(489c) Modular and Injectable Poly(Oligoethylene glycol methacrylate)-Based Hydrogels With Tunable Protein and Cell Interactions

 Fig. 1: Deswelling as a function of temperature: POEGMA (●, 90:10) and  (○, 0:100).

Fig. 2: Swelling test of the POEGMA hydrogels as a function of polymer incorporation. Effect of (90:10):(0:100) composition. (D, 25/75), (○, 0/100), (♦ 50/50) , (▼, 75/25) and (● , (100:0).

			Hydrogel

Fig. 3: Chronic in vivo result after implantation in Balb-c mice with POEGMA 0:100

RESULTS AND DISCUSSION

Control over volume phase transition temperature (VPTT) of the polymers can be achieved by varying the M(EO)₂MA and OEGMA₄₇₅ copolymerization ratio. The large VPTT range that can be achieved by using oligoethylene glycol methacrylate monomers provides an advantage over the use of e.g. NIPAAm. The effect of the precursor composition on the thermosensitivity of the POEGMA hydrogels is shown in Fig. 1. Both POEGMA hydrogels display a volume phase transition; however, the temperature response from the 90:10 hydrogel occurs at lowertemperature, lower initial water content, and with a higher deswelling ratio relative to the 0:100 hydrogel, as expected based on the LCST values of the precursor polymers.

    The equilibrium water content of the hydrogels can easily be controlled by mixing the 0:100 and 10:90 polymer precursors at different ratios (see Fig. 2) As the weight fraction of 0:100 precursors was increased, swelling of the hydrogels also increased. Control over the water content of these hydrogels allows for control over the pore size and diffusion within the hydrogel matrix.  Analogously, the elastic moduli of the POEGMA hydrogels can be tuned by modulating the  polymer concentration used to prepare the hydrogels, with significantly higher elastic moduli achieved at higher polymer weight fractions.  In this way, the mechanical properties of the hydrogels can be controlled to match a range of stronger tissues, such as muscles, cartilage, and bone tissues as well as softer tissues such as neural and adipose tissue within the body.

The release of model proteins BSA (MW = 66 kDa) and fibrinogen (MW = 342 kDa) from POEGMA hydrogels can be controlled by the polymer precursor composition by exploiting differences in the swelling behaviors of the different hydrogels. POEGMA hydrogels (90:10) release both BSA and fibrinogen at a slower rate when compared to the 0:100 POEGMA hydrogels.. The rate of release is governed by the intermolecular interactions within the two gels; the 90:10 hydrogel collapses when warmed from room temperature (as injected) to 37°C (as inside the body), trapping the proteins within the gels, while the 0:100 hydrogel continuously swells at 37°C to enable fast release.  Improved performance can be achieved by mixing the polymer precursors at intermediate ratios, enabling both prolonged release with minimal long-term entrapment.

    Finally, both the high and low transition temperature POEGMA-based hydrogels exhibit highly favorable protein and cell adhesion properties.  Adsorption/adhesion of proteins (BSA and fibrinogen) as well as cells (NIH 3T3 fibroblasts) to the 90:10 and 0:100 hydrogels was measured to be comparable to conventional PEG-based hydrogels. Furthermore, in vitro MTT assays performed on NIH 3T3 fibroblasts grown in the presence of POEGMA precursors and hydrogels show that high cell viability and non-cytotoxicity is maintained over a large range of concentrations. In vivo studies on BALB-c mice show successful implantation with a mild inflammatory response at the acute time point but with no significant inflammation persisting at the chronic time point of 28 days post-implantation (Fig. 3, suggesting that these hydrogels are highly bioinert. Degradation of the hydrogels is also confirmed both in vitro and in vivo, enabling clearance of the hydrogel over time frames as short as a few days or as long as a few months depending on the precursor polymer composition.

CONCLUSIONS

     POEGMA-based polymers functionalized with hydrazide and aldehyde groups can be used for the synthesis of modular injectable and degradable hydrogels for drug delivery and tissue engineering applications. The physiochemical and mechanical properties can be controlled by tuning the precursor composition (i.e. the M(EO)₂MA:OEGMA₄₇₅ molar ratio) as well as by mixing polymeric precursors with different compositions to achieve intermediate hydrogel properties. Protein and cell adhesion assays show low adsorption and adhesion comparable to conventional PEG-based systems. Furthermore, the polymer precursors display no significant in vitro or in vivo cytotoxicity.

ACKNOWLEDGMENTS:  Funding from NSERC CREATE-IDEM and 20/20: NSERC Ophthalmic Materials Research Network is gratefully acknowledged.

REFERENCES:

1. Patenaude, M.; Hoare, T. Biomacromolecules, 2012, 13 (2), 369?378

2. Lutz, J. Journal of Polymer Chemistry, 2008, 46, 3459-3470.4.