Thermoinduced Crystallization-Driven Self-Assembly of Bioinspired Block Copolymers in Aqueous Solution

Combining Crystallization-Driven Self-Assembly with Reverse Sequence Polymerization-Induced Self-Assembly Enables the Efficient Synthesis of Hydrolytically Degradable Anisotropic Block Copolymer Nano-objects Directly in Concentrated Aqueous Media

Herein we combine the well-known processing advantages conferred by polymerization-induced self-assembly (PISA) with crystallization-driven self-assembly (CDSA) to achieve the efficient synthesis of hydrolytically degradable, highly anisotropic block copolymer nano-objects directly in aqueous solution at 30% w/w solids. This new strategy involves a so-called reverse sequence PISA protocol that employs poly(l-lactide) (PLLA) as the crystallizable core-forming block and poly(N,N'-dimethylacrylamide) (PDMAC) as the water-soluble non-ionic coronal block. Such syntheses result in PDMAC-rich anisotropic nanoparticles. Depending on the target diblock copolymer composition, either rod-like nanoparticles or diamond-like platelets can be obtained. Furthermore, N-Acryloylmorpholine is briefly evaluated as an alternative hydrophilic vinyl monomer to DMAC. Given that the PLLA block can undergo either hydrolytic or enzymatic degradation, such nanoparticles are expected to offer potential applications in various fields, including next-generation sustainable Pickering emulsifiers.

Antimicrobial Nanostructured Assemblies with Extremely Low Toxicity and Potent Activity to Eradicate Staphylococcus Aureus Biofilms

Self-assembled cationic polymeric nanostructures have been receiving increasing attention for efficient antibacterial agents. In this work, a new type of antibacterial agents is developed by preparing pH-dependent nanostructured assemblies from cationic copolypeptoid poly(N-allylglycine)-b-poly(N-octylglycine) (PNAG-b-PNOG) modified with cysteamine hydrochloride ((PNAG-g-NH₂ )-b-PNOG) driven by crystallization and hydrophobicity of the PNOG blocks. Due to the presence of confined domains arising from crystalline PNOG, persistent spheres and fiber-like assemblies are obtained from the same polymer upon a heating-cooling cycle. This allows for direct comparison of antimicrobial efficiency of nanostructured assemblies with various morphologies that are otherwise similar. Both nanostructured assemblies exhibit extremely low toxicity to human red blood cells, irrespective of the presence of the hydrophobic block. Enhanced antimicrobial performance of the fiber-like micelles compared to the spheres, which result in high selectivity of the fibers, is shown. Notably, the fiber-like micelles show great efficacy in inhibition of the Staphylococcus aureus (S. aureus) biofilm formations and eradication of the mature biofilms, superior to vancomycin. The micelles also show potent in vivo antimicrobial efficacy in a S. aureus infection mouse skin model. With a systematic study, it is demonstrated that both micelles kill the bacteria through a membrane disruption mechanism. These results imply great potential of polypeptoid assemblies as promising excellent candidates for antibacterial treatment and open up new possibilities for the preparation of a new generation of nanostructured antimicrobials.

Hierarchical Approach for Controlled Assembly of Branched Nanostructures from One Polymer Compound by Engineering Crystalline Domains

The interplay of crystalline packing, which governs atomic length-scale order, and hierarchical assembly, which governs longer length scales, is essential to fabricate complex superstructures from polymers for many applications. Here, we demonstrate that a diblock copolymer containing an N-octylglycine peptoid block, which has a propensity to crystallize, can form distinct hierarchical superstructures including a star-like morphology, a superbrush, or a nanosheet by tuning the balance between surface energy arising from the solubility of the copolymers and crystallization energy of the solvophobic polypeptoid blocks. We show that partially ordered micellar aggregates (clusters) are key intermediates that form early in the assembly process and template the formation of superstructures via the oriented fusion of individual micelles as the growth materials. Notably, the fiber-like branch of the superstructures is driven by crystallization and exhibits growth in a living linear manner. The superstructures can be internalized by mammalian cells and hold promise for biomedical applications.

(Bio)degradable and Biocompatible Nano-Objects from Polymerization-Induced and Crystallization-Driven Self-Assembly

Polymerization-induced self-assembly (PISA) and crystallization-driven self-assembly (CDSA) techniques have emerged as powerful approaches to produce a broad range of advanced synthetic nano-objects with high potential in biomedical applications. PISA produces nano-objects of different morphologies (e.g., spheres, vesicles and worms), with high solids content (∼10-50 wt %) and without additional surfactant. CDSA can finely control the self-assembly of block copolymers and readily forms nonspherical crystalline nano-objects and more complex, hierarchical assemblies, with spatial and dimensional control over particle length or surface area, which is typically difficult to achieve by PISA. Considering the importance of these two assembly techniques in the current scientific landscape of block copolymer self-assembly and the craze for their use in the biomedical field, this review will focus on the advances in PISA and CDSA to produce nano-objects suitable for biomedical applications in terms of (bio)degradability and biocompatibility. This review will therefore discuss these two aspects in order to guide the future design of block copolymer nanoparticles for future translation toward clinical applications.

Self-Assembly of Copolymers Containing Crystallizable Blocks: Strategies and Applications

The self-assembly of copolymers containing crystallizable block in solution has received increasing attentions in the past few years. Various strategies including crystallization-driven self-assembly (CDSA) and polymerization-induced CDSA (PI-CDSA) have been widely developed. Abundant self-assembly morphologies were captured and advanced applications have been attempted. In this review, the synthetic strategies including the mechanisms and characteristics are highlighted, the survey on the advanced applications of crystalline nano-assemblies are collected. This review is hoped to depict a comprehensive outline for self-assembly of copolymers containing crystallizable block in recent years and to prompt the development of the self-assembly technology in interdisciplinary field. This article is protected by copyright. All rights reserved.

Solution Self-Assembly of Coil-Crystalline Diblock Copolypeptoids Bearing Alkyl Side Chains

Polypeptoids, a class of synthetic peptidomimetic polymers, have attracted increasing attention due to their potential for biotechnological applications, such as drug/gene delivery, sensing and molecular recognition. Recent investigations on the solution self-assembly of amphiphilic block copolypeptoids highlighted their capability to form a variety of nanostructures with tailorable morphologies and functionalities. Here, we review our recent findings on the solutions self-assembly of coil-crystalline diblock copolypeptoids bearing alkyl side chains. We highlight the solution self-assembly pathways of these polypeptoid block copolymers and show how molecular packing and crystallization of these building blocks affect the self-assembly behavior, resulting in one-dimensional (1D), two-dimensional (2D) and multidimensional hierarchical polymeric nanostructures in solution.

Emerging applications for living crystallization-driven self-assembly

The use of crystallization as a tool to control the self-assembly of polymeric and molecular amphiphiles in solution is attracting growing attention for the creation of non-spherical nanoparticles and more complex, hierarchical assemblies. In particular, the seeded growth method termed living crystallization-driven self-assembly (CDSA) has been established as an ambient temperature and potentially scalable platform for the preparation of low dispersity samples of core-shell fiber-like or platelet micellar nanoparticles. Significantly, this method permits predictable control of size, and access to branched and segmented structures where functionality is spatially-defined. Living CDSA operates under kinetic control and shows many analogies with living chain-growth polymerizations of molecular organic monomers that afford well-defined covalent polymers of controlled length except that it covers a much longer length scale (ca. 20 nm to 10 μm). The method has been applied to a rapidly expanding range of crystallizable polymeric amphiphiles, which includes block copolymers and charge-capped homopolymers, to form assemblies with crystalline cores and solvated coronas. Living CDSA seeded growth methods have also been transposed to a wide variety of π-stacking and hydrogen-bonding molecular species that form supramolecular polymers in processes termed "living supramolecular polymerizations". In this article we outline the main features of the living CDSA method and then survey the promising emerging applications for the resulting nanoparticles in fields such as nanomedicine, colloid stabilization, catalysis, optoelectronics, information storage, and surface functionalization.

Dimension control on self-assembly of a crystalline core-forming polypeptoid block copolymer: 1D nanofibers versus 2D nanosheets

The balance between the crystallization and solubility of the block copolymer dominates the nanostructures.

Thermoresponsive Polypeptoids

Stimuli-responsive polymers have been widely studied in many applications such as biomedicine, nanotechnology, and catalysis. Temperature is one of the most commonly used external triggers, which can be highly controlled with excellent reversibility. Thermoresponsive polymers exhibiting a reversible phase transition in a controlled manner to temperature are a promising class of smart polymers that have been widely studied. The phase transition behavior can be tuned by polymer architectures, chain-end, and various functional groups. Particularly, thermoresponsive polypeptoid is a type of promising material that has drawn growing interest because of its excellent biocompatibility, biodegradability, and bioactivity. This paper summarizes the recent advances of thermoresponsive polypeptoids, including the synthetic methods and functional groups as well as their applications.