No description available.

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 use of dichromated gelatin (DCG) for the formation of holographic optical elements is investigated. In particular, a study is made of the possible sources of spurious recording and replay in such diffracting media. The formation of spurious gratings due to boundary mismatch, when recording a transmission grating in air, is investigated. Experimental results are treated using a simple linear theory which is capable of predicting the relative modulation strengths of each of six recorded gratings. The efficiencies of each of these gratings is related to Fresnel's Laws of reflection and therefore the beam ratio. A brief experimental study of the beam ratio is made. It is found that linear theories do not explain replay of gratings recorded at high exposure energies. This is because DCG exhibits a saturating recording characteristic. A theoretical model is developed to verify experimental results of modulation versus exposure energy for the recording of single and double exposure transmission gratings and their subsequent harmonics. This gives good agreement for most cases, however, it does not explain fully the replay of a difference grating formed due to nonlinearities in the double exposure hologram. A coupled wave theory is therefore developed to take account of both multiple grating interactions between the two primary recordings and the recording of a third grating with a spatial frequency equal to the difference of the two fundamental frequencies. The model gives good agreement with experimental results for varying replay angles and wavelengths. DCG is finally used as a tool to investigate the formation of noise gratings in silver halide emulsions. In particular, results are presented for experiments which were performed to study the effect of high angular scatter upon the selectivity of the noise grating and the recording of reflection noise gratings.

Thesis (Ph. D.)--Auburn University. / Abstract. Vita. Includes bibliographical references.

Please read the abstract in the section 00front of this document / Thesis (PhD(Food Science))--University of Pretoria, 2005. / Food Science / unrestricted

Experiments were performed to characterize the pH, gelation time, diffusion processes, material properties, adhesive properties, and the drying variables on the material and adhesive properties of Gelatin Resorcinol Dialdehyde (GR-DIAL) tissue adhesives by varying formulation. Three adhesive formulations with altered weight content of water and glyoxal (a dialdehyde) were utilized. The adhesive formulations were characterized by pH and gelation time in situ, and absorption/desorption of water in the formed resin. Thermal analysis, mechanical testing, and lap shear adhesive bond testing were utilized to characterize fresh GR-DIAL adhesive formulations and formulations dried at 370C. From the results, the diffusion processes, material and adhesive properties of the adhesive formulations were primarily affected by hydrogen bonding, chemical cross-linking, and the existence of bound water within the bulk adhesive. Formulations with increased glyoxal content had both a higher degree of cross-linking and proportion of bound water within the bulk adhesive. The increased number of chemical cross-links greatly increased the swelling resistance of the adhesives, while, the existence of bound water within the adhesive increased the resistance to drying, and plasticized the resin by depressing the resin glass transition temperature, and increased the adhesive ductility. Hydrogen bonding increased with increased gelatin content or decreased water content, resulting in increased strength and modulus of the adhesives as well as increased adhesive strength. / Master of Science

During embryo development, extracellular matrix (ECM) remodeling by matrix metalloproteinases (MMPs) and promotes downstream cell specifications. Pluripotent stem cell (PSC) aggregates can recapitulate various aspects of embryogenesis in vitro, and incorporation of biomaterial microparticles also provides an ideal platform to study cell-biomaterial interactions. Stem cell interactions with ECM-based biomaterials can impact tissue remodeling and differentiation propensity via modulation of MMP activity. This work investigated the MMP activity and subsequent mesenchymal differentiation of embryonic stem cell (ESC) aggregates with incorporated gelatin methacrylate (GMA) MPs with either low (20%) or high (90%) cross-linking densities, corresponding to faster or slower degradation rate, respectively. GMA MP incorporation increased total MMP and MMP-2 levels within 3D ESC aggregates in a substrate-dependent manner. GMA MP-incorporated aggregates also expressed higher levels of epithelial-to-mesenchymal transition markers and displayed enhanced mesenchymal morphogenesis than aggregates without MPs, and the MP-mediated effects were completely abrogated with MMP inhibitor treatment. This work predicts that control of proteolytic responses via introducing ECM-based MPs may offer a novel avenue to engineer the ECM microenvironment to modulate stem cell differentiation.

No description available.

As an artist, I am fascinated by surfaces and the stories they tell. I have observed that places and objects, like people, wear the effects of age in different ways. Their stories are revealed through pealing paint, rusty metal, and surface patina. My photographs are a record of their state of existence at the moment I am present. I have chosen a point in time when each is at rest, with only the aged surface to hint of a life of use. Their stories unfold with observation through the lens of my camera.

A quitosana é um biopolímero estudado em diversas áreas, tais como, ambiental, alimentícia, farmacêutica, biomédica e biotecnológica. Ela pode ser obtida de diferentes formas polimórficas de quitina, dentre as quais a forma β tem se mostrado vantajosa, pois favorece modificações químicas mais homogêneas e leva a um produto final menos alergênico. A quitosana pode ser combinada com outros compostos a fim de interagir e/ou reagir com eles e modificar suas propriedades. O objetivo deste trabalho foi estudar como uso de ácido adípico, em substituição ao acético, afeta as propriedades de géis e esponjas de quitosana e de quitosana/gelatina, que foram posteriormente reticuladas com os agentes reticulantes EDC/NHS. As técnicas utilizadas para os estudos foram: reologia, FTIR, MEV, absorção em PBS e ensaios de citotoxicidade. Por reologia, observou-se que o aumento na concentração dos géis de quitosana tornou os géis mais elásticos e viscosos. O mesmo ocorreu na presença de gelatina ou EDC/NHS. O efeito do uso de ácido adípico em substituição ao acético também foi mostrado nos ensaios reológicos, pois os géis com 2% de quitosana e com quitosana/gelatina sem EDC/NHS se mostraram mais elásticos e mais viscosos quando o ácido adípico foi usado. Os espectros FTIR mostraram a presença de interações entre a quitosana e a gelatina e a formação de ligações amidas II após reticulação com EDC/NHS. Na preparação das esponjas observou-se que os géis de quitosana em ácido adípico geravam esponjas instáveis que se desfizeram durante a neutralização, mas essa instabilidade não ocorreu com a blenda. As esponjas preparadas com a blenda foram estudadas após neutralização e o MEV mostrou que o uso de EDC/NHS alterou a morfologia levando a formação de poros interconectados. Nos ensaios de absorção em tampão de PBS foi observado que o uso de ácido acético aumenta a absorção para as esponjas sem EDC/NHS, enquanto para as esponjas com EDC/NHS a absorção é maior quando se usa ácido adípico. Todas as esponjas foram não citotóxicas o que torna esses materiais promissores para serem estudados em aplicações na área médica, tais como material de curativo, implantes, liberação controlada de fármacos. / Chitosan is a natural polymer studied in various fields such as environmental, food, pharmaceutical, biomedical and biotechnology. It can be obtained from different polymorphic forms of chitin, of which the form β has proven advantageous because it promotes more homogeneous and chemical modifications leads to a final product less allergenic. Chitosan can be combined with other compounds and thus further improve its properties. The aim of this study was to analyze how the use of adipic acid, replacing acetic acid affects the properties of gels and sponges of chitosan and chitosan/gelatin, which were subsequently crosslinked with EDC/NHS. The techniques used for these studies were: rheology, FTIR, SEM, absorption in PBS and cytotoxicity assays. In rheology, it was observed that increasing the concentration of chitosan was possible to prepare more elastic and viscous gels. The same occurs in the presence of gelatin or EDC/NHSO. The effect of the use of adipic acid to replace the acetic acid was also shown on rheological measurements, because the gels with 2% chitosan or chitosan/gelatin without EDC/NHS were more elastic and more viscous when the adipic acid has been used. The FTIR spectra showed the presence of interactions between chitosan and gelatin and the formation of amide II Bonds after crosslinking with EDC/NHS. In the preparation of the sponges it was observed that the gels of chitosan with adipic acid generated unstable sponges crumbled during neutralization, but this instability does not occur with the blend. Sponges prepared with the blend were studied after neutralization and SEM showed that the use of EDC/NHS altered the morphology leading to the formation of interconnected pores. The use of acetic acid increases the absorption in PBS for sponges without EDC/NHS, while for sponges with EDC/NHS the absorption is greater when adipic acid was used. All sponges were non-cytotoxic making them promising materials to be studied for applications in the medical field, such as dressing materials, implants, controlled drug release.