(675g) Stimuli-Responsive Hydrogel Microparticle Populations As a ‘Plug and Play’ Model for Creating Controlled and Tailorable Therapeutic Delivery

Personalized therapeutic regimens are of increasing interest for the treatment of various ailments from cancer to wound healing. The desire for these platforms has increased as the number of protein therapeutics on the market and the understanding that each patient responds differently to any given treatment continues to grow. Additionally, the use of multiple therapeutics, deemed combination therapies, are becoming widespread as they afford a motif for improving therapeutic efficacy. However, the main limitation associated with many protein therapeutics is systemic toxicity associated with the high dose required for therapeutic efficacy to be realized. Dynamic and stimuli-responsive hydrogels offer a facile platform for the encapsulation and controlled release of hydrophilic proteins therapeutics towards the design of personalized combination therapies with minimal adverse side effects.^1,2 Additionally, many hydrogel systems can be easily modified to incorporate targeting moieties to ensure localization in a tissue of interest.^3,4

Here, hydrogel microparticle populations that respond to either internal (i.e., reducing environments) or external (i.e., light) cues were designed to release multiple therapeutics across several time scales. These microparticles were synthesized using microfluidic devices, and the chemical nature of the hydrogel crosslink was engineered to respond to either glutathione, over several days, or light, over minutes. A thiol-Michael addition reaction between maleimide functionalized linear poly(ethylene glycol) (PEG) and PEG-tetra-thiol was utilized for hydrogel polymerization. Reduction sensitivity to glutathione (GSH), a tripeptide upregulated in diseased tissue, was imparted using aryl-thiol based thioether succinimide bonds which can undergo a retro-Michael reaction in the presence of exogenous alkyl thiols.^5,6 To control the rate of degradation in response to GSH the ratio of aryl- to alkyl-thiol based crosslinks in the hydrogel backbone was altered, as the latter do not undergo the retro reaction leading to hydrogel degradation.⁷ Light sensitivity was added to particles through the incorporation of o-nitrobenzyl linkers, which respond to long wavelength UV light, short wavelength visible light, and two-photon near infrared light.⁸

Hydrogel microparticle size, degradation rate, and protein release rate were determined in vitro. The size of microparticles was minimally affected by the polymerization mechanism, chemical nature of the crosslink, or the loaded cargo. The degradation and protein release profiles for each of the different hydrogel microparticle formulations were assessed in silico using a statistical-kinetic model for degradation and in vitro using fluorescent microscopy and a plate reader to monitor the concentration of model fluorescent proteins encapsulated within the hydrogels. After individual assessment of the microparticle formulations, particles that responded differently to a given stimulus were loaded with dissimilar model proteins and mixed together to investigate combinatorial release profiles. The ability to mix microparticles that respond to stimuli on different time scales together provides a ‘plug and play’ mechanism for creating personalized therapeutic regimens for combination therapy.

References

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