Papers by Author: Günter Ziegler

Abstract: In this study the degradation behaviour of pure hydroxyapatite (HA), pure tricalcium phosphate (β-TCP) and four biphasic calcium phosphate ceramics was studied to gain information about the influence of the phase composition on this property with the aim to tailor individually adapted bone substitute materials. The chemical dissolution of each ceramic composition was measured by its release of calcium ions into a buffered solution. With decreasing HA content in the ceramics the degradation rate increased. Cell experiments were carried out with stimulated osteoclast-like RAW 264.7 cells. Using biochemical, genetic and microscopic analysis, the differentiation of the cells on the ceramic samples was studied. The monocytic precursor cells differentiated into osteoclast-like cells on all ceramics. The strongest cell differentiation into osteoclast-like cells was found on ceramics with HA/β-TCP ratios of 80/20, 60/40 and 40/60. Cells on these ceramics had many nuclei and the largest cell size. As a result of resorption, lacunas were found on all ceramics except β-TCP. All these experimental results proved the influence of the phase composition on degradation and resorption of calcium phosphate ceramics. Biphasic calcium phosphate ceramics with HA/β-TCP ratios of 80/20 and 60/40 exhibited the most promising properties to serve as synthetic bone substitute materials because for integration in the physiological bone remodeling process the implanted bone substitute materials should have optimized dissolution and resorption properties.

Abstract: In the last few years new fabrication methods, called rapid prototyping (RP) techniques, have been developed for the fabrication of hydroxyapatite scaffolds for bone substitutes or tissue engineering applications. With this generative fabrication technology an individual tailoring of the scaffold characteristics can be realised. In this work two RP techniques, a direct (dispense-plotting) and an indirect one (negative mould technique), are described by means of fabricating hydroxyapatite (HA) scaffolds for bone substitutes or bone tissue engineering. The produced scaffolds were characterised, mainly regarding their pore and strut characteristics. By these data the performance of the two fabrication techniques was compared. Dispense-plotting turned out to be the faster technique while the negative mould method was better suited for the fabrication of exact pore and strut geometries.

Abstract: The aim of this study is to analyse the influence of differently fabricated HA-scaffolds on bone marrow stromal cells. Therefore, three methods were used (a polyurethane (PU)-replica technique, the dispense-plotting and a negative mould technique) to produce porous hydroxyapatite (HA) ceramics. The different HA-scaffolds were then cultivated with an osteoblastic precursor cell line. In our study, highest cell proliferation and differentiation was achieved by using (PU)-replica technique. However, this study shows also that all three types of scaffolds are suitable for tissue engineering applications and as bone substitute material. The knowledge about the influence of pore size and geometry on the cell behaviour will help to tailor scaffolds, by different 3D fabrication methods, for the needs of tissue engineering laboratories or patients.

Abstract: Bone remodelling is a coupled process of bone formation and resorption. This process is physiologically controlled and involves the synthesis of bone matrix by osteoblasts and bone resorption by giant cells called osteoclasts. It includes a complex interaction of cells, with specific chemokine signalling. In order to study bone remodelling in vitro, we cultivated two precursor cellline types in a model coculture system on synthetic hydroxyapatite ceramic (HA) for 14 days. The monocytes have the capacity to differentiate into osteoclast-like cells, and the bone marrow stromal cells can differentiate into osteoblast-like cells. This coculture was used to analyse the in vitro cell interaction between monocytes and stromal cells. Furthermore, the attachment of the bone marrow stromal cells to the resorbed HA-surfaces was studied. In this in vitro study we demonstrated osteoclast-like differentiation and bone marrow stromal growth in a coculture system on a synthetic bone substitute material. Under optimal conditions, HA can be resorbed and bone marrow cells can grow into the lacunas to form new bone. These results give important cues for the adjustment of synthetic bone substitute materials for optimal remodelling behaviour.

Abstract: Hydroxyapatite ceramics for biomedical applications are used in form of layers, granulates and bulk materials. A new method to produce layers or bulk materials is the electrophoretic deposition. To achieve layers with a thickness between 5 and 50 m the use of a fine powder with particle size in the sub micron range is essential. In this work we show that commercially available hydroxyapatite powders, which usually have a strong tendency to agglomerate, can be milled to particle sizes smaller than 500 nm. Using one of these powders and optimizing the parameters for the electrophoretic deposition thin, homogenous layers were produced.