Mechanical properties are one of the most important characteristics of biomaterials for many different applications, including biomedicine. Soft biomaterials, such as hydrogels, are difficult to characterize by conventional mechanical testing, because their mechanical properties are much lower than required by conventional testing machines. In this work, we aimed to systematically study the mechanical behavior of a model soft material, polyacrylamide hydrogels, under different loading modes: tension, torsion, compression, and indentation. This allowed us to develop a comprehensive approach to the mechanical testing of soft materials. To overcome excessive compression and slippage of the hydrogel samples when fixed in the grips during tension, additional 3D-printed grips were designed. Digital image correlation was used to determine the Poisson’s ratio of the hydrogels. The Young’s modulus values obtained from all types of mechanical tests analyzed were highly correlated. However, for hydrogels with a low crosslinker concentration, 1–2%, tension–compression asymmetry was observed. Moreover, the results of the mechanical tests were verified in indentation tests, including analytical estimation, and full-scale and numerical experiments. We also discuss the limits of using a two-parameter Mooney–Rivlin model for fitting hydrogel uniaxial tension deformation curves, which was unstable for the hydrogels with 4 and 9% crosslinker concentration. The implemented approach provided a comprehensive analysis of the mechanical behavior of biomaterials. The elastic moduli for all hydrogels studied were in the range from 20 to 160 kPa, which corresponds well to human soft tissues, making them a promising material for application as tissue-mimicking phantoms.

Дегенеративно-дистрофические изменения межпозвонкового диска, сопровождающиеся хронической болью, ограничением подвижности и постепенным разрушением элементов позвоночника, являются cерьезной патологией, требующей оперативного вмешательства, лечение которой осуществляется посредством полной или частичной замены поврежденной ткани. В настоящее время 3D-печать активно используется при создании протезов межпозвонковых дисков благодаря высокой точности изготовления и возможности производства персонализированных имплантатов. В сочетании с имитацией интактной двухфазной структуры такой подход способствует сохранению естественного биомеханического отклика на физиологические нагрузки. Для искусственного фиброзного кольца перспективными являются конструкции на основе гироидной поверхности из биосовместимых материалов, обладающие уникальными механическими свойствами, а фантомами пульпозного ядра могут выступать гидрогели благодаря структурному сходству и вязкоупругому поведению. В работе предложены подходы к проектированию гироидного фиброзного кольца, изготовленного с помощью экструзионной 3D-печати, реализована технология получения гидрогеля с заданным модулем упругости для имитации пульпозного ядра с использованием прогнозируемого набухания. Проведены механические испытания, оценены упругогистерезисные характеристики прототипов гибридных имплантатов при физиологических нагрузках, показано их хорошее соответствие аналогичным характеристикам интактного диска.

The degeneration of the intervertebral disc, characterized by chronic pain, restricted range of motion, and progressive deterioration of functional spinal units, represents a serious surgical condition. For the treatment the total or partial arthroplasty is often suggested. Currently, 3D printing is frequently utilized in the development of disc prostheses, owing to its high precision and capacity to create patient-specific implants. Integrated with the replication of the intact biphasic structure, this approach facilitates the preservation of the natural biomechanical response to physiological loads. For the artificial annulus fibrosus, gyroid-based structures fabricated using biocompatible materials show significant promise due to their unique mechanical properties. Hydrogels can serve as candidates for the nucleus pulposus replacement, due to their structural similarity and viscoelastic behavior. This work proposes design methodologies for an annulus fibrosus with gyroid structure, manufactured via extrusion-based 3D printing. Furthermore, a fabrication technique for hydrogels exhibiting controlled swelling and a tailored elastic modulus to mimic the nucleus pulposus was implemented. Mechanical testing was conducted to evaluate the elastic-hysteretic properties of the hybrid implant prototypes under physiological loading conditions. The results demonstrate a close correspondence between these properties and those of the intact disc.