Biomedical subjects

H P Wiesmann

Publications and source records attributed to H P Wiesmann.

At least 19 recordsLinked to original sources

PubMed2006

Mineralization at the interface of implants.

Osseointegration of implants is crucial for the long-term success of oral implants. Mineralization of the bone's extracellular matrix as the ultimate step of a mature bone formation is closely related to implant osseointegration. Osteogenesis at oral implants is a complex process, driven by cellular and acellular phenomena. The biological process of the maintenance and emergence of minerals in the vicinity of oral implants is influenced to a great extent by biophysical parameters. Implant-related structural and functional factors, as well as patient-specific factors, govern the features of osteogenesis. To understand the influence of these factors in peri-implant bone mineralization, it is important to consider the basic biological processes. Biological and crystallographic investigations have to be applied to evaluate mineralization at implant surfaces at the different hierarchical levels of analysis. This review gives insight into the complex theme of mineral formation around implants. Special focus is given to new developments in implant design and loading protocols aimed at accelerating osseointegration of dental implants.

Bone and Bones↗

PubMed2005

Principles of bone formation driven by biophysical forces in craniofacial surgery.

Biophysical forces, particularly mechanical loading and electromagnetic signals, are important regulators of bone formation. Indeed, the regenerative capacity of bony tissue is largely the result of the bone's capacity to recognise the functional environment required for the emergence and maintenance of a structurally intact bone. Biophysical methods of stimulation have therefore been introduced and have proved successful in clinical practice with craniofacial bones. Distraction osteogenesis, application of ultrasound, calculated transfer of stresses, and exposure to an electromagnetic field are some examples of biophysically driven approaches to influencing bone formation. The purpose of this review is to provide an insight into cellular and tissue models that are used to study the effects of biophysical stimuli on bone.

Bone Remodeling↗

PubMed2005

Design and performance of a bioreactor system for mechanically promoted three-dimensional tissue engineering.

There is currently considerable interest in increasing the response of mesenchymal cells to physical forces, and numerous loading devices have been used to increase the formation of skeletal tissue in vivo and in vitro. We have developed a bioreactor system to apply cyclic strains on three-dimensional specimens over a range of 0-20,000 mustrain. The piezoelectric-driven mechanism allows the precise adjustment and control over load-related deformations of tissue, as shown by finite-element calculations of deformation of a collagen gel under load. We present the design of the bioreactor and its performance in specimens of tissue containing activated osteoblasts and chondrocytes. Biaxial tissue straining at 2,000 mustrain led to a substantial increase in the number of both types of cell compared with unstimulated controls. The synthesis of cell-specific extracellular matrix proteins increased when physiological loads (2,000 mustrain) were applied in the bioreactor, whereas higher deformations (20,000 mustrain) resulted in a reduction in proliferation and differentiation of cells. The mechanisms whereby mechanical stimulation leads to a defined cell reaction are not known, but the application of physiological micromovements in extracorporeal tissue chambers is a promising approach to the formation of hard tissue.

Animals↗

PubMed2005

Basic reactions of osteoblasts on structured material surfaces.

In order to assess how bone substitute materials determine bone formation in vivo it is useful to understand the mechanisms of the material surface/tissue interaction on a cellular level. Artificial materials are used in two applications, as biomaterials alone or as a scaffold for osteoblasts in a tissue engineering approach. Recently, many efforts have been undertaken to improve bone regeneration by the use of structured material surfaces. In vitro studies of bone cell responses to artificial materials are the basic tool to determine these interactions. Surface properties of materials surfaces as well as biophysical constraints at the biomaterial surface are of major importance since these features will direct the cell responses. Studies on osteoblastlike cell reactivity towards materials will have to focus on the different steps of protein and cell reactions towards defined surface properties. The introduction of new techniques allows nowadays the fabrication of materials with ordered surface structures. This paper gives a review of present knowledge on the various stages of osteoblast reactions on material surfaces, focused on basic cell events under in vitro conditions. Special emphasis is given to cellular reactions towards ordered nano-sized topographies.

Biocompatible Materials↗

PubMed2005

[Osteoblast reaction on SLA and microgrooved implant surfaces].

The osseointegration process of dental implants depends on the tissue reaction at the tissue-implant interface. Osteoblasts are the main cells responsible for the regulation of osteoinduction. The manner and kinetics of the tissue reaction crucially depend on the interaction between osteoblasts and the morphology of the implant surface. The aim of this study was to investigate osteoblast behaviour on different implant surfaces (smooth, microgrooved, SLA) under standardized conditions. For this in vitro investigation we used primary bovine osteoblasts. Attachment kinetics, proliferation rate and synthesis of bone-associated proteins were used as parameters for cell reaction. The results demonstrate that both attachment and adhesion strength of the primary cell surface interaction was higher on the microgrooved surfaces than on SLA surfaces. The proliferation rate of cells and the synthesis of bone-specific proteins were higher on microgrooved surfaces in contrast to SLA surfaces. Ultrastructural analysis revealed phenotypic osteoblast-like cells on smooth and microgrooved surfaces, whereas cells on SLA surfaces showed a more fibroblastic appearance. This study demonstrates that the morphology of the implant surface determined the subsequent osteoblast reaction. An optimal cell reaction was found at surfaces which are smooth in the microenvironment of osteoblasts.

Animals↗

PubMed2005

Aspects of collagen mineralization in hard tissue formation.

Collagen is the dominant fibrous protein not only in connective tissues but also in hard tissues, bone, dentin, cementum, and even the mineralizing cartilage of the epiphyseal growth plate. It comprises about 80-90% (by weight) of the organic substance in demineralized dentin and bone. When collagen fibers are arranged in parallel to form thicker bundles, as in lamellar bone and cementum, interior regions may be less mineralized; in dentin, however, the collagen fibers form a network and collagen fibers are densely filled with a mineral substance. In the biomineralization of collagen fibers in hard tissues, matrix vesicles play a fundamental role in the induction of crystal formation. The mineralization of matrix vesicles precedes the biomineralization of the collagen fibrils and the intervening ground substance. In addition, immobilized noncollagenous fibrous macromolecules, bound in a characteristic way to the fibrous collagen surface, initiate, more intensely than collagen, mineral nucleation in the hard tissue matrix.

Animals↗

PubMed2004

Ultrastructural characterization of the implant/bone interface of immediately loaded dental implants.

Primary stability and an optimized load transfer are assumed to account for an undisturbed osseointegration process of implants. Immediate loaded newly designed titanium dental implants inserted in the mandible of minipigs were used for the characterization of the interfacial area between the implant surface and the surrounding bone tissue during the early healing phase. Histological and electron microscopical studies were performed from implant containing bone specimens. Two different load regimens were applied to investigate the load related tissue reaction. Histological and electron microscopical analysis revealed a direct bone apposition on the implant surfaces, as well as the attachment of cells and matrix proteins in the early loading phase. A striking finding of the ultrastructural immunocytochemical investigations was the synthesis and deposition of bone related proteins (osteonectin, fibronectin, fibronectin receptor) by osteoblasts from day one of bone/biomaterial interaction. Calcium-phosphate needle-like crystallites were newly synthesized in a time-related manner directly at the titanium surface. No difference in the ultrastructural appearance of the interface was found between the two loading groups. Our experimental data suggest that loading of specially designed implants can be performed immediately after insertion without disturbing the biological osseointegration process.

Animals↗

PubMed2004

Biological and biophysical principles in extracorporal bone tissue engineering. Part II.

The aim of this review is to characterise the biological and biophysical background of in vitro bone tissue engineering. The paper focuses on basic principles in extracorporal engineering of bone-like tissues, considering parameters such as scaffold design, tissue construction, bioreactors, and cell stimulation in vivo and in vitro. Scaffolds have a key function concerning cellular invasion and bone formation. The intra-architectural scaffold geometry, as well as the scaffold material, play an important role in the process of bone regeneration. Various types of bioreactors have been tested for their utility in bone substitute fabrication that is clinically effective and reproducible. Sophisticated bioreactor systems are those that mimic the three-dimensional morphology and the mechanical situation of bones. Mechanical stimulation as well as other biophysical stimuli appear to be critical factors for proliferation and differentiation of bone cells and for bone mineral and structure formation. Furthermore an enhancement of bone regeneration by application of chemical stimulation factors is discussed.

Animals↗

PubMed2004

Biological and biophysical principles in extracorporal bone tissue engineering. Part III.

Over the last decade extracorporal bone tissue engineering has moved from laboratory to clinical application. The restoration of maxillofacial bones from cell harvesting through product manufacture and end-use has benefited from innovations in the fields of biomechanical engineering, product marketing and transplant research. Cell/scaffold bone substitutes face a variety of unique clinical challenges which must be addressed. This overview summarises the recent state of the art and future anticipations in the transplantation of extracorporally fabricated bone tissues.

Animals↗

PubMed2004

Biological and biophysical principles in extracorporal bone tissue engineering. Part I.

Advances in the field of bone tissue engineering have encouraged physicians to introduce these techniques into clinical practice. Bone tissue engineering is the construction, repair or replacement of damaged or missing bone in humans or animals. Engineering of bone can take place within the animal body or extracorporal in a bioreactor for later grafting into the body. Appropriate cell types and non-living substrata are minimal requirements for an extracorporal tissue engineering approach. This review discusses the biological and biophysical background of in vitro bone tissue engineering. Biochemical and biophysical stimuli of cell growth and differentiation are regarded as potent tools to improve bone formation in vitro. The paper focuses on basic principles in extracorporal engineering of bone-like tissues, intended to be implanted in animal experiments and clinical studies. Particular attention is given in this part to the contributions of cell and material science to the development of bone-like tissues. Several approaches are at the level of clinical applicability and it can be expected that widespread use of engineered bone constructs will change the surgeon's work in the near future.

Animals↗

PubMed2003

Evaluation of accuracy of insertion of dental implants and prosthetic treatment by computer-aided navigation in minipigs.

The survival of loaded implants is critically dependent on their biomechanical stability. We have used a computer-guided navigation technique to evaluate the accuracy of computer-assisted insertion for immediately-loaded implants in minipigs. On the basis of computed tomographical data, the Robodent system was used for preoperative planning and guidance of inserting the implant. An optical tracking system allowed positioning of the implant and immediate prosthetic rehabilitation by inserting it in a plaster model and during the operation. Postoperative computed tomograms (CT) showed that the implants were placed precisely in the preoperatively planned position. The accuracy achieved corresponded well with the spatial resolution of the CT used. Immediate placement of the prefabricated crowns resulted in favourable occlusal positioning. Histological cross-sections showed that the implants were biomechanically stable. The accuracy of insertion of oral implants illustrated here suggests that insertion and prosthetic modelling of implants may benefit from computer-assisted navigation.

Animals↗

PubMed2002

[Evaluating angiogenesis and osteogenesis modified by vascular endothelial growth factor (VEGF)].

PURPOSE: This intention of this study was to investigate the influence of controlled release of vascular endothelial growth factor (VEGF) on angiogenesis and osteogenesis in a mandibular defect model. METHODS: A total of 56 rabbits were operated and bicortical holes were placed in the mandible. The defects were filled with collagen type I implants, collagen implants complexed with 0.8-microgram VEGF165, or left without any filling. After 3, 7, 14, and 28 days specimens were taken and histologic, histomorphometric, and immunohistologic analyses were carried out concerning density of vessels, total surface of vessels, bone surface, and bone density. RESULTS: The number of vessels was increased in all groups up to 14 days, followed by physiologic regression in the control groups, whereas the study group showed persistently high numbers. The density of regenerated bone was significantly higher in the study group. CONCLUSION: The activation of angiogenesis using VEGF165 leads to more intensive angiogenesis and bone regeneration.

Animals↗

PubMed2001

[Mechanical stimulation of osteoblasts in cell culture].

BACKGROUND: Mechanical loading of bone is known to play a crucial role in bone remodeling and regeneration. Whereas the clinical effects of mechanically modulated bone healing have been extensively studied, less is known about the underlying mechanisms on a cellular level. This study was aimed at investigating the effects of uniaxial strains on osteoblast-like cells in culture. Mechanical loading was applied in physiological and hyperphysiological magnitudes. Nonstimulated cultures served as controls. RESULTS: Cultured primary bovine periosteal cells exhibited phenotypic features of osteoblast-like cells. Application of physiological strains (2,000 mu strain) led to a bone-specific expression of extracellular matrix proteins (osteonectin, osteocalcin, collagen type I). Hyperphysiological loads (10,000 mu strain) were associated with an increased synthesis of proteoglycans. Proliferation of cells was higher than the controls at 10,000 mu strain and showed no difference from physiologically loaded osteoblasts. DISCUSSION: Our study demonstrates that physiological loading of osteoblast-like cells enhances the regenerative capacity of bone, whereas hyperphysiological loads may impair bone regeneration.

Animals↗

PubMed2001

Quantitative analyses of the biomineralization of different hard tissues.

The primary crystallites of the different developing hard tissues have an apatite structure. However, they have crystal lattice distortions representing an intermediate state between amorphous and fully crystalline. We have applied energy-filtering transmission electron microscopy in the selected area electron diffraction mode to analyse different stages of crystal formation in dentine, bone, enamel and inorganic apatite mineral. We have obtained quantitative information on the degree of crystal lattice distortion using the paracrystal theory of Hosemann and Bagchi. We have found that the early formed crystallites of the hard tissues being analysed have a paracrystalline character comparable to biopolymers. However, with maturation, the lattice fluctuations of the crystallites of the hard tissues bone, enamel and dentine decrease to form a typical (para)crystalline character. Also the decrease of the organic proportion in the matrix corresponds to the decrease of the lattice fluctuation of the crystallites in the different hard tissues during maturation.

Animals↗

PubMed2001

Microstructural investigations of strain-related collagen mineralization.

Distraction osteogenesis in rabbit mandibles after osteotomy can be used as an experimental model to study the microstructural features of mineralization of callus under defined mechanical loads. Our aim was to study the relation between the micromotions in the gap and the resulting features of mineralization of the matrix. We found that assembly of collagen and formation of crystals depended on the magnitude of the mechanical stress applied. At physiological bone strains (2000 microstrains), the callus had collagen type I in a mature bone-like extracellular arrangement, whereas at 20000 microstrains bundles were orientated predominantly towards the tension vector. Maximum loads (200000 microstrains) resulted in disorganized assembly of the collagen. Quantitative energy-dispersive analysis by X-rays confirmed that high strains were associated with substantially lower concentrations of calcium and phosphate. In contrast to bone-like apatitic formation of crystals at physiological strains, significantly fewer but larger crystals were detected by electron diffraction analysis in samples exposed to high strains. We suggest that mechanical stress regulates the assembly and mineralization of collagen during distraction osteogenesis.

Animals↗

PubMed2001

Mechanical tension in distraction osteogenesis regulates chondrocytic differentiation.

Differentiation of chondrocytes to cells of osteoblastic phenotype occurs during an interim period of bone development, fracture repair and distraction osteogenesis. To study the relationship between tension-stress and chondrogenesis, uniaxial strains (0 microstrains, 2000 microstrains, 20000 microstrains, 200000 microstrains, 300000 microstrains) were applied in a rabbit model of mandibular distraction osteogenesis. The results demonstrated that cell differentiation, apoptosis and tissue development in the newly formed gap tissue showed a correlation to the applied strain magnitudes. Only strains of 20000 microstrains resulted in a statistically significant (P<0.05) formation of cartilage struts with embedded chondrocyte-like cells. However, chondrocyte-like cells were rarely detected in samples distracted at lower or higher strain magnitudes. Osteoblasts appeared to replace cartilaginous matrix by mineralized bone matrix. The phenotypic change from chondrocytes to osteoblasts was accompanied by a decreased proteoglycan synthesis. a change in the expression from type II collagen towards type I and involved asymmetric cell divisions and apoptotic cell death. Therefore, we suggest that mechanical strain is an external stimulus responsible for phenotypic cell alterations.

Analysis of Variance↗

PubMed2000

Periosteally derived osteoblast-like cells differentiate into chondrocytes in suspension culture in agarose.

Pluripotent cells from the periosteal layer adjacent to cortical bone attain an osteoblast-like phenotype in culture when reaching confluence in monolayer. It is unknown whether such newly differentiated osteoblast-like cells preserve the chondrogenic potential characteristics for stem cells derived from the periosteum. Primary osteoprogenitor cells derived from bovine metacarpal periosteum were differentiated into alkaline phosphatase-positive osteoblast-like cells by an established monolayer culture protocol. After transfer into suspension culture in agarose gels, the cells differentiated into chondrocytes demonstrated by the production of collagen II, but not of collagen I, as well as alkaline phosphatase activity was abated. Contrarily, with continuation of monolayer culture, the cells maintained their osteoblast-like phenotype and secreted large amounts of collagen I and a minor quantity of collagen III and V. The alkaline phosphatase activity steadily increased during the entire culture period of 2 weeks. Thus, our culture techniques can serve as useful tools to study mechanisms of differentiation by modulating the phenotypic potential of osteogenic cells. The results presented here support the notion that the extracellular environment strongly influences the cell type and its metabolism.

Alkaline Phosphatase↗

PubMed2000

Capacitively coupled electric fields accelerate proliferation of osteoblast-like primary cells and increase bone extracellular matrix formation in vitro.

Over the last few years, electric and electromagnetic fields have gained more and more significance in the therapy of bone fracture healing and bone disease. Yet, the underlying mechanisms on a cellular and molecular level are not completely understood. In the present study we have investigated the effects of capacitively coupled, pulsed electric fields on cellular proliferation, alkaline phosphatase activity, and matrix protein synthesis of osteoblast-like primary cells in vitro. Cells were derived from bovine periosteum and electrically stimulated by saw-tooth pulses of 100 V external voltage and 16 Hz frequency. This corresponds to an electric field of 6 kV/m across the cell membranes as could be shown by computer simulation. Field application caused acceleration of cell culture development. A significant increase of proliferation concurrent with an enhancement of alkaline phosphatase activity was observed in sub-confluent cultures. Exposure of confluent osteoblast-like primary cells to electric fields resulted in enhanced synthesis and secretion of extracellular matrix-related proteins. These findings suggest that capacitively coupled electric fields accelerate bone cell proliferation and differentiation in vitro and enhance the synthesis of cells leading to promoted matrix formation and maturation.

Alkaline Phosphatase↗