A smart thermoresponsive macroporous 4D structure by 4D printing of Pickering-high internal phase emulsions stabilized by plasma-functionalized starch nanomaterials for a possible delivery system

Abstract

Hierarchically porous structures combine microporosity, mesoporosity, and microporosity to enhance pore accessibility and transport, which are crucial to develop high performance materials for biofabrication, food, and pharmaceutical applications. This work aimed to develop a 4D-printed smart hierarchical macroporous structure through 3D printing of Pickering-type high internal phase emulsions (Pickering-HIPEs). The key was the utilization of surface-active (hydroxybutylated) starch nanomaterials, including starch nanocrystals (SNCs) (from waxy maize starch through acid hydrolysis) or starch nanoparticles (SNPs) (obtained through an ultrasound treatment). An innovative procedure to fabricate the functionalized starch nanomaterials was accomplished by grafting 1,2-butene oxide using a cold plasma technique to enhance their surface hydrophobicity, improving their aggregation, and thus attaining a colloidally stabilized Pickering-HIPEs with a low concentration of each surface-active starch nanomaterial. A flocculation of droplets in Pickering-HIPEs was developed after the addition of modified SNCs or SNPs, leading to the formation of a gel-like structure. The 3D printing of these Pickering-HIPEs developed a highly interconnected large pore structure, possessing a self-assembly property with thermoresponsive behavior. As a potential drug delivery system, this thermoresponsive macroporous 3D structure offered a lower critical solution temperature (LCST)-type phase transition at body temperature, which can be used in the field of smart releasing of bioactive compounds.

Keywords: 4D printing; Flocculated emulsion; Hydrodynamic radius; LCST behavior; Macroporous structures; Pickering-HIPEs; Thermoresponsive behavior.

Graphical abstract

Fig. 1

The particle size distribution of both SNCs and SNPs as affected by hydroxybutyl modification determined by DLS and related TEM images.

Fig. 2

(Top): Characterization of native waxy maize starch, unmodified or modified SNCs and SNPs: (a,b) FTIR, (c,d) XPS, (e,f) Zoomed XPS, (g,h) XRD. (Bottom): Contact angle measurement and related AFM images of native starch and modified SNCs or SNPs.

Fig. 3

(Row i): PSD, (Row ii): BS intensity profiles, and (Row iii): Confocal images (the top layers collected for each sample) of different Pickering-HIPEs. (Row iv): Visual observation of HIPEs (96 h after preparation).

Fig. 4

Storage (G′) and loss (G″) moduli as a function of (a): strain and (b): frequency, where G′ is solid symbols and G″ is open symbols; (c): Changes in viscosity and shear stress as a function of shear rate; and (d): viscosity dependence on applied time and deformation rate measured for different Pickering-HIPE-based inks.

Fig. .5

Normalized Lissajous–Bowditch plots of different Pickering-HIPEs. The results are shown for: Control (), E-SNP-N (), E-SNP-N () E-SNP-M (), and E–SNC–M ().

Fig. 6

(Row i): The fresh (non-freeze-dried) 3D printed Torres, and (Row ii): fresh 3D printed Cubic. (Row iii): CLSM images of different non-freeze-dried 3D structures. (Row iv): Representative images of a one-layer of freeze-dried 3D printed-grid. (Row v): FE-SEM images of freeze-dried 3D printed self-supporting scaffolds.

Fig. 7

(Top): Transmittance curves illustrating the hysteresis between heating and cooling cycles. (Bottom): Temperature dependence of R_h for printed SNCs or SNFs samples (0.5 mg mL^-1) at different temperatures.