Researchers 3D Print Clamping Systems to Cut Down on Slippage During Soft Tissue Testing

When I think about clamps, if I do at all, it’s in terms of holding wood steady in a scene shop while making sets for a play, or keeping two large objects that have been glued together tight while the glue dries. But there are many different purposes and applications for clamps, including in the medical field, demonstrated by the 3D printed cardioplegia clamps designed for King’s College Hospital Foundation Trust two years ago.

Recently, a collaborative group of researchers from the University of Otago and the Auckland University of Technology in New Zealand and the University of Leipzig in Germany published a paper, titled “Utilization of 3D printing technology to facilitate and standardize soft tissue testing,” in the Scientific Reports journal that detailed their work in creating 3D printed clamps and fixtures that can help mount soft tissues for testing purposes.

The abstract reads, “This report will describe our experience using 3D printed clamps to mount soft tissues from different anatomical regions. The feasibility and potential limitations of the technology will be discussed. Tissues were sourced in a fresh condition, including human skin, ligaments and tendons. Standardized clamps and fixtures were 3D printed and used to mount specimens. In quasi-static tensile tests combined with digital image correlation and fatigue trials we characterized the applicability of the clamping technique. Scanning electron microscopy was utilized to evaluate the specimens to assess the integrity of the extracellular matrix following the mechanical tests. 3D printed clamps showed no signs of clamping-related failure during the quasi-static tests, and intact extracellular matrix was found in the clamping area, at the transition clamping area and the central area from where the strain data was obtained. In the fatigue tests, material slippage was low, allowing for cyclic tests beyond 10⁵ cycles. Comparison to other clamping techniques yields that 3D printed clamps ease and expedite specimen handling, are highly adaptable to specimen geometries and ideal for high-standardization and high-throughput experiments in soft tissue biomechanics.

Soft tissues have several special characteristics, such as being diverse, directionally dependent (anistropic), and viscoelastic (exhibiting both viscous and elastic characteristics when undergoing deformation). The power of these qualities is increased by things like post-mortem delay, water content alterations, and traumatic pathology, all of which can cause issues when it comes to standardized mechanical tests of the tissue under strain.

Fixtures and clamps have been used to help with issues like material slippage, but are limited when working with soft tissue due to reasons like, as the paper lists, “avulsion at the clamping site or the risk of temperature-induced changes in the mechanical behavior.”

Over the last few years, the team developed a technique called partial plastination that uses ceramic-reinforced polyurethane resin at the clamp mounting sites to help with slippage. But it takes a long time to prepare this method, which also requires special (read expensive and hard to come by) equipment like casting fixtures and vacuum pumps, and errors can come up during the clamping due to how difficult it can be to position soft tissues in a test that involves the effects of gravity.

“As a consequence, we aimed to explore alternative techniques which may facilitate tissue clamping, and aid in standardizing the clamping of soft tissues for biomechanical testing in a less time-consuming manner,” the researchers explained in their paper. “3D printing has meanwhile become broadly available, and such professional extrusion solutions can be utilized for customizing and printing fixtures and adjustments for biomechanical testing using commercially-available filaments. Furthermore, it can be utilized to provide affordable add-ons to existing testing devices all over the world, going beyond just soft-tissue biomechanics. The possibility of sharing existing digital models enables a broad availability and exchange of research and knowledge. 3D printing may also be used for clamping mechanisms, and variations in clamping design appear to be eased by the rapid-prototyping approach with the ubiquitously-available software.”

Standardization in material testing and test setup. Focus of this study will be the boxes highlighted in red.

During a quick Internet search, I found models of 3D printable clamps on Thingiverse, Instructables, and 3D Hubs, though none were for medical purposes. The research team’s clamping systems were designed using Creo 4.0 3D CAD software, and printed on an Ultimaker 3 Extended in commercially available ABS, PLA, nylon, and TPU filaments.

In their paper, the research team described their experience mounting human soft tissues, from three different anatomical regions with differing properties, using 3D printed clamps, and also compared this new way of clamping to their previous partial plastination method.

Co-authors of the paper are Mario Scholze, Aqeeda Singh, Pamela F. Lozano, Benjamin Ondruschka, Maziar Ramezani, Michael Werner, and Niels Hammer.

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