Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 105-115). Also available via the Internet.

Around 170000 patients worldwide receive cardiac valve substitutes each year. Valve replacement with mechanical or bioprosthetic devices enhances patient survival and quality of life. Bioprosthetic valves have a significant advantage over mechanical valves: they do not necessarily require long-term anticoagulant therapy however, dystrophic calcification can lead to early failure. The actual mechanism of calcification is still poorly understood despite several established possible factors associated with it. Amongst these is the glutaraldehyde pre-treatment of the valves during their manufacture. Glutaraldehyde has been used for the treatment of bioprosthetic valves for the last thirty years, as a cross-linking agent and a sterilant. Whilst it is assumed to introduce stable inter- and intra-fibrillar collagen cross-links, which contribute to the durability of these valves, the specific chemistry of the fixation process is not fully understood. Additionally, glutaraldehyde is thought to be involved somehow in the process of dystrophic calcification of these same bioprosthetic valves. The primary aim of this study was to gain a greater understanding of the chemistry involved in the treatment of collagenous valve tissue with glutaraldehyde. Amino acids, peptides and proteins were thus used to mimic the effect of the glutaraldehyde treatment and to model potential reactions involved in such treatment. Techniques such as MALDI-TOF MS, ESI MS, NMR, FTIR-ATR and Raman spectroscopy were utilised to study the products of the glutaraldehyde reaction and their relationship with the calcification process. Data obtained from the products of the reactions between glutaraldehyde and model compounds showed the presence of: aldol and aldol/Michael condensation products of glutaraldehyde, Schiff base moieties (including cross-links) and various cyclisation products incorporating pyridinium and dihydropyridine ring structures. Some of these structures are in agreement with the literature, whilst others are essentially new structures that have never been proposed. Glutaric acid, used to mimic the oxidation of glutaraldehyde that can occur in-vivo, was shown to have the ability to form complexes with cations such as calcium in-vitro. A similar result was found with aqueous dilute solutions of glutaraldehyde (similar concentrations to the ones used in valve manufacture), thus leading to the hypothesis of its strong role in the initiation of calcification in-vivo. However, an extrapolation of these results to the role of the nucleophilic groups of amino acids or peptides, that could behave as the collagen macromolecule, was difficult to assess using FTIR because of the complex infrared spectra. However some findings corroborated the hypothesis that amino acids of the collagen tissue may also play a role in the initiation of calcification. Secondly, methodology was developed to allow successful analysis of tissue calcification using environmental scanning electron microscopy (ESEM). This is thought to be an important step in the analysis of tissues in their native state. Investigation of the calcification process with samples from clinical investigations (explanted human calcified valves), in-vivo screening (rat subcutaneous implantation model) and in-vitro screening (pericardial tissue incubated in metastable calcification solution) was thus undertaken using ESEM, along with other techniques such as FTIR-ATR, Raman, XRD spectroscopy and ICP-OES. The data revealed both similarities and differences between in-vivo and in-vitro calcification, although the process is unequivocally different. Late calcific deposits were assigned to poorly crystalline hydroxyapatite with high Ca/P ratios due to the probable presence of carbonate and possibly cations such as silicon and magnesium. A picture of the onset of mineralisation was hypothesised involving precursors, containing various amounts of calcium and phosphate, along with the incorporation of magnesium and silicon. These precursors phases evolved with time of implantation to the poorly crystalline form of hydroxyapatite found in the late stage of calcification. This work has provided an insight into how glutaraldehyde reacts with valve tissue and a possible explanation as to why valves fail by non-calcific or calcific mechanisms. A new approach to the study of calcified valve tissue has also been developed using ESEM methodology.

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No description available.

Microorganisms have traditionally been selected for fermentation of milk on their ability to grow in milk. However nowadays the trend is towards including probiotic bacteria, i.e. those bacteria that have been suggested to provide additional health benefits to the consumer. Probiotic microorganisms have beneficial effects when ingested such as lowered incidence of colon cancer, the suppression of putrefactive and pathogenic bacteria by competitive exclusion and the production of organic acids, diacetyl and bacteriocins and a hypocholesterolemic effect, to mention but a few. To be more effective, the proposed microorganisms must be of human origin. Lactobacillus acidophilus and Bifidobacterium bifidum, which are two of the most successful probiotic bacteria used commercially, are normal inhabitants of the intestine of many animals including humans. They must however maintain their viability and activity in the bio-product in which they are formulated to be available at the right level at the time of consumption. A number of factors affect their viability, including low pH, the type of culture used and availability of essential amino acids. The choice of ingredients in the mix is crucial since it affects a number of mix properties such as pH and availability of nutrients. The demand for low fat products is a very strong driving force on the market place. However, reducing the fat content of such complex products as frozen dairy desserts is very difficult, since fat forms an integral part of the product. Removing fat poses a number of challenges as to which other ingredients to add in its place. Microparticulated whey protein concentrates have been formulated by food technologists to mimic the functionalities of fat especially as far as creaminess is concerned. Little information is available on fat replacement in frozen yoghurt, in terms of both its effects on the survival of probiotic bacteria and on some important quality parameters. Likewise, little research, if any, has been done on the perception of strawberry flavour in fat-free ice-creams and similar products. The purpose of the present study was thus to provide information on fat replacement by a microparticulated whey protein concentrate (Simplesse® 500) in frozen yoghurts and its influence on the survival of 1. acidophilus and B. bifidum. Several quality parameters of the frozen yoghurts were also evaluated. Frozen yoghurts were prepared by inoculating the mix with an ABT (acidophilus, bifidum and thermophilus) culture. Four mixes were formulated to contain 10% (m/m) milk fat, 5% (m/m) milk fat, 5% (m/m) of the microparticulated whey protein concentrate (WPC) and 3.4% (m/m) of the microparticulated WPC respectively. Decreasing milk fat from 10% to 5%, together with the addition of more milk solids-not-fat, did not lead to a significant increase (p > 0.05) in the acidity of the mix. Likewise the buffering capacity in both alkaline and acidic conditions were not significantly different (p > 0.05). Substituting fat with Simplesse® 500 at 3.4% levelled to a significant decrease in the pH of the mix (p < 0.05), which was due to the presence of more weak acids. The addition of the microparticulated WPC also led to an increase in the buffering capacity of the mix, which was due to an increase in weak acids and other buffer systems present in milk such as the citrate and phosphate systems. The addition of more Simplesse® 500 did not result in a significantly higher acidity (p > 0.05) since whey proteins are only weak acids. The viability of all three the bacteria types present in the ABT culture did not seem to be related to the presence or absence of the microparticulated WPC. The numbers of Streptococcus salivarius subsp. thermophilus, 1. acidophilus and of B. bifidum did not differ significantly (p > 0.05) between the four yoghurt mixes after incubation, ageing, whipping and freezing and three weeks of storage. However, only S. salivarius subsp. thermophilus and 1. acidophilus increased in numbers during fermentation in all the yoghurt mixes and only S. salivarius subsp. thermophilus increased significantly (p < 0.05) as a result of ageing in all the yoghurt mixes. Although the addition of the microparticulated WPC led to an increase in the acidity of the yoghurt mixes it also led to an increase in the buffer capacity, which thus helped to maintain the numbers of S. salivarius subsp. thermophilus and 1. acidophilus at the same level as in the mixes containing milk fat. While S. salivarius subsp. thermophilus and 1. acidophilus grew to numbers greater than 107 cfu/g, B. bifidum did not grow at all in any of the yoghurt mixes and the results suggest that they might not be available at the right level to have any therapeutic benefits to the consumers. Decreasing fat content led to an obvious increase in coarseness of frozen yoghurts (p < 0.05). The increasing perceived coarseness could be related to the amount of ice nuclei formed during whipping and freezing. The addition of the microparticulated whey protein concentrate could have resulted in a decrease in the freezing point, low enough to lead to a decrease in the amount of ice nuclei formed as a result of whipping and freezing. Therefore, the amount of unfrozen water available to freeze during hardening increased, thereby leading to an increase in the size of ice crystals. Fat is also known to decrease the size of ice crystals and the presence of more fat could also have led to an increased perception of smoothness. Increasing fat content led to a decrease in the perception of strawberry flavour and an increased perception of an aftertaste (p < 0.05). Fat is known to bind lipophilic compounds as well as decrease the melting rate and mass transfer, both of which will decrease the release of flavour compounds. / Dissertation (MSc (Food Science))--University of Pretoria, 2006. / Food Science / unrestricted

3 pp. / Artificial sweeteners can help consumers cut down on calories and control weight, help to manage chronic conditions such as diabetes, and potentially prevent cavities. This publication explores the several different sugar substitutes approved by the USDA for consumer consumption.

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The number of clinical procedures performed in the USA using bone graft substitutes was estimated at 1.1 million in 2010 and is projected to reach 1.3 million in 2015. This increasing demand for bone graft substitutes is a result of an ever-ageing population coupled with recent reports in the clinical literature of concerns regarding the safety of allograft and recombinant bone morphogenetic proteins such as rh- BMP-2 and the supply of autograft, which has led to an increased clinical interest in synthetic alternatives to allograft; autograft; and recombinant growth factors. One such synthetic material is silicate-substituted hydroxyapatite (SiCaP). Mechanical testing revealed SiCaP to have similar mechanical behaviour to morcellised cancellous bone. In computated spinal and hip models the simulated stresses in SiCaP were determined to be low when in situ, indicating a stressshielding effect from the implanted metalwork and surrounding bone. We also found an inverse relationship between porosity and Young's Modulus. Our results indicated that the strut-porosity of a material substrate should be increased to maximise the potential for formation of a precursor to bone-like apatite after implantation in osseous defects and further confirmed previous reports that betatricalcium phosphate is less bioactive than hydroxyapatite. We demonstrated a direct link between the amount of strut-porosity and the osteoinductivity of SiCaP. We learned that adding a resorbable carrier phase did not impair the osteoinductive potential of SiCaP, suggesting that osteoinductivity is not necessarily determined in the first 24-48 hours post implantation. Most notably from our studies we determined that the osteoinductivity of SiCaP correlated with its performance in orthotopic defects. Our research confirmed our hypothesis that modifying the micron-scale physical structure of a hierarchical porous SiCaP based biomaterial influences its functional performance in vitro and such modifications can be applied to improve its performance outcomes in ectopic and orthotopic treatment sites in vivo.

published_or_final_version / Dental Surgery / Master / Master of Dental Surgery

Bone graft substitute is a continuously developing field in orthopedics. When compared to tradition biomaterial in the field such as PLA or PCL, elastomer like polyurethane offers advantages in its high elasticity and flexibility, which establish an intimate contact with surrounding bones. This tight contact can provide a stable bone-material interface for cell proliferation and ingrowth of bone. The aim of this study is to evaluate the osteogenesis capabilities of a porous polyurethane scaffold in a critical size bone defect. In this study, a porous scaffold synthesized from segmented polyurethane is put under in vitro and in vivo tests to evaluate its potential in acting as a bone graft substitute for critical size bone defects. In vitro results indicate osteoblast-like cells are proliferating on the polyurethane scaffold during the 21-days experiment. Cells express their normal morphology when seeded on polyurethane under fluorescent staining. Although cells show a relatively lower cell activity then that seeded on culture plate, they share a similar alkaline phosphatase activity profile with the controls during the experiment period. In the in vivo animal model, reconstructed images from micro CT scanning indicates there are bone ingrowth inside the scaffold. Histology also indicates a tight interface has formed between bone and polyurethane, with osteogenic cells proliferating on the surface. The result has indicates polyurethane is a potential material for orthopedics in acting as a bone graft substitute. / published_or_final_version / Orthopaedics and Traumatology / Master / Master of Philosophy