Growth Factor Binding Peptides in Poly (Ethylene Glycol) Diacrylate (PEGDA)-Based Hydrogels for an Improved Healing Response of Human Dermal Fibroblasts.

Growth factors (GF) are critical cytokines in wound healing. However, the direct delivery of these biochemical cues into a wound site significantly increases the cost of wound dressings and can lead to a strong immunological response due to the introduction of a foreign source of GFs. To overcome this challenge, we designed a poly(ethylene glycol) diacrylate (PEGDA) hydrogel with the potential capacity to sequester autologous GFs directly from the wound site. We demonstrated that synthetic peptide sequences covalently tethered to PEGDA hydrogels physically retained human transforming growth factor beta 1 (hTGFß1) and human vascular endothelial growth factor (hVEGF) at 3.2 and 0.6 ng/mm2, respectively. In addition, we demonstrated that retained hTGFß1 and hVEGF enhanced human dermal fibroblasts (HDFa) average cell surface area and proliferation, respectively, and that exposure to both GFs resulted in up to 1.9-fold higher fraction of area covered relative to the control. After five days in culture, relative to the control surface, non-covalently bound hTGFß1 significantly increased the expression of collagen type I and hTGFß1 and downregulated vimentin and matrix metalloproteinase 1 expression. Cumulatively, the response of HDFa to hTGFß1 aligns well with the expected response of fibroblasts during the early stages of wound healing.

Synthesis of ordered microporous/macroporous MOF-808 through modulator-induced defect-formation, and surfactant self-assembly strategies.

Ordered materials with interconnected porosity allow the diffusion of molecules within their inner porous structure to access the active sites located in the microporous core. As a follow-up of our work on engineering of MOF-808, in this contribution, we study the synthesis of defective MOF-808 using two different strategies: the use of modulators and the surfactant-assisted synthesis to obtain materials with ordered and interconnected pores. The results of the study indicated that (i) the use of modulators of different chain length led to the formation of microporous/mesoporous MOFs through the formation of missing linker defects. However, the use of the acetic acid contributes to the formation of MOFs with larger mesoporous size distributions compared to materials synthesized with formic and propionic acids as modulators, and (ii) the self-assembly of CTAB surfactant produced an ordered microporous/macroporous network which enhanced crystallinity. However, the surface properties of the materials seem to be unaffected by the use of surfactants during synthesis. These results contribute to the development of ordered materials with a broad range of pore size distributions and give rise to new opportunities to extend the applications of MOF-808.

Shell-anchor-core structures for enhanced stability and catalytic oxygen reduction activity.

Density functional theory is used to evaluate activity and stability properties of shell-anchor-core structures. The structures consist of a Pt surface monolayer and a composite core having an anchor bilayer where C atoms in the interstitial sites lock 3d metals in their locations, thus avoiding their surface segregation and posterior dissolution. The modified subsurface geometry induces less strain on the top surface, thus exerting a favorable effect on the surface catalytic activity where the adsorption strength of the oxygenated species becomes more moderate: weaker than on pure Pt(111) but stronger than on a Pt monolayer having a 3d metal subsurface. Here we analyze the effect of changing the nature of the 3d metal in the subsurface anchor bilayer, and we also test the use of a Pd monolayer instead of Pt on the surface. It is found that a subsurface constituted by two layers with an approximate composition of M(2)C (M = Fe, Ni, and Co) provides a barrier for the migration of subsurface core metal atoms to the surface. Consequently, an enhanced resistance against dissolution in parallel to improved oxygen reduction activity is expected, as given by the values of adsorption energies of reaction intermediates, delayed onset of water oxidation, and/or low coverage of oxygenated species at surface oxidation potentials.

Confinement effects on alloy reactivity.

Density functional theory is used to characterize reactivity in systems confined between alloy surfaces separated by a gap from three to 10 Å. It is found that the proximity of a second surface alters the geometric and electronic properties of the first one, and the changes are related to the nature of the interacting surfaces. These phenomena are explored by analysis of the dissociation of molecular oxygen and that of water in the confined systems. The results suggest that such confinement effects may be further designed for specific applications by tuning the alloy composition.

Surface segregation and stability of core-shell alloy catalysts for oxygen reduction in acid medium.

Density functional theory is used for the evaluation of surface segregation, trends for dissolution of Pt surface atoms in acid medium, and oxygen reduction reaction activity of core-shell materials, containing a monolayer of platinum over a monometallic or bimetallic core. Two groups of cores are investigated: Pt/X with X = Ir, Au; Pd, Rh, Ag; Co, Ni, Cu; and Pt/Pd(3)X, with X = Co, Fe, Cr, V, Ti, Ir, Re. It is found that all the 4d and 5d pure cores may serve as stable cores, and their beneficial effect on the Pt monolayer may be further tuned by alloying the core to another element, here chosen from 3d or 5d groups. The Pd(3)X cores enhance the stability of the surface Pt atoms both in vacuum and under adsorbed oxygen; however the high oxygen philicity of some of the X elements induces their surface segregation that may cause surface poisoning with oxygenated species and their dissolution in acid medium.