This work describes the formation of porous composite materials based on a combination of bioactive mesoporous silicon and bioerodible polymers such as poly-caprolactone (PCL). The fabrication of a range of composites prepared by both salt leaching and microemulsion techniques are discussed. Particular attention to the influence of Si content in the composite on in vitro calcification assays are assessed. For each system, cytotoxicity and cellular proliferation are explicitly evaluated through fibroblast cell culture assays.

ExperimentalGlassy solid electrolytes in the Li 2 S±P 2 S 5 system were prepared by the mechanical milling technique [13]. Highly pure Li 2 S (Idemitsu Kosan Co., > 99.9 %) and reagent-grade P 2 S 5 (Aldrich, 99 %) crystalline powders were used as starting materials to prepare the 70Li 2 S´30P 2 S 5 (70 mol-% Li 2 S, 30 mol-% P 2 S 5 ) samples. The mixture of these materials was mechanically milled at room temperature by a planetary ball-mill apparatus (Fritsch Pulverisette 7) using an alumina pot (volume of 45 mL) with ten alumina balls (10 mm in diameter); the milling time was 20 h and the rotation speed was 370 rpm. All the processes were performed in a dry, Ar-filled glove box (less than 1 ppm water). Glass-ceramic solid electrolytes were prepared by crystallization of the mechanically milled glass at 240 C for 2 h. Crystalline solid electrolytes with the same composition were prepared by a conventional solid-state reaction in which a mixture of Li 2 S and P 2 S 5 was put into a carbon-coated quartz tube and sealed under vacuum. The tube was heated at 700 C for 8 h, and then slowly cooled to room temperature.Electrical conductivities of pellets obtained by cold pressing the sample under a pressure of 3700 kg cm ±2 were measured; the diameters and thicknesses of the pellets were 10 mm and about 1 mm, respectively. A carbon paste was painted onto both sides of the sample and carbon electrodes were formed after heat treatment. Alternating current (AC) impedance measurements were carried out in a dry argon atmosphere using an impedance analyzer (SI1260, Solartron) in the frequency range of 10 Hz to 8 MHz. The temperature of the measurements ranged from 25 to 240 C. X-ray diffraction (XRD) measurements (Cu Ka) were performed using a diffractometer (M18XHF 22-SRA, MAC Science) to identify crystals in the glass-ceramics. Local structures of the samples were analyzed by Raman spectroscopy using a spectrometer (NR-1000, JASCO) equipped with an Ar + laser (514.5 nm).

In this study, the fabrication and characterization of highly porous composites composed of poly(epsilon-caprolactone) and bioactive mesoporous silicon (BioSilicon) prepared using salt-leaching and microemulsion/freeze-drying methods are described. The role of silicon, along with porosity, in the scaffolds on calcium phosphate deposition was assessed using acellular in vitro calcification analyses. The presence of bioactive silicon in these scaffolds is essential for the deposition of calcium phosphate while the samples are immersed in simulated body fluid (SBF). Silicon-containing scaffolds produced using salt-leaching methods are more likely to calcify as a consequence of SBF exposure than those produced using microemulsion methods. In vitro proliferation and cell viability assays of these porous composites using human embryonic kidney fibroblast cells indicate that no cytotoxic effects are present in the scaffolds under the conditions used. Preliminary analyses of bone sialoprotein and alkaline phosphatase expression using orthopedically relevant mesenchymal cells derived from bone marrow suggest that such scaffolds are capable of mediating osteoblast differentiation. Overall, the results show that these porous silicon-containing polymer scaffolds enhance calcification, can be considered nontoxic to cells, and support the proliferation, viability, attachment, and differentiation of bone precursor cells.

In this study the fabrication and characterization of an electrically conductive composite material comprised of poly(epsilon-caprolactone) (PCL), polyaniline (PANi), and bioactive mesoporous silicon (BioSilicon) is discussed. The influence of PANi and silicon on calcium phosphate induction was assessed via ex vitro calcification analyses (by acellular simulated body fluid (SBF) exposure) both with and without electrical bias. Acceleration of calcium phosphate formation is one possible desirable feature of "smart" synthetic scaffolds for selected orthopedic-relevant applications. In addition, electrical stability assays were performed in growth medium (DMEM) to determine the stability of such structures to bias in an authentic electrolyte during a typical cell experiment. The cytocompatibility of the composites was evaluated in vitro using human kidney fibroblasts (HEK 293) cell proliferation assays, along with more orthopedically relevant mesenchymal stem cells from mouse stroma. Importantly, these composites demonstrate accelerated calcification in SBF when electrical bias is applied cathodically to the scaffold. Furthermore, these scaffolds exhibit noncytotoxic behavior in the presence of fibroblasts over an 8-day culture period, and attachment of stromal cells to the semiconducting scaffold was directly imaged via scanning electron microscopy. Overall, these results suggest that materials of this type of composition have potential merit as a biomaterial.

We describe in this account a general, yet facile strategy for the directed assembly of bioactive composite materials comprised of an erodible organic polymer such as polycaprolactone and physiologically-resorbable inorganic mesoporous silicon. This method exploits a combination of capillary forces and selective interfacial coupling chemistry to produce isolable macroscale (mm sized) structures possessing a diverse range of geometries through simple mixing rather than intricate molding processes. Furthermore, we demonstrate the ability of such constructs to dissociate into their individual building blocks, with the concomitant release of embedded model compounds in a sustained manner.

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