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Hydrogels and, in particular, supramolecular hydrogels show promising properties for application in regenerative medicine because of their ability to adapt to the natural environment these materials are brought into. However, only few studies focus on the structure-property relationships in supramolecular hydrogels. Here, we study in detail both the structure and the mechanical properties of such a network, composed of poly(ethylene glycol), end-functionalized with ureido-pyrimidinone fourfold hydrogen bonding units. This network is responsive to triggers such as concentration, temperature and pH. To obtain more insight into the sol-gel transition of the system, both rheology and small-angle X-ray scattering (SAXS) are used. We show that the sol-gel transitions based on these three triggers, as measured by rheology, coincide with the appearance of a structural feature in SAXS. We attribute this feature to the presence of hydrophobic domains where cross-links are formed. These results provide more insight into the mechanism of network formation in these materials, which can be exploited for tailoring their behavior for biomedical applications, where one of the triggers discussed might be used. [ABSTRACT FROM AUTHOR]

We report the preparation and structural and mechanical characterization of a tough supramolecular hydrogel, based exclusively on hydrophobic association. The system consists of a multiblock, segmented copolymer of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic dimer fatty acid (DFA) building blocks. A series of copolymers containing 2K, 4K, and 8K PEG were prepared. Upon swelling in water, a network is formed by self-assembly of hydrophobic DFA units in micellar domains, which act as stable physical cross-link points. The resulting hydrogels are noneroding and contain 75-92 wt % of water at swelling equilibrium. Small-angle neutron scattering (SANS) measurements showed that the aggregation number of micelles ranges from 2 x 10² to 6 x 10² DFA units, increasing with PEG molecular weight. Mechanical characterization indicated that the hydrogel containing PEG 2000 is mechanically very stable and tough, possessing a tensile toughness of 4.12 MJ/m³. The high toughness, processability, and ease of preparation make these hydrogels very attractive for applications where mechanical stability and load bearing features of soft materials are required. [ABSTRACT FROM AUTHOR]

We describe the preparation of an injectable, biocompatible,andelastic segmented copolymer hydrogel for biomedical applications,with segmented hydrophobic bisurea hard segments and hydrophilic PEGsegments. The segmented copolymers were obtained by the step growthpolymerization of amino-terminated PEG and aliphatic diisocyanate.Due to their capacity for multiple hydrogen bonding within the hydrophobicsegments, these copolymers can form highly stable gels in water atlow concentrations. Moreover, the gels show shear thinning by a factorof 40 at large strain, which allows injection through narrow gaugeneedles. Hydrogel moduli are highly tunable via the physical cross-linkdensity and the length of the hydrophilic segments. In particular,the mechanical properties can be optimized to match the propertiesof biological host tissues such as muscle tissue and the extracellularmatrix. [ABSTRACT FROM AUTHOR]