Interactions between musculoskeletal tissue and biomaterial

In the musculoskeletal system, bone is the primary tissue/organ interacting with prosthetic implants/biomaterials and their interface is a crucial region where the interactions pertinent to new tissue formation and implant efficacy occur. Bone is a complex biological system that comprises both hierarchical structures and living boneremodeling components. The architecture of bone is composed of nanoscale fibrous 

Due to contaminations during the operation process, infection may also initiate before the bonding between bone and implant occurs. In many cases, there are multiple bacteria leading to the infection of implants. For example. Staphylococcus epider-midis exists on the human skin and can infiltrate to implant sites to cause infection. In contrast. Staphylococcus aureus is a natural tissue pathogen that may cause infection due to tissue damage around implants. 

However, the mechanisms behind nanotopographically mediated tissue responses are still not clear. The increased adsorption of cell adhesive proteins (such as fibronec-tin, vitronectin, etc.) on nanoscale rough surfaces, due to either uneven surface landscapes or inaeased specific surface area, is a plausible mechanism. However, this mechanism is not enough to explain aU the nanoscale roughness (or nanotopography) related tissue responses. For example, there is a lack of evidence to explain the fact the many different types of cells see the same roughness but their responses are different from cell type to cell type [64]. These questions will be further examined in Chapter 8. 

Many studies so far have demonstrated a proportional relationship between surface energy of nanomaterials and the adsorption of hydrophilic cell adhesive proteins (e.g., fibronectin and vitronectin). For example, maximum vitronectin adsorption was noted on hydrophilic surfaces compared to hydrophobic ones [65]. Therefore, it is speculated that hydrophilic (i.e., high surface energy) nanomaterials have a higher affinity for cell adhesive proteins and, subsequently, promote cell functions and tissue responses better than hydrophobic nanomaterials. The verifications and debates on this hypothesis will be further discussed in the following chapters. 

Mechanical properties of materials have recently been correlated to cellular or tissue responses [74,75]. To date, studies have demonstrated that stem cells and tissue cells (such as skin, muscle, and brain cells) sense and respond to local matrix (e.g., extracellular matrix or synthetic material) stiffness through the formation of molecular adhesion complexes and changes in the actin-myosin cytoskeleton, which provide a feedback of the matrix stiffness for cell adhesion, motility, and differentiation [74]. For example, epithelial cells and fibroblasts on a collagen-coated polyacrylamide substrate that allows the stiffness to be altered (elastic moduli from 5 to 80Pa) revealed less cytoskeletal spreading and higher rates of motility or lamelhpodial activity on flexible 

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