Pyrene-end-functionalized poly(L-lactide) as an efficient carbon nanotube dispersing agent in poly(L-lactide): mechanical performance and biocompatibility study.

In order to improve the mechanical properties of poly(L-lactide) (PLLA) based implants, a study was made of how far well dispersed multi-walled carbon nanotubes (MWCNTs) within a PLLA matrix were able to positively affect these properties. To this end, pyrene-end-functionalized poly(L-lactide) (py-end-PLLA) was evaluated as a dispersing agent. Transmission electron microscopy (TEM) analyses and mechanical tests of MWCNTs-based materials demonstrated an enhancement of MWCNT dispersion in the PLLA matrix and improved Young's modulus (E) when 4 wt% of py-end-PLLA was used as the dispersing agent. Subsequently, the bioacceptance of PLLA/py-end-PLLA/MWCNTs nanocomposites was evaluated using human bone marrow stromal cells (HBMC) in vitro. The inclusion of py-end-PLLA and MWCNTs supported HBMC adhesion and proliferation. The expression levels of the bone-specific markers indicated that the cells kept their potential to undergo osteogenic differentiation. The results of this study indicate that the addition of MWCNT combined with py-end-PLLA in PLLA/py-end-PLLA/MWCNTs nanocomposites may widen the range of applications of PLLA within the field of bone tissue engineering thanks to their mechanical strength and cytocompatibility.

Grooves affect primary bone marrow but not osteoblastic MC3T3-E1 cell cultures.

To elucidate the influence of microtextures on bone cell performance, primary adult rat bone marrow cells (RBMC) and osteoblastic MC3T3-E1 cells were cultured on tissue culture pretreated plates to which grooves at different density were applied. RBMC cells were found to be significantly affected by grooves in the substratum in contrast to osteoblastic MC3T3-E1 cells, taking culture morphology, total cell number, cell mass, and cell activity (MTT-dehydrogenase), parameter for differentiation of osteoblast progenitor cells into (pre-)osteoblasts (alkalinephosphatase activity, ALP) and tartrate-resistant acid phosphatase (TRAP) activity as indices. TRAP is located in lysosomes and secretory granules mainly although not solely in osteoclasts. By applying grooves to and/or by chemical treatment of unpretreated pure polysterene plates it could be concluded that the effects on RBMC cells were evoked not only by the presence of grooves but also by the surface chemistry of the grooved and ungrooved surface areas.

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.

The stiffness of bone marrow cell-knit composites is increased during mechanical load.

A novel device for mechanical stimulation of primary adult rat bone marrow cells cultured on three-dimensional knitted textiles has been prototyped. A method has been developed ensuring a well-defined, high-density, and reproducible cell seeding on the knitted fabric. After culturing for 18-52 days the cell-knit composites were subjected to uniaxial 2% stretching and relaxation. The frequency was altered between 0.1 Hz (196 min, loading phase) and 0.01 Hz (360 min, resting phase). Identically treated knits without cells exhibited a slight stiffness reduction, whereas the stiffness of knits with cells increased from cycle to cycle. The stiffness increase was found to depend on the duration of the culture period before mechanical loading. Our data suggest that the extracellular matrix deposited by the cells on the knit and intact microtubuli of living cells cause the observed stiffness increase. In comparison to the unstrained static cell-knit composites cell proliferation and bone cell differentiation were reduced by the mechanical load.

Reduction of ochratoxin A toxicity by heat-induced epimerization. In vitro effects of ochratoxins on embryonic chick meningeal and other cell cultures.

The widespread contamination of food by mycotoxins may present a serious hazard to human and animal health. The present study was designed to determine the toxic potential of three structurally related ochratoxins: ochratoxin A (OTA), ochratoxin B (OTB) and the heat-induced 3S-epimer of OTA (3S-OTA) recently discovered in roasted coffee and human serum. The toxicity was determined using serum-free cell cultures of embryonic chick meningeal fibroblasts, taking the effects on mitochondrial and lysosomal activity and culture protein content as an index for toxicity. OTA, OTB and 3S-OTA were toxic. However, the concentration necessary to induce comparable effects were nearly 19- and 10-fold higher for OTB and 3S-OTA, respectively, than those for OTA. In a next step the sensitivity of serum-free cell cultures of embryonic chick neural retina and brain were compared in relation to meningeal cell cultures. In the present study, no indications for differences in sensitivity could be detected. Furthermore, our study suggest that the OTA-induced toxic effects are not due to the inhibition by OTA of phenylalanine-tRNA synthetase.

[Biomaterials, human tolerance and integration]. / Biomaterialien--humane Toleranz und Integration.

Biomaterials and related process engineering in order to obtain optimal surface and structural biocompatibility of implants and devices are presented. Vital-avital composites for tissue engineering, cell culture models, porous ceramics and degradable polymers are introduced as examples. Emphasis is laid on the conversion of basic research results into clinical applications and on the exchange of technologies from the non-medical into the medical field and vice versa.

Tailored degradation of biocompatible poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/calcium silicate/poly(lactide-co-glycolide) ternary composites: an in vitro study.

Biodegradable materials, which are currently available for bone tissue regeneration, still have limitations regarding their degradation rate, mechanical stability and/or biological response. Thus, a novel generation of materials for bioactive bone scaffolds is needed that triggers hydroxyapatite formation and can be tailored to suit application-specific requirements. In this study we developed ternary bioactive composite materials composed of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), calcium silicate and poly(lactide-co-glycolide) (PHBV/CS/PLGA), which merged the good bioactivity of CS/PHBV composite and the improved degradation velocity of PHBV/PLGA blend. Bioactive character of all composites was proven by formation of hydroxyapatite-like crystals after already one week of incubation in simulated body fluid. Addition of PLGA significantly increased initial ultimate tensile strength (UTS0) and Young's modulus of the ternary composites from 14.3±1.1 MPa (binary composite) to 22.3±2.6 MPa and 1.23±0.05 GPa up to 1.64±0.14 GPa, respectively. Furthermore the degradation rate (measured as a decrease of UTS during degradation) could be successfully tailored and was in range of -0.033 UTS0 to -0.118 UTS0 MPa/week. The bioacceptance of the materials was proven in vitro using 2-D (conventional setup) and 3-D (multicellular spheroids) human bone marrow stromal cell cultures.

Investigating cell-material interactions by monitoring and analysing cell migration.

Cell-material interactions can on one hand be characterised by assessing the functional state and or shape of the cells at one or different discrete periods of time, on the other hand by observing cell migration and spreading behaviour. The object of this study was to investigate the migration behaviour of fluorescently labelled cells, and to evaluate the software analysing this migration. In the present study, the behaviour of fibroblasts cells on differently structured surfaces was taken as example. In the first step, the influence of seven different lipophilic dyes (Dil, DiO, DiA, DiD, DiR, PKH2 and PKH26) on cell performance was determined taking biochemical parameters as indices. In the second step, the fluorescence characteristics of these dyes were compared regarding their applicability. In the third step, migration behaviour of Dil-labelled fibroblastic cells on plane and grooved surfaces were monitored and analysed using specific software. Our data suggest that most of the dyes have optimal characteristics for studying cell-cell interactions. Cell migration behaviour regarding migration direction and cell spreading was different on plane and grooved surfaces. It could be shown that computer-based image analysis represents a practical, quick and objective tool to quantify exactly cell migration behaviour.