(G-263) Injectable Granular Hydrogels Enable Avidity-Controlled Biomolecule Delivery

Introduction:: Proteins are frontline biotherapeutics with excellent biocompatibility and target specificity, used to treat a range of diseases from cancer to autoimmune dysfunction.¹ The local and sustained delivery of therapeutic biomolecules is beneficial to instruct lengthy tissue-level processes such as healing and to concentrate drugs at the site of action, minimizing off-target effects. Affinity-based drug delivery systems enable selective retention of biomolecules in the scaffold, potentially overcoming challenges of burst release and affording prolonged presentation of biotherapeutics.² Here, we develop a generalizable approach to achieve sustained biomolecule delivery made possible by locally-injectable granular hydrogels with a favorable ‘host’ capacity. Interaction of these hydrogels with ‘guest’-modified proteins allows for sustained release through synthetically-tunable hydrogel avidity (Fig 1A). We sought to enable local biomolecule release across different time scales by tuning the avidity of the biomolecule-hydrogel interaction via synthetically introduced guest-host bonds.

Materials and Methods:: β-Cyclodextrin and dextran were methacrylated via esterification with glycidyl methacrylate (GMA), yielding methacrylated β-cyclodextrin (MeCD) and dextran (DexMA). MeCD/DexMA hydrogels (5%_w/v DexMA, 10%_w/v MeCD) were formed via co-polymerization (5mM LAP, 10mW/cm²); bulk hydrogels were subsequently processed into microgels by extrusion fragmentation through 18-30G needles and jammed via centrifugation to form injectable granular hydrogels, assessed by rheology. Bovine serum albumin (BSA, a model biomolecule) was conjugated to supramolecular guests (adamantane, Ad) via NHS/EDC; orthogonal fluorescent labels (AlexaFluor555, Fluorescein, Pacific Blue) were used to monitor release of each product. IL-10 was similarly modified with Ad. Methods allowed for the formation of hydrogels with a high host capacity (i.e., concentration of CD) and Ad-BSA with varying hydrogel avidity (i.e., guest modification). The cumulative release of BSA and IL-10 conjugates from host hydrogels was monitored in vitro.


Results, Conclusions, and Discussions:: Increasing feed ratios of GMA/CD enabled >1 methacrylate substitution per CD in good yield, necessary for covalent hydrogel incorporation (Fig 1B; DS=1.73 used in subsequent studies). Upon irradiation, MeCD alone provided modest polymerization, regardless of concentration (5%_w/v; G’~50Pa). Co-polymerization with DexMA (5%_w/v) was therefore used to stabilize the network (G’~15kPa). Following extrusion fragmentation, microgel diameters (34.0 ± 16.7 µm) were dependent on needle gauge but independent of CD inclusion. Granular hydrogels were strain-yielding and shear-thinning (to enable injectable delivery) and rapidly recovered their solid properties to allow for retention after injection (Fig 1C). BSA was modified by Ad in near quantitative coupling (Fig 1D); the avidity of Ad-BSA conjugates increased with the degree of modification, as assessed by surface plasmon resonance (SPR, Fig 1E). Guest modification attenuated burst release and retained BSA within the hydrogels for greater than one month, dependent upon the degree of guest modification (Fig 1F), as well as IL-10 for 14 days (Fig 1G).

The delivery of biomolecules via guest-host interactions allows for retention and sustained release, where release is tunable via biomolecule avidity. The bioconjugation proceeds under mild aqueous conditions, is non-selective, and is therefore applicable to a range of biotherapeutics (e.g., chemokines, cytokines, and antibodies) that now dominant the pharmacology market.


Acknowledgements (Optional): : Work was supported by Drexel University Startup Funds and the NIH (R35GM147184).


References (Optional): : [1] Lagassé HAD, et al. F100Research. 2017. [2] Dogan AB, et al. Pharmaceutics. 2022.