Cross-Linked Hydrogels Formed through Diels–Alder Coupling of Furan- and Maleimide-Modified Poly(methyl vinyl ether-<i>alt</i>-maleic acid)

The Diels–Alder [4 + 2] cycloaddition between furan- and maleimide-functional polyanions was used to form cross-linked synthetic polymer hydrogels. Poly­(methyl vinyl ether-<i>alt</i>-maleic anhydride) was reacted with furfurylamine or <i>N</i>-(2-aminoethyl)­maleimide in acetonitrile to form pairs of furan- and maleimide-functionalized poly­(methyl vinyl ether-<i>alt</i>-maleic acid)­s. Mixtures of these mutually reactive polyanions in water gelled within 15 min to 18 h, depending on degree of functionalization and polymer concentrations. Solution and magic-angle spinning ¹H NMR were used to confirm the formation of the Diels–Alder adduct, to analyze competing hydrolytic side reactions, and demonstrate postgelation functionalization. The effect of the degree of furan and maleimide functionalization, polymer concentration, pH, and calcium ion concentration, on gelation time, gel mechanical properties, and equilibrium swelling, are described. Release of dextran as a model drug was studied using fluorescence spectroscopy, as a function of gel composition and calcium treatment

Charge-Shifting Polycations with Tunable Rates of Hydrolysis: Effect of Backbone Substituents on Poly[2-(dimethylamino)ethyl acrylates]

While polycations based on 2-(dimethylamino)­ethyl methacrylate and 2-(dimethylamino)­ethyl acrylate are used in applications ranging from biomaterials to wastewater treatment, few studies have considered the remarkable differences in the hydrolytic stabilities of the respective ester groups. Here, we describe how the nature of nonmethyl α-substituents affect the rates of ester hydrolysis of such polymers, with an emphasis on the resulting shift of net polymer charge from cationic toward anionic. We introduce 2-(dimethylamino)­ethyl 2-hydroxymethyl acrylate (DHMA) as a new, very hydrolytically labile, cationic monomer that can be used to form homopolymers as well as a means to tune copolymer hydrolysis. DHMA synthesis and free radical polymerization are described, including reactivity ratios for hydroxyl-protected derivatives of DHMA and 2-(dimethylamino)­ethyl acrylate (DMAEA). Hydrolyses of PDHMA, P­[DHMA-<i>co</i>-DMAEA], PDMAEA, and PDMAEMA in pH 5 and 7 buffer are reported. The presence of the hydroxymethyl α-substituent in PDHMA led to rates of hydrolysis 2–3 orders of magnitude faster than the already rapid hydrolysis of PDMAEA. Furthermore, hydrolysis rates of P­[DHMA-<i>co</i>-DMAEA] copolymers were shown to increase as the DHMA mole fraction increased. As a result, a new route to adjusting the charge-shifting rates of such polycations in aqueous media is described

Tunable Hydrogel Thin Films from Reactive Synthetic Polymers as Potential Two-Dimensional Cell Scaffolds

This article describes the formation of cross-linked 10–200-nm-thick polymer hydrogel films by alternating the spin-coating of two mutually reactive polymers from organic solutions, followed by hydrolysis of the resulting multilayer film in aqueous buffer. Poly­(methyl vinyl ether-<i>alt</i>-maleic anhydride) (PMM) was deposited from acetonitrile solution, and poly­(<i>N</i>-3-aminopropylmethacrylamide-<i>co</i>-<i>N</i>-2-hydroxypropylmethacrylamide) (PAPM<i>_x</i>, where <i>x</i> corresponds to the 3-aminopropylmethacrylamide content ranging from 10 to 100%) was deposited from methanol. Multilayer films were formed in up to 20 deposition cycles. The films cross-linked during formation by reaction between the amine groups of PAPM<i>_x</i> and the anhydride groups of PMM. The resulting multilayer films were covalently postfunctionalized by exposure to fluoresceinamine, decylamine, d-glucamine, or fluorescently labeled PAPM<i>_x</i> solutions prior to the hydrolysis of residual anhydride in aqueous PBS buffer. This allowed tuning the hydrophobicity of the film to give static water contact angles ranging from about 5 to 90°. Increasing the APM content in PAPM<i>_x</i> from 10 to 100% led to apparent Young’s moduli from 300 to 700 kPa while retaining sufficient anhydride groups to allow postfunctionalization of the films. This allowed the resulting (PMM/PAPM<i>_x</i>) multilayer films to be turned into adhesion-promoting or antifouling surfaces for C2C12 mouse myoblasts and MCF 10A premalignant human mammary epithelial cells