Orestis G Andriotis | Tu Wien (original) (raw)
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Papers by Orestis G Andriotis
Journal of Biomechanics, 2012
Journal of Biomechanics, 2012
Crystal Research and Technology, 2010
The present work reports a method for preparing calcium phosphate ceramics by calcination of calc... more The present work reports a method for preparing calcium phosphate ceramics by calcination of calcium phosphate cements composed mainly of calcium deficient hydroxyapatite (CDHA). It was found that hardened cements calcinied at temperatures from to 600 °C to 1300 °C were transformed to tricalcium phosphates. Moreover the compressive strength was determined and porosity was estimated as a function of the calcination temperature.
The collagen molecule, which is the building block of collagen fibrils, is a triple helix of two ... more The collagen molecule, which is the building block of collagen fibrils, is a triple helix of two α1(I) chains and one α2(I) chain. However, in the severe mouse model of osteogenesis imperfecta (OIM), deletion of the COL1A2 gene results in the substitution of the α2(I) chain by one α1(I) chain. As this substitution severely impairs the structure and mechanics of collagen-rich tissues at the tissue and organ level, the main aim of this study was to investigate how the structure and mechanics are altered in OIM collagen fibrils. Comparing results from atomic force microscopy imaging and cantilever-based nanoindentation on collagen fibrils from OIM and wild-type (WT) animals, we found a 33% lower indentation modulus in OIM when air-dried (bound water present) and an almost fivefold higher indentation modulus in OIM collagen fibrils when fully hydrated (bound and unbound water present) in phosphate-buffered saline solution (PBS) compared with WT collagen fibrils. These mechanical changes were accompanied by an impaired swelling upon hydration within PBS. Our experimental and atomistic simulation results show how the structure and mechanics are altered at the individual collagen fibril level as a result of collagen gene mutation in OIM. We envisage that the combination of experimental and modelling approaches could allow mechanical phenotyping at the collagen fibril level of virtually any alteration of collagen structure or chemistry.
Cartilage grafts generated using conventional static tissue engineering strategies are characteri... more Cartilage grafts generated using conventional static tissue engineering strategies are characterised by low cell viability, suboptimal hyaline cartilage formation and, critically, inferior mechanical competency, which limit their application for resurfacing articular cartilage defects. To address the limitations of conventional static cartilage bioengineering strategies and generate robust, scaffold-free neocartilage grafts of human articular chondrocytes, the present study utilised custom-built microfluidic perfusion bioreactors with integrated ultrasound standing wave traps. The system employed sweeping acoustic drive frequencies over the range of 890 to 910 kHz and continuous perfusion of the chondrogenic culture medium at a low-shear flow rate to promote the generation of three-dimensional agglomerates of human articular chondrocytes, and enhance cartilage formation by cells of the agglomerates via improved mechanical stimulation and mass transfer rates. Histological examination and assessment of micromechanical properties using indentation-type atomic force microscopy confirmed that the neocartilage grafts were analogous to native hyaline cartilage. Furthermore, in the ex vivo organ culture partial thickness cartilage defect model, implantation of the neocartilage grafts into defects for 16 weeks resulted in the formation of hyaline cartilage-like repair tissue that adhered to the host cartilage and contributed to significant improvements to the tissue architecture within the defects, compared to the empty defects. The study has demonstrated the first successful application of the acoustofluidic perfusion bioreactors to bioengineer scaffold-free neocartilage grafts of human articular chondrocytes that have the potential for subsequent use in second generation autologous chondrocyte implantation procedures for the repair of partial thickness cartilage defects.
Bone structure a b s t r a c t An improved understanding of bone mechanics is vital in the develo... more Bone structure a b s t r a c t An improved understanding of bone mechanics is vital in the development of evaluation strategies for patients at risk of bone fracture. The current evaluation approach based on bone mineral density (BMD) measurements lacks sensitivity, and it has become clear that as well as bone mass, bone quality should also be evaluated. The latter includes, among other parameters, the bone matrix material properties, which in turn depend on the hierarchical structural features that make up bone as well as their composition. Optimal load transfer, energy dissipation and toughening mechanisms have, to some extent, been uncovered in bone. Yet, the origin of these properties and their dependence upon the hierarchical structure and composition of bone are largely unknown. Here we investigate load transfer in the osteonal and sub-osteonal levels and the mechanical behaviour of osteonal lamellae and interlamellar areas during loading. Using cantilever-based nanoindentation, in situ microtensile testing during atomic force microscopy (AFM) and digital image correlation (DIC), we report evidence for a previously unknown mechanism. This mechanism transfers load and movement in a manner analogous to the engineered ''elastomeric bearing pads'' used in large engineering structures. m-RAMAN microscopy investigations showed compositional differences between lamellae and interlamellar areas. The latter have lower collagen content but an increased concentration of noncollagenous proteins (NCPs). Hence, NC-enriched areas on the microscale might be similarly important for bone failure as ones on the nanoscale. Finally, we managed to capture stable crack propagation within the interlamellar areas in a time-lapsed fashion, proving their significant contribution towards fracture toughness. (P.J. Thurner). j o u r n a l o f t h e m e c h a n i c a l b e h a v i o r o f b i o m e d i c a l m a t e r i a l s 1 7 ( 2 0 1 3 ) 1 5 2 -1 6 5
Journal of Biomechanics, 2012
Journal of Biomechanics, 2012
Crystal Research and Technology, 2010
The present work reports a method for preparing calcium phosphate ceramics by calcination of calc... more The present work reports a method for preparing calcium phosphate ceramics by calcination of calcium phosphate cements composed mainly of calcium deficient hydroxyapatite (CDHA). It was found that hardened cements calcinied at temperatures from to 600 °C to 1300 °C were transformed to tricalcium phosphates. Moreover the compressive strength was determined and porosity was estimated as a function of the calcination temperature.
The collagen molecule, which is the building block of collagen fibrils, is a triple helix of two ... more The collagen molecule, which is the building block of collagen fibrils, is a triple helix of two α1(I) chains and one α2(I) chain. However, in the severe mouse model of osteogenesis imperfecta (OIM), deletion of the COL1A2 gene results in the substitution of the α2(I) chain by one α1(I) chain. As this substitution severely impairs the structure and mechanics of collagen-rich tissues at the tissue and organ level, the main aim of this study was to investigate how the structure and mechanics are altered in OIM collagen fibrils. Comparing results from atomic force microscopy imaging and cantilever-based nanoindentation on collagen fibrils from OIM and wild-type (WT) animals, we found a 33% lower indentation modulus in OIM when air-dried (bound water present) and an almost fivefold higher indentation modulus in OIM collagen fibrils when fully hydrated (bound and unbound water present) in phosphate-buffered saline solution (PBS) compared with WT collagen fibrils. These mechanical changes were accompanied by an impaired swelling upon hydration within PBS. Our experimental and atomistic simulation results show how the structure and mechanics are altered at the individual collagen fibril level as a result of collagen gene mutation in OIM. We envisage that the combination of experimental and modelling approaches could allow mechanical phenotyping at the collagen fibril level of virtually any alteration of collagen structure or chemistry.
Cartilage grafts generated using conventional static tissue engineering strategies are characteri... more Cartilage grafts generated using conventional static tissue engineering strategies are characterised by low cell viability, suboptimal hyaline cartilage formation and, critically, inferior mechanical competency, which limit their application for resurfacing articular cartilage defects. To address the limitations of conventional static cartilage bioengineering strategies and generate robust, scaffold-free neocartilage grafts of human articular chondrocytes, the present study utilised custom-built microfluidic perfusion bioreactors with integrated ultrasound standing wave traps. The system employed sweeping acoustic drive frequencies over the range of 890 to 910 kHz and continuous perfusion of the chondrogenic culture medium at a low-shear flow rate to promote the generation of three-dimensional agglomerates of human articular chondrocytes, and enhance cartilage formation by cells of the agglomerates via improved mechanical stimulation and mass transfer rates. Histological examination and assessment of micromechanical properties using indentation-type atomic force microscopy confirmed that the neocartilage grafts were analogous to native hyaline cartilage. Furthermore, in the ex vivo organ culture partial thickness cartilage defect model, implantation of the neocartilage grafts into defects for 16 weeks resulted in the formation of hyaline cartilage-like repair tissue that adhered to the host cartilage and contributed to significant improvements to the tissue architecture within the defects, compared to the empty defects. The study has demonstrated the first successful application of the acoustofluidic perfusion bioreactors to bioengineer scaffold-free neocartilage grafts of human articular chondrocytes that have the potential for subsequent use in second generation autologous chondrocyte implantation procedures for the repair of partial thickness cartilage defects.
Bone structure a b s t r a c t An improved understanding of bone mechanics is vital in the develo... more Bone structure a b s t r a c t An improved understanding of bone mechanics is vital in the development of evaluation strategies for patients at risk of bone fracture. The current evaluation approach based on bone mineral density (BMD) measurements lacks sensitivity, and it has become clear that as well as bone mass, bone quality should also be evaluated. The latter includes, among other parameters, the bone matrix material properties, which in turn depend on the hierarchical structural features that make up bone as well as their composition. Optimal load transfer, energy dissipation and toughening mechanisms have, to some extent, been uncovered in bone. Yet, the origin of these properties and their dependence upon the hierarchical structure and composition of bone are largely unknown. Here we investigate load transfer in the osteonal and sub-osteonal levels and the mechanical behaviour of osteonal lamellae and interlamellar areas during loading. Using cantilever-based nanoindentation, in situ microtensile testing during atomic force microscopy (AFM) and digital image correlation (DIC), we report evidence for a previously unknown mechanism. This mechanism transfers load and movement in a manner analogous to the engineered ''elastomeric bearing pads'' used in large engineering structures. m-RAMAN microscopy investigations showed compositional differences between lamellae and interlamellar areas. The latter have lower collagen content but an increased concentration of noncollagenous proteins (NCPs). Hence, NC-enriched areas on the microscale might be similarly important for bone failure as ones on the nanoscale. Finally, we managed to capture stable crack propagation within the interlamellar areas in a time-lapsed fashion, proving their significant contribution towards fracture toughness. (P.J. Thurner). j o u r n a l o f t h e m e c h a n i c a l b e h a v i o r o f b i o m e d i c a l m a t e r i a l s 1 7 ( 2 0 1 3 ) 1 5 2 -1 6 5