Specific pore structure is a vital essential for scaffolds applied in tissue engineering. In this article, poly(lactide-co-glycolide) (PLGA) scaffolds with a bimodal pore structure including macropores and micropores to facilitate nutrient transfer and cell adhesion were fabricated by combining supercritical CO 2 (scCO 2 ) foaming with particle leaching technique. Three kinds of NaCl particles with different scales (i.e., 100-250, <75, <10 lm) were used as porogens, respectively. In particular, heterogeneous nucleation occurred to modify scCO 2 foaming/particle leaching process when NaCl submicron particles (<10 lm) were used as porogens. The observation of PLGA scaffolds gave a formation of micropores (pore size <10 lm) in the cellular walls of macropores (pore size around 100-300 lm) to present a bimodal pore structure. With different mass fractions of NaCl introduced, the porosity of PLGA scaffolds ranged from 68.4 6 1.4 to 88.7 6 0.4% for three NaCl porogens. The results of SEM, EDS, and in vitro cytotoxicity test of PLGA scaffolds showed that they had uniform structures and were compatible for cell proliferation with no toxicity. This novel scCO 2 foaming/particle leaching method was promising in tissue engineering due to its ability to fabricate scaffolds with precise pore structure and high porosity.
A robust
Stille gem-difluoroallylation of arylstannanes
with 3-bromo-3,3-difluoropropenes has been established. The catalyst
was found to exert critical effect on the reaction chemoselectivity.
By using Pd(OH)2/C as the catalyst, a series of 3-(hetero)aryl/vinyl-3,3-difluoropropenes
were obtained in high efficiency with α-substitution regioselectivity.
The reaction has a broad substrate scope, and various substitution
patterns were well tolerated in both substrates. Notably, the reaction
can be easily extended to late-stage gem-difluoroallylation
of many bioactive molecules with good chemoselectivity.
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