Biomedical subjects

Kārlis A Gross

Publications and source records attributed to Kārlis A Gross.

6 recordsLinked to original sources

PubMed2005

Mouse embryonic stem cell colonisation of carbonated apatite surfaces.

Apatites play a crucial role in the body and have been used extensively in biomedical implants. The influence on stem cell behaviour is not known and so this study will explore whether sintered carbonated apatites are favourable for propagation of stem cells. Different weight substitutions of carbonated apatite, specifically 2.5 wt% (2.5 wt%CAP) and 5 wt% (5 wt%CAP), were sintered and characterised prior to the investigation of their potential as a matrix for the support of mouse embryonic stem (ES) cells. Characterisation of the apatites included elemental analysis, X-ray diffraction, surface roughness, specific surface area, density, and solubility. The ability of carbonated apatite to support mouse ES cell colonisation and maintenance in the presence of leukaemia inhibitory factor was determined by an enumeration of live versus dead cells within a population, and immunoreactivity to Oct4, a transcription factor and stem cell marker, following growth on each matrix. It was found that while both compositions allowed for the colonisation of mouse ES cells, the cells were not maintained in an undifferentiated state, as evidenced by a reduction in the number of cells staining positive for Oct4 expression. This study shows that an increase in carbonate content within sintered apatites leads to a higher cell number, a desired aspect for stem cells to populate scaffolds intended for tissue engineering. This study presents carbonated apatites as a suitable matrix for the initial colonisation and differentiation of ES cells for tissue engineering applications.

Animals↗

PubMed2004

Biodegradable composite scaffolds with an interconnected spherical network for bone tissue engineering.

Tissue engineering scaffolds are highly engineered structures that accommodate cells, facilitate their expression, and resorb to facilitate regeneration of tissue. A new technique for producing controlled pore shape and pore size interconnectivity offers promise for application as a tissue engineering scaffold. Salt particles were spheroidized in a flame and sintered to provide an interconnecting salt template. The salt template was filled with a carbonated fluorapatite powder and a polylactic polymer to produce a composite scaffold. It was found that a higher pore space is possible with the use of spherical and larger salt particle sizes. This technique can produce scaffolds with good interconnectivity and be suitable for producing pore size graded bodies.

Absorbable Implants↗

PubMed2004

Influence of fluorapatite on the properties of thermally sprayed hydroxyapatite coatings.

Thermally sprayed hydroxyapatite has been the widely used on orthopaedic prosthesis to induce bone growth and facilitate bone attachment. However, hydroxyapatite has a greater affinity for the formation of an amorphous phase in the thermally sprayed coating that results in the release of excessive amount of mineral ions from the implant coating leading to a saturated environment in the immediate vicinity of the bone cells. Fluorapatite however is highly crystalline and offers the potential for lower mineral ion release by dissolution. Thus study investigates the influence of fluorapatite in a thermally sprayed hydroxyapatite coating. Mechanical blends of fluorapatite with hydroxyapatite were thermally sprayed, characterized with X-ray diffraction, SEM, FTIR, optical microscopy for microstructure, roughness and tested for solubility. Cathodoluminescence microscopy was used to examine the resorbed coating surface. Fluorapatite coatings crystallized more readily and produce a greater coating roughness. The roughness in fluorapatite coatings arises from less flattened droplets that show a tendency for finger formation. Addition of fluorapatite increases coating crystallinity. The use of slower resorbing fluorapatite produces less particle release which favors improved osseointegration. Less change in the surface topography during resorption can be used to an advantage to control the coating surface presented to cells and extra cellular matrix proteins.

Apatites↗

PubMedDate not supplied

Sintered hydroxyfluorapatites. Part III: sintering and resultant mechanical properties of sintered blends of hydroxyapatite and fluorapatite.

The presence of chemically dissimilar apatites occurs widely in biological systems as a result of exposure to chemically enriched media, but also to optimize the mechanical properties. The use of mechanical blends of apatites can be used to manufacture high temperature processed fluoride containing hydroxyapatites with improved properties. Mechanical blends of fluorapatite and hydroxyapatite were produced with 0%, 20%, 40%, 60%, 80% and 100% fluorapatite. Pellets were sintered at 1150 degrees C, 1200 degrees C and 1250 degrees C and the density determined by the Archimedes method. Mechanical properties including hardness, elastic modulus and fracture toughness were measured using indentation. It was found that mechanical blends of 150 nm sized hydroxyapatite and 300 nm sized fluorapatite lead to solid solutions after sintering. The mechanical blends do not sinter as effectively as homogeneous hydroxyfluorapatite solid solutions and exhibit a minimum density at 80 wt.% fluorapatite. The hardness, elastic modulus and brittleness decreases with a higher flourapatite content, attributed primarily to a decrease in density. The higher fracture toughness for mechanical blends indicates that these materials are more crack resistant and provide a means for improving mechanical properties.

Apatites↗

PubMedDate not supplied

Sintered hydroxyfluorapatites. Part I: sintering ability of precipitated solid solution powders.

The presence of fluoride within apatites occurring naturally within the body provides the basis for investigating the sintering ability of fluoride containing hydroxyapatites for use as biomaterials. Hydroxyfluorapatites were synthesized and then calcined to produce a 0%, 20%, 40%, 60%, 80% and 100% replacement of the hydroxyl ions with fluoride in the hydroxyapatite structure. Fluoride ion occupancy within the apatites was found to be about 90% of the anticipated value. Pycnometry results revealed a constant true density for powders of low to medium fluoride content followed by a rapid increase to the fluorapatite composition. Powders were uniaxially pressed, cold-isostatically pressed and sintered at 1150 degrees C, 1200 degrees C and 1250 degrees C. All hydroxyfluorapatite powders displayed a comparable ability for densification except when hydroxyl groups and fluoride ions were present at a comparable concentration. The grain size revealed that this composition also exhibited the smallest grain size and displayed the highest activation energy for grain growth. The lower diffusion created by similar amounts of fluoride and hydroxide within the lattice decreases grain growth and densification.

Biocompatible Materials↗

PubMedDate not supplied

Sintered hydroxyfluorapatites. Part II: mechanical properties of solid solutions determined by microindentation.

Fluoride substitution within hydroxyapatite is an important occurrence for biological apatites and is a promising approach for the chemical modification of synthetic hydroxyapatite. Limited information on the influence of fluoride substitution for hydroxyl groups on the mechanical properties has provided the rationale for this study. Hydroxyfluorapatites with 0%, 20%, 40%, 60%, 80% and 100% replacement of hydroxyl groups with fluoride ions were assessed for hardness, elastic modulus, fracture toughness and brittleness using microindentation of sintered pellets. The production of samples with a similar grain size and density allowed the influence of fluoride on mechanical properties to be determined. It was found that the hardness remains unaffected until 80% replacement of hydroxyl groups with fluoride, after which the hardness rapidly increases. The elastic modulus increases linearly with fluoride content. Fracture toughness is improved with fluoride incorporation into the lattice and reaches a peak of 1.8 for a 95% dense sintered pellet with a 60% fluoride replacement, followed by a rapid decrease at higher fluoride concentrations. The brittleness index is lowered to a minimum at 60%, after which a rapid increase occurs. High fluoride levels are unfavourable from a mechanical perspective, are not recommended for biomaterials, and can lead to a higher incidence of fracture where sodium fluoride, for treatment of osteoporosis, may produce a highly fluoridated hydroxyapatite.

Biocompatible Materials↗