Biodegradable composites with antibiotics and growth factors for dual release kinetics.

Bone infections are still a major problem in surgery. To avoid severe side effects of systemically administered antibiotics, local antibiotic therapy is increasingly being considered. Using a pressure-based method developed in our group, microporous ß-TCP ceramics, which had previously been characterized, were loaded with 2% w/v alginate containing 50 mg/mL clindamycin and 10 µg/mL rhBMP-2. Release experiments were then carried out over 28 days with changes of liquid at defined times (1, 2, 3, 6, 9, 14, 21 and 28d). The released concentrations of clindamycin were determined by HPLC and those of rhBMP-2 by ELISA. Continuous release (anomalous transport) of clindamycin and uniform release (Fick's diffusion) of BMP-2 were determined. The composites were biocompatible (live/dead, WST-I and LDH) and the released concentrations were all antimicrobially active against Staph. aureus. The results were very promising and clindamycin was detected in concentrations above the MIC as well as a constant rhBMP-2 release over the entire study period. Biocompatibility was also not impaired by either the antibiotic or the BMP-2. This promising approach can therefore be seen as an alternative to the common treatment with PMMA chains containing gentamycin, as the new composite is completely biodegradable and no second operation is necessary for removal or replacement.

Simulation of Leather Visco-Elastic Behavior Based on Collagen Fiber-Bundle Properties and a Meso-Structure Network Model.

Simulation-based prediction of mechanical properties is highly desirable for optimal choice and treatment of leather. Nowadays, this is state-of-the-art for many man-made materials. For the natural material leather, this task is however much more demanding due to the leather's high variability and its extremely intricate structure. Here, essential geometric features of the leather's meso-scale are derived from 3D images obtained by micro-computed tomography and subsumed in a parameterizable structural model. That is, the fiber-bundle structure is modeled. The structure model is combined with bundle properties derived from tensile tests. Then the effective leather visco-elastic properties are simulated numerically in the finite element representation of the bundle structure model with sliding contacts between bundles. The simulation results are validated experimentally for two animal types, several tanning procedures, and varying sample positions within the hide. Finally, a complete workflow for assessing leather quality by multi-scale simulation of elastic and visco-elastic properties is established and validated.

Nanomechanical 3D Depth Profiling of Collagen Fibrils in Native Tendon.

Connective tissue displays a large compositional and structural complexity that involves multiple length scales. In particular, on the molecular and the nanometer level, the elementary processes that determine the biomechanics of collagen fibrils in connective tissues are still poorly understood. Here, we use atomic force microscopy (AFM) to determine the three-dimensional (3D) depth profiles of the local nanomechanical properties of collagen fibrils and their embedding interfibrillar matrix in native (unfixed), hydrated Achilles tendon of sheep and chickens. AFM imaging in air with controlled humidity preserves the tissue's water content, allowing the assembly of collagen fibrils to be imaged in high resolution beneath an approximately 5-10 nm thick layer of the fluid components of the interfibrillar matrix. We collect pointwise force-distance (FD) data and amplitude-phase-distance (APD) data, from which we construct 3D depth profiles of the local tip-sample interaction forces. The 3D images reveal the nanomechanical morphology of unfixed, hydrated collagen fibrils in native tendon with a 0.1 nm depth resolution and a 10 nm lateral resolution. We observe a diversity in the nanomechanical properties among individual collagen fibrils in their adhesive and in their repulsive, viscoelastic mechanical response as well as among the contact points between adjacent collagen fibrils. This sheds new light on the role of interfibrillar bonds and the mechanical properties of the interfibrillar matrix in the biomechanics of tendon.

Gas-Phase Fluorination on PLA Improves Cell Adhesion and Spreading.

For the regeneration or creation of functional tissues, biodegradable biomaterials including polylactic acid (PLA) are widely preferred. Modifications of the material surface are quite common to improve cell-material interactions and thereby support the biological outcome. Typical approaches include a wet chemical treatment with mostly hazardous substances or a functionalization with plasma. In the present study, gas-phase fluorination was applied to functionalize the PLA surfaces in a simple and one-step process. The biological response including biocompatibility, cell adhesion, cell spreading, and proliferation was analyzed in cell culture experiments with fibroblasts L929 and correlated with changes in the surface properties. Surface characterization methods including surface energy and isoelectric point measurements, X-ray photoelectron spectroscopy, and atomic force microscopy were applied to identify the effects of fluorination on PLA. Gas-phase fluorination causes the formation of C-F bonds in the PLA backbone, which induce a shift to a more hydrophilic and polar surface. The slightly negatively charged surface dramatically improves cell adhesion and spreading of cells on the PLA even with low fluorine content. The results indicate that this improved biological response is protein- but not integrin-dependent. Gas-phase fluorination is therefore an efficient technique to improve cellular response to biomaterial surfaces without losing cytocompatibility.