This work, comprising four studies, focuses on experimental implants and materials for orthopaedic applications designed to address the often concomitant issues of infections and bone loss. The first two studies examine silver (Ag) as an antibacterial agent and its effects on human cells when used as a coating on titanium (Ti) implants. The last two studies explore methods for regenerating bone defects.

In the first study, we compared two types of Ag-coated Ti implants provided by an implant manufacturer. One implant is used clinically, while the other was experimental and contained smaller amounts of Ag. Physicochemical analysis showed that the entire surface of the clinical implant was coated with Ag, while the Ag on the experimental implant formed aggregates on the surface. The clinically used implant released significantly more Ag, while, the experimental implant's release ceased after a few days. S. aureus and osteoblasts was cultured separately then on the implants, and we showed that smaller amounts of Ag on the implants maintained satisfactory antibacterial effects while minimising adverse effects on the osteoblasts.

The second study investigated the effects of different ionic Ag concentrations on osteoblasts and mesenchymal stem cells. Using various methods, including PCR, enzymatic analyses for cell differentiation, microscopy, and staining for mineralisation, we found that even small amounts of Ag could inhibit mineralisation by human osteoblasts. We observed no significant impact on the osteogenic differentiation of osteoblasts or mesenchymal stem cells regarding gene expression and ALP production. However, microscopic analysis revealed abnormal cell patterns, such as reduced confluence in Ag-treated groups compared to controls. These findings, suggest that Ag-coated implants should be used cautiously in clinical settings, especially in parts of the prosthesis intended for direct bone integration.

Study III employed the freeform reversible embedding of suspended hydrogels (FRESH) technique, to 3D-print collagen structures with trabecular geometry. This technique and its structures were compared to stereolithographic printing, an alternative 3D printing method, which produced analogous structures using a different material, polyethylene glycol diacrylate (PEGDA). Rheological and mechanical analyses were performed on the 3D-printed collagen structures to characterise their elasticity and stiffness; electron microscopy was used to map the surface geometry of the collagen and PEGDA structures. Cultures of human osteoblasts and osteosarcoma cell lines on the two types of structures showed that the 3D-printed collagen structures were better suited as carriers for osteogenic cells compared to the 3D-printed PEGDA structures.

In the fourth study, we successfully 3D-printed artificial bone of collagen and hydroxyapatite. The collagen in this material was modified by cross-linking. Mechanical and rheological analyses of the material in gel and solid forms were performed, and the distribution pattern of hydroxyapatite within the material was examined. Finally, we cultured human osteoblasts on the 3D-printed collagen-hydroxyapatite structures up to four weeks. We found that osteoblasts grew well and differentiated satisfactorily on structures printed with our new material.

Overall, this work shows how surface coatings and 3D printing might solve the two biggest issues in orthopaedics—infections and missing bone. We trust this dissertation will illuminate the underlying scientific principles of these techniques for orthopaedic surgeons.