Multifaceted Shape Memory Polymer Technology for Biomedical Application: Combining Self-Softening and Stretchability Properties

Abstract

Thiol-ene polymers are a promising class of biomaterials with a wide range of potential applications, including organs-on-a-chip, microfluidics, drug delivery, and wound healing. These polymers offer flexibility, softening, and shape memory properties. However, they often lack the inherent stretchability required for wearable or implantable devices. This study investigated the incorporation of di-acrylate chain extenders to improve the stretchability and conformability of those flexible thiol-ene polymers. Thiol-ene/acrylate polymers were synthesized using 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (TATATO), Trimethylolpropanetris (3-mercaptopropionate) (TMTMP), and Polyethylene Glycol Diacrylate (PEGDA) with different molecular weights (Mn 250 and Mn 575). Fourier Transform Infrared (FTIR) spectroscopy confirmed the complete reaction among the monomers. Uniaxial tensile testing demonstrated the softening and stretching capability of the polymers. The Young's Modulus dropped from 1.12 GPa to 260 MPa upon adding 5 wt% PEGDA 575, indicating that the polymer softened. The Young's Modulus was further reduced to 15 MPa under physiologic conditions. The fracture strain, a measure of stretchability, increased from 55% to 92% with the addition of 5 wt% PEGDA 575. A thermomechanical analysis further confirmed that PEGDA could be used to tune the polymer's glass transition temperature (T_g). Moreover, our polymer exhibited shape memory properties. Our results suggested that thiol-ene/acrylate polymers are a promising new class of materials for biomedical applications requiring flexibility, stretchability, and shape memory properties.

Keywords: conformal polymer; flexible polymer; polymer characterization; self-softening polymer; shape memory polymer; stretchable polymer; thiol-ene/acrylate polymer.

Figure 1

Synthesis process of thiol-ene/acrylate polymer.

Figure 2

Schematics showing possible ways for thiol-ene acrylate reaction.

Figure 3

Plot showing FTIR results for monomers and polymer.

Figure 4

(a) Swelling test result over a month for TATATO/TMTMP and PEGDA 575, and (b) swelling test result over a month for PEGDA 250.

Figure 5

Mechanical tensile testing result of polymers in the dry and soaked state. (a) Bar chart comparing the elongation of different compositions of polymers in the dry and soaked states, (b) bar chart comparing the Young’s Modulus of the different compositions of polymers in the dry and soaked states, (c) strain-stress curves demonstrating the increasing trend in elongation but decrease in Young’s Modulus with the addition of different molecular weight number PEGDA in dry conditions, (d) stress–strain curves from the cyclic run of the different compositions of polymer for soaked samples, stretched to 25%, and (e) stress–strain curves from the cyclic run for dry polymer samples stretched to 25%. n = 5, The data are presented as mean ± standard deviation either as error bars in bar graphics (a,b) or shaded area around stress-strain curves (c,d).

Figure 6

Thermomechanical characterization of thiol-ene/acrylate polymer. The top plots represent the tan delta (T_g), and the bottom plots represent the respective storage moduli of the dry and soaked polymers.

Figure 7

Photographs showing the temporarily fixed shape of polymer (folded configuration) and its subsequent recovery upon placing in an aqueous environment at 37 °C.

Figure 7

Photographs showing the temporarily fixed shape of polymer (folded configuration) and its subsequent recovery upon placing in an aqueous environment at 37 °C.

Figure 8

Representative 3D line plot demonstrating shape memory property of all polymer groups.

Figure 8

Representative 3D line plot demonstrating shape memory property of all polymer groups.

Figure 9

MTT cytotoxicity assay result showing all polymer compositions are biocompatible. Sample size: 3 replicates each group. Dashed line indicates the threshold of 70% above which the material is considered non-cytotoxic.