RESUMO
Triazole-based cross-linkers with different spacer lengths and different functional end groups (acrylamides, methacrylamides, maleimides and vinylsulfonamides) were synthesized, investigated for cytotoxic and antibacterial activity, and incorporated into poly(acrylamide) (PAAm) and poly(N,N-dimethylacrylamide) (PDMAAm) hydrogels by free-radical polymerization. Hydrogels prepared with different cross-linkers and cross-linker contents between 0.2% and 1.0% were compared by gel yields, equilibrium degrees of swelling (S) and storage moduli (G'). Generally with increasing cross-linker content, G' values of the hydrogels increased, while S values decreased. The different polymerizable cross-linker end groups resulted in a decrease of G' in the following order for cross-linkers with C4 spacers: acrylamide > maleimide > methacrylamide > vinylsulfonamide. Longer cross-linker alkyl spacer lengths caused an increase in G' and a decrease in S. Independent of the cross-linker used, a universal correlation between G' and equilibrium polymer volume fraction Ï was found. For PAAm hydrogels, G' ranged between 4 kPa and 23 kPa and Ï between 0.07 and 0.14. For PDMAAm hydrogels, G' ranged between 0.1 kPa and 4.9 kPa and Ï between 0.02 and 0.06. The collected data were used to establish an empirical model to predict G' depending on Ï. G' of PAAm and PDMAAm hydrogels is given by G' = 4034 kPa Ï 2.66 and G' = 4297 kPa Ï 2.46, respectively.
RESUMO
Polyelectrolyte hydrogels play an important role in tissue engineering and can be produced from natural polymers, such as the glycosaminoglycan hyaluronan. In order to control charge density and mechanical properties of hyaluronan-based hydrogels, we developed cross-linkers with a neutral or positively charged triazole core with different lengths of spacer arms and two terminal maleimide groups. These cross-linkers react with thiolated hyaluronan in a fast, stoichiometric thio-Michael addition. Introducing a positive charge on the core of the cross-linker enabled us to compare hydrogels with the same interconnectivity, but a different charge density. Positively charged cross-linkers form stiffer hydrogels relatively independent of the size of the cross-linker, whereas neutral cross-linkers only form stable hydrogels at small spacer lengths. These novel cross-linkers provide a platform to tune the hydrogel network charge and thus the mechanical properties of the network. In addition, they might offer a wide range of applications especially in bioprinting for precise design of hydrogels.
RESUMO
We report [Y{N(SiMe3)2}3] as a precatalyst for the dehydrocoupling of sterically demanding amines with ß-diketiminate stabilised aluminium dihydrides. While simple fluorinated anilines readily undergo Al-H/N-H dehydrocoupling under thermal conditions, catalytic methods are required to achieve reasonable rates of reaction for ortho-substituted anilines or hindered aliphatic amines.
