Erich Wintermantel

Tissue engineering scaffolds using superstructures

Here, scaffolds as cell and tissue carriers are approached from an engineering point of view, emphasizing material superstructuring in the design of supports. Superstructure engineering provides optimal spatial and nutritional conditions for cell maintenance by the arrangement of structural elements (e.g. pores or fibres) so as to vary the order of cell to cell contact. This approach is illustrated in the design of several scaffolds: knitted fabrics as three-dimensional superstructures for optimized osteosynthesis implants, a new injectable open porous implant system, an angiopolar non-degradable ceramic cell carrier, and an injectable or microsurgically implantable entangled carrier system. The implications for tissue engineering are discussed.

Titanium containing amorphous hydrogenated carbon films (a-C : H/Ti): surface analysis and evaluation of cellular reactions using bone marrow cell cultures in vitro

Amorphous hydrogenated carbon (a-C : H) coatings, also called diamond-like carbon (DLC), have many properties required for a protective coating material in biomedical applications. The purpose of this study is to evaluate a new surface coating for bone-related implants by combining the hardness and inertness of a-C : H films with the biological acceptance of titanium. For this purpose, different amounts of titanium were incorporated into a-C : H films by a combined radio frequency (rf) and magnetron sputtering set-up. The X-ray photoelectron spectroscopy (XPS) of air-exposed a-C : H/titanium (a-C : H/Ti) films revealed that the films were composed of TiO2 and TiC embedded in and connected to an a-C : H matrix. Cell culture tests using primary adult rat bone marrow cell cultures (BMC) were performed to determine effects on cell number and on osteoblast and osteoclast differentiation. By adding titanium to the carbon matrix, cellular reactions such as increased proliferation and reduced osteoclast-like cell activity could be obtained, while these reactions were not seen on pure a-C : H films and on glass control samples. In summary, a-C : H/Ti could be a valuable coating for bone implants, by supporting bone cell proliferation while reducing osteoclast-like cell activation.

Degradation of poly(D, L)lactide implants with or without addition of calciumphosphates in vivo

The study was aimed at examining the in vivo degradation of pure poly(D,L)lactide (PDLLA) or PDLLA with an admixture of calciumphosphates. One rod (20 x 3 x 2 mm) and one cube (3 x 2 x 2 mm) of pure PDLLA, PDLLA with tricalciumphosphate (PDLLA + TCP) or PDLLA with calciumhydrogenphosphate (PDLLA + CHP), respectively, were implanted into the dorsal muscles of 50 male Wistar Albino rats. After definite intervals (from 2nd to 72nd week), pH measurements were performed in the environment of the implants. Afterwards, the cubes with their surrounding tissues were excised for histological examinations, measurements of the outer dimensions and mechanical analyses of the explanted rods were performed. No drop of more than 0.1 pH units was detectable in the tissue surrounding any type of implants. No advantageous effect of the calciumphosphates could be proved. A mild foreign body reaction could be observed around PDLLA implants. After 72 weeks, pure PDLLA had been totally resorbed from the extracellular space, the degradation of calciumphosphate-enriched PDLLA was still in progress. A large amount of inflammations occurred in the tissues surrounding PDLLA with an admixture of slowly degrading TCP or CHP, leading to two abscesses and four fistulas at PDLLA + TCP, and two abscesses and three fistulas at PDLLA + CHP implantation site. Bending strength of pure PDLLA was constant up to the 4th week post-implantation and reduced to 60% of the initial value up to the 12th week. No traces of crystallinity could be observed during the degradation of PDLLA. As a conclusion of the study, complete resorption from the extracellular space and tissue tolerance of pure PDLLA is proved. An admixture of small calciumphosphate particles is not suitable to improve the biocompatibility of PDLLA but leads to a decrease in the mechanical characteristics.

Surface analysis of chemically-etched and plasma-treated polyetheretherketone (PEEK) for biomedical applications

Abstract Surface modifications of polyetheretherketone (PEEK) made by chemical etching or oxygen plasma treatment were examined in this study. Chemical etching caused surface topography to become irregular with higher roughness values R a and R q . Oxygen plasma treatment also affected surface topography, unveiling the spherulitic structure of PEEK. R a , R q and surface area significantly increased after plasma treatment; topographical modifications were, nonetheless, moderate. Wetting angle measurements and surface energy calculations revealed an increase of wettability and surface polarity due to both treatments. XPS measurements showed an increase of surface oxygen concentration after both treatments. An O:C ratio of 3.10 for the plasma-treated PEEK surface and 4.41 for the chemically-etched surface were determined. The results indicate that surface activation by oxygen plasma treatment for subsequent coating processes in supersaturated physiological solutions to manufacture PEEK for biomedical appiications is preferable over the chemical etching treatment.

Matrices for tissue engineering-scaffold structure for a bioartificial liver support system

This study proposes a new composite scaffold system. A woven polyethylenterephtalate (PET) fabric was coated on one side with a biodegradable PLGA film, in order to obtain a geometrically polarized scaffold structure for an bioartificial liver support system. The composite structure ensures the stability of the membrane during degradation of the membrane polymer. The mesh size of the composite does not significantly influence the degradation behavior. Hepatocyte culturing studies reveal that the formation of aggregates depends on the mesh size and on the pretreatment: The largest aggregates could be observed after 48 h when PVLA coating, large mesh size and EGF were combined. Thus, the combination of a geometrically structured, partially degradable scaffold with receptor-mediated cell attachment sites offers promising possibilities in liver tissue engineering.

Non-destructive three-dimensional evaluation of a polymer sponge by micro-tomography using synchrotron radiation

X-ray micro-tomography, a non-destructive technique is used to uncover the complex 3-D micro-architecture of a degradable polymer sponge designed for bone augmentation. The measurements performed at HASYLAB at DESY are based on a synchrotron radiation source resulting in a spatial resolution of about 5.4 microm. In the present communication we report the quantitative analysis of the porosity and of the pore architecture. First, we elucidate that synchrotron radiation at the photon energy of 9 keV has an appropriate cross section for this low-weight material. Modifications in sponge micro-architecture during measurement are not detected. Second, the treatment of the data, an amount of 2.5 Gbyte to generate binary data is described. We compare the 3-D with the 2-D analysis in a quantitative manner. The obtained values for the mean distance to material within the sponge calculated from 2-D and 3-D data of the whole tomogram differ significantly: 12.5 microm for 3-D and 17.6 microm for 2-D analysis. If the pores exhibit a spherical shape as frequently found, the derived mean pore diameter, however, is overestimated only by 6% in the 2-D image analysis with respect to the 3-D evaluation. This approach can be applied to different porous biomaterials and composites even in a hydrated state close to physiological conditions, where any surface preparation artifact is avoided.

Protein adsorption and monocyte activation on germanium nanopyramids

Germanium can form defect-free pyramidal islands on Si(1 0 0)-2 x 1 with a height of 15 nm and a width of 60 nm. Using chemical vapor deposition we have prepared substrates with different nanopyramid densities to study the impact on contact angles, protein adsorption and cell behavior. The advancing contact angle of a water droplet of millimeter size significantly raises with nanopyramid density. The dynamic contact angle measurements reveal that the substrate surface is highly hydrophilic. On such a surface the adsorption of hydrophilic proteins, i.e. albumin and globulin, is drastically increased by the presence of nanopyramids. More important, however, the globulin is inactive after adsorption on nanopyramid edges. This observation is supported by the cytokine release of IL-1beta and TNF-alpha of monocyte-like cell line U937. Consequently, the presence of nanopyramidal structures gives rise to less inflammatory reactions.

Plasma-sprayed hydroxylapatite coating on carbon fibre reinforced thermoplastic composite materials

Plasma-spraying of metallic impiant surfaces is an established method for the application of hydroxylapatite (HA) coatings. Carbon fibre reinforced thermoplastics show different thermal and mechanical properties, compared with titanium substrates. In this paper first results of the influence of the established coating method on carbon fibre reinforced thermoplastics are presented. First investigations of the tensile adhesion strength, tested with a newly developed testing device, showed that the adhesion between the HA coating and the carbon fibre reinforced polyetheretherketone (PEEK) composite is very low. Macromechanical bending tests showed a change to initial tensile instead of compression failure of the coated composite substrate. Micromechanical bending tests in a scanning electron microseope (SEM) hot tensile stage (Raith GmbH) revealed crack propagation within the ceramic coating and in the coating-substrate interface before the total failure of the composite substrate occurred.

Surface analysis and bioreactions of F and Si containing a-C:H

Abstract Amorphous hydrogenated carbon films containing different amounts of fluorine and silicon have been deposited by plasma activated chemical vapor deposition in a stainless steel high vacuum system, using different mixtures of acetylene and either trifluoromethane or tetramethylsilane. Film composition and the different chemical states present have been characterized by X-ray photoelectron spectroscopy. Cell culture tests with fibroblasts revealed a good surface biocompatibility by means of morphological behavior, but no dependence on the Si or F content in the a-C:H films could be seen. All cells showed good spreading on the surface. Within 2 days confluent cell layers were observed.

Nondestructive three-dimensional evaluation of biocompatible materials by microtomography using synchrotron radiation

Microtomography based on synchrotron radiation sources is a unique technique for the 3D characterization of different materials with a spatial resolution down to about 1 micrometers . The interface between implant materials (metals, ceramics and polymers) and biological matter is nondestructively accessible, i.e. without preparation artifacts. Since the materials exhibit different x-ray absorption, it can become impossible to visualize implant material and tissue, simultaneously. Here, we show that coating of polymer implants, which are invisible in bone tissue, does not only improve the interfacial properties but also allows the imaging of the interface in detail. Titanium implants, on the other hand, absorb the x-rays stronger than bone tissue. The difference, however, is small enough to quantify the bone formation near interface. Another advantage of microtomography with respect to classical histology is the capability to examine samples in a hydrated state. We demonstrate that ceramic hollow spheres can be imaged before sintering and fibroblasts marked by OsO4 are visible on polymer textiles. Consequently, scaffolds of different materials designed for tissue engineering and implant coatings can be optimized on the basis of the tomograms.