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Biomaterials

Biomaterials - Poster Session D

Poster C8 - Robust Biopolymer Double Network Hydrogels For Targeted Drug Delivery

Friday, October 25, 2024
3:30 PM - 4:30 PM EST
Location: Exhibit Hall E, F & G

Introduction:  Hydrogels are hydrophilic polymeric networks that allow the transfer of aqueous solutions through the material which is beneficial for drug delivery applications. Conventional hydrogels have limitations in drug loading and release, as well as weak mechanical properties[1].
Nitric Oxide (NO) is a small reactive molecule released naturally by cells in the body. It is a drug known to have antimicrobial and anticoagulant properties[2]. Therefore, a biomedical hydrogel that could release NO would have very beneficial antimicrobial and anticoagulant properties.
This work attempts to solve the limitation of conventional hydrogels and sustained and controlled NO release with the use of thiol-acrylate polymerization click chemistry. NO is released synthetically by RSNO groups with a free thiol[3]. However, by adding a secondary network polymer with free acrylate groups, thiol-acrylate polymerization will crosslink the two networks. This will increase the crosslinking density and strengthen the hydrogel[1]. This project aims to optimize and characterize a NO releasing thiolated biopolymer with crosslinking agent and its controllable mechanical properties.
This work aims to fabricate a mechanically robust double network hydrogel; a biopolymer was thiolated with a tertiary thiol molecule and combined with Polyethene Glycol Diacrylate (PEGDA) and crosslinked with a small molecule. Taking advantage of the excess free thiol groups for nitrosation of the thiolated biopolymer promote a prolonged and targeted delivery of NO. By changing the molar concentrations of the functional groups available for crosslinking we can modify the crosslinking density and thus the mechanical dissipation of the hydrogel and the level of NO release.

Materials and

Methods:  The thiolated biopolymer was fabricated by dissolving biopolymer in a basic buffer solution. The RSNO parent molecule (a modified amino acid) was added and kept at 40 ºC under nitrogen gas for 3 h. The solution then went through dialysis for 48 h to get rid of unconjugated thiols. The purified thiolated biopolymer was then lyophilized until dried completely. An Ellman’s assay was then done to measure the amount of free thiol groups covalently bonded to the biopolymer.
Material optimization was achieved by changing molar ratios to tune NO release and mechanical properties. The thiolated biopolymer was nitrosated using sodium nitrite and 0.1 M hydrochloric acid.
Swelling ratio was determined by lyophilizing samples to get the dry weight, then using the following equation to calculate swelling ratio for each time point.
Swelling ratio=(m(dry) –m(wet))/m(dry) ×100
The samples were swelled in phosphate buffer solution at 37 ºC to mimic physiological conditions.
Uniaxial compression testing was performed by a Mark-10 series 5 force gauge (Mark-10 Copiague, NY) at 25ºC with different molar ratios of DA and P. Rheological testing was performed at 25ºC with a TA Discovery HR-20 to determine the storage and loss modulus of the different hydrogels. Drug release kinetics were measured using Sievers Nitric Oxide Analyzers at 37 ºC; testing was carried out in humid conditions after neutralizing.

Results, Conclusions, and Discussions: Results and

Discussion:
Material Fabrication:
This work found that by using Poly(ethylene glycol) diacrylate (DA), with a small molecule containing thiol groups (P), this molecule increased crosslinking density of the inter and intra polymeric network interactions. This left a fully crosslinked hydrogel with double network biopolymer and DA with enough free thiols nitrosated for drug release. Hydrogels were synthesized at 40 ºC, hardened, then nitrosated.
Material Characterization:
All concentrations of DA and P plateaued swelling within 1.5 h. The hydrogel with 0.2:1 molar ratio DA and 0.04:1 molar ratio P got a swelling ratio of 191% increase in mass at 32 h while the hydrogel with 0.3:1 DA and 0.08:1 P only got up to 42%. This shows that depending on the molar ratios of DA and P, the swelling ratio can be tuned to fit the desire of its application.
Rheological testing showed the crossover point for the storage and loss modulus of thiolated biopolymer with and without PA was 315 and 300 seconds, respectively. However, the crossover point of thiolated biopolymer with DA and P was 220 seconds. This shorter gelation time shows more crosslinking is taking place with DA and P.
Compression results show toughness between 2.5 and 1 J m-2 and a modulus of elasticity between 0.35 and 0.1 MPa. The 0.3:1 DA and 0.08:1 P hydrogel had the highest modulus and toughness while the 0.2:1 DA and 0.08:1 P had the lowest. This variability shows that this material can have tunable mechanical properties. Three hydrogels were tested with different ratios of DA and P, and all had a flux between 2.5-3x10-10 mol min-1 mg-1.

Conclusions:
By combining one network: a large molar mass biopolymer, with a secondary network DA, and using a small molecule thiol as a crosslinker to tie the two together, we can create a hydrogel that is able to release NO, a fast gelation time, and tunable mechanical properties. This material can be applied and tuned for tissue engineering matrixes, soft actuators, biomedical coatings, and any other biomaterial in need of antimicrobial and anticoagulant properties with adjustable mechanical properties[2].

Acknowledgements (Optional):  This material is based upon work supported by a National Science Foundation Research Experiences for Undergraduates (REU) site program under Grant No. 1950581.
References
1. Controlled Delivery of Corticosteroids Using Tunable Tough Adhesives - Koh - 2023 - Advanced Healthcare Materials - Wiley Online Library. https://onlinelibrary.wiley.com/doi/full/10.1002/adhm.202201000.
2. Goudie, M. J., Pant, J. & Handa, H. Liquid-infused nitric oxide-releasing (LINORel) silicone for decreased fouling, thrombosis, and infection of medical devices. Sci Rep 7, 13623 (2017).
3. Singh, R. J., Hogg, N., Joseph, J. & Kalyanaraman, B. Mechanism of Nitric Oxide Release from S-Nitrosothiols*. Journal of Biological Chemistry 271, 18596–18603 (1996).