In cases of compromised bone remodeling like osteoporosis, insufficient osseointegration occurs and results in implant failure. Implant retention relies on proper secondary fixation, which is developed during bone remodeling. This process is disrupted in metastatic bone diseases like osteoporosis. Osteoporosis is characterized low bone mass and bone strength resulting from either accelerated osteoclast-mediated bone resorption or impaired osteoblast-mediated bone formation. These two processes are not independent phenomena. In fact, osteoporosis can be viewed as a breakdown of the cellular communication connecting bone resorption to bone formation. Because bone remodeling occurs at temporally generated specific anatomical sites and at different times, local regulators that control cross-talk among the cells of the BRU are important. Previous studies show Ti implant surface characteristics like roughness, hydrophilicity, and chemistry influence the osteoblastic differentiation of human MSCs and maturation of OBs. Furthermore, microstructured Ti surfaces modulate the production of factors shown to be important in the reciprocal communication necessary for the maintenance of healthy bone remodeling. Semaphorin signaling proteins are known to couple the communication of osteoblasts to osteoclasts and are capable of stimulating bone formation or bone resorption depending on certain cues. Implant surface properties can be optimized to exploit these effects to favor rapid osseointegration in patients with osteoporosis.

Lower respiratory diseases are currently the third leading cause of death worldwide. For many end-stage patients with these diseases, there is no cure and a shortage of donor organs available for transplant. A promising solution is to design regenerative scaffolds or complete bioengineered lungs, using decellularized lung tissues as a template for regeneration. Recent advances in the field have made significant strides towards developing a transplantable lung. However, the current technology has not produced a functional lung for in vivo transplant due to immature gas exchange barriers. The mechanisms driving alveolar barrier maturation and role that extracellular matrix (ECM) plays within the strengthening of each type of junction are not fully understood. This research has characterized and tailored a decellularized ECM (dECM) coating for the in vitro study of dECM component depletion and potential effects on cell barrier function, attachment, and survival. Adjustments to dECM digestion duration drastically changed the resulting structural and biochemical properties for each cellular microenvironment. Shorter digestion time resulted in a dense branching of the ECM architecture and biomimetic mechanical properties needed for epithelial culture. Also, through systematic supplementation of essential basement membrane (BM) proteins to dECM, we have found that supplementation with laminin enhanced barrier strength by ZO-1 junction stabilization. This indicates that dECM can promote barrier formation but may have lost vital proteins that need to be replenished. Laminin-mediated barrier function was determined to be caused by the upregulation of the Epac/Rap1 pathway. This pathway has previously been implicated in lung endothelial barriers but not alveolar epithelial junction strengthening. Finally, to establish the translatability of these findings to whole lung recellularization, the dECM coating was used to pre-treat the airways of decellularized lungs for recellularization. Culture of MLE12 mouse epithelial cells into dECM-coated lungs increased cell survival and distribution. In combination with dECM coatings, rotational cell seeding improved cell dispersal and viability. Altogether, these techniques, devised to promote healthy alveolar barriers, are vital to enhancing current lung recellularization strategies and the treatment of many edema-associated pulmonary diseases.

Silicon carbide (SiC) has been used for centuries as an industrial abrasive and has been actively researched since the 1960's as a robust material for power electronic applications. Despite being the first semiconductor to emit blue light in 1907, it has only recently been discovered that the material has crucial properties ideal for long-term, implantable biomedical devices. This is due to the fact that the material offers superior biocompatibility and hemocompatibility while providing rigid mechanical and chemical stability. In addition, the material is a wide-bandgap semiconductor that can be used for optoelectronics, light delivery, and optical sensors, which is the focus of this dissertation research. In this work, we build on past accomplishments of the USF-SiC Group to develop active SiC-based Brain Machine Interfaces (BMIs) and develop techniques for coating other biomaterials with amorphous SiC (a-SiC) to improve device longevity. The work is undertaken to move the state of the art in in vivo biomedical devices towards long term functionality. In this document we also explore the use of SiC in other bio photonics work, as demonstrated by the creation of the first reported photosensitive capacitor in semi-insulating 4H-SiC, thus providing the mechanism for a simple, biocompatible, UV sensor that may be used for biomedical applications. Amorphous silicon carbide coatings are extremely useful in developing agile biomaterial strategies. We show that by improving current a-SiC technology we provide a way that SiC biomaterials can coexist with other materials as a biocompatible encapsulation strategy. We present the development of a plasma enhanced chemical vapor deposition (PECVD) a-SIC process and include material characterization analysis. The process has shown good adhesion to a wide variety of substrates and cell viability tests confirm that it is a highly biocompatible coating whereby it passed the strict ISO 10993 standard tests for biomaterials and biodevices. In related work, we present a 64-channel microelectrode array (MEA) fabricated on a cubic 3C-SiC polytype substrate as a preliminary step in making more complex neurological devices. The electrode-electrolyte system electrical impedance is studied, and the device is tested against the model. The system is wire-bonded and packaged to provide a full neural test bed that will be used in future work to compare substrate materials during long-term testing. Expanding on this new MEA technology, we then use 3C-SiC to develop an active, implantable, BMI interface. New processes were developed for the dry etching of SiC neural probes. The developed 7 mm long implantable devices were designed to offer four channels of single-unit electrical recording with concurrent optical stimulation, a combination of device properties that is indeed at the state-of-the-art in neural probes at this time. Finally, work in SiC photocapacitance is presented as it relates to radio-frequency tuning circuits as well as bio photonics. A planar geometry UV tunable photocapacitor is fabricated to demonstrate the effect of below-bandgap optical tuning. The device can be used in a number of applications ranging from fluorescence sensing to the tuning of antennas for low-power communications. While technology exists for a wide variety of in vivo interfaces and sensors, few active devices last in the implantable environment for more than a few months. If these devices are going to reach a long-term implant capability, use of better materials and processing strategies will need to be developed. Potential devices and strategies for harnessing the SiC materials family for this very important application are reviewed and presented in this dissertation to serve as a possible roadmap to the development of advanced SiC-based biomedical devices.

Conventional glass ionomer cements (GICs), which continue to gain acceptance as superbly biocompatible dental materials, were first released in the early 1970s as a result of research into combining the advantages of silicate cements and polyalkenate cements. The chemistry of GICs is based upon the aqueous reaction between an ion-leachable fluoride glass and polyacid which yields the final cross-linked insoluble ionomer (ionic polymer). The significant advantages of GICs include direct adhesion to tooth structures, fluoride release, minimal dimensional change on curing, significant ease of use and superb biocompatibility, to the extent that affected proximal tooth structures may be retained, remineralised , and strengthened against further caries. GICs have, however, been unfavourably compared with other restorative materials in their mechanical properties and setting characteristics, in particular their relative weakness, the time limitations for the acid-base reaction to proceed to acceptable maturity, and the susceptibility of the immature cement to water sorption or desiccation.

This thesis deals with the differential response of healthy and cancerous cells to surface topography at the nanoscale and the microscale. Using a statistical method we developed we studied the interactions of cells with grooves of nanoscale depth. We demonstrate that healthy cells have a greater ability to align with deeper grooves, whereas cancerous cells are more sensitive to shallow grooves. Analysis reveals that the nucleus follows the alignment of the cell body more closely in cancerous cells, and that the nucleus of cancerous cells is more sensitive to shallow grooves.On microscale pillars we demonstrate for the first time that osteosarcoma cells deform to adopt the surface topography and that the deformation extends to the interior of the cell and in particular to the nucleus. We show that healthy cells only deform during the initial stages of adhesion and that immortalized cells show intermediate deformation between the healthy and cancerous cells. When the spacing between the pillars is reduced, differences in the deformation of different cancerous cell lines are detected. Deformation was also found to be related to the malignancy in keratinocytes, and related to the expression of Cdx2 in adenocarcinoma. The mechanism of deformation is tentatively attributed to the cytoskeleton and attempts to identify the main actors of deformation were performed using confocal microscopy and cytoskeleton inhibitors. Live cell imaging experiments reveal that the deformed cells are very mobile on the surfaces, loss of deformation is necessary for mitosis to occur and deformation after mitosis is more rapid than initial deformation upon adhesion to surfaces.

<p>This thesis describes a new <i>in vitro</i> slide chamber model that makes it possible to conduct studies of molecular and cellular interactions between whole blood and biomaterials. The model proved to be a suitable tool for detection of cell and platelet binding to a biomaterial surface. It was possible to monitor activation of the blood cascade systems and cells in the fluid phase and detect surface-bound molecules.</p><p>One finding was that thrombin generation is primarily triggered by FXII on a biomaterial surface since corn trypsin inhibitor, inhibited thrombin generation in blood.</p><p>Another finding was that thrombin generation was dependent on variety types of blood cells, since thrombin generation was almost negligible in platelet-rich plasma. When various preparations of blood cells were used to reconstitute platelet-rich and platelet-poor plasma, erythrocytes were shown to be the most efficient cell type in triggering thrombin generation. Inhibition of platelet aggregation with aspirin and Ro44-9883 was associated with a decrease in thrombin generation, confirming that platelet activation is necessary for normal coagulation activation. These findings suggest that the central events consist of an initial low-grade generation of thrombin that involves erythrocytes and possibly leukocytes which leads to activation of platelets; and a second platelet-dependent amplification loop that produces most of the thrombin.</p><p>Titanium exposed to whole blood produced high amounts of thrombin. Stainless steel and PVC, generated lower amounts. This indicates that titanium might be less suitable as a biomaterial in devices that are in direct contact with blood for prolonged time. Considering the superior osteointegrating properties of titanium and titanium's response to blood, a correlation between high thrombogenicity and good osteointegration seems to exist.</p><p>Compstatin, that binds to complement component C3, effectively inhibited the generation of C3a and sC5b-9 and the binding of C3/C3 fragments to the surface. Our results suggest that a biomaterial is able to activate complement through both the classical and alternative pathways and that the classical pathway alone is able to maintain a substantial bioincompatibility reaction. The results show that complement activation is a prerequisite for activation and binding of PMNs to the surface in the <i>in vitro</i> model.</p>

A suitable management of the pharmaceutical property is needed and helpful to design a desired nanoparticulate delivery system, which includes the carrier nature, particle size and size distribution, morphology, surfactant stabiliser according to the technique applied, drug-loading ratio and encapsulation efficiency, surface property, etc. All will influence the in vitro release, in vivo behaviour and tissue distribution of administered particulate drug loaded nanoparticles. The main purpose of the present work was to determine the effect of drug loading ratio when employing TPGS as surfactant stabiliser and/or matrix material to improve the nanoparticulate formulation. The model drug employed was paclitaxel. / Singapore-MIT Alliance (SMA)

This dissertation presents material design strategies to investigate cell-biomaterial interactions on specific biocompatible polymers and polymer blends by using mouse pre-osteoblastic MC3T3 cells aiming for potential applications in bone tissue engineering. Chapter 1 reviews some related background knowledge including polymeric biomaterials for tissue engineering, cell-biomaterial interaction, synthetic photo-crosslinkable and degradable polymers, and the effect of surface features on osteoblast cell responses. Chapter 2 presents photo-crosslinkable composites of poly(propylene fumarate) (PPF), an injectable and biodegradable polyester, and methacryl-polyhedral oligomeric silsesquioxane (mPOSS), which has eight methacryl groups tethered with a cage-like hybrid inorganic-organic nanostructure, for bone tissue engineering applications. Blending mPOSS with PPF was found to decrease the viscosity of PPF, expedite photo-crosslinking process, increase tensile modulus and accelerate hydrolytic degradation of crosslinked PPF/mPOSS while it did not significantly alter surface wettability, protein adsorption, and cell response. Chapter 3 demonstrates a polymer blend composed of amorphous PPF and semicrystalline poly(ε-caprolactone) (PCL), a widely used biocompatible and biodegradable polymer, in both uncrosslinked and photo-crosslinked forms. Thermal, rheological, mechanical properties as well as surface hydrophilicity and morphology can be well controlled by crosslinking density and crystallinity. Distinct cell attachment, spreading, and proliferation have been found to PPF/PCL blends in the presence or absence of cross-links. Chapter 4 and 5 describe the crystallization induced banded spherulitic morphologies in PPF/PCL blends and PCL homo-blends and their preliminary biological evaluation. Thermal properties, crystallization kinetics, and surface morphology of these blends can be regulated by isothermal crystallization temperature and composition. Surface roughness has been found to play an important role in influencing protein adsorption and cell response. Chapter 6 introduces a newly synthesized biodegradable elastomer, poly(ε-caprolactone) triacrylate (PCLTA), with two different molecular weights resulting in distinct mechanical properties at physiological temperature. Using replica molding from silicon wafers, photo-crosslinked PCLTA substrates with concentric micro-grooves have been successfully fabricated. MC3T3 cell attachment, proliferation, and differentiation could be better supported by stiffer substrates while not significantly influenced by micro-groove dimensions. Cell orientation, nuclei shape and localization, mineralization, and gene expression level of osteocalcin have been found to be more significant on narrower micro-grooves when groove depth was 10 μm.

Chitosan is widely investigated for biomedical applications due to its excellent properties, such as biocompatibility, biodegradability, bioadhesivity, antibacterial, etc. In the field of neural engineering, it has been extensively studied in forms of film and hydrogel, and has been used as scaffolds for nerve regeneration in the peripheral nervous system and spinal cord. One of the main issues in neural engineering is the incapability of neuron to attach on biomaterials. The present study, from a new aspect, aims to take advantage of the bio-adhesive property of chitosan to develop chitosan-based materials for neural engineering, specifically in the fields of brain repair and neuroprosthetics. Neuronal responses to the developed biomaterials will also be investigated and discussed. In the first part of this study (Chapter II), chitosan was blended with a well-studied hydrogel material (agarose) to form a simply prepared hydrogel system. The stiffness of the agarose gel was maintained despite the inclusion of chitosan. The structure of the blended hydrogels was characterized by light microscopy and scanning electron microscopy. In vitro cell studies revealed the capability of chitosan to promote neuron adhesion. The concentration of chitosan in the hydrogel had great influence on neurite extension. An optimum range of chitosan concentration in agarose hydrogel, to enhance neuron attachment and neurite extension, was identified based on the results. A “steric hindrance” effect of chitosan was proposed, which explains the origin of the morphological differences of neurons in the blended gels as well as the influence of the physical environment on neuron adhesion and neurite outgrowth. This chitosan-agarose (C-A) hydrogel system and its multi-functionality allow for applications of simply prepared agarose-based hydrogels for brain tissue repair. In the second part of this study (Chapter III), chitosan was blended with graphene to form a series of graphene-chitosan (G-C) nanocomposites for potential neural interface applications. Both substrate-supported coatings and free standing films could be prepared by air evaporation of precursor solutions. The electrical conductivity of graphene was maintained after the addition of chitosan, which is non-conductive. The surface characteristic of the films was sensitively dependent on film composition, and in turn, influenced neuron adhesion and neurite extension. Biological studies showed good cytocompatibility of graphene for both fibroblast and neuron. Good cell-substrate interactions between neurons and G-C nanocomposites were found on samples with appropriate compositions. The results suggest this unique nanocomposite system may be a promising substrate material used for the fabrication of implantable neural electrodes. Overall, these studies confirmed the bio-adhesive property of chitosan. More importantly, the developed chitosan-based materials also have great potential in the fields of neural tissue engineering and neuroprosthetics.

This thesis describes a new in vitro slide chamber model that makes it possible to conduct studies of molecular and cellular interactions between whole blood and biomaterials. The model proved to be a suitable tool for detection of cell and platelet binding to a biomaterial surface. It was possible to monitor activation of the blood cascade systems and cells in the fluid phase and detect surface-bound molecules. One finding was that thrombin generation is primarily triggered by FXII on a biomaterial surface since corn trypsin inhibitor, inhibited thrombin generation in blood. Another finding was that thrombin generation was dependent on variety types of blood cells, since thrombin generation was almost negligible in platelet-rich plasma. When various preparations of blood cells were used to reconstitute platelet-rich and platelet-poor plasma, erythrocytes were shown to be the most efficient cell type in triggering thrombin generation. Inhibition of platelet aggregation with aspirin and Ro44-9883 was associated with a decrease in thrombin generation, confirming that platelet activation is necessary for normal coagulation activation. These findings suggest that the central events consist of an initial low-grade generation of thrombin that involves erythrocytes and possibly leukocytes which leads to activation of platelets; and a second platelet-dependent amplification loop that produces most of the thrombin. Titanium exposed to whole blood produced high amounts of thrombin. Stainless steel and PVC, generated lower amounts. This indicates that titanium might be less suitable as a biomaterial in devices that are in direct contact with blood for prolonged time. Considering the superior osteointegrating properties of titanium and titanium's response to blood, a correlation between high thrombogenicity and good osteointegration seems to exist. Compstatin, that binds to complement component C3, effectively inhibited the generation of C3a and sC5b-9 and the binding of C3/C3 fragments to the surface. Our results suggest that a biomaterial is able to activate complement through both the classical and alternative pathways and that the classical pathway alone is able to maintain a substantial bioincompatibility reaction. The results show that complement activation is a prerequisite for activation and binding of PMNs to the surface in the in vitro model.