Fabrication and characterization of Ag- and Ga-doped mesoporous glass-coated scaffolds based on natural marine sponges with improved mechanical properties.

Natural marine sponges were used as sacrificial template for the fabrication of bioactive glass-based scaffolds. After sintering at 1050°C, the resulting samples were additionally coated with a silicate solution containing biologically active ions (Ag and Ga), well-known for their antibacterial properties. The produced scaffolds were characterized by superior mechanical properties (maximum compressive strength of 4 MPa) and total porosity of ~80% in comparison to standard scaffolds made by using PU foam templates. Direct cell culture tests performed on the uncoated and coated samples showed positive results in terms of adhesion, proliferation, and differentiation of MC3T3-E1 cells. Moreover, vascular endothelial growth factor (VEGF) secretion from cells in contact with scaffold dissolution products was measured after 7 and 10 days of incubation, showing promising angiogenic results for bone tissue engineering applications. The antibacterial potential of the produced samples was assessed by performing agar diffusion tests against both Gram-positive and Gram-negative bacteria.

Cell Interactions with Size-Controlled Colloidal Monolayers: Toward Improved Coatings in Bone Tissue Engineering.

The surface structure of biomaterials is of key importance to control its interactions with biological environments. Industrial fabrication and coating processes often introduce particulate nanostructures at implant surfaces. Understanding the cellular interaction with particle-based surface topologies and feature sizes in the colloidal length scale therefore offers the possibility to improve the biological response of synthetic biomaterials. Here, surfaces with controlled topography and regular feature sizes covering the relevant length scale of particulate coatings (100-1000 nm) are fabricated by colloidal templating. Using fluorescent microscopy, WST assay, and morphology analysis, results show that adhesion and attachment of bone-marrow derived murine stromal cells (ST2) are strongly influenced by the surface feature size while geometric details play an insignificant role. Quantitative analysis shows enhanced cell adhesion, spreading, viability, and activity when surface feature size decreases below 200 nm compared to flat surfaces, while larger feature sizes are detrimental to cell adhesion. Kinetic studies reveal that most cells on surfaces with larger features lose contact with the substrate over time. This study identifies colloidal templating as a simple method for creating highly defined model systems to investigate complex cell functions and provides design criteria for the choice of particulate coatings on commercial implant materials.

Bottom-Up Assembly of Silica and Bioactive Glass Supraparticles with Tunable Hierarchical Porosity.

We investigate the formation of spherical supraparticles with controlled and tunable porosity on the nanometer and micrometer scales using the self-organization of a binary mixture of small (nanometer scale) oxidic particles with large (micrometer scale) polystyrene particles in the confinement of an emulsion droplet. The external confinement determines the final, spherical structure of the hybrid assembly, while the small particles form the matrix material. The large particles act as templating porogens to create micropores after combustion at elevated temperatures. We control the pore sizes on the micrometer scale by varying the size of the coassembled polystyrene microspheres and produce supraparticles from both silica- and calcium-containing CaO/SiO2 particles. Although porous supraparticles are obtained in both cases, we found that the presence of calcium ions substantially complicated the fabrication process since the increased ionic strength of the dispersion compromises the colloidal stability during the assembly process. We minimized these stability issues via the addition of a steric stabilizing agent and by mixing bioactive and silica colloidal particles. We investigated the interaction of the porous particles with bone marrow stromal cells and found an increase in cell attachment with increasing pore size of the self-assembled supraparticles.