The loss of regenerative capacity of bone, from fetal to adult to aged animals, has been attributed not only to a decline in the function of cells involved in bone formation but also to alterations in the bone microenvironment that occur through development and aging, including extracellular matrix (ECM) composition and growth/trophic factor content. In the development of novel treatments for bone repair, one potential therapeutic goal is the restoration of a more regenerative microenvironment, as found during embryonic development. One approach to creating such a microenvironment is through the use of stem cells. In addition to serving as a differentiated cell source, pluripotent stem cells, such as embryonic stem cells (ESCs), may possess the unique potential to modulate tissue environments via local production of ECM and growth factors. ESC-produced factors may be harnessed and delivered to promote functional tissue regeneration. Such an approach to generate a naturally derived, acelluar therapy has been employed successfully to deliver osteoinductive factors found within adult bone, in the form of demineralized bone matrix (DBM), but the development of treatments derived instead from developing, more regenerative tissues or cells remains attractive. Furthermore, the derivation of regenerative materials from an ESC source also presents the added benefit of eliminating donor to donor variability of adult, cadaveric tissue derived materials, such as DBM. Thus, the objective of this project was to examine the osteoinductive potential harbored within the embryonic microenvironment, in vitro and in vivo. The osteogenic differentiation of mouse ESCs as embryoid bodies (EBs) was evaluated in response to phosphate treatment, in vitro, including osteoinductive growth factor production. The osteoinductivity of EB-derived material (EBM) was then compared to that of adult tissue-derived DBM, in vivo. Phosphate treatment enhanced osteogenic differentiation of EBs. EBM derived from phosphate treated EBs retained bioactive, osteoinductive factors and induced new bone formation, demonstrating that the microenvironment within osteogenic EBs can be harnessed in an acellular material to yield in vivo osteoinductivity. This work not only provides new insights into the dynamic microenvironments of differentiating stem cells but also establishes an approach for the development of an ESC-derived, tissue specific therapy.

Bone consists of collagen/hydroxyapatite (HA) composites in which poorly crystalline carbonated calcium phosphate is intercalated within the fibrillar structure. Normal bone mineral is a carbonated-apatite, but there are limited data on the effect of mineral containing carbonate on cell response. Although the exact biological role of silicate in bone formation is unclear, silicate has been identified at trace levels in immature bone and is believed to play a metabolic role in new bone formation. To mimic the inorganic and organic composition of bone we have developed a variety of bone graft substitutes. In the present body of research, we characterized the surface composition of human cortical and trabecular bone. When then characterized the surface compositions of the following potential bone substitutes: carbonated hydroxyapatite (CO₃²-HA), silicated hydroxyapatite (Si-HA), and collagen sponges mineralized with calcium phosphate using the polymer-induced liquid-precursor (PILP) process. In the latter substitutes, the PILP process leads to type I collagen fibrils infiltrated with an amorphous mineral precursor upon which crystallization leads to intrafibrillar HA closely mimicking physiological bone mineral. We then determined the osteoblast-like cell response to each bone substitute to characterize the substrate’s effect on osteoblast differentiation. The observations collectively indicate that cells are sensitive to the formatting of the mineral phase of a bone substitute and that this format can be altered to modulate cell behavior.

Tissue engineering is limited by inability to create early and adequate blood supply. In-vivo DCE-MRI has imaged angiogenesis in soft tissues, yet has not been considered in hard tissues. Bilateral critical defects created in parietal bones of eighteen adult rabbits were left void, treated with haluronic acid acellular matrix (HA-ACM), or HA-ACM impregnated with vascular endothelial growth factor (VegF). DCE- MRI was acquired at weeks 1,2,3,6, and 12. Histologic analysis of HA-ACM treated defects demonstrated quantitatively greater immature bone formation, increased quantity and larger blood vessels compared to void. Statistically significant greater angiogenesis evidenced by quantitative perfusion on MRI supported histologic findings. DCE MRI is a novel means of imaging angiogenesis in grafted bone defects. DCE-MRI discerns physiologically important phases of angiogenesis: Initial vasoactive response, vessel network initiation, establishment, and pruning. DCE-MRI is adaptable to non-invasive study of candidate tissue engineered constructs and in evaluating scaffolds and treatments on angiogenesis.

Tissue engineering is limited by inability to create early and adequate blood supply. In-vivo DCE-MRI has imaged angiogenesis in soft tissues, yet has not been considered in hard tissues. Bilateral critical defects created in parietal bones of eighteen adult rabbits were left void, treated with haluronic acid acellular matrix (HA-ACM), or HA-ACM impregnated with vascular endothelial growth factor (VegF). DCE- MRI was acquired at weeks 1,2,3,6, and 12. Histologic analysis of HA-ACM treated defects demonstrated quantitatively greater immature bone formation, increased quantity and larger blood vessels compared to void. Statistically significant greater angiogenesis evidenced by quantitative perfusion on MRI supported histologic findings. DCE MRI is a novel means of imaging angiogenesis in grafted bone defects. DCE-MRI discerns physiologically important phases of angiogenesis: Initial vasoactive response, vessel network initiation, establishment, and pruning. DCE-MRI is adaptable to non-invasive study of candidate tissue engineered constructs and in evaluating scaffolds and treatments on angiogenesis.

Objective: Injuries to the marrow cavity result in rapid bone formation followed by regeneration of the marrow. It is not known whether this process is affected by age, although the quality of marrow is markedly different in young and old animals. To test if marrow restoration differs with age, we used the rat tibial bone marrow ablation model, which has been used to examine calcification, osteointegration of metal implants, and remodeling of bone graft substitutes. Methods: Marrow was ablated in the left tibia of seven rats (rNu/rNu) per time point. At 0,7,14,21,28,35 and 42 days post-surgery, treated tibias and contralateral tibias were harvested and fixed in buffered formalin. Both tibias were scanned using microCT and trabecular and cortical BVF/TV calculated. Mid-sagittal sections of decalcified bones were stained with H&E and BVF/TV calculated. Results: MicroCT analysis of 1-month animals showed increased bone formation on day-7 and on day-21 the marrow was restored. Increased bone was seen in 3-month animals on day-7 and day-14, but it was significantly less than in 1-month rats. By day-21, trabecular bone was reduced by 50%. 10-month animals had less trabecular bone at day-7 and 14, but bone remained in the medullary canal through day-1. Histomorphometry indicated that bone formation peaked at day-7 in 1-month rats with remodeling underway by day-14. Bone formation in 3-month rats also peaked at day-7, but restoration occurred by day-21. However, in 10-month rats, peak bone occurred on day-14, with remodeling on day-28. Conclusions: Aged animals produced less primary bone than younger animals and remodeling was initiated later. Differences in micro-CT and histomorphometric analyses may reflect a reduction in calcification of the osteoid in the 10-month old animals. (Supported by Boston Scientific, Inc.)

Thesis (Ph.D.)--University of Alabama at Birmingham, 2009. / Title from first page of PDF file (viewed on June 11, 2009). Includes bibliographical references.

Thesis (M.S.)--Duquesne University, 2004. / Title from document title page. Abstract included in electronic submission form. Includes bibliographical references (p. 55-60) and index.

Thesis (M.S.)--University of Alabama at Birmingham, 2006. / Title from first page of PDF file (viewed Oct. 30, 2007). Page 55 blank. Includes bibliographical references (p. 52-54).

Orientador: Leila Aparecida Chiavacci / Coorientador: Rosemary Adriana Chierici Marcantonio / Banca: Eduardo Ferreira Molina / Banca: Luis Carlos Spolidorio / Banca: Marlus Chorilli / Banca: Luís Geraldo Vaz / Resumo: A técnica de Regeneração Óssea Guiada (ROG) auxilia a restauração do tecido ósseo impedindo a concorrência entre as células do tecido ósseo e as células dos tecidos moles pelo uso de membranas; entretanto, não existe no mercado uma membrana osteoindutora. O peptídeo de crescimento osteogênico (OGP) atua como estimulador hematopoiético, promovendo a diferenciação osteoblástica e é um bom candidato para ser incorporado em membranas. Sendo assim, o objetivo deste trabalho foi desenvolver membranas a partir de materiais híbridos contendo OGP para otimizar a ROG. Para o desenvolvimento das membranas, foram utilizadas misturas de três polímeros, sendo dois à base de polióxido de etileno (POE) de massa molecular 500 e 1900 g mol-1 e um à base de polióxido de propileno (POP) de massa molecular 400 g mol-1. Diferentes métodos de esterilização foram utilizados. A caracterização dos materiais foi realizada pelas técnicas de calorimetria exploratória diferencial (DSC), espalhamento de raios-x a baixo ângulo (SAXS), análise mecânica dinâmica (DMA), determinação do pH e microscopia de força atômica (MFA). O OGP foi sintetizado pelo método em fase sólida, purificado por HPLC e caracterizado por espectrometria de massas. Os resultados de esterilização revelaram que a radiação gama a 24 kGy não alterou a estrutura do material, confirmado pelo DSC. A técnica de SAXS revelou a homogeneidade estrutural da matriz, assim como, a nano distância entre os entre os "nós" de silício. Os resultados de D... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The Guided Bone Regeneration (GBR) technique helps to restore bone tissue through the principle of cellular selectivity, i.e., excluding the epithelium and connective tissues from the damaged area by the use of membranes; However, there is no osteoinductive membrane on the market. The osteogenic growth peptide (OGP) acts as a hematopoietic stimulator, promoting osteoblastic differentiation and is a good candidate to incorporated into membranes. Therefore, the objective of this work was to develop membranes from hybrid materials containing OGP to optimize GBR. For development of the membranes, blends of three polymers were used, being two poly oxide ethylene (POE) of molecular weight 500 and 1900 g mol-1 and one based on poly oxide propylene (POP) of molecular mass 400 g Mol-1. Different methods of sterilization were used. The characterization of the materials was performed by differential scanning calorimetry (DSC), small angle x-ray scattering (SAXS), dynamic mechanical analysis (DMA), pH determination and atomic force microscopy (AFM). OGP was synthesized by the solid phase method, purified by HPLC and characterized by mass spectrometry. Sterilization results revealed that gamma radiation at 24 kGy did not change the structure of the material, as confirmed by the DSC. The SAXS technique revealed the structural homogeneity of the matrix, as well as the nano distance between the "nodes" of silicon. The DMA results showed that the membranes were not ruptured when submitted to ... (Complete abstract click electronic access below) / Doutor

Le premier objectif de notre travail est de caractériser l'évolution temporelle de proprié-tés structurales et mécaniques de matériau osseux régénéré et immature sur un grand volume.Nous avons étudié ce tissu en évolution lors de sa genèse dans un environnement mécanique contrôlé. Pour caractériser l'évolution temporelle des propriétés mécaniques de ce tissu, à partir d'un modèle animal, nous mettons en place une étude couplant essais mécanique d'indentation,observations macroscopiques et étude histologique. Cette méthodologie combinée donne des informations complémentaires à différentes échelles : macroscopique par simple observation,mésoscopique avec les tests d'indentation et microscopique avec l'histologie. Le tissu osseux ré-généré évolue d'un matériau homogène, visqueux et souple vers un matériau hétérogènes, plus rigide et moins visqueux. D'un point de vue biologique, l'organisation cellulaire part d'un amas de nombreuses cellules et progresse vers une structure plus proche de celle de l'os. Mécanique et biologie révèlent une évolution similaire : d'abord le régénérat grossit, puis il se différencie en tissu ostéochondral et finalement, la calcification commence. Les résultats biologiques confirment les études de la littérature et les résultats mécaniques donnent les premières valeurs de caractéristiques mécaniques de ce tissu avec le module d'Young réduit.Le deuxième objectif de cette étude est de développer une bioprothèse avec un biomatériau biodegradebable afin de régénérer un défaut d'os de taille critique. Notre étude est originale carelle propose d'utiliser le biomatériau comme tuteur de la régénération. Une étude préliminaire a été menée avec un modèle animal et un biomatériau céramique phosphocalcique. De premiers résultats encourageant ont été obtenus mais le processus clinique reste à concrétiser. / The first objective of our work was to experimentally characterise the temporal evolutionof the structural and mechanical properties of large volume immature regenerated tissues. Westudied these evolving tissues from their genesis in controlled mechanical conditions. To characterizethe temporal evolution of mechanical properties, based on animal model, we carried outindentation tests coupled with macroscopic examinations and histological studies. This combinedmethodology yielded a range of information on osteogenesis at different scales : macroscopic bysimple observation, mesoscopic by indentation test and microscopic by histological study. Resultsallowed us to identify different periods, providing a link between biological changes and materialproperty evolution in bone tissue regeneration. The regenerated tissue evolves from a viscous,homogeneous, soft material to a heterogeneous stiffer material endowed with a lower viscosity.From a biological point of view, cell organization progresses from a proliferated cell clot to a maturestructure closer to that of the bone. During the first seven days, mechanical and biologicalresults revealed the same evolution : first, the regenerated tissue grew, then, differentiated into anosteochondral tissue and finally calcification began. While our biological results confirm those ofother studies, our mechanical results provide the first experimental mechanical characterizationby reduced Young's modulus of such tissue.In a second time,we develop a bioprothesis with a biodegradebable biomaterial to regenerate acritical size bone defect. Our study is original because it proposes to use the biomaterial to initiatethe regeneration. A study was performed with an animal model and phosphocalcic ceramic.First observation gave some encouraging results but the clinical process should be realized