Decellularized bone has been widely used as a scaffold for bone formation, due to its similarity ... more Decellularized bone has been widely used as a scaffold for bone formation, due to its similarity to the native bone matrix and excellent osteoinductive and biomechanical properties. We have previously shown that human mesenchymal and embryonic stem cells form functional bone matrix on such scaffolds, without the use of growth factors. In this study, we focused on differences in bone matrix that exist even among identical harvesting sites, and the effects of the matrix architecture and mineral content on bone formation by human embryonic stem cells (hESC). Mesenchymal progenitors derived from hESCs were cultured for 5 weeks in decellularized bone scaffolds with three different densities: low (0.281 ± 0.018 mg/mm(3)), medium (0.434 ± 0.015 mg/mm(3)) and high (0.618 ± 0.027 mg/mm(3)). The medium-density group yielded highest densities of cells and newly assembled bone matrix, presumably due to the best balance between the transport of nutrients and metabolites to and from the cells, space for cell infiltration, surface for cell attachment and the mechanical strength of the scaffolds, all of which depend on the scaffold density. Bone mineral was beneficial for the higher expression of bone markers in cultured cells and more robust accumulation of the new bone matrix.
ABSTRACT The polycondensation behavior of water-soluble melamine formaldehyde (MF) resins under a... more ABSTRACT The polycondensation behavior of water-soluble melamine formaldehyde (MF) resins under acidic polymerization conditions was studied within a bicontinuous microemulsion comprising an oil phase (an alkane), a water phase (containing the reactive resin), and surfactant. The intrinsic nanoscopic feature size of such microemulsions was used as a structural template. Nonionic surfactants were found to be highly compatible with MF resin chemistry. Polycondensation using unmodified MF resins lead to gels showing large spherical voids arising from the separation of the oil phase. In contrast, by incorporating hydrophobic monomers such as benzoguanamine and caprinoguanamine into the resin (amphiphilic resin approach), a gel was formed consisting of aggregated nanoparticles confined within a continuous pore network. In this way, the effects of phase separation were successfully diminished, and porosities of 86 vol % (ρ = 240 g/L) were achieved with 65 nm pore sizes. Characterization of the materials was performed via scanning electron microscopy, nitrogen sorption at 77 K, and mercury intrusion.
ABSTRACT Polyurethane xerogels with open pore networks were created via solution-gelation (sol-ge... more ABSTRACT Polyurethane xerogels with open pore networks were created via solution-gelation (sol-gel) polymerization. The solubility parameters of the solvent(s) and prepolymers and equilibrium swelling and extraction data were both used to select solvent(s) giving porous xerogels. Polycaprolactone (PCL) diol was combined with either poly(tetramethylene glycol) (PTMEG) or castor oil (CO), and the prepoplymer mixture gelled in an array of solvents through reaction with a triisocyanate. The behavior of the PCL/PTMEG system was mapped vs. all pure solvents used as well as several binary blends, and regions generating porous bodies were identified. Both this and the PCL/CO system were also prepared as dense materials, with equilibrium swelling and extractable fraction data generated in various solvents Analysis of this data also allowed for selection of appropriate solvents for porous xerogel formation. Porous xerogels were characterized via scanning electron microscopy and mercury intrusion porosimetry.
ABSTRACT We report the first in-depth comparison of the mechanical properties and equilibrium sol... more ABSTRACT We report the first in-depth comparison of the mechanical properties and equilibrium solvent uptake of a range of polysiloxane nanocomposites based on treated and untreated montmorillonite and fumed silica nanofillers. We demonstrate the ability of equilibrium solvent uptake data (and, thus, overall physical and chemical cross-link density) to serve as a proxy for modulus (combining rubber elasticity and Flory−Rehner theory), hardness (via the theory of Boussinesq), and elongation at break, despite the nonideal nature of these networks. In contrast, we find that tensile and tear strength are not well-correlated with solvent uptake. Interfacial strength seems to dominate equilibrium solvent uptake and the mechanical properties it predicts. In the montmorillonite systems in particular, this results in the surprising consequence that equilibrium solvent uptake and mechanical properties are independent of dispersion state. We conclude that edge interactions play a more significant role than degree of exfoliation, a result unique in the field of polymer nanocomposites. This demonstrates that even a combination of polymer/nanofiller compatibility and thermodynamically stable nanofiller dispersion levels may not give rise to reinforcement. These findings provide an important caveat when attempting to connect structure and properties in polymer nanocomposites, and useful guidance in the design of optimized polymer/layered silicate nanocomposites in particular.
Decellularized bone has been widely used as a scaffold for bone formation, due to its similarity ... more Decellularized bone has been widely used as a scaffold for bone formation, due to its similarity to the native bone matrix and excellent osteoinductive and biomechanical properties. We have previously shown that human mesenchymal and embryonic stem cells form functional bone matrix on such scaffolds, without the use of growth factors. In this study, we focused on differences in bone matrix that exist even among identical harvesting sites, and the effects of the matrix architecture and mineral content on bone formation by human embryonic stem cells (hESC). Mesenchymal progenitors derived from hESCs were cultured for 5 weeks in decellularized bone scaffolds with three different densities: low (0.281 ± 0.018 mg/mm(3)), medium (0.434 ± 0.015 mg/mm(3)) and high (0.618 ± 0.027 mg/mm(3)). The medium-density group yielded highest densities of cells and newly assembled bone matrix, presumably due to the best balance between the transport of nutrients and metabolites to and from the cells, space for cell infiltration, surface for cell attachment and the mechanical strength of the scaffolds, all of which depend on the scaffold density. Bone mineral was beneficial for the higher expression of bone markers in cultured cells and more robust accumulation of the new bone matrix.
ABSTRACT The polycondensation behavior of water-soluble melamine formaldehyde (MF) resins under a... more ABSTRACT The polycondensation behavior of water-soluble melamine formaldehyde (MF) resins under acidic polymerization conditions was studied within a bicontinuous microemulsion comprising an oil phase (an alkane), a water phase (containing the reactive resin), and surfactant. The intrinsic nanoscopic feature size of such microemulsions was used as a structural template. Nonionic surfactants were found to be highly compatible with MF resin chemistry. Polycondensation using unmodified MF resins lead to gels showing large spherical voids arising from the separation of the oil phase. In contrast, by incorporating hydrophobic monomers such as benzoguanamine and caprinoguanamine into the resin (amphiphilic resin approach), a gel was formed consisting of aggregated nanoparticles confined within a continuous pore network. In this way, the effects of phase separation were successfully diminished, and porosities of 86 vol % (ρ = 240 g/L) were achieved with 65 nm pore sizes. Characterization of the materials was performed via scanning electron microscopy, nitrogen sorption at 77 K, and mercury intrusion.
ABSTRACT Polyurethane xerogels with open pore networks were created via solution-gelation (sol-ge... more ABSTRACT Polyurethane xerogels with open pore networks were created via solution-gelation (sol-gel) polymerization. The solubility parameters of the solvent(s) and prepolymers and equilibrium swelling and extraction data were both used to select solvent(s) giving porous xerogels. Polycaprolactone (PCL) diol was combined with either poly(tetramethylene glycol) (PTMEG) or castor oil (CO), and the prepoplymer mixture gelled in an array of solvents through reaction with a triisocyanate. The behavior of the PCL/PTMEG system was mapped vs. all pure solvents used as well as several binary blends, and regions generating porous bodies were identified. Both this and the PCL/CO system were also prepared as dense materials, with equilibrium swelling and extractable fraction data generated in various solvents Analysis of this data also allowed for selection of appropriate solvents for porous xerogel formation. Porous xerogels were characterized via scanning electron microscopy and mercury intrusion porosimetry.
ABSTRACT We report the first in-depth comparison of the mechanical properties and equilibrium sol... more ABSTRACT We report the first in-depth comparison of the mechanical properties and equilibrium solvent uptake of a range of polysiloxane nanocomposites based on treated and untreated montmorillonite and fumed silica nanofillers. We demonstrate the ability of equilibrium solvent uptake data (and, thus, overall physical and chemical cross-link density) to serve as a proxy for modulus (combining rubber elasticity and Flory−Rehner theory), hardness (via the theory of Boussinesq), and elongation at break, despite the nonideal nature of these networks. In contrast, we find that tensile and tear strength are not well-correlated with solvent uptake. Interfacial strength seems to dominate equilibrium solvent uptake and the mechanical properties it predicts. In the montmorillonite systems in particular, this results in the surprising consequence that equilibrium solvent uptake and mechanical properties are independent of dispersion state. We conclude that edge interactions play a more significant role than degree of exfoliation, a result unique in the field of polymer nanocomposites. This demonstrates that even a combination of polymer/nanofiller compatibility and thermodynamically stable nanofiller dispersion levels may not give rise to reinforcement. These findings provide an important caveat when attempting to connect structure and properties in polymer nanocomposites, and useful guidance in the design of optimized polymer/layered silicate nanocomposites in particular.
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