A review on the identification of the mechanical properties of soft tissues and tissue-mimicking phantoms

Characterising the mechanical properties of soft materials - such as gels and biological tissues - presents significant challenges compared to conventional, stiff engineering materials like ceramics, metals, and polymers. A major issue identified is the considerable variability in measured properties across different techniques, or even between different laboratories employing the same method. This comprehensive review addressed the need for a thorough examination of existing techniques, their limitations, and their drawbacks. Both laboratory-based and clinical methods were explored, including laboratory techniques such as tensile testing, compression test, indentation, atomic force microscopy, and rheometry, as well as clinical methods including ultrasound elastography and magnetic resonance elastography. The principles of operation and the theoretical foundations underlying the most widely employed modalities for material and tissue characterisation were presented. The limitations of these techniques were detailed, and numerous studies on the mechanical properties of soft tissues and tissue-mimicking phantoms were reported. The mechanical properties of various soft materials identified using these diverse techniques were compared and evaluated. The findings highlighted a clear need for the development of more reliable test apparatus and standardised procedures to accurately characterise these properties across nano, micro, and macro scales. These findings offer a valuable resource for researchers in the field, facilitating informed selection of characterisation methods and promoting greater accuracy and consistency in future work.