In addition, we review current commercial biomedical applications of fibrin and collagen gels, as well as recent research of in vivo applications. In this paper, we will give an overview of modifications of collagen and fibrin hydrogels with natural and synthetic polymers leading to augmentation of mechanical properties. More detailed information about the classification of hydrogel materials and the preparation of hydrogels can be found in recent reviews. The resulting materials combine the inherent bioactivity of collagen and fibrin with tailor-made mechanical properties. To overcome these drawbacks, more stable materials can be achieved by blending with natural and synthetic polymers or by influencing the crosslink density. However, the production of collagen from these sources is still limited.ĭespite the fact that collagen and fibrin-based hydrogels are already widespread in clinical applications, in practice they display some disadvantages like mechanical instability or in the case of fibrin gels, rapid degradation. These include poultry as well as marine sources of collagen like fish, shark, jellyfish and marine sponges. As the extraction of biomedical material from mammalian tissue is always accompanied by concerns about the safety of the material, new sources have received attention in recent years. placenta) provides a good source of collagen. The most common materials are from a bovine or porcine origin but also discarded human tissue (e.g. Collagen biomaterial can be obtained from a variety of natural sources. When using extracted collagen, a fibrillar scaffold similar to the ECM can be formed by increasing the pH and temperature of the collagen solution. Native collagen polymerizes into fibrils on its own. It should be noted that the fibrinogen material for biomedical research is typically sourced from blood, which always carries a residual risk of pathogen transmission. Increased mechanical stability can be achieved by casting techniques leading to a compacted fibrin matrix. Polymerization can be influenced by temperature, as well as thrombin and fibrinogen concentrations. Further stabilization of this network is achieved by covalent crosslinking which is catalyzed by factor XIIIa (as reviewed in ). As a consequence, polymerization sites within the molecule are exposed, which leads to the polymerization of single fibrinogen molecules to a 3D fibrin network. Thrombin cleaves two small amino acid sequences in the amino-termini of the Aα and Bβ chain of the fibrin precursor fibrinogen. The formation of a hydrogel from fibrin is based on its natural polymerization process with thrombin following vascular injury. Fibrin and collagen are an ideal biomaterial for hydrogel scaffolds, because of their distinguished biocompatibility and cell adhesion capability. Both proteins serve as a scaffold for tissue regeneration and can promote the migration and ingrowth of cells. The fibrin matrix during wound healing provides attachment sites for cells, which in turn lay out a novel extracellular matrix, composed predominantly of collagen. The ECM serves as the mechanical framework for cells and tissues by providing adhesion molecules and growth factors. Collagen, as a major constituent of the ECM, adds to the mechanical strength and flexibility of different tissues, and contains important RGD binding sites. Fibrin plays an important role in wound healing, hemostasis and angiogenesis, and serves as a provisional matrix. Especially proteins from the extracellular matrix (ECM) like collagen or fibrin are promising candidates in the field of tissue implants due to their ability to mimic key biochemical factors vital for tissue regeneration. Ĭlassical hydrogels with excellent biocompatibility and bioactivity are natural, protein-based polymers like collagen, gelatine, silk fibroin and fibrin. The application of hydrogel scaffolds in tissue engineering and biomedicine has taken great steps since then. Langer and Vacanti gave an overview of the first hydrogels in tissue engineering. Materials like collagen, alginate and carrageenan were used as an immobilization matrix for fibroblasts and microbial cells. Complex reactions in a tissue-like system could not be properly investigated at the time. The first hydrogels used in the biomedical context appeared in the 1970s, when the need for a new material for cell cultivation was high.
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