Andreas Hoess

Mesoporous titanium dioxide coating for metallic implants.

A bioactive mesoporous titanium dioxide (MT) coating for surface drug delivery has been investigated to develop a multifunctional implant coating, offering quick bone bonding and biological stability. An evaporation induced self-assembly (EISA) method was used to prepare a mesoporous titanium dioxide coating of the anatase phase with BET surface area of 172 m(2)/g and average pore diameter of 4.3 nm. Adhesion tests using the scratch method and an in situ screw-in/screw-out technique confirm that the MT coating bonds tightly with the metallic substrate, even after removal from bone. Because of its high surface area, the bioactivity of the MT coating is much better than that of a dense TiO(2) coating of the same composition. Quick formation of hydroxyapatite (HA) in vitro can be related to enhance bonding with bone. The uptake of antibiotics by the MT coating reached 13.4 mg/cm(3) within a 24 h loading process. A sustained release behavior has been obtained with a weak initial burst. By using Cephalothin as a model drug, drug loaded MT coating exhibits a sufficient antibacterial effect on the material surface, and within millimeters from material surface, against E.coli. Additionally, the coated and drug loaded surfaces showed no cytotoxic effect on cell cultures of the osteoblastic cell line MG-63. In conclusion, this study describes a novel, biocompatiblemesoporous implant coating, which has the ability to induce HA formation and could be used as a surface drug-delivery system.

Self-supporting nanoporous alumina membranes as substrates for hepatic cell cultures †

Membranes made from nanoporous alumina exhibit interesting properties for their use in biomedical research. They show high porosity and the pore diameters can be easily adjusted in a reproducible manner. Nanoporous alumina membranes are thus ideal substrates for the cultivation of polar cells (e.g., hepatocytes) or the establishment of indirect co-cultures. The porous nature of the material allows supply of nutrients to both sides of adherent cells and the exchange of molecules across the membrane. However, it is well-known that surface features in the nanometer range affect cellular behavior. In this study, the response of HepG2 cells to nanoporous alumina membranes with three different pore diameters, ranging from 50 to 250 nm, has been evaluated. The cellular interactions with the nanoporous materials were assessed by investigating cell adhesion, morphology, and proliferation. Cell functionality was measured by means of albumin production. The membranes supported good cell adhesion and spreading. Compared to tissue culture plastic, the cells on the porous substrates developed distinct focal adhesion sites and actin stress fibers. Additionally, electron microscopical investigations revealed the penetration of cellular extensions into pores with diameters bigger than 200 nm. Furthermore, cell proliferation significantly increased with an increase in pore diameter, whereas the albumin production followed a reverse trend. Thus, it seems to be possible to direct cellular behavior of HepG2 cells growing on nanoporous alumina by changing the pore diameter of the material. Hence, nanoporous alumina membranes can be useful culture substrates to develop new approaches in the field of liver tissue engineering.

The influence of Sr content in calcium phosphate coatings

In this study calcium phosphate coatings with different amounts of strontium (Sr) were prepared using a biomineralization method. The incorporation of Sr changed the composition and morphology of coatings from plate-like to sphere-like morphology. Dissolution testing indicated that the solubility of the coatings increased with increased Sr concentration. Evaluation of extracts (with Sr concentrations ranging from 0 to 2.37 μg/mL) from the HA, 0.06Sr, 0.6Sr, and 1.2Sr coatings during in vitro cell cultures showed that Sr incorporation into coatings significantly enhanced the ALP activity in comparison to cells treated with control and HA eluted media. These findings show that calcium phosphate coatings could promote osteogenic differentiation even in a low amount of strontium.

Effects of nanoporous alumina on inflammatory cell response.

The present study focuses on the effects of nanoscale porosity on inflammatory response in vitro and in vivo. Nanoporous alumina membranes with different pore sizes, 20 and 200 nm in diameter, were used. We first evaluated cell/alumina interactions in vitro by observing adhesion, proliferation, and activation of a murine fibroblast and a macrophage cell line. To investigate the chronic inflammatory response, the membranes were implanted subcutaneously in mice for 2 weeks. Cell recruitment to the site of implantation was determined by histology and the production of cytokines was measured by protein array analysis. Both in vitro and in vivo studies showed that 200 nm pores induced a stronger inflammatory response as compared to the alumina with 20 nm pores. This was observed by an increase in macrophage activation in vitro as well as higher cell recruitment and generation of proinflammatory cytokines around the alumina with 200 nm pores, in vivo. Our results suggest that nanofeatures can be modulated in order to control the inflammatory response to implants.

The effect of oligo(trimethylene carbonate) addition on the stiffness of acrylic bone cement

ABSTRACT With the increasing elderly population an increase in the number of bony fractures associated to age-related diseases such as osteoporosis also follows. The relatively high stiffness of the acrylic bone cements used in these patients has been suggested to give raise to a suboptimal load distribution surrounding the cement in vivo, and hence contribute to clinical complications, such as additional fractures. The aim of this study was to develop a low-modulus bone cement, based on currently used, commercially available poly(methyl methacrylate) (PMMA) cements for vertebroplasty. To this end, acrylate end-functionalized oligo(trimethylene carbonate) (oTMC) was incorporated into the cements, and the resulting compressive mechanical properties were evaluated, as well as the cytotoxic and handling properties of selected formulations. Sixteen wt%oTMC was needed in the vertebroplastic cement Osteopal V to achieve an elastic modulus of 1063 MPa (SD 74), which gave a corresponding compressive strength of 46.1 MPa (SD 1.9). Cement extracts taken at 1 and 12 hours gave a reduced MG-63 cell viability in most cases, while extracts taken at 24 hours had no significant effect on cell behavior. The modification also gave an increase in setting time, from 14.7 min (SD 1.7) to 18.0 min (SD 0.9), and a decrease in maximum polymerization temperature, from 41.5°C (SD 3.4) to 30.7°C (SD 1.4). While further evaluation of other relevant properties, such as injectability and in vivo biocompatibility, remains to be done, the results presented herein are promising in terms of approaching clinically applicable bone cements with a lower stiffness.

Comparison of a quasi-dynamic and a static extraction method for the cytotoxic evaluation of acrylic bone cements

In this study, two different extraction approaches were compared in order to evaluate the cytotoxicity of 7 different acrylic bone cements, mainly developed for spinal applications, to osteoblastic cells. Firstly, a static extraction was carried out continuously over 24h, a method widely used in literature. Secondly, a quasi-dynamic extraction method that allowed the investigation of time-dependent cytotoxic effects of curing acrylic bone cements to cells was introduced. In both cases the extraction of the cements was started at a very early stage of the polymerization process to simulate the conditions during clinical application. Data obtained by the quasi-dynamic extraction method suggest that the cytotoxicity of the setting materials mainly originates from the release of toxic components during the first hour of the polymerization reaction. It was also shown that a static extraction over 24h generally represents this initial stage of the curing process. Furthermore, compared to the static extraction, time-dependent cytotoxicity profiles could be detected using the quasi-dynamic extraction method. Specifically, a modification of commercial OsteopalV with castor oil as a plasticizer as well as a customized cement formulation showed clear differences in cytotoxic behavior compared to the other materials during the setting process. In addition, it was observed that unreacted monomer released from the castor oil modified cement was not the main component affecting the toxicity of the material extracts. The quasi-dynamic extraction method is a useful tool to get deeper insight into the cytotoxic potential of curing acrylic bone cements under relevant biological conditions, allowing systematic optimization of materials under development.