Polymer Adsorbed Bilayer Membranes Form Self-Healing Hydrogels with Tunable Superstructure

Abstract

We report that polymers can support bilayer membranes to form physical hydrogels of self-healing and tunable isotropic/anisotropic structure. The system consists of poly(dodecyl glyceryl itaconate) (PDGI) that forms lamellar bilayers and polyacrylamide (PAAm) that adsorbs on the bilayer surfaces via hydrogen bond formation. Adsorption of PAAm brings two effects: disturbs the bilayer packing and causes bending of the bilayers; increases the effective thickness of the bilayers and enhances the repulsion between the bilayers due to excluded volume effect. Competition of these two effects brings about sharp super-structure transition from isotropic multi-layer foam phase to unidirectionally aligned lamellar phase.Accompany with this structure transition, the bulk hydrogel exhibits isotropic/anisotropic swelling. The physical gels exhibit high tensile strength and self-healing properties that can be understood by the sacrificial bonds mechanism.2

Self‐Healing Hydrogels

“…Uniaxial elongation measurements have been performed on cylindrical and dog‐bone‐/dumbbell‐shaped hydrogels of varying sizes that have been cut and the pieces pressed together for a specified heal time . Elongation at break measures the percentage increase in length of a stretched hydrogel before it breaks.…”

“…This SELF hydrogel exhibited shear‐thinning and bio‐antifouling properties with potential use in bioengineering applications . A fully physical poly(dodecyl glyceryl itaconate) (PDGI) and polyacrylamide (PAAm) IPN was developed, which self‐recovered . Greater than 90% recovery of the mechanical characteristics during cyclic tensile loading/unloading was exhibited within 30 min at RT (20 °C).…”

“…The reversible hydrophobic interactions of the bilayers are utilized as the self‐recovery mechanism, while the adsorption and the large extensibility of the PAAm chains sustain very large deformations. The strength of these hydrogels is a result of the rupture of the hydrophobic bonds between the bilayers that serve to dissipate mechanical energy …”

“…Additionally SELF hydrogels exhibit poor mechanical properties, a consequence of the weaker and reversible nature of the noncovalent interactions compared to that of covalent bonding. Approaches for designing tough SELF hydrogels are centerd on the efficient dissipation of mechanical energy induced around the damaged area via the breakage of sacrificial bonds . In this instance sacrificial bonds are purposefully included in the hydrogel networks and are designed to prevent backbone cleavage .…”

Supramolecular hydrogels with multi-cylindrical lamellar bilayers: Swelling-induced contraction and anisotropic molecular diffusion

“…[17] The PDGI layers and the PAAm network weakly interact through hydrogen bonds to maintain the structural integrity of the gel, which has been confirmed from the absorption peak shift of hydroxyl group (-OH) of DGI and amide group (-CONH2) of AAm observed with infrared spectroscopy. [18] Here, we describe the swelling-induced contraction and quasi one-dimensional diffusion of PDGI/PAAm gels formed into string-like shapes (as opposed to the reported rectangular sheet shape). To synthesize these string PDGI/PAAm gels, a gel precursor solution was suctioned into a polyethylene tube (instead of the rectangular cell) at a high shear rate (approximately 1,300 s -1 ) to align the DGI lamellar bilayers along the inner wall of the tube.…”