Surface modification of the cellulose nanocrystals through vinyl silane grafting.

Incompatibility of nanocellulose with non-polar polymer matrices disrupts the interfacial interaction and results in aggregation and phase separation. In this study a facile and environmentally friendly method was used to partially substitute the surface hydroxyl groups by attaching polysiloxane to impart hydrophobic properties. The silanization reaction proceeded with hydrolysis of triethoxyvinylsilane (TEVS) into reactive silanols followed by condensation to form the branched polymer. These polysiloxane oligomers were chemically grafted to form alkoxy silane bonds on the surface of CNCs. A suitable degree of hydrophilic-hydrophobic balance of the modified CNCs was achieved which improved their dispersion in hydrophobic matrix poly(butylene adipate-co-terephthalate) (PBAT). FTIR, NMR (13C and 29Si) and XPS demonstrated successful surface chemical modification and confirmed extent of silanization as a function of silane concentration. XRD showed successful grafting of the vinyl silane agent and confirmed polymorph structure of the nanocellulose was retained. The results from TEM and AFM demonstrated successful coating of nano whiskers at 5 wt% silane loading. The successful grafting of the silane agent with pendant vinyl groups improved surface hydrophobicity. These results show that this facile method produces adequately surface modified CNC which can be used as filler in hydrophobic matrices of bioplastics.

A review of nanocellulose as a new material towards environmental sustainability.

Synthetic polymers, commonly referred to as plastics, are anthropogenic contaminants that adversely affect the natural ecosystems. The continuous disposal of long lifespan plastics has resulted in the accumulation of plastic waste, leading to significant pollution of both marine and terrestrial habitats. Scientific pursuit to seek environment-friendly materials from renewable resources has focused on cellulose, the primary reinforcement component of the cell wall of plants, as it is the most abundantly available biopolymer on earth. This paper provides an overview on the current state of science on nanocellulose research; highlighting its extraction procedures from lignocellulosic biomass. Literature shows that the process used to obtain nanocellulose from lignocellulosic biomass greatly influences its morphology, properties and surface chemistry. The efficacy of chemical methods that use alkali, acid, bleaching agents, ionic liquids, deep eutectic solvent for pre-treatment of biomass is discussed. There has been a continuous endeavour to optimize the pre-treatment protocol as it is specific to lignocellulosic biomass and also depends on factors such as nature of the biomass, process and environmental parameters and economic viability. Nanofibers are primarily isolated through mechanical fibrillation while nanocrystals are predominantly extracted using acid hydrolysis. A concise overview on the ways to improve the yield of nanocellulose from cellulosic biomass is also presented in this review. This work also reviews the techniques used to modify the surface properties of nanocellulose by functionalizing surface hydroxyl groups to impart desirable hydrophilic-hydrophobic balance. An assessment on the emerging application of nanocellulose with an emphasis on development of nanocomposite materials for designing environmentally sustainable products is incorporated. Finally, the status of the industrial production of nanocellulose presented, which indicates that there is a continuously increased demand for cellulose nanomaterials. The demand for cellulose is expected to increase further due to its increasing and broadening applications.

Approaches for the inhibition and elimination of microbial biofilms using macromolecular agents.

Biofilms are complex three-dimensional structures formed at interfaces by the vast majority of bacteria and fungi. These robust communities have an important detrimental impact on a wide range of industries and other facets of our daily lives, yet their removal is challenging owing to the high tolerance of biofilms towards conventional antimicrobial agents. This key issue has driven an urgent search for new innovative antibiofilm materials. Amongst these emerging approaches are highly promising materials that employ aqueous-soluble macromolecules, including peptides, proteins, synthetic polymers, and nanomaterials thereof, which exhibit a range of functionalities that can inhibit biofilm formation or detach and destroy organisms residing within established biofilms. In this Review, we outline the progress made in inhibiting and removing biofilms using macromolecular approaches, including a spotlight on cutting-edge materials that respond to environmental stimuli for "on-demand" antibiofilm activity, as well as synergistic multi-action antibiofilm materials. We also highlight materials that imitate and harness naturally derived species to achieve new and improved biomimetic and biohybrid antibiofilm materials. Finally, we share some speculative insights into possible future directions for this exciting and highly significant field of research.

Honey-inspired antimicrobial hydrogels resist bacterial colonization through twin synergistic mechanisms.

Inspired by the interesting natural antimicrobial properties of honey, biohybrid composite materials containing a low-fouling polymer hydrogel network and an encapsulated antimicrobial peroxide-producing enzyme have been developed. These synergistically combine both passive and active mechanisms for reducing microbial bacterial colonization. The mechanical properties of these materials were assessed using compressive mechanical analysis, which revealed these hydrogels possessed tunable mechanical properties with Young's moduli ranging from 5 to 500 kPa. The long-term enzymatic activities of these materials were also assessed over a 1-month period using colorimetric assays. Finally, the passive low-fouling properties and active antimicrobial activity against a leading opportunistic pathogen, Staphylococcus epidermidis, were confirmed using bacterial cell counting and bacterial adhesion assays. This study resulted in non-adhesive substrate-permeable antimicrobial materials, which could reduce the viability of planktonic bacteria by greater than 7 logs. It is envisaged these new biohybrid materials will be important for reducing bacterial adherence in a range of industrial applications.

Antimicrobial Honey-Inspired Glucose-Responsive Nanoreactors by Polymerization-Induced Self-Assembly.

The rise of antimicrobial resistance is at the forefront of global healthcare challenges, with antimicrobial infections on track to overtake cancer as a leading cause of death by 2050. The high effectiveness of antimicrobial enzymes used in combination with the protective, inert nature of polymer materials represents a highly novel approach toward tackling microbial infections. Herein, we have developed biohybrid glucose oxidase-loaded semipermeable polymersome nanoreactors, formed using polymerization-induced self-assembly, and demonstrate for the first time their ability to "switch on" their antimicrobial activity in response to glucose, a ubiquitous environmental stimulus. Using colony-counting assays, it was demonstrated that the nanoreactors facilitate up to a seven-log reduction in bacterial growth at high glucose concentrations against a range of Gram-negative and Gram-positive bacterial pathogens, including a methicillin-resistant Staphylococcus aureus clinical isolate. After demonstrating the antimicrobial properties of these materials, their toxicity against human fibroblasts was assessed and the dosage of the nanoreactors further optimized for use as nontoxic agents against Gram-positive bacteria under physiological blood glucose concentrations. It is envisaged that such biohybrid nanomaterials will become an important new class of antimicrobial biomaterials for the treatment of bacterial infections.

An introduction to zwitterionic polymer behavior and applications in solution and at surfaces.

Zwitterionic polymers, including polyampholytes and polybetaines, are polymers with both positive and negative charges incorporated into their structure. They are a unique class of smart materials with great potential in a broad range of applications in nanotechnology, biomaterials science, nanomedicine and healthcare, as additives for bulk construction materials and crude oil, and in water remediation. In this Tutorial Review, we aim to highlight their structural diversity and design criteria, and their preparation using modern techniques. Their behavior, both in solution and at surfaces, will be examined under a range of environmental conditions. Finally, we will exemplify how their unique behaviors give rise to specific properties tailored to a selection of their numerous applications.

Comparing Gene Silencing and Physiochemical Properties in siRNA Bound Cationic Star-Polymer Complexes.

The translation of siRNA into clinical therapies has been significantly delayed by issues surrounding the delivery of naked siRNA to target cells. Here we investigate siRNA delivery by cationic acrylic polymers developed by Reversible Addition-Fragmentation chain Transfer (RAFT) mediated free radical polymerization. We investigated cell uptake and gene silencing of a series of siRNA-star polymer complexes both in the presence and absence of a protein "corona". Using a multidisciplinary approach including quantitative nanoscale mechanical-atomic force microscopy, dynamic light scattering and nanoparticle tracking analysis we have characterized the nanoscale morphology, stiffness, and surface charge of the complexes with and without the protein corona. This is one of the first examples of a comprehensive physiochemical analysis of siRNA-polymer complexes being performed alongside in vitro biological assays, allowing us to describe a set of desirable physical features of cationic polymer complexes that promote gene silencing. Multifaceted studies such as this will improve our understanding of structure-function relationships in nanotherapeutics, facilitating the rational design of polymer-mediated siRNA delivery systems for novel treatment strategies.

Synthesis and evaluation of degradable polyurea block copolymers as siRNA delivery agents.

Chain extension by diisocyanate condensation provides a versatile and convenient means for preparing block copolymers. We have utilized this chemistry to prepare reducible multiblock polycations for siRNA delivery. This approach, an alternative to oxidative coupling, was suitable for preparing multiblock polycations with defined molecular weight and architecture. The polymer, PEG-b-multi-(polyhexylurea-co-oligo-L-lysine)-b-PEG, was capable of electrostatically condensing siRNA to form nano-sized polyplexes across a broad compositional range. We demonstrated that the polyplexes enter the cells via endocytosis and interact with the endosome membrane leading to destabilization and hence endosome escape. Another feature of these polymers is their multiple intra-chain disulfide linkages. This enables weakening of the polyplex via chain scission within the cytosol's reductive environment. In addition to the controlled preparation of the polymer, the polyplexes were capable of delivering siRNA in vitro to silence greater than 50% green fluorescent protein expression with negligible toxicity.

Preparation of hydrogels via ultrasonic polymerization.

Several acrylic hydrogels were prepared via ultrasonic polymerization of water soluble monomers and macromonomers. Ultrasound was used to create initiating radicals in viscous aqueous monomer solutions using the additives glycerol, sorbitol or glucose in an open system at 37 degrees C. The water soluble additives were essential for the hydrogel production, glycerol being the most effective. Hydrogels were prepared from the monomers 2-hydroxyethyl methacrylate, poly(ethylene glycol) dimethacrylate, dextran methacrylate, acrylic acid/ethylene glycol dimethacrylate and acrylamide/bis-acrylamide. For example a 5% w/w solution of dextran methacrylate formed a hydrogel in 6.5min in a 70% w/w solution of glycerol in water at 37 degrees C with 20kHz ultrasound, 56Wcm(-2). The ultrasonic polymerization method described here has a wide range of applications such a biomaterial synthesis where initiators are not desired.