Unique Crystallization Characteristics of Pickering High Internal Phase Emulsion Templated Porous Constructs

To study the crystallization behavior of polymeric chains under the influence of porosity, the thermal properties of various nonporous and porous poly(ε-caprolactone) (PCL) based constructs were investigated. Porous cross-linked PCL nanocomposite constructs were fabricated utilizing in situ polymerization of CL-based surfactant-free Pickering high internal phase emulsions (HIPEs), stabilized using modified fumed silica nanoparticles (mSiNP) at a minimal concentration of 0.6 wt %. The corresponding nanocomposite constructs exhibited polyhedral pore morphology with significant pore roughness due to the presence of mSiNP. DSC thermograms of nonporous constructs illustrated diminished crystallization temperature and kinetics upon cross-linking and inclusion of mSiNP which confirmed suppressed mobility of polymer chains. Further introduction of porosity led to substantial supercooling, resulting in crystallization temperatures as low as -24 °C. Changes in the crystal structure of various nonporous and porous constructs were also studied using XRD. The crystallization behavior of porous constructs was finally evaluated using Jeziorny, Ozawa, and Mo theories under nonisothermal conditions. Significant deviation from the theoretical model, as observed in the case of porous constructs, implied a complex crystallization mechanism that eventually was not only controlled by the chain immobility due to cross-linking but also heterogeneity present in the wall thickness of the constructs. The unique melting-crystallization phenomenon observed in such constructs may further be expanded to other systems of high heat capacity for utilization as energy storage materials.

Hydrolytic Degradation of Porous Crosslinked Poly(ε-Caprolactone) Synthesized by High Internal Phase Emulsion Templating

Porous poly(ε-caprolactone) (PCL) scaffolds were fabricated using the high internal polymerization emulsion (HIPE) technique. Bis(ε-caprolactone-4-yl) (BCY) was utilized as crosslinker. The crosslinking density and the volume fraction of the dispersed phase were varied in order to study the potential effect of these parameters on the hydrolytic degradation at 37 °C and 60 °C. After different hydrolysis times the remaining solid samples were analyzed by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), while the degradation products in the aqueous aging solutions were analyzed by laser desorption ionization-mass spectrometry (LDI-MS). The effect of temperature on the degradation process and release of degradation products was, as expected, significant. The temperature effect was also shown by FTIR analysis that displayed a pronounced increase in the intensity of the hydroxyl-group absorption band after 70 days of hydrolysis at 60 °C indicating significant cleavage of the polymer chains. LDI-MS analysis proved the release of oligomers ranging from dimers to hexamers. The product patterns were similar, but the relative m/z signal intensities increased with increasing time, temperature and crosslinking density, indicating larger amounts of released products. The latter is probably due to the decreasing degree of crystallinity as a function of amount of crosslinker. The porous structure and morphology of the scaffolds were lost during the aging. The higher the crosslinking density, the longer the scaffolds retained their original porous structure and morphology.

Facile Fabrication of Composite Electrospun Nanofibrous Matrices of Poly(ε-caprolactone)-Silica Based Pickering Emulsion

Functionalized matrices have been sought for their application in sensors, filtration, energy storage, catalysis, and tissue engineering. We report formation of an inorganic-organic composite matrix based on poly(ε-caprolactone) (PCL) functionalized with hydrophobically modified silica (m-silica) fabricated with reduced organic solvent usage. The matrix was obtained via electrospinning of a water-in-oil emulsion of PCL that was stabilized by judicious choice of m-silica as a Pickering agent resulting into an emulsifier free matrix. Inclusion of m-silica in PCL matrix resulted in enhancing tensile properties and cell proliferation efficiency. The electrospun composite matrix was free from any emulsifier or template polymer; thus any abrupt loss in mechanical properties was prevented when the matrix was subjected to aqueous conditions. The inorganic-organic biodegradable composite matrices thus produced using an emulsifier free emulsion find applications in tissue engineering and may further be evaluated for other areas including selective sorption and separation.