Kathirvel Ganesan | German Aerospace Center (DLR) (original) (raw)

Papers by Kathirvel Ganesan

Nature Materials, 2011

Biominerals exhibit morphologies, hierarchical ordering and properties that invariably surpass th... more Biominerals exhibit morphologies, hierarchical ordering and properties that invariably surpass those of their synthetic counterparts. A key feature of these materials, which sets them apart from synthetic crystals, is their nanocomposite structure, which derives from intimate association of organic molecules with the mineral host. We here demonstrate the production of artificial biominerals where single crystals of calcite occlude a remarkable 13 wt% of 20 nm anionic diblock copolymer micelles, which act as 'pseudo-proteins'. The synthetic crystals exhibit analogous texture and defect structures to biogenic calcite crystals and are harder than pure calcite. Further, the micelles are specifically adsorbed on {104} faces and undergo a change in shape on incorporation within the crystal lattice. This system provides a unique model for understanding biomineral formation, giving insight into both the mechanism of occlusion of biomacromolecules within single crystals, and the relationship between the macroscopic mechanical properties of a crystal and its microscopic structure.

Aerogels of polysaccharides can be used as bio-based template materials for many applications inc... more Aerogels of polysaccharides can be used as bio-based template materials for many applications including separation techniques, catalysis, tissue engineering and drug delivery vehicles because of their abundance in renewable natural source, ease of production, bio-compatibility and biodegradability [1-3]. Aerogels of polysaccharides such as cellulose and carrageenan were successfully synthesized in three consecutive steps: a) preparation of hydrogels; b) solvent exchange; and c) drying the organogels under supercritical condition (supercritical fluid is carbon dioxide). Their properties were investigated by envelope density analyzer, scanning electron microscopy and nitrogen adsorption-desorption analysis. The density of carrageenan aerogel was about two times higher than cellulose aerogel because of the difference in shrinkage behavior of polysaccharides under supercritical condition. The macro- and mesoporous fibrillar structure was observed with a fibre thickness of about 10-20 nm...

-1: Comparison of EDX spectra of aerogels with commercial κ-carrageenan. The samples were not spu... more -1: Comparison of EDX spectra of aerogels with commercial κ-carrageenan. The samples were not sputtered. A circular disc-like shape with a thickness of 2-3 mm was used for EDX analysis. The K/S value was obtained from four different spots of each sample. Commercial κ-carrageenan has few percentages of sodium and chlorine. In the aerogel samples, a little of chlorine was observed and no trace of sodium was found. The absence of KSCN in the sample was also supported by EDX analysis where no trace of the element nitrogen was found. In this data, "deformed κ-carrageenan aerogel" means the sample shown in .

Humans in space suffer loss of bone mass that weakens their bone. This is due to bone remodeling ... more Humans in space suffer loss of bone mass that weakens their bone. This is due to bone remodeling processes in the spongious bone areas under the disuse conditions in near zero gravity. On the way to a better understanding of those processes interdisciplinary expertise inside DLR has been pulled together to develop and apply numerical and physical simulation methods. In this context the typical open porous sponge structure of polysaccharide aerogel coated with the bone mineral calcium phosphate, i.e., aerogel composite can be used as model system for structural and mechanical behaviour of cancellous bone, with a later option of using it as biocompatible bone surrogate or scaffold material. Bone-like material based on aerogels can be synthesized by mineralizing inorganic component, calcium phosphate in organic matrix of polysaccharides. Aerogels of polysaccharides, e.g., cellulose, chitosan, chitin and κ-carrageenan were used as organic matrix in this study because of their nanofelt f...

Humans in space suffer from losses of bone mass accompanied by bone restructuration. The structur... more Humans in space suffer from losses of bone mass accompanied by bone restructuration. The structural adaption depends on prevailing loading conditions. It can be assumed that the resulting structure is optimized with respect to the given restrictions, which are governed by biological mechanisms. It is not understood how structure and mechanical properties of cancellous bone are linked and how the structure can be characterized precisely. The challenges are the complex spongy architecture of the bone as well as the anisotropy of mechanical properties of the trabeculae due to their evolution from collagen fibrils. For achieving a better understanding of dependence between structure and mechanical response researchers from 3 DLR-Institutes work together. We expect to gain insight in remodelling mechanisms, which can be considered as load dependent structural optimization processes. The knowledge can be translated into adapting the load, e.g. by systematic physical training of astronauts...

Biomedical Materials, 2010

The effect of radiation processing and filler morphology on the biodegradation and biomechanical ... more The effect of radiation processing and filler morphology on the biodegradation and biomechanical stability of a poly(propylene fumarate)/hydroxyapatite composite was investigated. Radiation processing influenced both cross-linking and biodegradation of the composites. Irradiation with a dose of 3 Mrad resulted in enhanced cross-linking, mechanical properties and a higher storage modulus which are favourable for dimensional stability of the implant. The particle morphology of the added hydroxyapatite in the highly cross-linked state significantly influenced the biomechanical and interfacial stability of the composites. Reorganization of agglomerated hydroxyapatite occurred in the cross-linked polymeric matrix under dynamic mechanical loading under simulated physiological conditions. Such a reorganization may increase the damping characteristics of the composite.

Microsized open porous beads of cellulose were made using the dissolution medium containing mixtu... more Microsized open porous beads of cellulose were made using the dissolution medium containing mixtures of 7 wt% NaOH and 12 wt% urea and additionally various concentrations of ZnO to study its effect on physical and morphological properties of the cellulose beads formed. It has been observed that such cellulose aerogel beads prepared with lower concentrations of ZnO show shrinkage while drying whereas beads prepared with higher concentrations of ZnO do not exhibit much shrinkage. The dried cellulose aerogel beads were spherical with diameters between 2 and 2.5 mm. The skeletal density of all dried cellulose beads was measured as 1.5 g cm−3. FT-IR spectra reveal that the structure of cellulose I transformed to cellulose II during dissolution and regeneration in a coagulation medium, which was also confirmed from XRD measurements. The beads prepared with a NaOH/urea/ZnO aqueous solution exhibit better thermal stability. We found that the addition of 0.5 wt% ZnO to the NaOH/urea mixture greatly increased the specific surface area of the cellulose beads up to 407 m2 g−1 compared to control cellulose beads (341 m2 g−1). SEM images indicate that a dense nano-fibrillar network structure was formed in the interior of the cellulose aerogel beads prepared with 0.5 wt% ZnO.

To the best of our knowledge, it is the first study reporting the synthesis of monolithic κ-carra... more To the best of our knowledge, it is the first study reporting the synthesis of monolithic κ-carrageenan aerogels with meso- and macroporous structures, being unique in physical and chemical properties. We demonstrate a novel method to synthesize κ-carrageenan aerogels in which potassium thiocyanate was used as the source of specific ions. Aerogels were characterized by envelope density analysis, scanning electron microscopy, nitrogen adsorption–desorption analysis, X-ray powder diffractometry and IR spectroscopy. By varying the concentration of κ-carrageenan between 0.5 and 3 wt%, the envelope density can be linearly increased from 40 to 160 kg m−3. The sulphate functional groups in the wet gel and the specific ions are the key factors controlling the volume shrinkage of aerogels which average about 66%. The aerogels exhibit a fibrillar structure similar to cellulose aerogels. The fibril thickness was observed to be 10–15 nm and the specific surface area was about 230 m2 g−1. The existing meso- and macroporous structures were confirmed by nitrogen adsorption–desorption isotherm analysis and scanning electron microscopy. The aerogels were completely pure, free of specific ions and confirmed to be amorphous by powder X-ray diffraction. Hence, these porous materials can provide a matrix with a chelating function which can be used as a host in many applications.

Cellulose-based biocomposites from nature exhibit remarkable mechanical properties which inspire ... more Cellulose-based biocomposites from nature exhibit remarkable mechanical properties which inspire to prepare synthetic biocomposites. The detailed studies of the porous cellulose materials having hierarchical structures are essential to understand how the cellulose nanofiber network and interconnected macro- and mesoporous structures exclusively influence the mechanical properties. We have designed the hierarchical open porous structures of cellulose scaffolds by a novel method in which an intricate trap of oil droplets in the cellulose-dissolved molten salt hydrate acts as a structural template assisting the formation of interconnected macroporous structures. After washing, the wet gels of cellulose were employed in three different drying techniques, namely supercritical drying, freeze drying and ambient drying. The diversity in physical and mechanical properties of the cellulose scaffolds were characterized by X-ray μ-computed tomography, density analyser, scanning electron microscopy, nitrogen adsorption–desorption analysis, X-ray powder diffraction, FTIR spectroscopy and mechanical testing. In the resulting products, the variations in physical properties were the size of the macropores produced by the emulsion template, the change in surface features of the cell walls and the presence of nanopores in the cell walls. The mechanical properties of hierarchically porous cellulose materials were diverged from lightweight soft materials to hard, stiff and dense material.

Journal of Materials Chemistry, 2011

Nanoparticles of calcium phosphate assemble spontaneously within a few seconds into hollow sphere... more Nanoparticles of calcium phosphate assemble spontaneously within a few seconds into hollow spheres with a diameter around 200-300 nm in the presence of dissolved amino acids and dipeptides. The process of formation was followed by cryo-transmission electron microscopy (cryoTEM), proving their hollow nature which was also confirmed by nano-indentation by atomic force microscopy (AFM). The hollow spheres were analyzed by scanning electron microscopy (SEM), dynamic light scattering (DLS), nanoparticle tracking analysis (NTA) and elemental analysis. The hollow spheres were moderately stable against heating and ultrasonication. A self-assembly of the primarily formed calcium phosphate nanoparticles around amino acid-rich domains in water is proposed. As this process was observed with different amino acids, it appears to be a more general phenomenon.

New Journal of Chemistry, 2008

Colloidal calcium phytate was prepared by anion-exchange of phosphate by phytate, starting from c... more Colloidal calcium phytate was prepared by anion-exchange of phosphate by phytate, starting from calcium phosphate nanoparticles. Scanning electron microscopy (SEM) showed spherical nanoparticles of narrow size distribution, in good agreement with dynamic light scattering (DLS) results, whose diameter could be adjusted between about 40 to 250 nm depending on the employed synthesis conditions. The particle surface is covered by phytate anions as indicated by the strongly negative zeta potential of À40 to À50 mV. The preparation of a stable colloid was only possible within a narrow range of the ratio of calcium to phytate. Infrared spectroscopy, X-ray diffraction and elemental analysis showed that the particles consisted of X-ray amorphous calcium phytate. The colloidal dispersions were stable for about two weeks before precipitation occurred.

Nature Materials, 2011

Biominerals exhibit morphologies, hierarchical ordering and properties that invariably surpass th... more Biominerals exhibit morphologies, hierarchical ordering and properties that invariably surpass those of their synthetic counterparts. A key feature of these materials, which sets them apart from synthetic crystals, is their nanocomposite structure, which derives from intimate association of organic molecules with the mineral host. We here demonstrate the production of artificial biominerals where single crystals of calcite occlude a remarkable 13 wt% of 20 nm anionic diblock copolymer micelles, which act as 'pseudo-proteins'. The synthetic crystals exhibit analogous texture and defect structures to biogenic calcite crystals and are harder than pure calcite. Further, the micelles are specifically adsorbed on {104} faces and undergo a change in shape on incorporation within the crystal lattice. This system provides a unique model for understanding biomineral formation, giving insight into both the mechanism of occlusion of biomacromolecules within single crystals, and the relationship between the macroscopic mechanical properties of a crystal and its microscopic structure.

Journal of Materials Chemistry, 2010

Journal of Materials Chemistry, 2011

Nanoparticles of calcium phosphate assemble spontaneously within a few seconds into hollow sphere... more Nanoparticles of calcium phosphate assemble spontaneously within a few seconds into hollow spheres with a diameter around 200-300 nm in the presence of dissolved amino acids and dipeptides. The process of formation was followed by cryo-transmission electron microscopy (cryoTEM), proving their hollow nature which was also confirmed by nano-indentation by atomic force microscopy (AFM). The hollow spheres were analyzed by scanning electron microscopy (SEM), dynamic light scattering (DLS), nanoparticle tracking analysis (NTA) and elemental analysis. The hollow spheres were moderately stable against heating and ultrasonication. A self-assembly of the primarily formed calcium phosphate nanoparticles around amino acid-rich domains in water is proposed. As this process was observed with different amino acids, it appears to be a more general phenomenon.

Journal of Materials Chemistry, 2008

Acta Biomaterialia, 2010

The effect of hydroxyapatite (HAP) on the performance of nanocomposites of an unsaturated polyest... more The effect of hydroxyapatite (HAP) on the performance of nanocomposites of an unsaturated polyester, i.e., hydroxy-terminated high molecular weight poly(proplyene fumarate) (HT-PPFhm), was investigated. A thermoset nanocomposite was prepared with nanoparticles of calcined HAP (<100 nm, rod-like shape, filler content 30 wt.%), HT-PPFhm and N-vinyl pyrrolidone, dibenzoyl peroxide and N,N-dimethyl aniline. Two more nanocomposites were prepared with precipitated HAP nanoparticles (<100 nm rod-like shape) and commercially available HAP nanoparticles (<200 nm spherical shape), respectively. Calcined HAP nanoparticles resulted in very good crosslinking in the resin matrix with high crosslinking density and interfacial bonding with the polymer, owing to the rod-like shape of the nanoparticles; this gave improved biomechanical strength and modulus and also controlled degradation of the nanocomposite for scaffold formation. The tissue compatibility and osteocompatibility of the nanocomposite containing calcined HAP nanoparticles was evaluated. The tissue compatibility was studied by intramuscular implantation in a rabbit animal model for 3 months as per ISO standard 10993/6. The in vivo femoral bone repair was also carried out in the rabbit animal model as per ISO standard 10993/6. The nanocomposite containing calcined HAP nanoparticles is both biocompatible and osteocompatible.

RSC Advances, 2012

One of the main problems in dental medicine is the growth of bacterial biofilms on tooth surfaces... more One of the main problems in dental medicine is the growth of bacterial biofilms on tooth surfaces which cause caries and periodontitis. We have developed a new system for oral hygiene and dental treatment that consists of either a paste or a rinsing solution containing calcium phosphate nanoparticles, functionalized with the antibacterial agent chlorhexidine. As calcium phosphate is the natural component of tooth mineral, it can lead to the remineralization of damaged enamel, while chlorhexidine prevents the colonization of the tooth surface by bacteria. In the form of a paste, a bifunctional system with both mineralizing and antibacterial properties is obtained. The nanoparticles may also stick to open dentin tubules at the root surface due to their coating with carboxymethyl cellulose. In vitro studies on teeth show that the paste sticks well to the root surface and closes dentin tubules.

Nature Materials, 2011

Biominerals exhibit morphologies, hierarchical ordering and properties that invariably surpass th... more Biominerals exhibit morphologies, hierarchical ordering and properties that invariably surpass those of their synthetic counterparts. A key feature of these materials, which sets them apart from synthetic crystals, is their nanocomposite structure, which derives from intimate association of organic molecules with the mineral host. We here demonstrate the production of artificial biominerals where single crystals of calcite occlude a remarkable 13 wt% of 20 nm anionic diblock copolymer micelles, which act as &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;pseudo-proteins&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;. The synthetic crystals exhibit analogous texture and defect structures to biogenic calcite crystals and are harder than pure calcite. Further, the micelles are specifically adsorbed on {104} faces and undergo a change in shape on incorporation within the crystal lattice. This system provides a unique model for understanding biomineral formation, giving insight into both the mechanism of occlusion of biomacromolecules within single crystals, and the relationship between the macroscopic mechanical properties of a crystal and its microscopic structure.

Aerogels of polysaccharides can be used as bio-based template materials for many applications inc... more Aerogels of polysaccharides can be used as bio-based template materials for many applications including separation techniques, catalysis, tissue engineering and drug delivery vehicles because of their abundance in renewable natural source, ease of production, bio-compatibility and biodegradability [1-3]. Aerogels of polysaccharides such as cellulose and carrageenan were successfully synthesized in three consecutive steps: a) preparation of hydrogels; b) solvent exchange; and c) drying the organogels under supercritical condition (supercritical fluid is carbon dioxide). Their properties were investigated by envelope density analyzer, scanning electron microscopy and nitrogen adsorption-desorption analysis. The density of carrageenan aerogel was about two times higher than cellulose aerogel because of the difference in shrinkage behavior of polysaccharides under supercritical condition. The macro- and mesoporous fibrillar structure was observed with a fibre thickness of about 10-20 nm...

-1: Comparison of EDX spectra of aerogels with commercial κ-carrageenan. The samples were not spu... more -1: Comparison of EDX spectra of aerogels with commercial κ-carrageenan. The samples were not sputtered. A circular disc-like shape with a thickness of 2-3 mm was used for EDX analysis. The K/S value was obtained from four different spots of each sample. Commercial κ-carrageenan has few percentages of sodium and chlorine. In the aerogel samples, a little of chlorine was observed and no trace of sodium was found. The absence of KSCN in the sample was also supported by EDX analysis where no trace of the element nitrogen was found. In this data, "deformed κ-carrageenan aerogel" means the sample shown in .

Humans in space suffer loss of bone mass that weakens their bone. This is due to bone remodeling ... more Humans in space suffer loss of bone mass that weakens their bone. This is due to bone remodeling processes in the spongious bone areas under the disuse conditions in near zero gravity. On the way to a better understanding of those processes interdisciplinary expertise inside DLR has been pulled together to develop and apply numerical and physical simulation methods. In this context the typical open porous sponge structure of polysaccharide aerogel coated with the bone mineral calcium phosphate, i.e., aerogel composite can be used as model system for structural and mechanical behaviour of cancellous bone, with a later option of using it as biocompatible bone surrogate or scaffold material. Bone-like material based on aerogels can be synthesized by mineralizing inorganic component, calcium phosphate in organic matrix of polysaccharides. Aerogels of polysaccharides, e.g., cellulose, chitosan, chitin and κ-carrageenan were used as organic matrix in this study because of their nanofelt f...

Humans in space suffer from losses of bone mass accompanied by bone restructuration. The structur... more Humans in space suffer from losses of bone mass accompanied by bone restructuration. The structural adaption depends on prevailing loading conditions. It can be assumed that the resulting structure is optimized with respect to the given restrictions, which are governed by biological mechanisms. It is not understood how structure and mechanical properties of cancellous bone are linked and how the structure can be characterized precisely. The challenges are the complex spongy architecture of the bone as well as the anisotropy of mechanical properties of the trabeculae due to their evolution from collagen fibrils. For achieving a better understanding of dependence between structure and mechanical response researchers from 3 DLR-Institutes work together. We expect to gain insight in remodelling mechanisms, which can be considered as load dependent structural optimization processes. The knowledge can be translated into adapting the load, e.g. by systematic physical training of astronauts...

Biomedical Materials, 2010

The effect of radiation processing and filler morphology on the biodegradation and biomechanical ... more The effect of radiation processing and filler morphology on the biodegradation and biomechanical stability of a poly(propylene fumarate)/hydroxyapatite composite was investigated. Radiation processing influenced both cross-linking and biodegradation of the composites. Irradiation with a dose of 3 Mrad resulted in enhanced cross-linking, mechanical properties and a higher storage modulus which are favourable for dimensional stability of the implant. The particle morphology of the added hydroxyapatite in the highly cross-linked state significantly influenced the biomechanical and interfacial stability of the composites. Reorganization of agglomerated hydroxyapatite occurred in the cross-linked polymeric matrix under dynamic mechanical loading under simulated physiological conditions. Such a reorganization may increase the damping characteristics of the composite.

Microsized open porous beads of cellulose were made using the dissolution medium containing mixtu... more Microsized open porous beads of cellulose were made using the dissolution medium containing mixtures of 7 wt% NaOH and 12 wt% urea and additionally various concentrations of ZnO to study its effect on physical and morphological properties of the cellulose beads formed. It has been observed that such cellulose aerogel beads prepared with lower concentrations of ZnO show shrinkage while drying whereas beads prepared with higher concentrations of ZnO do not exhibit much shrinkage. The dried cellulose aerogel beads were spherical with diameters between 2 and 2.5 mm. The skeletal density of all dried cellulose beads was measured as 1.5 g cm−3. FT-IR spectra reveal that the structure of cellulose I transformed to cellulose II during dissolution and regeneration in a coagulation medium, which was also confirmed from XRD measurements. The beads prepared with a NaOH/urea/ZnO aqueous solution exhibit better thermal stability. We found that the addition of 0.5 wt% ZnO to the NaOH/urea mixture greatly increased the specific surface area of the cellulose beads up to 407 m2 g−1 compared to control cellulose beads (341 m2 g−1). SEM images indicate that a dense nano-fibrillar network structure was formed in the interior of the cellulose aerogel beads prepared with 0.5 wt% ZnO.

To the best of our knowledge, it is the first study reporting the synthesis of monolithic κ-carra... more To the best of our knowledge, it is the first study reporting the synthesis of monolithic κ-carrageenan aerogels with meso- and macroporous structures, being unique in physical and chemical properties. We demonstrate a novel method to synthesize κ-carrageenan aerogels in which potassium thiocyanate was used as the source of specific ions. Aerogels were characterized by envelope density analysis, scanning electron microscopy, nitrogen adsorption–desorption analysis, X-ray powder diffractometry and IR spectroscopy. By varying the concentration of κ-carrageenan between 0.5 and 3 wt%, the envelope density can be linearly increased from 40 to 160 kg m−3. The sulphate functional groups in the wet gel and the specific ions are the key factors controlling the volume shrinkage of aerogels which average about 66%. The aerogels exhibit a fibrillar structure similar to cellulose aerogels. The fibril thickness was observed to be 10–15 nm and the specific surface area was about 230 m2 g−1. The existing meso- and macroporous structures were confirmed by nitrogen adsorption–desorption isotherm analysis and scanning electron microscopy. The aerogels were completely pure, free of specific ions and confirmed to be amorphous by powder X-ray diffraction. Hence, these porous materials can provide a matrix with a chelating function which can be used as a host in many applications.

Cellulose-based biocomposites from nature exhibit remarkable mechanical properties which inspire ... more Cellulose-based biocomposites from nature exhibit remarkable mechanical properties which inspire to prepare synthetic biocomposites. The detailed studies of the porous cellulose materials having hierarchical structures are essential to understand how the cellulose nanofiber network and interconnected macro- and mesoporous structures exclusively influence the mechanical properties. We have designed the hierarchical open porous structures of cellulose scaffolds by a novel method in which an intricate trap of oil droplets in the cellulose-dissolved molten salt hydrate acts as a structural template assisting the formation of interconnected macroporous structures. After washing, the wet gels of cellulose were employed in three different drying techniques, namely supercritical drying, freeze drying and ambient drying. The diversity in physical and mechanical properties of the cellulose scaffolds were characterized by X-ray μ-computed tomography, density analyser, scanning electron microscopy, nitrogen adsorption–desorption analysis, X-ray powder diffraction, FTIR spectroscopy and mechanical testing. In the resulting products, the variations in physical properties were the size of the macropores produced by the emulsion template, the change in surface features of the cell walls and the presence of nanopores in the cell walls. The mechanical properties of hierarchically porous cellulose materials were diverged from lightweight soft materials to hard, stiff and dense material.

Journal of Materials Chemistry, 2011

Nanoparticles of calcium phosphate assemble spontaneously within a few seconds into hollow sphere... more Nanoparticles of calcium phosphate assemble spontaneously within a few seconds into hollow spheres with a diameter around 200-300 nm in the presence of dissolved amino acids and dipeptides. The process of formation was followed by cryo-transmission electron microscopy (cryoTEM), proving their hollow nature which was also confirmed by nano-indentation by atomic force microscopy (AFM). The hollow spheres were analyzed by scanning electron microscopy (SEM), dynamic light scattering (DLS), nanoparticle tracking analysis (NTA) and elemental analysis. The hollow spheres were moderately stable against heating and ultrasonication. A self-assembly of the primarily formed calcium phosphate nanoparticles around amino acid-rich domains in water is proposed. As this process was observed with different amino acids, it appears to be a more general phenomenon.

New Journal of Chemistry, 2008

Colloidal calcium phytate was prepared by anion-exchange of phosphate by phytate, starting from c... more Colloidal calcium phytate was prepared by anion-exchange of phosphate by phytate, starting from calcium phosphate nanoparticles. Scanning electron microscopy (SEM) showed spherical nanoparticles of narrow size distribution, in good agreement with dynamic light scattering (DLS) results, whose diameter could be adjusted between about 40 to 250 nm depending on the employed synthesis conditions. The particle surface is covered by phytate anions as indicated by the strongly negative zeta potential of À40 to À50 mV. The preparation of a stable colloid was only possible within a narrow range of the ratio of calcium to phytate. Infrared spectroscopy, X-ray diffraction and elemental analysis showed that the particles consisted of X-ray amorphous calcium phytate. The colloidal dispersions were stable for about two weeks before precipitation occurred.

Nature Materials, 2011

Biominerals exhibit morphologies, hierarchical ordering and properties that invariably surpass th... more Biominerals exhibit morphologies, hierarchical ordering and properties that invariably surpass those of their synthetic counterparts. A key feature of these materials, which sets them apart from synthetic crystals, is their nanocomposite structure, which derives from intimate association of organic molecules with the mineral host. We here demonstrate the production of artificial biominerals where single crystals of calcite occlude a remarkable 13 wt% of 20 nm anionic diblock copolymer micelles, which act as &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;pseudo-proteins&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;. The synthetic crystals exhibit analogous texture and defect structures to biogenic calcite crystals and are harder than pure calcite. Further, the micelles are specifically adsorbed on {104} faces and undergo a change in shape on incorporation within the crystal lattice. This system provides a unique model for understanding biomineral formation, giving insight into both the mechanism of occlusion of biomacromolecules within single crystals, and the relationship between the macroscopic mechanical properties of a crystal and its microscopic structure.

Journal of Materials Chemistry, 2010

Journal of Materials Chemistry, 2011

Nanoparticles of calcium phosphate assemble spontaneously within a few seconds into hollow sphere... more Nanoparticles of calcium phosphate assemble spontaneously within a few seconds into hollow spheres with a diameter around 200-300 nm in the presence of dissolved amino acids and dipeptides. The process of formation was followed by cryo-transmission electron microscopy (cryoTEM), proving their hollow nature which was also confirmed by nano-indentation by atomic force microscopy (AFM). The hollow spheres were analyzed by scanning electron microscopy (SEM), dynamic light scattering (DLS), nanoparticle tracking analysis (NTA) and elemental analysis. The hollow spheres were moderately stable against heating and ultrasonication. A self-assembly of the primarily formed calcium phosphate nanoparticles around amino acid-rich domains in water is proposed. As this process was observed with different amino acids, it appears to be a more general phenomenon.

Journal of Materials Chemistry, 2008

Acta Biomaterialia, 2010

The effect of hydroxyapatite (HAP) on the performance of nanocomposites of an unsaturated polyest... more The effect of hydroxyapatite (HAP) on the performance of nanocomposites of an unsaturated polyester, i.e., hydroxy-terminated high molecular weight poly(proplyene fumarate) (HT-PPFhm), was investigated. A thermoset nanocomposite was prepared with nanoparticles of calcined HAP (<100 nm, rod-like shape, filler content 30 wt.%), HT-PPFhm and N-vinyl pyrrolidone, dibenzoyl peroxide and N,N-dimethyl aniline. Two more nanocomposites were prepared with precipitated HAP nanoparticles (<100 nm rod-like shape) and commercially available HAP nanoparticles (<200 nm spherical shape), respectively. Calcined HAP nanoparticles resulted in very good crosslinking in the resin matrix with high crosslinking density and interfacial bonding with the polymer, owing to the rod-like shape of the nanoparticles; this gave improved biomechanical strength and modulus and also controlled degradation of the nanocomposite for scaffold formation. The tissue compatibility and osteocompatibility of the nanocomposite containing calcined HAP nanoparticles was evaluated. The tissue compatibility was studied by intramuscular implantation in a rabbit animal model for 3 months as per ISO standard 10993/6. The in vivo femoral bone repair was also carried out in the rabbit animal model as per ISO standard 10993/6. The nanocomposite containing calcined HAP nanoparticles is both biocompatible and osteocompatible.

RSC Advances, 2012

One of the main problems in dental medicine is the growth of bacterial biofilms on tooth surfaces... more One of the main problems in dental medicine is the growth of bacterial biofilms on tooth surfaces which cause caries and periodontitis. We have developed a new system for oral hygiene and dental treatment that consists of either a paste or a rinsing solution containing calcium phosphate nanoparticles, functionalized with the antibacterial agent chlorhexidine. As calcium phosphate is the natural component of tooth mineral, it can lead to the remineralization of damaged enamel, while chlorhexidine prevents the colonization of the tooth surface by bacteria. In the form of a paste, a bifunctional system with both mineralizing and antibacterial properties is obtained. The nanoparticles may also stick to open dentin tubules at the root surface due to their coating with carboxymethyl cellulose. In vitro studies on teeth show that the paste sticks well to the root surface and closes dentin tubules.