Drinkable and tough hydrogel niches for oral protein and microbial therapeutics

Introduction:: Difficulty swallowing solids is a prevalent problem, afflicting >50% of children and 37% of adults. This presents a major challenge in healthcare, as a majority of medications are solids for cost and stability reasons. Consequently, patients may skip doses out of hesitancy and discomfort. Patients have crushed their medications in extreme cases, which can lead to death due to modified pharmacokinetics. Here, we sought to engineer a formulation capable of transforming from a liquid to a solid, to facilitate drinkability (as a liquid) and therapeutic stabilization and modulation (as a solid). Termed LIFT (liquid in situ-forming and tough) hydrogels, these materials were engineered to be mechanically tough to resist the compressive forces within the gastrointestinal tract. The LIFT formulation comprises an initial crosslinker solution “drink” containing dithiols and calcium, followed by a polymer solution containing alginate and multi-arm poly(ethylene glycol) (PEG)-maleimide. All materials were either generally recognized as safe (GRAS) or FDA-approved. Upon contact and mixing with the crosslinker solution in the stomach, the polymer solution undergoes rapid crosslinking and forms a tough hydrogel. We demonstrate that LIFT can form in the stomachs of pigs, are mechanically tough, and can encapsulate excipients that protect the activity of enzymes and viability of therapeutic bacteria in rats and pigs.


Materials and Methods:: All animal experiments were performed after MIT CAC review and approval. To test LIFT formation, crosslinker solution (200 mM CaCl₂, 10 mM PEG-dithiol [1 kDa]) followed by polymer solution (0.5% alginate, 5% 4-arm PEG-maleimide [20 kDa]) were administered endoscopically into the stomachs of pigs. Hydrogels were retrieved and mechanically characterized via compressive testing. The enzymes lactase and cellulase and bacteria strain L. lactis were used as model therapeutics. To test the capacity of LIFT to protect therapeutics from gastric exposure, therapeutics were mixed into the polymer solution along with CaCO₃ as an acid-buffering excipient. LIFT hydrogels were retrieved from the stomachs of rats and/or pigs after gastric challenge and assayed for enzyme activity or bacterial viability.


Results, Conclusions, and Discussions:: To test in vivo formation, crosslinker and polymer solutions were endoscopically administered into the stomachs of pigs. To confer mechanical toughness, LIFT hydrogels contained an alginate and PEG polymer network that undergo crosslinking once in contact with the crosslinker solution (Fig. 1A, 1B). Hydrogels were observed to form in vivo and were retrieved for mechanical testing. Throughout 5 cycles of compression, LIFT hydrogels were able to sustain greater forces compared to single-network alginate hydrogels. Whereas LIFT hydrogels recovered its original geometry after deformation, alginate hydrogels remained permanently deformed (flattened) (Fig. 1C, 1D).



Enzymes and engineered bacteria with advanced sensing and therapeutic functions have great potential in modulating systemic disease through interactions with endogenous materials in the gastrointestinal tract. To test the potential of LIFT to protect the viability of these therapeutics, we mixed CaCO₃ as an acid-buffering excipient alongside enzymes or bacteria into the polymer solution. In rats and pigs, LIFT was able to protect the activity of lactase and cellulase in the stomach (Fig. 1E, 1F). LIFT was also able to augment the viability of L. lactis, an important therapeutic bacteria strain in synthetic biology engineering applications, in the stomach of pigs (Fig. 1G).



Collectively, these data support the capacity of LIFT hydrogels to form in porcine stomachs, which exhibit a similar size scale to that of humans. The hydrogel is initially a liquid, but rapidly forms a solid when in contact with crosslinker solution in the stomach. LIFT hydrogels are mechanically tough and able to support encapsulated enzyme and bacteria activity in the challenging gastric environment. Stabilizing these sensitive therapeutics typically requires solid drug forms to enable co-formulation with stabilizers and excipients. Here, through thoughtful selection of materials we are able to achieve a formulation that is drinkable but forms a tough solid, enabling co-formulation with excipients. We envision that these hydrogels form a compliant “niche” that mitigates gastric fluid acidity and enables therapeutic activity. More broadly, LIFT could expand access to advanced therapeutics for vulnerable pediatric and geriatric patients who struggle with swallowing solid dosage forms.


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