Macromolecular Solute Transport in Supramolecular Hydrogels Spanning Dynamic to Quasi-Static States

Abstract

Hydrogels prepared from supramolecular cross-linking motifs are appealing for use as biomaterials and drug delivery technologies. The inclusion of macromolecules (e.g., protein therapeutics) in these materials is relevant to many of their intended uses. However, the impact of dynamic network cross-linking on macromolecule diffusion must be better understood. Here, hydrogel networks with identical topology but disparate cross-link dynamics are explored. These materials are prepared from cross-linking with host–guest complexes of the cucurbit[7]­uril (CB[7]) macrocycle and two guests of different affinity. Rheology confirms differences in bulk material dynamics arising from differences in cross-link thermodynamics. Fluorescence recovery after photobleaching (FRAP) provides insight into macromolecule diffusion as a function of probe molecular weight and hydrogel network dynamics. Together, both rheology and FRAP enable the estimation of the mean network mesh size, which is then related to the solute hydrodynamic diameters to further understand macromolecule diffusion. Interestingly, the thermodynamics of host–guest cross-linking are correlated with a marked deviation from classical diffusion behavior for higher molecular weight probes, yielding solute aggregation in high-affinity networks. These studies offer insights into fundamental macromolecular transport phenomena as they relate to the association dynamics of supramolecular networks. Translation of these materials from in vitro to in vivo is also assessed by bulk release of an encapsulated macromolecule. Contradictory in vitro to in vivo results with inverse relationships in release between the two hydrogels underscores the caution demanded when translating supramolecular biomaterials into application.

Dynamic Imine Bonding Facilitates Mannan Release from a Nanofibrous Peptide Hydrogel

“…The discrepancy between our in vivo and in vitro results highlights the inability of in vitro release assays to adequately model the in vivo environment. Many other studies investigating supramolecular hydrogel drug delivery have seen similar discrepancies between in vitro and in vivo release kinetics. ,, The results of the current study and these related investigations demonstrate that the complex biological environment (complete with proteins, cells, etc.) plays a large role in governing the release kinetics from supramolecular materials.…”

Dynamic Covalent Bond Exchange Enhances Penetrant Diffusion in Dense Vitrimers

“…Dynamic crosslinks have also been investigated for particle transport via simulations, and it was found that diffusion can be greatly accelerated when bonds can exchange in the network. 46 Recently, it has been shown how hydrogels with dynamic bonds can influence macromolecular solute transport 47 and how protein diffusion through rigid DNA networks is impacted by dynamic exchange. 48 However, experimental tests of how dynamic bonds control molecular transport in dense, dry systems are currently lacking.…”

Supramolecular Phenylalanine-Derived Hydrogels for the Sustained Release of Functional Proteins

“…To gain insight into the relationship between hydrogel mesh size and protein release profiles we calculated the approximate mesh size of each hydrogel from the average storage moduli ( G ′) using eq 1 as previously reported by Shibayama 50 and Webber (see the Materials and Methods section and Table S4 in the Supporting Information for calculated mesh size values). 49 For NaCl hydrogels, the mesh size slightly increases in the following order: TI (9.0 nm) < RNase A (14.3 nm) < BSA (15.4 nm) < human IgG (17.0 nm). Although this trend is inversely proportional to G ′ ( Table S4 ), there is no clear correlation between the release profiles and rate of diffusion with the calculated mesh sizes.…”

“…The mesh size of the hydrogel network is also likely to influence the release rates of proteins from these hydrogels, with smaller proteins released at more rapid rates. To gain insight into the relationship between hydrogel mesh size and protein release profiles we calculated the approximate mesh size of each hydrogel from the average storage moduli ( G ′) using eq as previously reported by Shibayama and Webber (see the Materials and Methods section and Table S4 in the Supporting Information for calculated mesh size values) . For NaCl hydrogels, the mesh size slightly increases in the following order: TI (9.0 nm) < RNase A (14.3 nm) < BSA (15.4 nm) < human IgG (17.0 nm).…”

“…The average storage moduli ( G ′) of each system was used to calculate the mesh size (ξ) using eq , where G ′ is the average storage modulus, k B is the Boltzmann constant, and T is the temperature. , ξ = true( G false′ k normalB T true) − 1 / 3 …”