Zwitterionic polymers in drug delivery: A review

Developments of novel drug delivery vehicles are sought-after to augment the therapeutic effectiveness of standard drugs. An urgency to design novel drug delivery vehicles that are sustainable, biocompatible, have minimized cytotoxicity, no immunogenicity, high stability, long circulation time, and are capable of averting recognition by the immune system is perceived. In this pursuit for an ideal candidate for drug delivery vehicles, zwitterionic materials have come up as fulfilling almost all these expectations. This comprehensive review is presenting the progress made by zwitterionic polymeric architectures as prospective sustainable drug delivery vehicles. Zwitterionic polymers with varied architecture such as appending protein conjugates, nanoparticles, surface coatings, liposomes, hydrogels, etc, used to fabricate drug delivery vehicles are reviewed here. A brief introduction of zwitterionic polymers and their application as reliable drug delivery vehicles, such as zwitterionic polymer-protein conjugates, zwitterionic polymer-based drug nanocarriers, and stimulus-responsive zwitterionic polymers are discussed in this discourse. The prospects shown by zwitterionic architecture suggest the tremendous potential for them in this domain. This critical review will encourage the researchers working in this area and boost the development and commercialization of such devices to benefit the healthcare fraternity.

Polybetaines in Biomedical Applications

Polybetaines, that have moieties bearing both cationic (quaternary ammonium group) and anionic groups (carboxylate, sulfonate, phosphate/phosphinate/phosphonate groups) situated in the same structural unit represent an important class of smart polymers with unique and specific properties, belonging to the family of zwitterionic materials. According to the anionic groups, polybetaines can be divided into three major classes: poly(carboxybetaines), poly(sulfobetaines) and poly(phosphobetaines). The structural diversity of polybetaines and their special properties such as, antifouling, antimicrobial, strong hydration properties and good biocompatibility lead to their use in nanotechnology, biological and medical fields, water remediation, hydrometallurgy and the oil industry. In this review we aimed to highlight the recent developments achieved in the field of biomedical applications of polybetaines such as: antifouling, antimicrobial and implant coatings, wound healing and drug delivery systems.

Kill-Resist-Renew Trinity: Hyperbranched Polymer with Self-Regenerating Attack and Defense for Antifouling Coatings

Traditional antifouling coatings are generally based on a single antifouling mechanism, which can hardly meet the needs of different occasions. Here, a single "kill-resist-renew trinity" polymeric coating integrating fouling killing, resistance, and releasing functions is reported. To achieve the design, a novel monomer-tertiary carboxybetaine ester acrylate with the antifouling group N-(2,4,6-trichlorophenyl)maleimide (TCB-TCPM) is synthesized and copolymerized with methacrylic anhydride via reversible addition-fragmentation chain transfer polymerization yielding a degradable hyperbranched polymer. Such a polymer at the surface/seawater is able to hydrolyze and degrade to short segments forming a dynamic surface (releasing). The hydrolysis of TCB-TCPM generates the antifouling groups TCPM (killing) and zwitterionic groups (resistance). Such a polymeric coating exhibits a controllable degradation rate, which increases with the degrees of branching. The antibacterial assay demonstrates that the antifouling ability arise from the synergistic effect of "attacking" and "defending". This study provides a new strategy to solve the challenging problem of marine biofouling.

Two-Photon-Induced Charge-Variable Conjugated Polyelectrolyte Brushes for Effective Gene Silencing

Cationic conjugated polyelectrolytes can absorb negatively charged small interfering RNA (siRNA) and also visualize the cellular internalization of siRNA, which thus have been extensively explored as siRNA carriers. However, their low charge density cannot afford a high carrying capability, severely impeding gene transfection efficiency. Moreover, the intracellular controlled release of siRNA is another factor that limits the widespread use of siRNA therapeutics. Herein, we present a novel two-photon-induced charge-variable conjugated polyelectrolyte brush as an efficient siRNA carrier. This cationic conjugated polyelectrolyte brush (PPENBr-ONB) with densely cationic charges produces remarkable carrying capability with siRNA. In addition, PPENBr-ONB with large two-photon absorption (TPA) cross-section represents effective fluorescence resonance energy transfer (FRET) to photoresponsive side chain with 720 nm illumination for two-photon-induced photolysis. Hence, the charge transformation of the photoresponsive side chain from cations to zwitterions would remarkably elevate siRNA release. The obtained PPENBr-ONB shows considerable fluorescence quantum yields (0.16) in aqueous solution, sufficient to serve as a reporter for cellular imaging. Agarose gel electrophoresis experiments indicate that PPENBr-ONB exhibit excellent siRNA-loading capacity (1 mol PPENBr-ONB to more than 20 mol siRNA). Furthermore, PPENBr-ONB with large TPA cross-section (1.47 × 10⁵ GM) exhibits promoted siRNA release (78%) under 720 nm illumination. In vitro experiment shows that PPENBr-ONB/siRNA complex could efficaciously knock out of targeted Plk1 mRNA to 24.7% under 720 nm illumination for 1 h. This two-photon excitation siRNA carrier offers an efficacious strategy for the exploitation of photo controlled gene delivery system.

Responsive and Synergistic Antibacterial Coatings: Fighting against Bacteria in a Smart and Effective Way

Antibacterial coatings that eliminate initial bacterial attachment and prevent subsequent biofilm formation are essential in a number of applications, especially implanted medical devices. Although various approaches, including bacteria-repelling and bacteria-killing mechanisms, have been developed, none of them have been entirely successful due to their inherent drawbacks. In recent years, antibacterial coatings that are responsive to the bacterial microenvironment, that possess two or more killing mechanisms, or that have triggered-cleaning capability have emerged as promising solutions for bacterial infection and contamination problems. This review focuses on recent progress on three types of such responsive and synergistic antibacterial coatings, including i) self-defensive antibacterial coatings, which can "turn on" biocidal activity in response to a bacteria-containing microenvironment; ii) synergistic antibacterial coatings, which possess two or more killing mechanisms that interact synergistically to reinforce each other; and iii) smart "kill-and-release" antibacterial coatings, which can switch functionality between bacteria killing and bacteria releasing under a proper stimulus. The design principles and potential applications of these coatings are discussed and a brief perspective on remaining challenges and future research directions is presented.

Smart Antibacterial Surfaces with Switchable Bacteria-Killing and Bacteria-Releasing Capabilities

The attachment and subsequent colonization of bacteria on the surfaces of synthetic materials and devices lead to serious problems in both human healthcare and industrial applications. Therefore, antibacterial surfaces that can prevent bacterial attachment and biofilm formation have been a long-standing focus of considerable interest and research efforts. Recently, a promising "kill-release" strategy has been proposed and applied to construct so-called smart antibacterial surfaces, which can kill bacteria attached to their surface and then undergo on-demand release of the dead bacteria and other debris to reveal a clean surface under an appropriate stimulus, thereby maintaining effective long-term antibacterial activity. This Review focuses on the recent progress (particularly over the past 5 years) on such smart antibacterial surfaces. According to the different design strategies, these surfaces can be divided into three categories: (i) "K + R"-type surfaces, which have both a killing unit and a releasing unit; (ii) "K → R"-type surfaces, which have a surface-immobilized killing unit that can be switched to perform a releasing function; and (iii) "K + (R)"-type surfaces, which have only a killing unit but can release dead bacteria upon the addition of a release solution. In the end, a brief perspective on future research directions and the major challenges in this promising field is also presented.

Field responsive materials: photo-, electro-, magnetic- and ultrasound-sensitive polymers

Recent advances in field-responsive polymers, which have emerged as highly promising materials for numerous applications, are highlighted.

Co-deposition towards mussel-inspired antifouling and antibacterial membranes by using zwitterionic polymers and silver nanoparticles

Bacterial attachment and the subsequent colonization on the surfaces of bio-materials usually result in biofilm formation, and thus lead to implant failure, inflammation and so on.

O-Nitrobenzyl-alt-(phenylethynyl)benzene copolymer-based nanoaggregates with highly efficient two-photon-triggered degradable properties via a FRET process

This paper reports on O-nitrobenzyl-alt-(phenylethynyl)benzene copolymer-based nanoaggregates which could be efficiently degraded under two-photon excitation.

Engineered non-toxic cationic nanocarriers with photo-triggered slow-release properties

A simple and versatile strategy using cationic amphiphilic diblock copolymers synthesized by a combination of ATRP and post-polymerization quaternization to prepare photo-responsive nanocarriers showing slow-release properties and low cytotoxicity was reported.

Light-Responsive Polyion Complex Micelles with Switchable Surface Charge for Efficient Protein Delivery

In this letter, light-responsive protein-encapsulated polyion complex (PIC) micelles were prepared by self-assembly of cationic block copolymer poly(N,N-dimethyl-N-(2-(methacryloyloxy)ethyl)-N-((2-nitrobenzyl)oxy)-2-oxoethanaminium bromide)-block-poly(carboxybetaine methacrylate) (PDMNBMA-b-PCBMA) and negatively charged bovine serum albumin (BSA). The PIC micelles were well characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). From the zeta potential measurement, the increase of the zeta potential of PIC micelles from ∼10 to ∼20 mV was observed when the solution pH decreased from 7.4 to 6.5, which could enhance the intracellular protein delivery efficiency. Moreover, the positively charged PDMNBMA blocks can be transformed to zwitterionic carboxybetaine units under UV irradiation, which could result in the disassembly of the PIC micelles. The release of BSA can therefore be drastically accelerated in the presence of UV irradiation. Meanwhile, the circular dichroism (CD) spectroscopy confirmed that the secondary structure of BSA was unaffected during the UV irradiation process.

A photo-degradable gene delivery system for enhanced nuclear gene transcription

There currently exists a significant gap in our understanding of how the detailed chemical characteristics of polycation gene carriers influence their delivery performances in overcoming an important cellular-level transport barrier, i.e., intranuclear gene transcription. In this study, a UV-degradable gene carrier material (ENE4-1) was synthesized by crosslinking low molecular weight branched polyethylenimine (bPEI-2k) molecules using UV-cleavable o-nitrobenzyl urethane (NBU) as the linker molecule. NBU degrades upon exposure to mild UV irradiation. Therefore, this UV-degradable carrier allows us to control the chemical characteristics of the polymer/DNA complex (polyplex) particles at desired locations within the intracellular environment. By using this photolytic DNA carrier, we found that the exact timing of the UV degradation significantly influences the gene transfection efficiencies of ENE4-1/DNA(pGL2) polyplexes in HeLa cells. Interestingly, even if the polyplexes were UV-degraded at different intracellular locations/times, their nuclear entry efficiency was not influenced by the location/timing of UV degradation. The UV treatment did not influence the size or binding strength of the polyplexes. However, we confirmed that the degradation of the carrier molecules impacts the chemical characteristics of the polyplexes (it produces carbamic acid and nitrosobenzyl aldehyde groups on ENE4-1). We believe that these anionic acid groups enhance the interaction of the polyplexes with nuclear transcription proteins and thus the final gene expression levels; this effect was found to occur, even though UV irradiation itself has a general effect of reducing transfection efficiencies. Excess (uncomplexed) ENE4-1 polymers appear to not play any role in the UV-enhanced gene transcription phenomenon.