Biomedical subjects

K A Gross

Publications and source records attributed to K A Gross.

At least 19 recordsLinked to original sources

PubMed2005

Morphology and gelation of thermosensitive chitosan hydrogels.

The morphology of physical hydrogels is often difficult to examine due to the delicate nature of the system and therefore has not been studied in detail. Chitosan/GP (glycerophosphate salt) is a significant hydrogel in the biomedical and cosmetic fields as it is thermosensitive and contains less than 5% polysaccharide. The morphology of this system was examined with laser scanning confocal microscopy (LSCM) to image the gel morphology. The images indicate that the gel is quite heterogeneous, and power spectra reveal a fractal-like morphology. A study of composition found that increasing chitosan concentration increased the amount of polymer-rich phase present in the gel, and that the smallest aggregates decreased in size.

Biocompatible Materials↗

PubMed2005

Influence of ferrous iron incorporation on the structure of hydroxyapatite.

Iron is a vital element of cellular function within the body. High concentrations of iron can be found in the kidneys and the circulatory system. In bones and teeth it is present as a trace element. The use of iron-based compounds in combination with hydroxyapatite offers a new alternative for prosthetic devices. This work investigates the synthesis and processing of iron containing apatites as a possible new type of ceramic for biomedical devices. Stoichiometric and calcium deficient iron containing apatites were synthesized by a wet chemical reaction with di-ammonium-hydrogen-phosphate, calcium nitrate and a ferrous iron nitrate solution. A secondary phase of tri-calcium-phosphate (TCP) was observed after heat treatment of iron containing, calcium deficient, hydroxyapatite. The apatite structure was maintained after heat treatment of stoichiometric apatite, synthesized in the presence of iron. Sintering in air produced oxidation of Fe2+ to Fe3+, resulting in the formation of hematite as a secondary phase. The introduction of iron into the synthesis of hydroxyapatite causes: (i) an increase of the a-lattice parameter after synthesis and heat treatment in air; (ii) an increase in the c-lattice parameter after sintering in air.

Bone Substitutes↗

PubMed2005

Dissolution and mineralization of sintered and thermally sprayed hydroxy-fluoroapatites.

Hydroxyapatites are commonly used as bone cement, coatings on implants for dental and orthopaedic applications, but also as middle ear implants. These applications all require a different tissue healing response that can be attained by different manufacturing processes or by chemically modifying the composition. During implantation apatites undergo a process of dissolution and mineralization. The degree of dissolution is dependent upon the manufacturing process & is higher for thermally sprayed implant materials. This allows them to integrate to the natural bone. This study tests the dissolution and mineralization of fluoride containing hydroxyapatites through immersion in simulated body fluid. It shows that mineralization occurs more readily in hydroxyapatites than fluorapatites because of their higher dissolution rate. Mineralization was detected most readily by image analysis using scanning electron microscopy than by weight changes using a microbalance. Microscopy allowed small heterogeneous precipitates to be observed during the initial stages of mineralization.

Absorbable Implants↗

PubMed2005

Changes in the innate immune response of Atlantic salmon, Salmo salar L., exposed to experimental infection with Neoparamoeba sp.

An experiment was conducted to determine the effect of Neoparamoeba sp. infection on the innate immune responses of Atlantic salmon. Atlantic salmon were experimentally infected with Neoparamoeba sp. and serially sampled 0, 1, 4, 6, 8 and 11 days post-exposure (dpe). Histological analysis of infected fish gill arches identified the presence of characteristic amoebic gill disease lesions as early as 1 dpe with a steady increase in the number of affected gill filaments over time. Immune parameters investigated were anterior kidney phagocyte function (respiratory burst, chemotaxis and phagocytosis) and total plasma protein and lysozyme. In comparison with non-exposed control fish basal respiratory burst responses were suppressed at 8 and 11 dpe, while phorbol myristate acetate-stimulated activity was significantly suppressed at 11 dpe. Variable differences in phagocytic activity and phagocytic rate following infection were identified. There was an increase in the chemotactic response of anterior kidney macrophages isolated from exposed fish relative to control fish at 8 dpe. Total protein and lysozyme levels were not affected by Neoparamoeba sp. exposure.

Animals↗

PubMed2004

Colonization and maintenance of murine embryonic stem cells on poly(alpha-hydroxy esters).

The aim of this study was to determine the ability of various poly(alpha-hydroxy esters) to support the in vitro propagation of murine embryonic stem (ES) cells in an undifferentiated state. To this end, ES cell colonization, growth and Oct-4 immunoreactivity following a 48 h culture period upon poly((D,L)-lactide), poly((L)-lactide), poly(glycolide) and poly((D,L)-lactide-co-glycolide) (PLGA) were assessed. By the analysis of live and dead cell number indices and Oct-4 immunoreactivity, ES cell colonization rate during a 48 h culture period was found to be significantly greater on PLGA compared to all the other unmodified poly(alpha-hydroxy esters) tested. Surface treatment of all polymers with 0.1m potassium hydroxide revealed a significant increase in ES cell live numbers when compared to all unmodified polymers, thus revealing a correlation between polymer content, hydrophilicity and colonization rate. These data suggest that surface treated poly(alpha-hydroxy esters) may be employed for ES cell scale up procedures and in tissue engineering applications requiring the colonization of scaffolds by ES cells in an undifferentiated state. According to such applications, once the designated scaffold has been colonized, ES cell directed differentiation into the desired and fully differentiated, functional adult tissue may then be effected.

Analysis of Variance↗

PubMed2004

Sintered hydroxyfluorapatites--IV: The effect of fluoride substitutions upon colonisation of hydroxyapatites by mouse embryonic stem cells.

Biodegradable scaffolds serve a central role for tissue engineering scaffolds and guiding tissue regeneration. Some of these scaffolds, including apatites, display a significant effect upon cell adhesion and cell proliferation. The incorporation of scaffold technology with the developing embryonic stem (ES) cell field and the capacity of ES cells for self-renewal and differentiation are believed to hold enormous potential for applications in biomedical research and regenerative medicine. The purpose of this work was to determine the effect of hydroxyapatite (HAP) and fluoride substitutions of HAP upon ES cell growth and colonisation. Sintered hydroxyfluorapatite discs were found to support cellular proliferation and colonisation, and the ES cells displayed a tendency for differentiation on the apatite surface as determined by reductions in colony Oct4 immunoreactivity. Fluoride-containing HAPs were found to provide equivalent support to gelatin in terms of cell numbers, yet superior support for cellular colonisation when compared to HAP. This study indicates that fluoride substitutions of HAP may represent a viable strategy for the development of certain engineered tissue replacements and tissue regeneration systems using ES cells.

Analysis of Variance↗

PubMed2004

Atlantic salmon, Salmo salar L., previously infected with Neoparamoeba sp. are not resistant to re-infection and have suppressed phagocyte function.

Previous studies have indicated that Atlantic salmon, Salmo salar L., affected by amoebic gill disease (AGD) are resistant to re-infection. These observations were based upon a comparison of gross gill lesion abundance between previously infected and naïve control fish. Anecdotal evidence from Atlantic salmon farms in southern Tasmania suggests that previous infection does not protect against AGD as indicated by a lack of temporal change in freshwater bathing intervals. Experiments were conducted to determine if previous infection of Atlantic salmon with Neoparamoeba sp. would provide protection against challenge and elucidate the immunological basis of any protection. Atlantic salmon were infected with Neoparamoeba sp. for 12 days then treated with a 4-h freshwater bath. Fish were separated into two groups and maintained in either sea water or fresh water for 6 weeks. Fish were then transferred to one tank with a naïve control group and challenged with Neoparamoeba sp. Fish kept in sea water had lower mortality rates compared with first time exposed and freshwater maintained fish, however, these data are believed to be biased by ongoing mortalities during the sea-water maintenance phase. Phagocyte function decreased over exposure time and freshwater maintained fish demonstrated an increased ability to mount a specific immune response. These results suggest that under the challenge conditions herein described, antigen exposure via infection does not induce protection to subsequent AGD.

Amebiasis↗

PubMed2003

Juniper wood as a possible implant material.

Natural materials, such as wood and bone, possess structures fulfilling the requirements of support and transport of nutrients. Similarity in function and properties provides inspiration for investigating the possible use of wood as an implant material. Juniperus communis wood is dense, durable, and strong and has naturally impregnated essential oils that display antiseptic properties. This study investigated the toxicity of the oil, the effect of sterilization on the mechanical properties of the wood, and bone attachment with animal studies. The possible toxicity of the oil was determined orally and by intravenous injection. At low concentrations, the dose that would be released by the wood in the body could be tolerated without any detrimental effects. Sterilization of the wood in boiling water lowered the elastic modulus and modulus of rupture to a level at which the elastic modulus could be better matched to bone. Wood shaped into the form of femoral implants were implanted into rabbits and displayed good acceptance by the body up to a period of 3 years, indicating bone apposition, abutment into pores, and growth into drilled cavities.

Animals↗

PubMed2003

Influence of fluorine in the synthesis of apatites. Synthesis of solid solutions of hydroxy-fluorapatite.

Hydroxy-fluorapatites (OH-FAps) occur biologically in teeth and form the basis for application as biomaterials. This work aims to synthesize a series of fluoride substituted calcium hydroxyapatites (OHAps) to determine how fluoride influences the synthesis and the resulting characteristics of solid solutions. OH-FAPs powders were synthesized with a chemical composition of Ca(10)(PO(4))(6)(OH)(2-x) F(x), with x=0.0, 0.4, 0.8, 1.2, 1.6 and 2.0. The synthesis of partially substituted OHAp yields materials with lower crystallinity and higher specific surface area than OHAp or fluorapatite (FAp). The smallest crystal size of 263A, occurs at less than 50% hydroxyl substitution with fluoride at x=0.4, and the highest surface area of 132m(2)/g occurs at x=0.8. Reaction kinetics occur faster at higher fluoride content, producing the expected Ca/P ratio of 1.67 only for x=2.0. X-ray and IR studies show that OH-FAPs are homogeneous solid solutions instead of mixtures of OHAp and FAp. The presence of a high fluoride concentration increases the driving force for crystal growth during the calcination process.

Apatites↗

PubMed2003

Encapsulation of apatite particles for improvement in bone regeneration.

The layering of fluorapatite on hydroxyapatite bodies provides a means of decreasing the solubility of hydroxyapatite, providing fluoride for possible stimulation of bone formation and delaying the release of calcium and phosphate from the more soluble hydroxyapatite. The purpose of this work was to encapsulate hydroxyapatite particles with fluorapatite spanning a thickness more than several crystallites deep. A three-step procedure was employed. Hydroxyapatite powder was immersed in an electrolyte solution until an equilibrium was established between the solid and the dissolved calcium at pH 4.67 and 37 degrees C. Equilibrium was determined by measurement of dissolved calcium with a calcium-specific ion-specific electrode. A 5x10(-2) M ammonium fluoride added to the suspension resulted in a rapid decrease of both calcium and fluoride in the solution. Analysis with X-ray diffraction indicated that a fluoride rich layer containing calcium fluoride deposited onto the particle surface. Scanning electron microscopy revealed submicron spherical precipitate clusters on the hydroxyapatite particles. These clusters transformed to fluorapatite by soaking in a 0.1 M K(2)HPO(4) solution at pH 8 and 70 degrees C. A total time of 10 h was necessary for complete transformation of CaF(2) into fluorapatite.

Journal Article↗

PubMed2002

The contribution of coating microstructure to degradation and particle release in hydroxyapatite coated prostheses.

Plasma-sprayed coatings of hydroxyapatite powder are widely used on hip replacements. Commercially, they are supplied by a large number of companies and thus offer different coating design philosophies. This study focuses on a retrieved prosthetic stem that exhibited coating loss on the femoral stem occurring concurrently with third-body wear. The purpose of the research was to establish possible links between the coating microstructure and the clinical findings. A coated stem and cup were sectioned and the cross section was prepared to reveal the coating microstructure. Characterization included X-ray diffraction, FTIR spectroscopy, and crystalline particle quantification within the coating. It was found that the coating has a high amorphous content that provides fast resorption. The amount of crystalline particles increased on the distal location of the stem, the threads of the acetabular shell, and was generally higher on the cup. Accelerated degradation illustrated how the coating may be a particle-generating source by preferential dissolution of the amorphous phase, possibly allowing liberation of crystalline areas and other particulates at the substrate-coating interface. Such particles mainly include the less soluble hydroxyapatide formed from unmelted particles in the plasma or recrystallisation in the coating, but may also include entrapped grit lodged in the substrate during the roughening process. This study accents the importance of coating microstructure in understanding coating resorption.

Coated Materials, Biocompatible↗

PubMed2002

Influence of abrasion on the surface characteristics of thermally sprayed hydroxyapatite coatings.

The surface condition of hydroxyapatite thermal sprayed coatings can be measured in terms of smooth melted and unmelted regions. Both these areas collectively contribute to abrasion resistance of a coated implant. The purpose of this work was to determine the influence of abrasion on the surface characteristics of coatings. Coatings with three degrees of roughness (R(a) of 7, 10 and 24 microm) were produced by thermal spraying. These coatings were subjected to abrasion in a pin-on-disk test. It was found that the majority of weight loss occurs within the first minute of the abrasion. Raised areas from the coating are removed and the bone analogue pin spreads amongst the elevated areas to produce a smoother coating. Further, abrasion is dependent upon the applied load. Small loads produce a smaller or negligible increase in coating loss, however, a higher load is able to displace more material from the coating surface. It is expected that the coating loss from plasma sprayed coatings amounts to a value of less than 3 wt% during the insertion into bone. Modification of the coating surface from abrasion is dependent upon the surface roughness of the coating.

Biocompatible Materials↗

PubMed2001

Material fundamentals and clinical performance of plasma-sprayed hydroxyapatite coatings: a review.

The clinical use of plasma-sprayed hydroxyapatite (HA) coatings on metal implants has aroused as many controversies as interests over the last decade. Although faster and stronger fixation and more bone growth have been revealed, the performance of HA-coated implants has been doubted. This article will initially address the fundamentals of the material selection, design, and processing of the HA coating and show how the coating microstructure and properties can be a good predictor of the expected behavior in the body. Further discussion will clarify the major concerns with the clinical use of HA coatings and introduce a comprehensive review concerning the outcomes experienced with respect to clinical practice over the past 5 years. A reflection on the results indicates that HA coatings can promote earlier and stronger fixation but exhibit a durability that can be related to the coating quality. Specific relationships between coating quality and clinical performance are being established as characterization methods disclose more information about the coating.

Arthroplasty, Replacement, Hip↗

PubMed1999

Ultrasonographic diagnosis and guided compression repair of femoral artery pseudoaneurysm: an update for the vascular nurse.

Rapid advances in technology have led to the use of radiographic technology for therapeutic interventions. This article is an all-inclusive procedure guide for the imaging nurse as well as the bedside nurse caring for the patient before or after the procedure. Key aspects of the nurse's functions are educating the patients to gain their cooperation and improve their understanding of the procedure and post-procedure expectations, physiologic monitoring, and administering sedation and analgesia. Ultrasonographic guided compression repair is a safe, cost-effective first approach to treatment for many femoral artery pseudoaneurysms and does not affect possible surgical intervention if the ultrasonographic guided compression repair attempt fails.

Aged↗

PubMed1998

Thermal processing of hydroxyapatite for coating production.

Thermally processed hydroxyapatite coatings used on dental implants and hip prostheses for enhanced fixation may typically consist of a number of chemical and structural phases. These phases affect coating performance and tissue attachment. Hydroxyapatite was plasma sprayed to examine the phase evolution during processing. Coatings were examined with X-ray diffraction and elemental analysis. Results indicate that phase transformations are produced by (a) preferential removal of hydroxyl and phosphate leading to a change in melt composition, and (b) the high cooling rate due to the thermal spray process. Hydroxyl group removal promotes the amorphous phase and oxyapatite. Further heating produces a less viscous melt facilitating decomposition of hydroxyapatite to tricalcium and tetracalcium phosphate. Phosphate removal during flight produces a more calcium-rich melt preferring tetracalcium phosphate and calcium oxide formation. A proposed model shows the phase location within the lamellae of these coatings. Coating processes must thus prevent removal of hydroxide and phosphate during processing to maximize the hydroxyapatite content.

Biocompatible Materials↗

PubMed1998

Amorphous phase formation in plasma-sprayed hydroxyapatite coatings.

The amorphous phase content of air plasma-sprayed hydroxyapatite coatings is dependent upon spraying and deposition conditions. X-ray diffraction and optical microscopy were used to investigate the influence of spray parameters on the formation of the amorphous phase. Results show three factors which most influence the formation of the amorphous phase: dehydroxylation of the molten particle during flight, the cooling rate as it impinges onto the metal substrate, and the substrate temperature. Crystalline regions were identified as unmelted particles and elongated recrystallized areas. Amorphous phase regions vary throughout the coating but are more commonly found at the coating-substrate interface, i.e., the regions decrease toward the surface of the coating. Such an inhomogeneous distribution of phase content is expected to affect the clinical process of bone deposition, and therefore successful implant fixation.

Biocompatible Materials↗

PubMed1998

Critical ageing of hydroxyapatite sol-gel solutions.

It has been established that hydroxyapatite coatings can be produced using an alkoxide based sol-gel technique. Previous work showed that in addition to hydroxyapatite other phases including CaO were observed. A critical factor in determining the composition of the final coating is the period between solution preparation and coating deposition. The current study addresses how the ageing time affects the composition of the coating and the time required before a solution can be used to deposit monophasic coatings. Powders and coatings were produced with ageing times up to one week and examined with X-ray diffraction, thermal gravimetric analysis and differential thermal analysis. By depositing coatings after various ageing times, it was found that a solution ageing time of at least 1 day was required before monophasic hydroxyapatite coatings could be deposited. Thermogravimetric analysis showed that heating of the gel in air or in nitrogen both produced hydroxyapatite. Thermogravimetric analysis could be used as a simple and effective tool for identifying the critical ageing time required to produce high-purity hydroxyapatite coatings.

Biocompatible Materials↗

PubMed1998

Thin hydroxyapatite coatings via sol-gel synthesis.

Production of hydroxyapatite coatings using an alkoxide-based sol-gel route requires control of solution aging time and heating schedule. 31P nuclear magnetic resonance spectroscopy was used to investigate the changes during aging of the sol and thermal gravimetric analysis employed to study the behavior of the xerogels as a function of temperature, while final products were determined using X-ray diffraction. Results from 31P nuclear magnetic resonance spectroscopy and thermal analysis revealed that sols must be aged for at least 24 h to complete the reaction of the two reactants. Deposition of the sol for coating production will then yield monophasic hydroxyapatite. Coatings produced from sols aged for less than 24 h yielded calcium oxide in addition to hydroxyapatite. Prefiring is necessary to remove most of the residual organic materials. Final heating up to 800 degrees C produces crystallization at 550 degrees C and removal of the remaining organic constituents for the formation of a thin hydroxyapatite layer.

Journal Article↗