4D Printed Protein-AuNR Nanocomposites with Photothermal Shape Recovery

Abstract

4D printing is the 3D printing of objects that change chemically or physically in response to an external stimulus over time. Photothermally responsive shape memory materials are attractive for their ability to undergo remote activation. While photothermal methods using gold nanorods (AuNRs) have been used for shape recovery, 3D patterning of these materials into objects with complex geometries using degradable materials has not been addressed. Here, we report on the fabrication of 3D printed shape memory bioplastics with photo-activated shape recovery. Protein-based nanocomposites based on bovine serum albumin (BSA), poly (ethylene glycol) diacrylate and gold nanorods were developed for vat photopolymerization. These 3D printed bioplastics were mechanically deformed under high loads, and the proteins served as mechanoactive elements that unfolded in an energy-dissipating mechanism that prevented fracture of the thermoset. The bioplastic object maintained its metastable shape-programmed state under ambient conditions. Subsequently, up to 99% shape recovery was achieved within 1 min of irradiation with near-infrared light. Mechanical characterization and small angle X-ray scattering (SAXS) analysis suggest that the proteins mechanically unfold during the shape programming step and may refold during shape recovery. These composites are promising materials for the fabrication of biodegradable shape-morphing devices for robotics and medicine.

Keywords: 3D printing; Gold Nanorod; Photothermal; Protein; Shape recovery.

Figure 1.

a) Illustration of the SLA 3D printing of aqueous BSA or MABSA resins with PEGDA and AuNRs, and a molecular-level depiction of the printed protein-polymer network. b) General scheme for the workflow of shape programming and recovery. The 3D printed constructs are first dehydrated to afford bioplastics that can be mechanically compressed to program a new metastable shape, which remains stable under ambient conditions for an indefinite period of time. Irradiation of the metastable construct with a NIR laser leads to rapid recovery of the original shape. The cartoon networks show the proposed conformations of BSA: the native-like globular structure of the original bioplastic construct, the outstretched form in the metastable construct, and the non-native like globular structure of the shape-recovered construct.

Figure 2.

a) DSC curves for protein-PEGDA bioplastic composites with 0.0035 wt % AuNRs. b) Graph showing the change in temperature with irradiation time for BSA/PEGDA 2:1 with varying amounts of AuNRs. c) Comparison of the compression and recovery of a cylindrical disk with a BSA/PEGDA 2:1 composition (i) without AuNRs and (ii) with AuNRs (0.005 wt%). The dimension of the original cylinder was 8.3 mm × 5.2 mm, and the compressed sample was 3.2 mm × 11.8 mm.

Figure 3.

Compressive stress vs strain curves of 3D printed bioplastics a) BSA/PEGDA 3:1 bioplastics with 0-0.005% AuNRs, b) MABSA/PEGDA 3:1 bioplastic with 0-0.005% AuNRs, c) 4 different formulated bioplastics without gold nanorod, d) BSA/PEGDA 3:1 0.00375% AuNRs bioplastics compare with its laser-recovered bioplastic (red) or heat treatment (120°C for 30 min) bioplastic (purple).

Figure 4.

SAXS plots for BSA/PEGDA 3:1 composites with (0.00375 wt % AuNRs).

Figure 5.

a) Shape recovery of BSA/PEGDA 3:1 0.00375 wt % AuNRs 3D printed bioplastic ball under the pork gelatin skin. b) Selective shape recovery of folded 3D-printed BSA/PEGDA 3:1 0.00375 wt % AuNRs 3:1 four arms flower.