Standardized tensile testing of soft tissue using a 3D printed clamping system

Abstract

Biomechanical testing of soft tissues forms the backbone in the experimental validation of tissue engineering and for modelling purposes. The standardized testing of soft tissues requires different experimental protocols and fixtures compared to hard tissues or non-biological materials due to their characteristics. Some of the most commonly-used clamping methods for soft tissue testing affect the tissues' mechanical properties as chemicals are involved to decelerate degradation and autolysis. Moreover, they are unsuitable for standardized and high-throughput testing. Material slippage is also a recurrent unwanted influence on the testing routine with impact on measurement validity. Addressing these issues, this protocol presents a clamping system for simplified testing of biological soft tissues with all necessary components manufactured utilizing 3D printing technology. Templates allow trimming the samples into standardized shapes and sizes while preparation tables facilitate clamping in a fixed distance. The key parts of the system are clamps with a pyramid design, which allow the mounting of biological soft tissues before transferring it into the testing device and minimize material slippage during tensile testing. Flexible holder arms are used to transfer samples from preparation tables into the testing device and simplify positioning. Mechanical testing itself is performed with digital image correlation for precise strain measurements.

Keywords: 3D printing; Biomechanical testing; Clamps; Soft tissues; Tensile testing.

Graphical abstract

Fig. 1

Overview – all parts from the clamping system for standardized tensile testing can be 3D printed. Parts printed in polylactic acid (PLA) are depicted grey while parts printed in thermoplastic polyurethane (TPU) are depicted in red. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 2

Cutting plate for dog bone-shaping of biological soft tissues as well as the final dimensions of the soft tissues after preparation. The recommended paths for cutting (from point to arrow) by a scalpel are highlighted in green (1 = first path), blue (2 = second path) and red (3 = third path) alongside dotted lines. After cutting the first side of the sample, the template is rotated and cutting is repeated for the opposite paths. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 3

A) Instruments required for the preparation and biological soft tissue (from left to right: scissors, scalpel, blade, human/biological sample, two forceps), B) Trimming of the samples with a cutting template into a dog bone shape.

Fig. 4

A) For determination of the specimen’s cross-sectional area a dental impression material is used. B) The trimmed sample is placed on the clamps on top of the preparation table as well as the molding device which helps forming the cast.

Fig. 5

A) After mounting the flexible holder arms it is recommended to speckle the sample if using a digital image correlation-system is intended. B) The sample is placed within the testing machine by the flexible holder arms.

Fig. 6

Digital image correlation-setup using a Limess Q400 system by Dantec Dynamics. A) First, the camera is placed allowing the recording of the specimen’s area of interest. After focusing the camera, B) the digital image correlation-system is calibrated using a standardized calibration target.