Abstract
Collagen type I is the main organic constituent of the bone extracellular matrix and has been used for decades as scaffolding material in bone tissue engineering approaches when autografts are not feasible. Polymeric collagen can be easily isolated from various animal sources and can be processed in a great number of ways to manufacture biomaterials in the form of sponges, particles, or hydrogels, among others, for different applications. Despite its great biocompatibility and osteoconductivity, collagen type I also has some drawbacks, such as its high biodegradability, low mechanical strength, and lack of osteoinductive activity. Therefore, many attempts have been made to improve the collagen type I-based implants for bone tissue engineering. This review aims to summarize the current status of collagen type I as a biomaterial for bone tissue engineering, as well as to highlight some of the main efforts that have been made recently towards designing and producing collagen implants to improve bone regeneration.
Highlights
Bone is one of the tissues with the highest intrinsic ability to repair itself after an injury.there are unfavorable scenarios in which an affected bone might not be able to repair itself successfully
Al-Ahmady and co-workers designed a collagen scaffold combined with platelet-rich fibrin and nanohydroxyapatite seeded with autologous bone marrow mononuclear cells for bone regeneration in a small clinical study with patients suffering from unilateral alveolar cleft defects
Collagen-based biomaterials have been loaded with bone morphogenetic protein (BMP) in combination with epidermal growth factor (EGF) [91], platelet-derived growth factor-BB (PDGF-BB) [92], insulin-like growth factor-1 (IGF-1) [93], or vascular endothelial growth factor (VEGF) [94,95] and in all these examples a clear and significant improvement in the respective bone regeneration models was reported in comparison to the administration of the BMP alone
Summary
Bone is one of the tissues with the highest intrinsic ability to repair itself after an injury. An autograft provides four biological elements of the so-called diamond concept (Figure 1) of bone healing: osteoinductive and pro-angiogenic molecular signals (growth factors, cytokines and other molecules), osteogenic cells (osteoblasts and skeletal precursors), and an osteoconductive matrix (formed mainly by collagen and hydroxyapatite (HA)). Using different types of digestion, demineralization, and heat denaturation, these authors showed that the osteoinductive properties of bone matrix are related to a protein fraction different than the helical portion of collagen. They named this protein bone morphogenetic protein (BMP) and, with their discovery, opened an entire field in skeletal development and regeneration research [28,29,30,31]. Certain BMPs, such as BMP-2, -4, -6, -7, and -9 have a great osteoinductive effect in different settings, both in vitro and in vivo [32]
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