their ultimate extension (%) and Young's modulus (MPa).Overall statistical significance observed in ultimate tensile ( p = 0.0096), ultimate extension ( p = 0.0215) and Young's modulus ( p = 0.0060).*Pairwise comparison p < 0.05.+ Pairwise comparison p < 0.05.T A B L E 1 Summary of survey results and participant feedback regarding their experience with the 3D printed suture material.

7 Q3/ 5 :
): Standard vs. 3D Q1: Current level of training PGY-1: 11, PGY-2: 9, PGY-3: 5, Faculty: 1 Q2: Number of suture procedures performed 1-20: 1, 21-40: 7, 41-60: 11, 60+: Rate suture pull through tissue 8.7 (SD 1.5) vs. 7.1 (SD 3.8) Difficult to pull needle through tissue at site of suture attachment of 3D-printed suture Less usable b/c difficult to pull through tissue b/c of attachment of suture to needle, otherwise just as usable Need improved method of connecting suture to the needle but seems to hold initial tie better 3D-printed felt smooth, nice tensile strength Would prefer it if the needle was easier to pass through the tissue Needle on the 3D-printed was a problem Easier through tissue.Felt more difficult to hold knot 3D-printed did not twist, coil as much as commercial sutures Seemed similar.Was not hard to use Tied really well Difficult to assess pulling due to needle Really strong.I pulled hard NGUYEN ET AL. material stiffness between the 3D-printed suture, 3-0 Novafil and 3-0 WeGo nylon (1692.84 vs. 1233.41vs. 1354.42MPa, p = 0.0060).
Study concept/design, acquisition of the data, analysis/interpretation data, drafting of manuscript, acquisition of funding, statistical expertise.Jason G. Langenfeld: Acquisition of the data, drafting of manuscript.Benjamin C. Reinhart: Acquisition of the data, drafting of manuscript.Elizabeth I. Lyden: Analysis/ interpretation data, drafting of manuscript, statistical expertise.Abraham S. Campos: Analysis/interpretation data, drafting of manuscript.Michael C. Wadman: Acquisition of the data, drafting of manuscript.Matthew R. Jamison: Acquisition of the data, interpretation data, drafting of manuscript.Stephen A. Morin: Acquisition of the data, interpretation data, drafting of manuscript.Aaron N. Barksdale: Study concept/design, analysis/interpretation data, drafting of manuscript, critical revision, statistical expertise.