Blood protein coated model biomaterials : preparation, and cell and tissue response

Abstract: Solid biomaterials are widely used in bone and in soft tissue applications. Problems may then arise due to a prolonged inflammation in the proximity of the implant, resulting in the formation of a fibrous capsule and a low vascularisation near the interface.The formation of a blood plasma clot is the starting point of a normal wound healing process. One hypothesis in this thesis work was that a thin immobilised blood plasma clot may improve the integration during the early wound healing period. Model surfaces were made from titanium and silicon, and nm-μm thick blood plasma clots or protein multilayers immobilised onto the surfaces. Another hypothesis was that a submicron surface porosity further improves the integration process, and to study this some of the titanium surfaces were etched in sodium hydroxide, a treatment that resulted in 200 nm wide pores. Such porous titanium surfaces adsorbed 2 to 11 times more albumin and lgG in vitro than the corresponding smooth surfaces at varied pH and protein concentrations.The blood plasma clot coated submicron porous titanium samples were implanted subcutaneously in the back of the rat or in rabbit bone. The soft tissue response was investigated after 3 or 24 hours and the fibrous encapsulation and vessel formation after 7 or 28 days of implantation. The bone ingrowth and the implant stability in the rabbit bone were investigated after 4 weeks of implantation.The monocyte response on multilayer plasma protein coated surfaces was investigated through the analysis of tumor necrosis factor α (TNF-α) and interleukin-10 (IL-10) concentrations in the culture medium, the proportions of Annexin V and propidium iodide (PI) positive cells, and the amounts of nucleated cells. In parallel, the stability of the protein layers and the activation of the complement and coagulation cascades were investigated in vitro by ellipsometry.The results from the monocyte culture and animal experiments show that the early soft tissue inflammatory response and vascularisation can be modulated through the introduction of a surface porosity and by the immobilised protein and plasma clot coatings. However, no significant differences were observed between the different surface modifications in rabbit bone with respect to bone-to-metal contact or percentage of bone area inside the threads.