Repair of a rodent nasal critical-size osseous defect with osteoblast augmented collagen gel

Administration of growth factors for bone regeneration

Growth factors (GFs) such as BMPs, FGFs, VEGFs and IGFs have significant impacts on osteoblast behavior, and thus have been widely utilized for bone tissue regeneration. Recently, securing biological stability for a sustainable and controllable release to the target tissue has been a challenge to practical applications. This challenge has been addressed to some degree with the development of appropriate carrier materials and delivery systems. This review highlights the importance and roles of those GFs, as well as their proper administration for targeting bone regeneration. Additionally, the in vitro and in vivo performance of those GFs with or without the use of carrier systems in the repair and regeneration of bone tissue is systematically addressed. Moreover, some recent advances in the utility of the GFs, such as using fusion technology, are also reviewed.

Matrices and scaffolds for delivery of bioactive molecules in bone and cartilage tissue engineering

Regeneration of bone and cartilage defects can be accelerated by localized delivery of appropriate growth factors incorporated within biodegradable carriers. The carrier essentially allows the impregnated growth factor to release at a desirable rate and concentration, and to linger at injury sites for a sufficient time to recruit progenitors and stimulate tissue healing processes. In addition, the carrier can be formulated to have particular structure to facilitate cellular infiltration and growth. In this review, we present a summary of growth factor delivery carrier systems for bone and cartilage tissue engineering. Firstly, we describe a list of growth factors implicated in repair and regeneration of bone and cartilage by addressing their biological effects at different stages of the healing process. General requirements for localized growth factor delivery carriers are then discussed. We also provide selective examples of material types (natural and synthetic polymers, inorganic materials, and their composites) and fabricated forms of the carrier (porous scaffolds, microparticles, and hydrogels), highlighting the dose-dependent efficacy, release kinetics, animal models, and restored tissue types. Extensive discussion on issues involving currently investigated carriers for bone and cartilage tissue engineering approaches may illustrate future paths toward the development of an ideal growth factor delivery system.

Biomineralization of polyanionic collagen–elastin matrices during cavarial bone repair

The polyanionic collagen-elastin matrices (PCEMs) are osteoconductive scaffolds that present high biocompatibility and efficacy in the regeneration of bone defects. In this study, the objective was to determine if these matrices are directly mineralized during the osteogenesis process and their influence in the organization of the new bone extracellular matrix. Samples of three PCEMs, differing in their charge density, were implanted into critical-sized calvarial bone defects created in rats and evaluated from 3 days up to 1 year after implantation. The implanted PCEMs were directly biomineralized by osteoblasts as shown by ultrastructural, histoenzymologic, and morphologic analysis. The removal of the implants occurred during the bone remodeling process. The organization of the new bone matrix was evaluated by image texture analysis determining the Shannon's entropy and the fractal dimension of digital images. The bone matrix complexity decreased as the osteogenesis progressed approaching the values obtained for the original bone structure. These results show that the PCEMs allow faster formation of new bone by direct biomineralization of its structure and skipping the biomaterial resorption phase.

Efficacy of polyanionic collagen matrices for bone defect healing

Polyanionic collagen-elastin matrices (PCEMs) possess attractive properties, such as extra negative charges, piezoelectricity, and extra RGD sites, which could make them effective in the treatment of bone defects. Although they are biocompatible with the osteogenesis process, it is unknown if PCEMs could aid in the recovery of bone defects in challenging situations. To evaluate this hypothesis, three PCEMs, differing in their negative charge density, were implanted in rat calvarial defects. Specimens harvested at 3, 7, 15, 30, and 60 days after implantation were evaluated radiographically and histologically. Two matrices were able to sustain the osteogenesis process and quickly recover the lost bone structure. The third, and most electronegative, left matrix remnants amidst the areas of new bone. The control showed bone formation limited to the boundaries of the defect. These results suggest that some PCEMs might become a useful resource in the treatment of bone defects.

Osteoinductive molecules in orthopaedics: basic science and preclinical studies

Osteoinductive molecules are characterized by their ability to promote the formation of bone. Most osteoinductive molecules are cytokines, which are extracellular proteins or peptides that mediate cell to cell signaling. Examples of osteoinductive cytokines are certain bone morphogenetic proteins and some growth and differentiation factors. Some osteoinductive molecules are not secreted molecules. LIM mineralization protein-1 is an example of an intracellular osteoinductive molecule. Significant advances have been made in characterizing the molecular composition and mechanism of action of these osteoinductive molecules. Preclinical studies with these molecules have provided better understanding of the doses, formulation, and delivery mechanism necessary for effective bone formation in model systems of spinal fusion and other orthopaedic problems. The current authors will review the most important basic science and preclinical studies involving these osteoinductive molecules.

Biocompatibility of anionic collagen matrix as scaffold for bone healing

The basic approach to the treatment of bone defects involves the use of scaffolds to favor tissue growth. Although several bioscaffolds have been proposed for this purpose, the search for new and enhanced materials continues in an attempt to address the drawbacks of the present ones. Modifying current materials can be a fast and cheap way to develop new ones. Among them, type I collagen allows its structure to be modified using relatively simple techniques. By means of an alkaline treatment, anionic collagen with enhanced piezoelectric properties can be obtained through hydrolysis of carboxyamides groups of asparagine and glutamine residues from collagen in carboxylic. The process applied to a raw source of collagen, bovine pericardium, provided a sponge-like structure, with heterogeneous pore size, and, moreover, the complete removal of interstitial cells. For the evaluation of the biocompatibility of such matrices, they were implanted in surgically created bone defects in rat tibias. Empty defects served as controls. This experimental model allowed a preliminary evaluation of the osteoconductiveness of the matrices. The histological results presented a low inflammatory response and bone formation within a short period of time, similar to that of controls. The low cost of production associated to the biocompatibility and osteoconductivity performance make the anionic collagen matrices promising alternatives for bone defects treatment.