Polymer Self-Assembly Induced Enhancement of Ice Recrystallization Inhibition

Abstract

Ice binding proteins modulate ice nucleation/growth and have huge (bio)technological potential. There are few synthetic materials that reproduce their function, and rational design is challenging due to the outstanding questions about the mechanisms of ice binding, including whether ice binding is essential to reproduce all their macroscopic properties. Here we report that nanoparticles obtained by polymerization-induced self-assembly (PISA) inhibit ice recrystallization (IRI) despite their constituent polymers having no apparent activity. Poly(ethylene glycol), poly(dimethylacrylamide), and poly(vinylpyrrolidone) coronas were all IRI-active when assembled into nanoparticles. Different core-forming blocks were also screened, revealing the core chemistry had no effect. These observations show ice binding domains are not essential for macroscopic IRI activity and suggest that the size, and crowding, of polymers may increase the IRI activity of “non-active” polymers. It was also discovered that poly(vinylpyrrolidone) particles had ice crystal shaping activity, indicating this polymer can engage ice crystal surfaces, even though on its own it does not show any appreciable ice recrystallization inhibition. Larger (vesicle) nanoparticles are shown to have higher ice recrystallization inhibition activity compared to smaller (sphere) particles, whereas ice nucleation activity was not found for any material. This shows that assembly into larger structures can increase IRI activity and that increasing the “size” of an IRI does not always lead to ice nucleation. This nanoparticle approach offers a platform toward ice-controlling soft materials and insight into how IRI activity scales with molecular size of additives.

Ice Recrystallization Inhibition by Amino Acids: The Curious Case of Alpha- and Beta-Alanine

“…We also note that, while this assay is usually performed in PBS, the use of saline solution for IRI measurements is not uncommon in this field. 24 , 25 …”

Simultaneous Synthesis and Self‐Assembly of Bottlebrush Block Copolymers at Room Temperature via Photoinitiated RAFT Dispersion Polymerization

“…Recently, a new heterogeneous reversible deactivation radical polymerization (RDRP) method, named polymerization‐induced self‐assembly (PISA) has been developed for in situ preparation of block copolymer nano‐objects with a diverse set of morphologies at high concentrations (10–50% w/w). [ 14–47 ] Typically, a macromolecular chain transfer agent (macro‐CTA) dissolved in the reaction medium is chain‐extended with a core‐forming monomer to generate a block copolymer. When the second block increases to a critical length, the formed block copolymer precipitates from the reaction medium and self‐assembles into various structures.…”

Size and Shape Control of Ice Crystals by Amphiphilic Block Copolymers and Their Implication in the Cryoprotection of Mesenchymal Stem Cells

“…27−29 We applied the similar strategies by varying the molecular weight of amphiphilic block copolymers consisting of hydrophobic and hydrophilic blocks to control the size and shape of ice crystals because the generation of new interfaces of solid in water is similar in both cases. 30 The block copolymers are in equilibrium as unimers (single chains) and self-assembled micelles in water, can be located at the water/air interface, or ideally adhere to the surface of ice crystals, and thus control the size and shape of the ice crystals depending on the structure and concentration of block polymers (Figure 1). In addition, the block copolymers might affect stability of cell membranes.…”

“…The block copolymer topology with the amphiphilic character at the molecular level contrasts with the facially amphiphilic polymers with the amphiphilic character within a repeating unit, which has been considered to exhibit excellent IRI activity. − Amphiphilic molecules have been extensively used for the preparation of inorganic nanostructured materials and nanoparticles from water. The shape and size of nanoparticles were controlled by the nature and hydrophobic/hydrophilic balance of the amphiphilic molecules. − We applied the similar strategies by varying the molecular weight of amphiphilic block copolymers consisting of hydrophobic and hydrophilic blocks to control the size and shape of ice crystals because the generation of new interfaces of solid in water is similar in both cases . The block copolymers are in equilibrium as unimers (single chains) and self-assembled micelles in water, can be located at the water/air interface, or ideally adhere to the surface of ice crystals, and thus control the size and shape of the ice crystals depending on the structure and concentration of block polymers (Figure ).…”