Fracture non-unions and bone defects represent a recalcitrant problem in the field of orthopaedic surgery. Although the current gold-standard treatment, autologous bone grafting, has a relatively high success rate, the technique is not without serious problems. The emerging field of regenerative medicine may have the potential to provide an alternative treatment. One promising strategy involves the delivery of both cells and multiple growth factors with different release profiles. A range of scaffolds was developed from Poly( -caprolactone) (PCL), Poly(lactideco- glycolide) (PLGA), and two blends of PCL (Mn 42,500) and PLGA. The scaffolds were manufactured utilising a novel modified fused deposition modelling system, using polymer/dichloromethane solutions. The scaffolds were found to have pore sizes suitable for bone regenerative medical applications (373±9.5 μm in the Ydirection and 460±13 μm in the X-direction). However, the scaffolds were found to be only 52±3 μm in height. This means that the two-layer scaffolds were relatively flat. This was undesirable, as direct control of the complete 3D geometry was the favoured strategy, though it may not be a necessary requirement. Five scaffold coatings were also developed from alginate, chitosan (crosslinked using sodium hydroxide or tripolyphosphate), Type-I collagen and Type-A gelatin. The scaffold coatings were screened in vitro for their cell-compatibility with human marrow stromal cells (hMSCs), human osteoblasts and MG63 cells. This was assessed using an assay for cell death, and assessing total cell counts. From these studies, Type-I collagen was found to be the optimum coating. For hMSCs, their death rates were found to be 19.1±6.3% for alginate, 5.3±3.6% and 2.9±1.4% for chitosan crosslinked with tripolyphosphate and sodium hydroxide respectively, compared to 0.11±0.07% for Type-I collagen, and 0.15±0.13% and 0.16±0.12% for 0.1% and 0.2% gelatin respectively. Type-I collagen was found to be the most cellcompatible coating, as it was consistently associated with higher cell counts than Type-A gelatin. Similarly, PCL scaffolds vacuum dried for 1 hr were found to be cell-compatible. No detectable clinically significant difference was found in either total cell counts, or the proportion of cell death in; hMSCs exposed to PCL scaffolds processed with dichloromethane, hMSCs either exposed to scaffolds known to be biocompatible, or hMSCs cultured in the absence of scaffolds. When cell morphology was compared, scaffolds vacuum dried for 1 hr or more were found to have a similar morphology to the cells cultured in the absence of scaffolds. It was therefore concluded that a vacuum drying time of 1 hr was sufficient for cell-compatibility. The scaffold materials were screened both for their encapsulation efficiencies and release characteristics using the model drug, methylene blue. The encapsulation efficiency was found to be both relatively high and consistent for both Mn 42,500 and 80,000 PCL as well as PCL:PLGA 66:33, at 71±6%, 71±5%, and 78±10% respectively, relative to the low efficiencies recorded for both PCL:PLGA 66:33 and PLGA: 57±5% and 38±10% respectively. The release rate of methylene blue from PCL (Mn 42,500), was found to be relatively slow, controlled, and consistent between batches (between 21±2% and 20±3% released in the first 24 hr). Despite the release rate being consistent for PCL (Mn 80,000), the release rate was thought to be too high, since between 29±3% and 39±5% of the test compound was released in the first 24 hr period. The release rate of methylene blue from the PCL/PLGA blends (between 17±2% – 30±7% and 18±4% – 31±6% in the first 24 hr) and PLGA (between 7.1±3.4% – 9.3±2.9% in the first 24 hr) were found to be inconsistent, and low in the case of PLGA, even taking the different loading efficiencies into account. Therefore, PCL (Mn 42,500) was selected as the favoured candidate scaffold material. The loading content and release profiles from methylene blue loaded collagen scaffold coatings were also evaluated. The drug loading capacity was found to be suitable for use as a drug delivery system (65±5 μg/g of methylene blue per unit scaffold mass). The release of methylene blue was observed to be rapid (between 54±10% – 70±17% in the first 24 hr), which was thought to be desirable for the coating delivery system. Recombinant human bone morphogenetic protein-7 (rhBMP-7) was used as a representative growth factor of interest for bone regenerative medical applications. It was loaded in collagen scaffold coatings (CoatBMP 1.25) and encapsulated within PCL (Mn 42,500) scaffolds (ScaffBMP 1.25). Control coatings and scaffolds were designated CoatPBS and ScaffPBS respectively. Both delivery systems were found to release detectable quantities of rhBMP-7 (releasing 2.8±0.2 μg/g and 87±7 ng/g respectively in the first 24 hr), even after 14 days. The release rate of the growth factor from the scaffold coating was higher than that from the encapsulating scaffolds. However, the cumulative release profiles were found to deviate from the desired ideal release profiles, and burst release was observed from both delivery systems. Although differences were observed for the two delivery systems, this difference may not be of clinical significance. Nevertheless, scaffolds with less than ideal delivery properties may still be of potential clinical use. The bioactivity of the rhBMP-7 released from the test scaffolds was therefore assessed by quantifying the area of normalised ALP staining of hMSCs. The release of rhBMP-7 from the collagen coating of the PCL (Mn 42,500) scaffolds (CoatBMP 1.25ScaffPBS) was capable of statistically significantly increasing hMSC normalised ALP expression, although the actual differences were often relatively small. Therefore, at least a proportion of the growth factor released is likely to have been bioactive. The release from scaffolds encapsulating rhBMP-7 (CoatPBSScaffBMP 1.25) did not have this effect on the hMSCs, indicating that either the concentration released was too low, or the growth factor released was no longer bioactive. However, when the cells were seeded directly onto the scaffolds, the activity of ALP, normalised by a DNA assay, was statistically significantly increased for the CoatPBSScaffBMP 1.25 scaffolds, in hMSCs from all three test patient donors (by 35±10% on the control). ALP activity was also significantly increased in hMSCs from two of the three patients seeded onto CoatBMP 1.25ScaffBMP 1.25 scaffolds (by 39±10% on the control). ALP activity was only statistically significantly increased for one of the hMSC patients when seeded onto CoatBMP 1.25ScaffPBS scaffolds (by 35±14% on the control). The functional osteoinductive capacity of Type-I collagen coated PCL (Mn 42,500) scaffolds loaded with rhBMP-7 was assessed using C2C12 cells seeded onto the scaffolds, and quantified using qRT-PCR. The genes of interest were; Type-I collagen (Col1), osteopontin (OP), ALP, osteocalcin (OC) and runt related transcription factor 2 (Runx2). The CoatBMP 1.25ScaffPBS scaffolds had an early osteoinductive effect on the C2C12 cells, as ALP, OC and Runx2 were elevated during the first 2 days only, compared to the control (e.g. by 44±12%, 128±42%, 60±25% and 46±25% respectively at the 24 hr mark). The CoatPBSScaffBMP 1.25 scaffolds also had an osteoinductive effect on the cells, which was more sustained than that observed for the CoatBMP 1.25ScaffPBS group. While OP, ALP and Runx2 were up-regulated in the first 24 hr compared to the control (by 38±10%, 208±82% and 72±31% respectively), statistically significant up-regulation of the late marker OC was delayed until the 48 hr mark (by 73±49%). The effect was found to be sustained until day 7, when OC and Runx2 were both statistically significantly up-regulated compared to the control (by 151±91% and 93±27% respectively). The CoatBMP 1.25ScaffBMP 1.25 scaffolds were found to combine the early effect of the CoatBMP 1.25ScaffPBS scaffolds, with the more sustained effect of the CoatPBSScaffBMP 1.25 scaffolds. ALP, OC and Runx2 were all up-regulated at the 24 hr mark (by 312±56%, 329±39% and 96±25% respectively). This osteoinductive effect was sustained until day 7 when Col1, ALP and Runx2 were still up-regulated compared to the control (by 174±78%, 72±24% and 178±78% respectively). These data suggest that the scaffolds containing rhBMP-7 have a weak osteoinductive effect on the cells seeded onto them. The different delivery systems were found to affect the cells differently. The clinical significance of this was not assessed in these studies. 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) was used as a model drug to assess the feasibility of releasing lipid-soluble active factors from the scaffolds. This was assessed by quantifying the area of normalised ALP staining of hMSCs. The release of 1,25(OH)2D3 from the loaded collagen scaffold coatings and the encapsulating scaffolds significantly increased ALP expression compared to the control scaffold groups (by 115±28% and 69±25% respectively). Furthermore, ALP expression was significantly increased when the two delivery systems were used together, when compared to either delivery system on its own. These data suggest that the delivery of lipid-soluble active factors is feasible from collagen coated PCL scaffolds, and that the coating and encapsulating delivery systems are mutually compatible.

Polycaprolactone (PCL) is a biodegradable synthetic polymer that is currently used in a number of biomedical applications. A number of concerns have been raised over the toxicity of initiators commonly employed for the synthesis of PCL. Therefore, more biocompatible initiators have been studied. The biocompatibility of PCL, itself, is adequate; however, improved bioactivity is desirable for several applications. Copolymerisation, and incorporation of bioactive fillers can both be used as ways of enhancing the bioactivity of PCL. Therefore, the global objective of this project was to enhance the bioactivity of PCL by copolymerisation of PCL with poly(ethylene glycol) (PEG) using a biocompatible calcium-based initiator. This calcium-initiator was expected to leave potentially bioactive calcium-initiator residues in the synthesised copolymers. A study of the ring-opening polymerisation of epsilon-caprolactone (CL) in the presence of a poly(ethylene glycol) (PEG) / calcium hydride (CaH2) co-initiation system was performed. Polymerisation kinetics were monitored by following the degree of conversion of CL by Fourier transform-Raman (FT-Raman) spectroscopy and 1H nuclear magnetic resonance spectroscopy (NMR). Resultant PCL-b-PEG-b-PCL (PCL/PEG/PCL) triblock copolymers were analysed by NMR and gel permeation chromatography (GPC). The observed rates of polymerisation for the synthesis of PCL/PEG/PCL triblock copolymers using the PEG / CaH2 co-initiator were much lower than expected. 1H NMR and Raman microspectroscopy analysis showed that the concentration of the active calcium-PEG alkoxide was much lower than the initial feed concentration of PEG. Even so, the molecular weight of PCL/PEG/PCL triblock copolymers could be predicted from the CL : PEG feed ratio. This was found to be due to a fast reversible transfer process. Inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analysis of solutions containing acid digested, pure PCL/PEG/PCL copolymers showed calcium concentrations at equal to or greater than 77 % of the calcium feed concentration. These calcium-initiator residues were isolated and their structures confirmed by Fourier transform infrared-attenuated total reflectance spectroscopy (FTIR-ATR). They were found to be a mixture of calcium hydroxide (Ca(OH)2) and calcium carbonate (CaCO3). The effect of calcium-initiator residues on the in vitro mineralisation of PCL/PEG/PCL triblock copolymers, as well as the same effect on a model calcium-salt-doped PCL homopolymer system, was studied by immersion in simulated body fluid (SBF). In the model studied, PCL homopolymer was doped with low concentrations (0.2 - 2 w / w % Ca) of Ca(OH)2, or CaCO3. Results from the model study showed calcium phosphate (CaP) mineral deposition on Ca(OH)2-doped PCL, and not on CaCO3-doped PCL. This was attributed to the higher solubility of Ca(OH)2, compared to CaCO3. Minimal CaP deposition was observed on PCL/PEG/PCL triblock copolymers. This was attributed to the low Ca(OH)2 concentration in these samples. For all mineralised samples in the SBF studies, the formation of carbonated HAP was observed. Overall, the synthesis of PCL/PEG/PCL copolymers using the PEG / CaH2 co-initiator was found to be a suitable method for preparing reproducible materials. The calcium-based initiator was also found to have potential for increasing the bioactivity of PCL-based materials.

Bone is a dynamic tissue that in some cases, due to fractures, infection or interruption of blood supply, does not repair completely, leading to bone loss; therefore it is necessary to recur to bone grafts. However, bone grafts (i.e.autografts) may require additional surgery and present risks associated with potential disease transmission from donor to recipient (i.e.allografts). The limitations of these grafts have encouraged the pursuit of engineered alternatives that are based on the synchronous interplay between biomaterials, biological macromolecules and cells. 3-D gelatin-based scaffolds were prepared and evaluated for their ability to promote osteogenesis. Three types of gelatin based scaffolds were prepared via the crosslinking of gelatin B with glutaraldehyde or EDC/NHS in the presence or absence of PLG . The porosity and pore size of the scaffolds were controlled by varying the freeze-drying temperature (-20°C and -80°C). To promote osteogenesis, human stromal MIAMI cells were incorporated in the scaffolds. Results demonstrated MIAMI cells grew and spread actively throughout gelatin and gelatin/PLG scaffolds after 14 days of incubation. The rate of osteogenic activity was confirmed through histochemical staining for alkaline phosphatase and calcium. Mineral deposition was increased in the gelatin scaffold as opposed to the gelatin/PLG scaffold after at day 35.

The Spl polymorphism of the Collagen I alpha 1 gene has previously been associated with low bone density and increased risk of fracture in a number of clinical studies. In chapter 3 the association with fracture was shown to be driven by the Spl polymorphism rather than other single nucleotide polymorphisms located in and around the collagen I alpha 1 gene. In chapter 4, the relationship between the Spl polymorphism and osteoporotic fracture was determined in a prospective population study of men and women. This study confirmed the association between "s" alleles and fracture and showed that COLIA1 genotyping interacted significantly with bone density measurements to enhance prediction of individuals at risk of osteoporotic fracture. In chapter 5, the "s" allele was found to be associated with body size in a population study of young adults. Although there was no association with BMD, individuals who carried the "s" allele were lighter at birth and this trend continued through adolescence and into young adulthood. This suggests that "s" individuals are at increased risk of osteoporosis from an early age, since body size is, in itself a risk factor for osteoporosis. In chapter 6, the effect of Spl alleles on quantitative ultrasound (QUS) was determined in a young post-menopausal population. It was found that there were no significant genotype related differences in broadband ultrasound attenuation (BUA). In chapter 7, family studies were conducted using the quantitative transmission disequilibrium test (qTDT). This showed evidence of a polygenic effect on BMD at the spine and hip and confirmed evidence of an association between Spl "s" alleles and BMD at the femoral neck. The data suggests that the previous associations of Spl alleles and BMD are genuine and not due to population admixture.

No description available.

No description available.

Os princípios biológicos da regeneração óssea guiada (ROG) têm contribuído para o desenvolvimento de membranas que, em odontologia, são utilizadas em diversas situações como tratamentos com implantes dentários, aumento de rebordo alveolar e reparo de defeitos ósseos de origem traumática e patológica. Resultados de experimentos in vitro comparando a membrana obtida pela associação do polímero poli(fluoreto de vinilideno-trifluoretileno) e da cerâmica titanato de bário (P(VDFTrFE)/ BT) à membrana de politetrafluoretileno (PTFE) mostraram uma resposta favorável de osteoblastos, fibroblastos e queratinócitos à membrana de P(VDFTrFE)/ BT. O objetivo do presente estudo foi avaliar o efeito da membrana de P(VDFTrFE)/ BT sobre a formação óssea in vivo. Foram criados defeitos ósseos com 5 mm de diâmetro em calvárias de ratos machos Wistar (peso 200-250 g), distribuídos em três grupos com relação à utilização ou não de membranas nos defeitos ósseos: (1) membrana de P(VDF-TrFE)/BT; (2) membrana de PTFE; (3) nenhum tipo de membrana. Ao final de 4 e 8 semanas os animais foram eutanasiados e as amostras foram submetidas à: (1) análise por microtomografia computadorizada (micro-CT) para avaliar volume ósseo, superfície óssea, superfície óssea específica, número de trabéculas, separação trabecular e espessura trabecular, (2) análise histológica com base em cortes histológicos não descalcificados, (3) análise por reação em cadeia da polimerase em tempo real (PCR em tempo real) para avaliar a expressão gênica dos marcadores ósseos runt-related transcription factor 2 (RUNX2), fosfatase alcalina (ALP), sialoproteína óssea (BSP), osteocalcina (OC), osteoprotegerina (OPG) e receptor activator of nuclear factor-kappa B ligand (RANKL) e (4) análise da expressão de microRNAs (miRs) pela técnica de sequenciamento na plataforma Illumina. Os dados das análises morfométricas e da expressão gênica foram submetidos ao teste de Kruskal-Wallis, seguido pelo teste de Fischer quando apropriado, e para a análise da expressão de miRs foi utilizado o teste de Mann-Whitney para comparar a membrana de P(VDF-TrFE)/BT à de PTFE. Para todas as comparações o nível de significância adotado foi de 0,05. Os defeitos que não receberam a membrana tiveram uma formação óssea insignificante. Ambas as membranas favoreceram a formação óssea, sendo a superfície óssea maior sobre a membrana de P(VDF-TrFE)/BT comparada à de PTFE em 4 (p=0,01) e 8 (p=0,001) semanas e a separação trabecular maior sobre a membrana de PTFE comparada à de P(VDF-TrFE)/BT em 4 (p=0,05) e 8 (p=0,001) semanas. A expressão gênica de BSP (p=0,01), OC (p=0,001) e OPG (p=0,001) foi maior e de RANKL (p=0,001) foi menor sobre a membrana de P(VDFTrFE)/ BT comparada à de PTFE em 4 semanas. A expressão gênica de RUNX2 (p=0,001) e OC (p=0,05) foi maior e de ALP (p=0,05), RANKL (p=0,01) e OPG (p=0,001) foi menor sobre a membrana de P(VDF-TrFE)/BT comparada à de PTFE em 8 semanas. Quarenta e cinco e 13 miRs foram regulados positivamente (>2 vezes) em 4 semanas e 8 semanas, respectivamente, e 11 e 39 miRs foram regulados negativamente (>2 vezes) em 4 semanas e 8 semanas, respectivamente, pela membrana de P(VDF-TrFE)/BT comparada à de PTFE. Os resultados indicam que a membrana de P(VDF-TrFE)/BT favorece a formação óssea quando comparada à membrana de PTFE e, portanto, pode ser considerada um biomaterial promissor para ser utilizado em procedimentos de ROG. / Biological principles of guided bone regeneration (GBR) have contributed to development of membranes that, in dentistry, are used in several situations such as treatment with dental implants, alveolar bone augmentation and repair of traumatic and pathological bone defects. Results of in vitro experiments comparing membrane obtained by the combination of poly(vinylidene fluoride-trifluoroethylene) and barium titanate ceramics (P(VDF-TrFE)/BT) with polytetrafluoroethylene (PTFE) membrane showed a favorable response of osteoblasts, fibroblasts and keratinocytes to the P(VDF-TrFE)/BT membrane. The aim of this study was to evaluate the effect of P(VDFTrFE)/ BT membrane on in vivo bone formation. Bone defects with 5 mm in diameter were created in calvaria of male Wistar rats (weight 200-250 g), distributed into three groups regarding the use or not of membranes on defects: (1) P(VDF-TrFE)/BT membrane; (2) PTFE membrane; (3) no membrane. At the end of 4 and 8 weeks, the animals were euthanized and samples were subjected to: (1) computed microtomography analysis (micro-CT) to assess bone volume, bone surface, specific bone surface, trabecular number, trabecular thickness and trabecular separation; (2) histological analysis based on non-decalcified histological sections; (3) real time polymerase chain reaction (real time PCR) to evaluate gene expression of the bone markers runt-related transcription factor 2 (RUNX2), alkaline phosphatase (ALP), bone sialoprotein (BSP), osteocalcin (OC), osteoprotegerin (OPG) and receptor activator of nuclear factor-kappa B ligand (RANKL); (4) microRNAs (miRs) sequencing analysis at Illumina platform. Data from morphometric and gene expression analyses were submitted to the Kruskal-Wallis test followed by Fischer\'s test, when appropriate, and from miRs expression to the Mann-Whitney test to compare P(VDF-TrFE)/BT with PTFE membrane. For all comparisons, the significance level was 0.05. Defects without membrane exhibit a non significant bone formation. Both membranes favored osteogenesis with an increased bone formation on the P(VDF-TrFE)/BT membrane compared with PTFE at 4 (p=0.05) and 8 weeks (p=0.001). Trabecular separation was greater on PTFE membrane compared with the P(VDF-TrFE)/BT at 4 (p=0.05) and 8 weeks (p=0.001). At 4 weeks, the gene expression of BSP (p=0.01), OC (p=0.001) and OPG (p=0.001) were higher on P(VDF-TrFE)/BT membrane compared with PTFE, while RANKL (p=0.001) was lower. The gene expression of RUNX2 (p=0.001) and OC (p=0.05) were higher and ALP (p=0.05), RANKL (p=0.01) and OPG (p=0.001) were lower on the membrane of P(VDF- TrFE)/BT compared with PTFE at 8 weeks. Fortyfive and 13 miRs were up-regulated (> 2 fold) at 4 weeks and 8 weeks, respectively, and 11 and 39 miRs were negatively regulated (> 2 fold) at 4 weeks and 8 weeks, respectively, on the P(VDF-TrFE)/BT membrane compared with PTFE membrane. The results indicate that the P(VDF-TrFE)/BT membrane favors bone formation compared with PTFE membrane and, therefore, may be considered a promising biomaterial for using in GBR procedures.

Grandes defectos óseos constituyen un reto para el campo clínico, ya que no puede ser reparado por el propio organismo, sino que requieren la implantación de injertos de hueso adecuado. Para superar los inconvenientes de los injertos procedentes de fuentes autólogas o allogeneicas, la ingeniería de tejidos óseos pretende sustituir el tejido perdido utilizando el cultivo de células in vitro sobre biomateriales porosos. El cultivo de células en grandes andamios porosos ha demostrado ser difícil, que requiere bioreactores, que se utilizan para el cultivo de tejidos y el estudio del comportamiento de células en 3D de los andamios. De interés especial es el condicionamiento mecánico de los tejidos cultivados por bioreactor de la ingeniería del tejido óseo, que es capaz de aumentar el potencial osteogénico de los injertos sintéticos.En este trabajo, dos sistemas de bioreactores fueron desarrollados para permitir comprender las propiedades bioactivas de andamios de diferentes materiales y la mecanoregulación del comportamiento de células o tejidos. Un sistema de bioreactor de perfusión in vitro fue desarrollado para el sembrado y cultivo de células incorporadas en cilindros de un biomaterial poroso. Varios estudios para la determinación de los parámetros del sembrado de células aplicable se llevaron a cabo, así como experimentos de cultivo de células bajo flujo de fluido constante con una estimulación mecánica adicional por alternancia del flujo.Un sistema de cámara ósea fue desarrollado como un bioreactor in vivo. El sistema produjo un defecto óseo grande en tibias de perros y permitió la implantación repetida de grandes andamios porosos de materiales diferentes. El tejido creciendo en los andamios permite extraer conclusiones sobre las propiedades de osteoconductividad u osteinductividad de los andamios. Además, un dispositivo de compresión se ha desarrollado para aplicar cargas cíclicas en los andamios en vivo para estudiar el efecto de la estimulación mecánica en el desarrollo de los tejidos.Los estudios con el sistema de perfusión desarrollado han demostrado que el sembrado de células en grandes andamios porosos es posible, lo que se considera crucial para el cultivo celular. El largo tiempo de cultivo de células mostró la proliferación de las células madre mesenquimales hasta dos semanas. El patrón de estimulación utilizado en el estudio aumentó la expresión de la osteocalcina, lo que indica una mayor actividad de las células, pero la ausencia de expresión de RunX2 y colágeno I impidió la determinación concluyente de la diferenciación.El sistema desarrollado de la cámara ósea demostró su funcionalidad en el entorno quirúrgico durante los experimentos in vivo. Complicaciones durante los experimentos no permitieron la aplicación de las cargas cíclicas de los andamios implantados. La formación de hueso retrasada debido al defecto óseo creado y material de andamios restantes no permitieron conclusiones definitivas acerca de las propiedades del material del andamio. Sin embargo, el estudio proporciona datos para el desarrollo futuro del dispositivo y protocolo clínico.Los estudios realizados constituyen una novedad en respecto a la creación de bioreactores para el estudio de la andamios porosos sintéticos de grandes dimensiones in vitro e in vivo. Los sistemas desarrollados constituyen la base para otros estudios en mecanobiología de las células óseas y los tejidos. / Large bone defects constitute a challenge for the clinical field, because they cannot be repaired by the body itself, but require the implantation of suitable bone grafts. To overcome the drawbacks of grafts from autologous or allogous sources, modern bone tissue engineering aims to replace lost tissue by cultivating cells in vitro on porous biomaterials. The cell culture on large porous scaffolds has shown to be difficult, requiring bioreactors, which are used for tissue culture and the study of cell behaviour in 3D scaffolds. Of special interest is the mechanical conditioning of the cultured tissue for bioreactor-based bone tissue engineering, which is able to enhance the osteogenic potential of the synthetic grafts.In this work two bioreactor systems were developed to allow insight into bioactive properties of different scaffold materials and the mechanoregulation of cell or tissue behaviour. An in vitro perfusion bioreactor system was developed for the cell seeding and culture on porous biomaterial cylinders. Several studies for the determination of applicable cell seeding parameters were conducted, as well as experiments of cell culture under steady fluid flow with additional mechanical stimulation by alternating fluid flow. A bone chamber system was developed as an in vivo bioreactor. The system produced a large bone defect in dog tibia and allowed the repeated implantation of large porous scaffolds of different material compositions.The ingrowing tissue was observed to allow conclusions about osteoconductive or osteinductive properties of the scaffolds. Additionally a compression device was developed to apply cyclic loading on the scaffolds in vivo to study the effect of mechanical stimulation on tissue development.The studies with the developed in vitro perfusion bioreactor system have shown that it is possible to seed cells throughout large porous scaffolds, which is deemed crucial for the further cell culture. The long time cell culture showed the proliferation of mesenchymal stem cells up to two weeks. The stimulation pattern used in the study enhanced the expression of osteocalcin, indicating an enhanced cell activity, but the absence of RunX2 and collagen I expression rendered the determination of differentiation inconclusive.The developed bone chamber system proved to be functional in the surgical environment during the in vivo experiments. Occurring complications during the experiments did not allow the application of the cyclic loading of implanted scaffolds. Delayed bone formation due to created bone defect and remaining scaffold material did not allow final conclusions about the scaffold material properties. Nevertheless the study provides input for further development of the device and clinical protocol.The conducted studies constitute a novelty regarding the creation of bioreactors for the study of synthetic porous scaffolds of large dimensions in vitro and in vivo. The developed systems form the basis for further studies in mechanobiology of bone cells and tissue.

Bone grafts are used to treat more than 300,000 fracture patients yearly, as well as patients with congenital defects, bone tumors, and those undergoing spinal fusion. Given the established limitations of autograft and allograft bone, there is a substantial need for bone graft substitutes. Tissue engineering strategies employing the addition of osteogenic cells and/or osteoinductive factors to porous scaffolds represent a promising alternative to traditional bone grafts. While many bone defects are in load-bearing sites, very little is known about the response of bone grafts and their substitutes to mechanical loading, despite vast documentation on the ability of normal bone to adapt to its mechanical environment. The goal of this research was to quantify the effects of controlled in vivo mechanical stimulation on bone graft repair and bone graft substitutes and identify the local stress/strain environment associated with load-induced changes in bone formation. The global hypothesis that cyclic in vivo mechanical loading improves mineralized matrix formation within bone grafts and bone graft substitutes was addressed in this work using orthotopic and ectopic models specifically designed to facilitate modeling of local stresses and strains. In the first study, a bone defect repair model utilizing an orthotopic implant capable of supplying a controlled mechanical stimulus to a trabecular allograft showed a significant reduction in new bone formation with controlled in vivo mechanical loading. Although the reason remains unclear, loading conditions may not have been ideal for increased bone formation or potential micromotion may have influenced the results. A second study demonstrated for the first time that controlled in vivo mechanical stimulation enhances mineralized matrix production on a mesenchymal stem cell-seeded polymeric construct using a novel subcutaneous implant system. In addition, the local stresses and strains associated with this adaptive response were predicted. The novel subcutaneous implant represents technology which may be adapted for the preparation of tissue-engineered bone constructs, capitalizing on the benefits of mechanical loading and a vascularized in vivo environment. Such an approach may produce larger, stronger, and more homogeneous constructs than could be developed in a static culture system subject to diffusional limitations.

Currently, organ transplant procedures are insufficient to address the needs of the number of patients that suffer of organ failure related disease. In the United States alone, only around 19% of the patients are able to get an organ transplant surgery and 25% die while waiting for a suitable donor. Tissue engineering (TE) has emerged as an alternative to organ transplant; thus, the aim of the present study was to validate a poly(ethylene glycol) diacrylate (PEG-DA) hydrogel system as a model for material scaffolding in TE applications. This work explores the influence of scaffold material properties on cell behavior. Specifically, scaffold modulus, mesh size, and biochemical stimuli were characterized and their influence on cell response was analyzed at the biochemical, histological and microenvironmental levels. Three different TE targets were evaluated: vocal fold restoration, vascular grafts and osteochondral applications. Vocal fold fibroblast (VFF) phenotype and extracellular matrix (ECM) production were impacted by initial scaffold mesh size and modulus. The results showed increasing levels of SM-α-actin and collagen production with decreasing initial mesh size/increasing initial modulus, which indicated that VFFs were induced to take an undesirable myofibroblast-like phenotype. In addition, it was possible to preserve VFF phenotype in long-term cultured hydrogels containing high molecular weight hyaluronan (HAHMW). On the other hand, regarding vascular graft applications, smooth muscle cell (SMC) phenotype was enhanced by increasing scaffold mesh size and modulus. Finally, the effect of scaffold inorganic content (siloxane) on rat osteoblasts and mouse mesenchymal stem cells was evaluated. Interestingly, the impact of inorganic content on cell differentiation seemed to be highly dependent on the initial cell state. Specifically, mature osteoblasts underwent transdifferentiation into chondrocyte-like cells with increasing inorganic content. However, Mesenchymal stem cells appeared to be preferentially driven toward osteoblast-like cells with an associated increase in osteocalcin and collagen type I production.