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We report the structural and mechanical behavior of multicomponent hydrogels comprising the commercial poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) block copolymer F127 and alginate. Previous studies on this system have shown thermoreversible behavior in shear rheology. Here we explore the properties of these materials under compression and large deformations, relevant to applications such as wound dressings that require mechanical robustness. For gels with lower F127 concentration, we find that the stiffness of the gels can be ascribed to the alginate network, and that the Young's modulus and fracture stress do not strongly depend on temperatures. However, for gels with an F127 concentration of 30 wt %, the Young's modulus is enhanced at higher temperatures. Under large deformations, the fracture stress and fracture strain of the materials can be independently varied using the alginate and F127 concentrations, respectively; without the trade‐off in these properties that is often observed in rigid polymer networks. Small‐angle X‐ray scattering shows a power‐law dependence scattering intensity on q arising from the alginate network and scattering peaks consistent with rearranging micelles. For gels with lower F127 concentrations, we find a disordered–body‐centered cubic (BCC)‐face‐centered cubic (FCC) progression of states with temperature, and a BCC/FCC mixture for gels with higher F127 concentrations. [ABSTRACT FROM AUTHOR]

• Microscale structures are observed in hydrogels of PLA-PEO-PLA block copolymers. • Nature of the microstructure depends on stereochemistry of the PLA block. • Clear micropores and mass fractal structure for gels with a higher l / d -lactide ratio. • More uniform surface fractal structure for gels with a 50/50 l / d -lactide ratio. • Stereochemistry can be used to tune microstructure of polymeric biomaterials. Understanding the development of microstructure (e.g., structures with length scales roughly 0.5–500 μm) in hydrogels is crucial for their use in several biomedical applications. We utilize ultra-small-angle neutron scattering (USANS) and confocal microscopy to explore microstructure of poly(lactide)-poly(ethylene oxide)-poly(lactide) (PLA-PEO-PLA) triblock copolymer hydrogels with varying l / d -lactide ratio. We have previously found that these polymers self-assemble on the nanoscale into micelles. Here, we observe large-scale structures with diverse morphologies, including highly porous self-similar networks with characteristic sizes spanning approximately 120 nm–200 μm. These structural features give rise to power-law scattering indicative of fractal structures in USANS. Mass fractal and surface fractal structures are found for gels with l/d ratios of 80/20 and 50/50, respectively. Confocal microscopy shows microscale water-filled channels and pores that are more clearly evident in gels with a higher fraction of l -lactide in the PLA block as compared to the 50/50 hydrogels. Tuning block stereochemistry may provide a means of controlling the self-assembly and structural evolution at both the nanoscale and microscale, impacting application of these materials in tissue engineering and drug delivery. [ABSTRACT FROM AUTHOR]

We report on the nanoscale assembly of poly(lactic acid)- b- poly(ethylene oxide)- b- poly(lactic acid) (PLA-PEO-PLA) triblock copolymers in water, focusing on the effect of stereochemistry, where the PLA blocks are statistical copolymers of l -lactide and d -lactide with l/d ratios of 100/0, 95/5, 90/10, 85/15, 75/25, and 50/50. Small-angle neutron scattering (SANS) shows a nearly constant d -spacing as concentration varies in triblock systems with l/d ratios of 90/10 and 95/5, which we attribute to inhomogeneity in the structure of these gels, supported by previous USANS and confocal microscopy studies. The SANS data fit well to a core-shell ellipsoid form factor model with a hard-sphere structure factor. Polymeric micelles with l/d ratios from 75/25 to 85/15 displayed very high aggregation numbers, consistent with a strong interaction between PLA chains and the enhanced storage modulus observed in rheological studies of these systems. While the 90/10 and 95/5 samples showed lower aggregation numbers, their SANS profiles shows close spacing between micelles, which may promote a high fraction of intermicellar bridging chains, also consistent with a higher storage modulus. Overall, these results provide insight into the micellar assembly behavior of block copolymers with a crystallizable block, and indicate that tuning stereochemistry of PLA-based block copolymers is an effective means of modifying micellar properties for specific applications. [Display omitted] • Assembly of block copolymer gels with varying block stereochemistry was explored. • SANS shows a nearly constant d -spacing with concentration for intermediate l/d ratios. • Profiles are consistent with inhomogeneity in the gel structure. • Data also suggest a high fraction of bridging chains at intermediate l/d ratios. • Results give insight into the unique rheology observed in these systems. [ABSTRACT FROM AUTHOR]