No abstract

This article analyzes the use of supercritical CO 2 green technology in the reactive crystallization processes involved in the formation of a bioMOF that contains curcumin and Zn II metal centers. A new phase with a [Zn(curcumin)] n composition, termed sc-CCMOF-1, is presented. The developed scCO 2 protocol allows high yields of the small-sized crystalline material, which was characterized by the use of the recently developed electron diffraction tomography method applied to the resolution of submicrometric crystals. A remarkable 3D macrostructure with a complex morphology was obtained. To analyze the crystallization mechanism, multiple identical runs were performed under similar experimental conditions to study in each time period the crystal growth progress ex situ by X-ray diffraction and scanning electron microscopy. These experiments indicated that the process to achieve the sc-CCMOF-1 in a crystalline form involves the formation of amorphous or semicrystalline metastable phases that derived into hierarchical stable and crystalline nanoflower aggregates. In addition, a potential therapeutic application of the bioMOF has been tested by studying the released of the curcumin molecule at neutral pH.

We have previously reported the fabrication of a polycaprolactone and hydroxyapatite composite scaffold incorporating growth factors to be used for bone regeneration. Two growth factors were incorporated employing a multilayered coating based on polydopamine (PDA). In particular, Bone morphogenetic protein-2 (BMP-2) was bound onto the inner PDA layer while vascular endothelial growth factor (VEGF) was immobilized onto the outer one. Herein, the in vitro release of both growth factors is evaluated. A fastest VEGF delivery followed by a slow and more sustained release of BMP-2 was demonstrated, thus fitting the needs for bone tissue engineering applications. Due to the relevance of the crosstalk between bone-promoting and vessel-forming cells during bone healing, the functionalized scaffolds are further assessed on a co-culture setup of human mesenchymal stem cells and human endothelial progenitor cells. Osteogenic and angiogenic gene expression analysis indicates a synergistic effect between the growth factor-loaded scaffolds and the co-culture conditions. Taken together, these results indicate that the developed scaffolds hold great potential as an efficient platform for bone-tissue applications.

Fine chemical and pharmaceutical companies often employ reactive crystallization or precipitation to make crystalline intermediates and finished products. In this work, the supercritical reactive crystallization route is used for the precipitation of diverse metal–organic frameworks (MOFs). 1D and 2D MOFs were obtained by reacting either bypyridil (two linking positions) or triazine (three linking positions)-based bridging molecules, respectively, with supercritical CO2 soluble M­(hfacac)2 (where M = Zn2+ or Cu2+ and hfacac– stands for hexafluoroacetylacetonate). Additionally, miscellaneous reactions were designed for the crystallization of 3D MOFs in scCO2, embracing the precipitation of MIL-88B­(Fe), ZIF-8, and a new Zn2+–curcumin coordination polymer. Obtained crystals in each case were analyzed from a morphological point of view by scanning electron microscopy analysis to elucidate potential formation mechanisms. The focus was on the obtained crystal habits at different reaction points, linked to the precipitation mode and the role of kinetic and thermodynamic crystal growth control. The supercritical procedure led to the crystallization of stable hierarchical nanostructures with micro- and mesoporosity and the precipitation of nanocrystals.