(B-44) 3D-printable, solvent-free macromer with tunable, pH-sensitive degradation for delivery of poorly soluble drugs

Introduction:: Many pharmaceuticals have low water solubility, limiting strategies for their processing and delivery. Previous research shows that by polymerizing low-molecular-weight polycaprolactone (PCL) with an acid-labile linker, a copolymer (PA20) with pH-responsive degradation is formed [1]. Further, this macromer is a liquid at room temperature, enabling solvent-free drug loading without thermal processing. Here we demonstrate that by end-capping the macromer PA20 with 2-hydroxyethyl methacrylate (HEMA), we create a photo-curable macromer pPA20 (Mw ~5400, Đ ~1.55) that retains the properties of the PA20 macromer. Using pPA20 macromer, we demonstrate the formation of photo-cured 3D scaffolds and nanoparticles with controlled particle size, which have the potential for tissue engineering [2, 3] and intracellular drug delivery [4].

Materials and Methods:: To synthesize the macromer, low-molecular-weight PCL diol was polymerized with an excess of triethylene glycol divinyl ether using p-toluenesulfonic acid as a catalyst. In one-pot HEMA was added to endcap the chains with a cross-linkable methacrylate group. The pPA20 macromer was dissolved in a 90%/10% v/v mixture of d₆-dimethyl sulfoxide (d-DMSO) and deuterated water and monitored for pH-dependent degradation via proton NMR analysis of the peaks from the acid-labile linkage. To form a photo-cured 3D scaffold, a 1:1 ratio of photo-initiators Irgacure 2959 and diphenyl-(2,4,6-trimethylbenzoyl)-phosphine oxide) was added to pPA20 at 1% w/w, mixed without solvent, and exposed to 360 nm ultraviolet light (UV) for 60 s. Nanoparticles were synthesized by taking 1 mg per mL of pPA20 in distilled water and probe-sonicating at a moderate amplitude until 100 to 500 J were delivered, followed by UV cross-linking for 60 s. Particle size was determined using dynamic light scattering. To determine the gel fraction of the polymer network, uniform discs of photo-cured pPA20 were washed in 50/50 DMSO and dichloromethane overnight, and the weight difference before and after solvent extraction was recorded.

Results, Conclusions, and Discussions:: Figure 1a demonstrates the formation of a 3D solid material by photo-curing the solvent-free pPA20 macromer loaded with a solubilized dye (indocyanine green). The pPA20 macromer undergoes accelerated hydrolytic degradation at mildly acidic pH (5.0) and elevated temperature (60 ^oC) in comparison with physiological condition (pH 7.4, 37 ^oC) (Figure 1b). Photo-curing of pPA20 macromer under sonication produced nano- and sub-micron particles with nearly uniform size distribution, which are also stable without additional surfactant. The particle size can be easily tuned by adjusting the energy level of sonication (Figure 1c). Figure 1d indicates that the photo-cross-linking of pPA20 macromer produced a network with >60% gel fraction that requires the chain-end-capping by HEMA, whereas a physical mixture of HEMA and non-methacrylated macromere PA20 is unable to be photo-cured. In conclusion, a new biodegradable photo-curable macromer was synthesized and characterized. The macromer undergoes hydrolytic degradation in response to mildly acidic pH. A low-melt liquid at room temperature, the macromer enables solvent-free drug loading and mild-temperature processing into photo-cured 3D scaffold and narrowly dispersed nanoparticles with tunable size. This photo-curable macromer presents a new biomaterial option for use in the engineering of regenerative tissues and drug delivery systems [2-4].

Acknowledgements (Optional): :

References (Optional): : [1] Zhang, L., Zhang, Z., Wang, W., Tabet, A., Hanson, S., Zhang, L., Zhu, D., & Wang, C. (2021). Polymer-based dual-responsive self-emulsifying nanodroplets as potential carriers for poorly soluble drugs. ACS Applied Bio Materials, 4(5), 4441–4449. https://doi.org/10.1021/acsabm.1c00194

[2] Kupfer, M. E., Lin, W.-H., Ravikumar, V., Qiu, K., Wang, L., Gao, L., Bhuiyan, D. B., Lenz, M., Ai, J., Mahutga, R. R., Townsend, D., Zhang, J., McAlpine, M. C., Tolkacheva, E. G., & Ogle, B. M. (2020). In situ expansion, differentiation, and electromechanical coupling of human cardiac muscle in a 3D bioprinted, chambered organoid. Circulation Research, 127(2), 207–224. https://doi.org/10.1161/circresaha.119.316155

[3] Lutter, G., Puehler, T., Cyganek, L., Seiler, J., Rogler, A., Herberth, T., Knueppel, P., Gorb, S. N., Sathananthan, J., Sellers, S., Müller, O. J., Frank, D., & Haben, I. (2022). Biodegradable poly-ε-caprolactone scaffolds with ecfcs and imscs for tissue-engineered heart valves. International Journal of Molecular Sciences, 23(1), 527. https://doi.org/10.3390/ijms23010527

[4] Tabet, A., Antonini, M.-J., Sahasrabudhe, A., Park, J., Rosenfeld, D., Koehler, F., Yuk, H., Hanson, S., Stinson, J., Stok, M., Zhao, X., Wang, C., & Anikeeva, P. (2021). Modular integration of Hydrogel Neural interfaces. ACS Central Science, 7(9), 1516–1523. https://doi.org/10.1021/acscentsci.1c00592