Assessment of Mechanical and Tribological Properties of Alginate-polyacrylamide Hydrogel Matrix Composites As Minimally Invasive Cartilage Implants
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The advent of orthopaedic prostheses and their widespread applications have helped millions of patients worldwide to be relieved from pain and gain their mobility. However, they are still not suitable for young or middle-aged patients suffering from localised cartilage damage, due to the limited life span of these load-bearing devices. All available remedies for those patients are temporary and some of them might result in regeneration of tissues with different properties to the existing one, and hence limited functionality and durability. Therefore, an alternative way should be investigated to prevent further tissue degeneration through replacing damaged regions of the tissue and preserving the remaining healthy portion. This will result in prolonging the tissue functionality, and further postponing the total joint replacement. Different hydrogels have been studied extensively as potential cartilage replacement candidates, as they are biocompatible and can mimic the lubrication mechanisms found in cartilage tissue. As for the mechanical properties, there is still room for improvement. Alginate-Polyacrylamide (ALG-PAAm) hybrid hydrogel was suggested as an orthopaedic prosthesis due to their biocompatibility and promising properties. However, their friction and wear performances remained under-explored. Thus, the current study focused on ALG-PAAm and in an attempt to improve its mechanical performance, silica nanoparticles (Si-NPs) were introduced to the interpenetrating polymer network (IPN) hydrogel matrix as a reinforcement and the mechanical and tribological characteristics of the resultant nanocomposite were investigated. Furthermore, two different weave patterns were developed and produced as three-dimensional woven form, out of biocompatible polymers, to reinforce the hydrogel matrix. Inspired by the articular cartilage tissue, the woven preforms featured a through-the-thickness stiffness gradient and could resist delamination. Beside experimental approach, wear simulation was performed by employing Archard’s wear law in finite element (FE) models. Wear in a unit cell of 3D woven fabrics as well as hydrogel composites were simulated using a user-defined subroutine, UMESHMOTION, linked with ABAQUS CAE package and the model was validated with experimental results. FE simulations were further employed for parametric studies to attain information that could not be obtained directly from the experiments. It was found that ultra-low coefficient of friction coupled with high wear-resistance and tuneable elastic and viscoelastic characteristics observed in the manufactured samples, were mainly due to the strong interfacial bonding between the nanoparticles and the polymer matrix, allowing effective stress transfer between the two main constituents. Moreover, the infiltration of hydrogel into the woven fabric led to a decrease in surface roughness and an increase in load-to-failure capacity. The wear rate and friction coefficient of the reinforced hydrogel matrix were greatly reduced under the range of applied loads and sliding velocities. These promising results are attributed to the synergistic interaction between the fibre phase and the hydrogel matrix. The findings of this research give an insight into the tribology of hydrogel matrix composites for use as load-bearing biomedical components.