Effect of temperature on the conformation and functionality of poly(N-isopropylacrylamide) (PNIPAM)-grafted nanocellulose hydrogels

Vikram Singh Raghuwanshi; David Joram Mendoza; Christine Browne; Meri Ayurini; Gediminas Gervinskas; Joel F Hooper; Jitendra Mata; Chun-Ming Wu; George P Simon; Gil Garnier

doi:10.1016/j.jcis.2023.08.152

Effect of temperature on the conformation and functionality of poly(N-isopropylacrylamide) (PNIPAM)-grafted nanocellulose hydrogels

J Colloid Interface Sci. 2023 Dec 15;652(Pt B):1609-1619. doi: 10.1016/j.jcis.2023.08.152. Epub 2023 Aug 24.

Authors

Affiliations

¹ Bioresource Processing Research Institute of Australia (BioPRIA), Department of Chemical and Biological Engineering, Monash University, Clayton, Victoria 3800, Australia. Electronic address: Vikram.raghuwanshi@monash.edu.
² Bioresource Processing Research Institute of Australia (BioPRIA), Department of Chemical and Biological Engineering, Monash University, Clayton, Victoria 3800, Australia.
³ School of Chemistry, Monash University, Clayton, Victoria 3800, Australia.
⁴ Ramaciotti Centre for Cryo-electron Microscopy, Monash University, Clayton, Victoria 3800, Australia.
⁵ Bioresource Processing Research Institute of Australia (BioPRIA), Department of Chemical and Biological Engineering, Monash University, Clayton, Victoria 3800, Australia; School of Chemistry, Monash University, Clayton, Victoria 3800, Australia.
⁶ Australian Centre for Neutron Scattering (ACNS), Australian Nuclear Science and Technology Organisation (ANSTO), Lucas Heights, NSW 2234, Australia; School of Chemistry, University of New South Wales, Sydney, NSW 2052, Australia.
⁷ Australian Centre for Neutron Scattering (ACNS), Australian Nuclear Science and Technology Organisation (ANSTO), Lucas Heights, NSW 2234, Australia; National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.
⁸ Bioresource Processing Research Institute of Australia (BioPRIA), Department of Chemical and Biological Engineering, Monash University, Clayton, Victoria 3800, Australia; Department of Materials Science and Engineering, Monash University, Clayton, Victoria 3800, Australia.
⁹ Bioresource Processing Research Institute of Australia (BioPRIA), Department of Chemical and Biological Engineering, Monash University, Clayton, Victoria 3800, Australia. Electronic address: gil.ganier@monash.edu.

PMID: 37666193
DOI: 10.1016/j.jcis.2023.08.152

Abstract

Hypothesis: Poly(N-isopropylacrylamide) [PNIPAM]-grafted cellulose nanofibers (CNFs) are new thermo-responsive hydrogels which can be used for a wide range of applications. Currently, there is no clear understanding of the precise mechanism by which CNFs and PNIPAM interact together. Here, we hypothesize that the physical crosslinking of grafted PNIPAM on CNF inhibits the free movement of individual CNF, which increases the gel strength while sustaining its thermo-responsive properties.

Experiments: The thermo-responsive behaviour of PNIPAM-grafted CNFs (PNIPAM-g-CNFs), synthesized via silver-catalyzed decarboxylative radical polymerization, and PNIPAM-blended CNFs (PNIPAM-b-CNFs) was studied. Small angle neutron scattering (SANS) combined with Ultra-SANS (USANS) revealed the nano to microscale conformation changes of these polymer hybrids as a function of temperature. The effect of temperature on the optical and viscoelastic properties of hydrogels was also investigated.

Findings: Grafting PNIPAM from CNFs shifted the lower critical solution temperature (LCST) from 32 °C to 36 °C. Below LCST, the PNIPAM chains in PNIPAM-g-CNF sustain an open conformation and poor interaction with CNF, and exhibit water-like behaviour. At and above LCST, the PNIPAM chains change conformation to entangle and aggregate nearby CNFs. Large voids are formed in solution between the aggregated PNIPAM-CNF walls. In comparison, PNIPAM-b-CNF sustains liquid-like behaviour below LCST. At and above LCST, the blended PNIPAM phase separates from CNF to form large aggregates which do not affect CNF network and thus PNIPAM-b-CNF demonstrates low viscosity. Understanding of temperature-dependent conformation of PNIPAM-g-CNFs engineer thermo-responsive hydrogels for biomedical and functional applications.

Keywords: Grafting; LCST; Poly(N-isopropylacrylamide) (PNIPAM); Rheology; Small angle neutron scattering (SANS); Thermo-responsive; Ultra small angle neutron scattering (USANS); cellulose nanofibers (CNF).