Indirect Solid Freeform Fabrication of an Initiator-Free Photocrosslinkable Hydrogel Precursor for the Creation of Porous Scaffolds.

In the present work, a photopolymerized urethane-based poly(ethylene glycol) hydrogel is applied as a porous scaffold material using indirect solid freeform fabrication (SFF). This approach combines the benefits of SFF with a large freedom in material selection and applicable concentration ranges. A sacrificial 3D poly(ε-caprolactone) structure is generated using fused deposition modeling and used as template to produce hydrogel scaffolds. By changing the template plotting parameters, the scaffold channel sizes vary from 280 to 360 µm, and the strut diameters from 340 to 400 µm. This enables the production of scaffolds with tunable mechanical properties, characterized by an average hardness ranging from 9 to 43 N and from 1 to 6 N for dry and hydrated scaffolds, respectively. Experiments using mouse calvaria preosteoblasts indicate that a gelatin methacrylamide coating of the scaffolds results in an increased cell adhesion and proliferation with improved cell morphology.

2-Acyl-dimedones as UV-active protective agents for chiral amino acids: enantiomer separations of the derivatives on chiral anion exchangers.

2-Acetyldimedone and 12 related compounds were employed as UV-active pre-column derivatizing agents for amino acids. Direct enantioseparation of the products was achieved using chiral anion exchanger stationary phases in polar-organic mobile phase mode. Under basic conditions, the reagents´ cyclic ß-tricarbonyl motifs can give rise to exo- and endocyclic enols through tautomerization. However, with primary amines (proteinogenic and unusual amino acids, aminosulfonic and aminophosphonic acids), we exclusively observed the formation of exocyclic enamine-type products. Reaction yields depended strongly on the 2-acyl modification of the reagent; in particular, we observed a significant decrease when electronegative or sterically demanding substituents were present in α-position to the exocyclic carbonyl group. In addition to improving UV detectability of the products, the introduction of this protective group facilitated successful enantiomer separations of the amino acid derivatives on Cinchona-based chiral anion exchangers. Particularly high enantiomer selectivity was observed in combination with stationary phases bearing a new variation of selectors with π-acidic (electron-poor) bis(trifluoromethyl)phenyl groups. No racemization of the analytes occurred at any stage of the analytical method including the deprotection, which was achieved with hydrazine.