Biomedical subjects

Hans-Peter Wiesmann

Publications and source records attributed to Hans-Peter Wiesmann.

12 recordsLinked to original sources

PubMed2007

Prospects of micromass culture technology in tissue engineering.

Tissue engineering of bone and cartilage tissue for subsequent implantation is of growing interest in cranio- and maxillofacial surgery. Commonly it is performed by using cells coaxed with scaffolds. Recently, there is a controversy concerning the use of artificial scaffolds compared to the use of a natural matrix. Therefore, new approaches called micromass technology have been invented to overcome these problems by avoiding the need for scaffolds. Technically, cells are dissociated and the dispersed cells are then reaggregated into cellular spheres. The micromass technology approach enables investigators to follow tissue formation from single cell sources to organised spheres in a controlled environment. Thus, the inherent fundamentals of tissue engineering are better revealed. Additionally, as the newly formed tissue is devoid of an artificial material, it resembles more closely the in vivo situation. The purpose of this review is to provide an insight into the fundamentals and the technique of micromass cell culture used to study bone tissue engineering.

Animals↗

PubMed2006

Decreased CD90 expression in human mesenchymal stem cells by applying mechanical stimulation.

BACKGROUND: Mesenchymal stem cells (MSC) are multipotent cells which can differentiate along osteogenic, chondrogenic, and adipogenic lineages. The present study was designed to investigate the influence of mechanical force as a specific physiological stress on the differentiation of (MSC) to osteoblast-like cells. METHODS: Human MSC were cultured in osteoinductive medium with or without cyclic uniaxial mechanical stimulation (2000 mustrain, 200 cycles per day, 1 Hz). Cultured cells were analysed for expression of collagen type I, osteocalcin, osteonectin, and CD90. To evaluate the biomineral formation the content of bound calcium in the cultures was determined. RESULTS: After 14 days in culture immunfluorescence staining revealed enhancement of collagen type I and osteonectin expression in response to mechanical stimulation. In contrast, mechanically stimulated cultures stained negative for CD90. In stimulated and unstimulated cultures an increase in the calcium content over time was observed. After 21 days in culture the calcium content in mechanical stimulated cultures was significantly higher compared to unstimulated control cultures. CONCLUSION: These results demonstrate the influence of mechanical force on the differentiation of human MSC into osteoblast-like cells in vitro. While significant enhancement of the biomineral formation by mechanical stimulation is not detected before 21 days, effects on the extracellular matrix became already obvious after 14 days. The decrease of CD90 expression in mechanically stimulated cultures compared to unstimulated control cultures suggests that CD90 is only transiently expressed expression during the differentiation of MSC to osteoblast-like cells in culture.

Journal Article↗

PubMed2006

Kinetic oxygen measurements by CVC96 in L-929 cell cultures.

Generally animal and human cells use oxygen during their whole life. Consequently the oxygen use is a simple indicator to test the vitality of cells. When the vitality decreases by the delivery of toxic substances the decrease can be observed directly by the oxygen-use of the cells. To get fast information of the vitality of cells we have measured the O2-tension by testing a new model of a bioreactor, the Cell Vitality Checker 96 (CVC96), in practical application. With this CVC96, soon a simple test will exist for the measurement of the oxygen use. In this respect the question had to be answered whether the use in the laboratory is easy and whether oxygen as a parameter in the vitality test can also be applied in future for problems in the field of material testing.

Animals↗

PubMed2006

Biological and biomechanical evaluation of interface reaction at conical screw-type implants.

BACKGROUND: Initial stability of the implant is, in effect, one of the fundamental criteria for obtaining long-term osseointegration. Achieving implant stability depends on the implant-bone relation, the surgical technique and on the microscopic and macroscopic morphology of the implant used. A newly designed parabolic screw-type dental implant system was tested in vivo for early stages of interface reaction at the implant surface. METHODS: A total of 40 implants were placed into the cranial and caudal part of the tibia in eight male Göttinger minipigs. Resonance frequency measurements (RFM) were made on each implant at the time of fixture placement, 7 days and 28 days thereafter in all animals. Block biopsies were harvested 7 and 28 days (four animals each) following surgery. Biomechanical testing, removable torque tests (RTV), resonance frequency analysis; histological and histomorphometric analysis as well as ultrastructural investigations (scanning electron microscopy (SEM)) were performed. RESULTS: Implant stability in respect to the measured RTV and RFM-levels were found to be high after 7 days of implants osseointegration and remained at this level during the experimented course. Additionally, RFM level demonstrated no alteration towards baseline levels during the osseointegration. No significant increase or decrease in the mean RFM (6029 Hz; 6256 Hz and 5885 Hz after 0-, 7- and 28 days) were observed. The removal torque values show after 7 and 28 days no significant difference. SEM analysis demonstrated a direct bone to implant contact over the whole implant surface. The bone-to-implant contact ratio increased from 35.8 +/- 7.2% to 46.3 +/- 17.7% over time (p = 0,146). CONCLUSION: The results of this study indicate primary stability of implants which osseointegrated with an intimate bone contact over the whole length of the implant.

Journal Article↗

PubMed2005

Strain driven fast osseointegration of implants.

BACKGROUND: Although the bone's capability of dental implant osseointegration has clinically been utilised as early as in the Gallo-Roman population, the specific mechanisms for the emergence and maintenance of peri-implant bone under functional load have not been identified. Here we show that under immediate loading of specially designed dental implants with masticatory loads, osseointegration is rapidly achieved. METHODS: We examined the bone reaction around non- and immediately loaded dental implants inserted in the mandible of mature minipigs during the presently assumed time for osseointegration. We used threaded conical titanium implants containing a titanium2+ oxide surface, allowing direct bone contact after insertion. The external geometry was designed according to finite element analysis: the calculation showed that physiological amplitudes of strain (500-3,000 ustrain) generated through mastication were homogenously distributed in peri-implant bone. The strain-energy density (SED) rate under assessment of a 1 Hz loading cycle was 150 Jm-3 s-1, peak dislocations were lower then nm. RESULTS: Bone was in direct contact to the implant surface (bone/implant contact rate 90%) from day one of implant insertion, as quantified by undecalcified histological sections. This effect was substantiated by ultrastructural analysis of intimate osteoblast attachment and mature collagen mineralisation at the titanium surface. We detected no loss in the intimate bone/implant bond during the experimental period of either control or experimental animals, indicating that immediate load had no adverse effect on bone structure in peri-implant bone. CONCLUSION: In terms of clinical relevance, the load related bone reaction at the implant interface may in combination with substrate effects be responsible for an immediate osseointegration state.

Dental Implants↗

PubMed2005

Tissue engineering: a challenge of today's medicine.

During the last years, tissue engineering-based therapies have been introduced in clinical practice in the head and face area. The regeneration of complex tissue structures for all sites of the body is envisioned for the future. In the present situation, specialists of the different fields publish excellent research papers in specialised journals. As a result, the scientific community, separated towards distinct sub-specialities, has difficulties in communication. To overcome this problem, the demanding, complex and interdisciplinary aspects of tissue engineering has to be approached from new ways. We have conceptualised Head & Face Medicine therefore as a thematically broad ranged journal, including all disciplines involved in the head and neck area. We hope this journal will attract basic researchers and clinicians who are involved in investigating and applying complex themes (examplified by tissue engineering) in the head and face region and will contribute to a gain in scientific information, communication, and collaboration in order to improve the outcome of patient treatments.

Biomedical Research↗

PubMed2005

VEGF-activated angiogenesis during bone regeneration.

PURPOSE: The aim of this study was to investigate the influence of controlled release of recombinant human vascular endothelial growth factor (rhVEGF(165)) on angiogenesis and osteogenesis in a mandibular defect model. MATERIAL AND METHODS: A total of 56 rabbits were operated and bicortical holes were placed at the lower border of the mandible. The defects were filled with type-I collagen, with collagen complexed with 0.8 mug rhVEGF(165), 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 number of vessels, cross-sectional area of vessels, and area and density of regenerated bone. RESULTS: Bone formation occurred in a typical centripetal direction and showed all stages of bone regeneration and maturation. New vessel formation took place in front of the osteogenic regeneration front. The number of vessels increased in all groups until day 14, followed by physiologic regression in the control groups as opposed to persisting high numbers in the study group. The area of newly formed bone showed no difference to the control group but the density of regenerated bone was significantly higher in the study group. CONCLUSION: Blood vessels are an important component of bone formation and maintenance and the bone tissue differentiation is related to the local presence of blood vessels. The activation of angiogenesis using rhVEGF(165) leads to more intensive angiogenesis and bone regeneration.

Animals↗

PubMed2004

Influence of titanium surfaces on attachment of osteoblast-like cells in vitro.

Implant surface topography influences osteoblastic proliferation, differentiation and extracellular matrix protein expressions. Studies on preliminary interactions of osteoblast-like cells on implant interface through in vitro systems, can give lucid insights to osseo-integrative efficacies of when in vivo implants. In the present investigation two titanium surfaces of dental implants, a sandblasted and acid-etched surface and an experimental grooved surface were compared through in vitro systems. The titanium implants were seeded with osteoblast-like primary cells and maintained for a period of 1-7 days. Expressions of fibronectin and osteonectin were assessed through immunogold labelling by scanning electron microscopy. The grooved surface, supported better osteoblastic cell adhesion and proliferation than the rough surfaces. Further, osteoblastic cells on the grooved surfaces also displayed a strong labelling for fibronectin at the cytoplasmic extensions coupled with intense osteonectin expression in comparison to the rough surfaced implants. In conclusion, grooved surfaces offered better cell attachment and proliferation than the other rough surfaces studied.

Animals↗

PubMedDate not supplied

Early tissue reaction at the interface of immediately loaded dental implants.

PURPOSE: The treatment of patients with early or immediately loaded dental implants has renewed interest in the behavior of osteoblasts at the implant surface under load. A newly designed dental implant indicated for immediate loading was tested in vivo for early stages of osteoblast behavior at the implant surface. MATERIALS AND METHODS: Thirty-two implants were placed in the mandibles of 8 minipigs. Half of the implants (n = 16) were immediately loaded under occlusal contacts, and implants placed in non-occlusal relations served as a control. RESULTS: All implants, except 1 that showed signs of tissue infection, healed uneventfully and were stable throughout the experimental period. Ultrastructural analysis of mandibular specimens revealed an intimate attachment of osteoblasts to the material surface beginning as early as day 1. Application of either occlusal or non-occlusal load did not alter the phenotypic morphology of the attached osteoblasts. Transmission electron microscopy and x-ray diffraction analysis demonstrated a direct contact of bone-like minerals over the whole implant surface with no signs of crestal hard tissue alteration. Electron diffraction analysis showed a slight release of titanium from the implant side. DISCUSSION: These results indicate that immediate loading of specially designed dental implants can be performed without disruption of the titanium/bone interface or disturbance of osteoblast physiology in the early loading phase. CONCLUSION: Immediate loading protocols can be performed without disturbance of normal bone biology.

Animals↗

PubMedDate not supplied

Image-based extracorporeal tissue engineering of individualized bone constructs.

PURPOSE: Computer-aided technologies have been recently employed for use in extracorporeal bone tissue engineering strategies. In this pilot animal experimental study, the intention was to test whether autologous osteoblast-like cells cultured in vitro on individualized scaffolds can be used to support bone regeneration in a clinical environment. MATERIALS AND METHODS: For this purpose, mandibular bone defects were surgically introduced into the mandibles of minipigs and the scaffold of the defect site was modeled by computer-aided design/computer-aided manufacturing technique. Autologous bone cells from porcine calvaria were harvested from minipigs and grown in culture. Cells were seeded on scaffolds generated by rapid prototyping of polylactic acid/polyglycolic acid copolymers. The defects were then reconstructed by implanting the tissue constructs. RESULTS: The intraoperative sites as well as the postoperative computerized tomographic scans demonstrated an accurate fit in the defect sites. The implanted scaffold constructs enriched with osteoblast-like cells were well tolerated and appeared to support bone formation, as revealed by histologic and immunohistochemical analyses. DISCUSSION: These results indicated that in vitro expanded osteoblast-like cells spread on a resorbable individualized scaffold can be capable of promoting the repair of bony defects in vivo. CONCLUSION: These results warrant further attempts to combine computer modeling and tissue engineering for use in bone reconstructive surgery.

Animals↗

PubMedDate not supplied

Cell-based bone reconstruction therapies--cell sources.

Over the last few decades, reconstructive surgery has shifted from a resection-oriented approach toward strategies focusing on repair and regeneration of tissues. As the main aim of maxillofacial reconstruction has been the restoration of bone form and function, surgeons used artificial tissue substitutes in the early decades of bone reconstruction. These artificial materials significantly improved the ability of surgeons to restore the form and, to some extent, the function of defective bones. Despite the fact that every artificial material has specific disadvantages, the use of biomaterials is a common treatment option in clinical practice even today. Due to the more detailed understanding that exists concerning transplantation of cells and tissues, autogenous grafts are the second mainstay in clinical practice. However, the main disadvantage of using autogenous grafts is donor site morbidity and donor shortage. Research is currently in progress into the use of cell-based approaches in reconstructive surgery, since cells are the driving elements for all repair and regeneration processes. Various cell populations have been reported on in the relevant literature. These cells can be classified according to differentiation capacity and the tissue from which they originated. In this review, unrestricted cells, multipotential progenitor cells, determined cells, and genetically modified cells are described systematically, and their advantages as well as limitations are discussed. (More than 50 references.)

Bone and Bones↗

PubMedDate not supplied

Cell-based bone reconstruction therapies-principles of clinical approaches.

Cell-based bone tissue engineering is a rapidly evolving therapy option in bone reconstruction strategies. Some cell-driven approaches, especially the biophysical stimulation of the host cell population surrounded by the bone defect, are common treatment methods in maxillofacial surgery. Others, such as autologous cell implantation, have now gained acceptance for clinical trials. More advanced or complex therapeutical options (extracorporeal tissue engineering, stem cell use, genetic engineering) have been tested in preclinical investigations but have not reached the level of clinical use. Two different aspects are of special relevance in cell-based bone reconstruction therapies. The source of cells used to regenerate bone (discussed in detail in a complementary review in this issue of The International Journal of Oral and Maxillofacial Implants) as well as the principal approach of a cell-driven bone regeneration therapy influence the outcome of such engineering strategies. All of the cell-driven repair strategies are under intensive investigation in an effort to provide surgeons with a limitless supply of tissue for bone repair and reconstruction in future procedures. An overview of the basic biological aspects as well as the inherent constraints of different cell-based approaches are given in this paper.

Animals↗