Structure Property Relationship of Micellar Waterborne Poly(Urethane-Urea): Tunable Mechanical Properties and Controlled Release Profiles with Amphiphilic Triblock Copolymers

Abstract

Waterborne polyurethane (WPU) has attracted significant interest as a promising alternative to solvent-based polyurethane (SPU) due to its positive impact on safety and sustainability. However, significant limitations of WPU, such as its weaker mechanical strength, limit its ability to replace SPU. Triblock amphiphilic diols are promising materials to enhance the performance of WPU due to their well-defined hydrophobic-hydrophilic structures. Yet, our understanding of the relationship between the hydrophobic-hydrophilic arrangements of triblock amphiphilic diols and the physical properties of WPU remains limited. In this study, we show that by controlling the micellar structure of WPU in aqueous solution via the introduction of triblock amphiphilic diols, the postcuring efficiency and the resulting mechanical strength of WPU can be significantly enhanced. Small-angle neutron scattering confirmed the microstructure and spatial distribution of hydrophilic and hydrophobic segments in the engineered WPU micelles. In addition, we show that the control of the WPU micellar structure through triblock amphiphilic diols renders WPU attractive in the applications of controlled release, such as drug delivery. Here, curcumin was used as a model hydrophobic drug, and the drug release behavior from WPU-micellar-based drug delivery systems was characterized. It was found that curcumin-loaded WPU drug delivery systems were highly biocompatible and exhibited antibacterial properties in vitro. Furthermore, the sustained release profile of the drug was found to be dependent on the structure of the triblock amphiphilic diols, suggesting the possibility of controlling the drug release profile via the selection of triblock amphiphilic diols. This work shows that by shedding light on the structure-property relationship of triblock amphiphilic diol-containing WPU micelles, we may enhance the applicability of WPU systems and move closer to realizing their promising potential in real-life applications.

Scheme 1. Synthetic Scheme of WPU-H

Scheme 2. Synthetic Scheme of WPU-E and WPU-Cur

Figure 1

Synthesis of WPU polymers with varied arrangements of hydrophobic segments: (a) illustration of WPU with amphiphilic segments, which scattered the acrylate groups on the surface of micelles; (b) FT-IR spectra of WPU with varied diols (e.g., EPE diols, PEP diols, and PPG)

Figure 2

Structure property relationship of the WPU polymeric structure and the self-assembled micelles. (a) ELS for the ζ potential of WPU-H. The EO content is detailed in Experimental Section. (b) DLS for the particle size distribution of WPU-H. The TEM images of EPE20-H7 (c), PEP25-H7 (d), and EPE20-H3 (e) were stained by OsO4, and HEMA is shown in darker shade.

Figure 3

Mechanical properties of WPU-H films. (a) Storage modulus (E′) of WPU-H with respect to temperature. E′ at the rubbery plateau of samples was used to determine the cross-linking density. (b) Stress–strain curves of PPG-, EPE diol-, and PEP-diol-based WPU-H compared with those of WPU-E. (c) Stress–strain curves of EPE-based WPU-H with varied HEMA contents. (d) Stress–strain curves of PEP-based WPU-H with varied HEMA contents.

Figure 4

Characterization of WPU-Cur. (a) FTIR spectra of WPU-Cur and WPU-E. The peak at 1509 cm^–1 is related to curcumin in WPU-Cur. (b) Particle size distribution of WPU-Cur. (c) ζ potential of WPU-Cur. (d) Loading efficiency of WPU-Cur, and the curcumin concentration versus storage time, at room temperature, pH = 7.8. (e) Accumulative released curcumin curve of WPU-Cur and the fitted curve of EPE40-Cur and PEP35-Cur according to the Gallagher–Corrigan model.

Figure 5

Drug release mechanistic studies and biocompatibility of WPU-Cur. (a) Weight loss of WPU-Cur during the incubation. (b) Weight loss of WPU-Cur during the incubation (PBS, 0.5% Tween-80, 37 °C). (c) Water uptake of PEP35-Cur and EPE40-Cur during the incubation. (d) Cytotoxicity assessment of WPU-E and WPU-Cur toward A549 cells (mean ± SD, N = 2).