Key Engineering Materials Vols. 361-363

Abstract: A series of ceramic-polymer scaffolds were studied for bone tissue engineering applications. These applications require bone reactivity as well as suitable scaffold properties and structure. Bioactive glass (BAG) and sol-gel derived silicas were chosen for ceramic components of the scaffolds, and crosslinked poly(ε-caprolactone/D,L-lactide) copolymers with monomer ratios 90/10 and 70/30 were used as polymer matrices. Scaffolds were prepared by photo-curing crosslinkable oligomers in the presence of the ceramic component and porosity producing salt. Scaffolds with 60-80 vol-% continuous phase macroporosity were obtained by using calcium chloride hexahydrate (CaCl2⋅6H2O), and were further tested in simulated body fluid (SBF). The ceramics remained highly reactive during scaffold preparation resulting in in vitro calcium phosphate formation.

Abstract: Cellular activities of human mesenchymal stem cells (MSCs) and osteoblasts (HOBs) on a silicon-releasable scaffold, which is siloxane-doped poly(lactic acid) / vaterite composite coated with hydroxycarbonate apatite (SPV-H), were estimated using two types of media, with or without organic factors, dexamethasone (Dex) and β-glycerophosphate (β-GP). The culture tests using MSCs shows that the level of alkaline phosphatase (ALP) activity in the cells cultured on SPV-H increased for 21-day culturing in medium without Dex and β-GP. The proliferation of MSCs on SPV-H was significantly higher than that on a poly(lactic acid) / vaterite composite coated with hydroxyapatite (PV-H) at all time points. In the case of supplementing Dex and β-GP to the medium, the level of ALP activity in MSCs cultured on SPV-H was higher in comparison with that on PV-H at all time points. Scanning electron microscopy showed that there were some agglomerates in HOBs cultured on the SPV-H surface after 21-day culturing in the medium without the factors, while there are no agglomerates on PV-H. The agglomerates were regarded from laser Raman spectroscopy as bone nodules. This result implies stimulation to HOBs by silicon species in SPV-H. SPV-H is expected to be useful as the scaffold for bone tissue engineering.

Abstract: In this study we show that mechanical properties of bioceramic scaffolds can be significantly improved by repeated infiltration with a low-viscosity polycaprolactone solution. Biphasic calcium phosphate (BCP: 70% hydroxyapatite, 30% β-tricalcium phosphate) scaffolds characterized by a bimodal pore size distribution and a global porosity of 70% have been chosen as starting materials. Polymer content in the ceramic scaffold was varied so that an inorganic/organic ratio close to that of bone may be achieved. Work of fracture at maximum stress was 36 J/m2 for the ceramic scaffold alone and reached 127 J/m2 for the 8-times infiltrated samples. These results are superior to the ones previously obtained with polycaprolactone infiltrated alumina due to higher micropore content. We show that during bending tests, polycaprolactone phase formed fibrils while the crack propagated. Crack bridging by polycaprolactone ensured the integrity of the composite once the ceramic scaffold was broken and directly involved in the composite toughening. Because of its composition, microstructure and mechanical behavior of this kind composite can be an interesting candidate for bone substitution.

Abstract: Co-continuous degradable polymer-ceramic composites were produced via in-situ polymerization of (D,L-lactic)acid monomer within a porous β-tricalcium phosphate matrix. The mechanical properties of both the composite and the unfilled porous ceramic were investigated with compressive testing. The average stress to failure increased from 1.3±0.1 MPa for the unfilled ceramic matrix to 82±2 MPa for the composite. The Young’s modulus increased from approximately 20 MPa to 700±42 MPa. A combination of X-ray micro-tomography and mechanical testing provided insight into the failure mechanisms of the composite. Stress may be deflected by crack bridging around the polymer phase leading to debonding of the polymer along the crack lines.

Abstract: Resorbable osteosynthesis based on PLLA and derivatives will be associated to bone substitute for bone reconstruction. We have performed rand evaluated a composite combining PL DLLA and Biphasic calcium phosphate able to have a), a better controlled hydrolysis in the purpose to preserve on time the mechanical property, and b), for long term efficiency, bone ingrowth at the expense of the osteosynthesis and the associated bone substitute. A new calcium phosphate cement MCPC® was tested with such composite. The novel macroporous calcium phosphate cement MCPC sets to poorly crystalline apatite after mixing the powder component and an aqueous solution. Interconnective macroporosity was induced on time by resorption of one part of the MCPC®. The multiphasic calcium phosphate components in the cement, are resorbed at different rates allowing the replacement by newly formed bone. This study reports the biocompatibility and the interactions of a composite using PL DLLA (Poly [L-Lactide-co-D,L-Lactide] acid) charged with biphasic calcium phosphate granules and a self setting calcium phosphate cement of new generation.

Abstract: Biocompatible and water-soluble fibers (sodium carboxymethyl cellulose (CMC)) were fabricated via a wet-spinning method. The CMC fibers/ polymethyl methacrylate (PMMA) mixtures and CMC fibers/Poly (L-lactide-co-glycolide-co- -caprolactone) (PLGC) mixtures were prepared by a heat-kneading method. For CMC fibers/PMMA, after removal of the CMC fibers from the mixtures, the interconnected porous scaffolds with porosity from 27.79 % to 60.98 % (volume percent) were obtained. For CMC fibers/PLGC, the interconnected porous scaffolds with porosity 38.55 % and 76.83 % (volume percent) were prepared. The solid CMC fibers/PLGC mixtures had the higher ultimate tensile strength and Young, s modulus than those of porous PLGC scaffolds.

Abstract: Composites of hydroxyapatite (HA) and multiwalled carbon nanotubes (CNTs) have been prepared and characterised for potential application in major load-bearing medical devices. We have studied the effect of nanotube surface chemistry, composite preparation methods, and heat treatment conditions on the microstructure of the composites, dispersion of CNTs, and interaction between the HA and CNTs. The samples were characterised using SEM, XRD, FTIR, and BET surface area. It was found that, compared with pure HA, the composites had lower densities and higher surface areas. Additionally, functionalisation improved the dispersion of CNTs in the HA matrix and the interaction between the two phases.

Abstract: The present work deals with the preparation and characterization of ceramic composites for the substitution of load-bearing bone portions, made of hydroxyapatite (HA) and bioactive β- calcium silicate (β-Ca2SiO4) as a reinforcing phase. The composite materials were prepared by Fast Hot-Pressing technique (FHP), which allowed the rapid sintering of monolithic ceramics at temperatures up to 1500 °C, well above the commonly adopted temperatures for sintering of hydroxyapatite (1200-1300 °C), in order to achieve the densification of the reinforcing phase also. XRD analysis reported no formation of secondary phases other than HA and β-Ca2SiO4, after FHP cycles. Flexural strength tests were performed on selected samples sintered at different temperatures: the composite materials exhibited increased mechanical resistance compared to samples constituted of HA only. These preliminary results confirmed that composites of HA and β- Ca2SiO4 are promising for the development of bioactive load-bearing ceramic bone substitutes.

Abstract: Extracellular matrix (ECM) proteins play an essential role during biomineralization in bone and engineered tissues. In a previous study [1], we showed that calcite preferentially nucleated on pure elastin fibers. However, the actual cellular ECM fibers are composed of a combination of proteins, primarily collagen, fibronectin and some elastin. Here we follow the calcium carbonate- and calcium phosphate- mineralization process in vitro when these ECM proteins are combined and determine the differences between these proteins in the biomineralization process. The surface morphology and mechanical properties of the protein fibers during the early stages were probed by atomic force microscopy (AFM) and shear modulation force microscopy (SMFM). The nucleation of the mineral crystals on the protein matrices was investigated by scanning electron microscopy (SEM). Preliminary data showed that the moduli of all protein fibers increased at the early stages, with collagen having the largest increase in supersaturated calcium bicarbonate solution. In metastable calcium phosphate solutions the modulus of the mixed elastin-fibronectin fibres increased to a greater extent than the moduli of the fibers composed of the single proteins. Longer exposure in the mineral solutions led to the formation of crystals templated along the self-assembled fiber structures.

Abstract: Effect of osteogenic activities of MG63 on the HAp/Col membrane was examined at day 10 and 14 by reverse-transcript and real-time polymerase chain reactions. Osteogenic activities of MG63 were upregulated by culture them on the HAp/Col membrane in comparison to those on tissue culture polystyrene. The novel three-dimensional HAp/Col scaffold was prepared from the HAp/Col wavy membrane. The cylindrical HAp/Col scaffold was successfully prepared and indicated at least 2.5-times higher compressive strength and Young's modulus compared to the previous HAp/Col composites. The novel scaffold could be useful for regenerative medicine.