Disturbances of host integrity have the potential to evoke activation of innate immunologic and hemostatic protection mechanisms in blood. Irrespective of whether the activating stimulus is typically immunogenic or thrombotic, it will generally affect both the complement system and platelets to a certain degree. The theme of this thesis is complement and platelet activity, which is intersected in all five included papers. The initial aim was to study the responses and mechanisms of the complement cascade in relation to platelet activation. The secondary aim was to use an applied approach to regulate platelets and complement on model biomaterial and cell surfaces.    Complement activation was found in the fluid phase in response to platelet activation in whole blood. The mechanism was traced to platelet release of stored chondroitin sulfate-A (CS-A) and classical pathway activation via C1q. C3 was detected at the platelet surface, though its binding was independent of complement activation. The inhibitors factor H and C4-binding protein (C4BP) were detected on activated platelets, and their binding was partly dependent on surface-exposed CS-A. Collectively, these results showed that platelet activation induces inflammatory complement activation in the fluid phase. CS-A was shown to be a central molecule in the complement-modulatory functions of platelets by its interaction with C1q, C4BP, and factor H. Platelet activation and surface adherence were successfully attenuated by conjugating an ADP-degrading apyrase on a model biomaterial. Only minor complement regulation was seen, and was therefore targeted specifically on surfaces and cells by co-immobilizing a factor H-binding peptide together with the apyrase. This combined approach led to a synchronized inhibition of both platelet and complement activation at the interface of biomaterials/xenogeneic cells and blood. In conclusion, here presents a novel crosstalk-mechanism for activation of complement when triggering platelets, which highlights the importance of regulating both complement and platelets to lower inflammatory events. In addition, a strategy to enhance the biocompatibility of biomaterials and cells by simultaneously targeting ADP-dependent platelet activation and the alternative complement C3-convertase is proposed.

The aim of this pilot study was to evaluate the bioactive, surface-coated polycaprolactone-co-lactide scaffolds as bone implants in a tibia critical size defect model. Polycaprolactone-co-lactide scaffolds were coated with collagen type I and chondroitin sulfate and 30 piled up polycaprolactone-co-lactide scaffolds were implanted into a 3 cm sheep tibia critical size defect for 3 or 12 months (n¼5 each). Bone healing was estimated by quantification of bone volume in the defects on computer tomography and microcomputer tomography scans, plain radiographs, biomechanical testing as well as by histological evaluations. New bone formation occurred at the proximal and distal ends of the tibia in both groups. The current pilot study revealed a mean new bone formation of 63% and 172% after 3 and 12 months, respectively. The bioactive, surface coated, highly porous three-dimensional polycaprolactone-co-lactide scaffold stack itself acted as a guide rail for new bone formation along and into the implant. These preliminary data are encouraging for future experiments with a larger group of animals.

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No description available.

Collagen and glycosaminoglycans, such as hyaluronan and chondroitin sulfate, are the major components of bone extracellular matrix, and extracellular matrix composites are being evaluated for a wide range of clinical applications. The molecular and cellular effects of native and sulfatemodified glycosaminoglycans on osteocytes were investigated as critical regulators of bone remodeling. The effects of glycosaminoglycans on viability, necrosis, apoptosis, and regulation of gene expression were tested in two osteocyte-like cell lines, the murine MLO-Y4 and the rat UMR 106-01 cells. Glycosaminoglycans were non-toxic and incorporated by osteocytic cells. In MLO-Y4 cells, sulfation of glycosaminoglycans led to a significant inhibition of osteocyte apoptosis, 42% inhibition for highly sulfated chondroitin sulfate and 58% for highly sulfated hyaluronan, respectively. Cell proliferation was not affected. While treatment with highly sulfated chondroitin sulfate increased cell viability by 20% compared to the native chondroitin sulfate. In UMR 106- 01 cells, treatment with highly sulfated hyaluronan reduced the receptor activator of nuclear factor-κB ligand/osteoprotegerin ratio by 58% compared to the non-sulfated form, whereas highly sulfated chondroitin sulfate led to 60% reduction in the receptor activator of nuclear factor-κB ligand/osteoprotegerin ratio in comparison to the native chondroitin sulfate. The expression of SOST, the gene encoding sclerostin, was reduced by 50% and 45% by highly sulfated hyaluronan and chondroitin sulfate, respectively, compared to their native forms. The expression of BMP- 2, a marker of osteoblast differentiation, was doubled after treatment with the highly sulfated hyaluronan in comparison to its native form. In conclusion, highly sulfated glycosaminoglycans inhibit osteocyte apoptosis in vitro and promote an osteoblast-supporting gene expression profile.