Expansile crosslinked polymersomes for pH sensitive delivery of doxorubicin

Structural Determinants of Stimuli-Responsiveness in Amphiphilic Macromolecular Nano-assemblies

Stimuli-responsive nano-assemblies from amphiphilic macromolecules could undergo controlled structural transformations and generate diverse macroscopic phenomenon under stimuli. Due to the controllable responsiveness, they have been applied for broad material and biomedical applications, such as biologics delivery, sensing, imaging, and catalysis. Understanding the mechanisms of the assembly-disassembly processes and structural determinants behind the responsive properties is fundamentally important for designing the next generation of nano-assemblies with programmable responsiveness. In this review, we focus on structural determinants of assemblies from amphiphilic macromolecules and their macromolecular level alterations under stimuli, such as the disruption of hydrophilic-lipophilic balance (HLB), depolymerization, decrosslinking, and changes of molecular packing in assemblies, which eventually lead to a series of macroscopic phenomenon for practical purposes. Applications of stimuli-responsive nano-assemblies in delivery, sensing and imaging were also summarized based on their structural features. We expect this review could provide readers an overview of the structural considerations in the design and applications of nanoassemblies and incentivize more explorations in stimuli-responsive soft matters.

Polymersome Membrane Engineering with Active Targeting or Controlled Permeability for Responsive Drug Delivery

Polymersomes have been extensively investigated for drug delivery as nanocarriers for two decades due to a series of advantages including high stability under physiological conditions, simultaneous encapsulation of hydrophilic and hydrophobic drugs inside inner cavities and membranes, respectively, and facile adjustment of membrane and surface properties, as well as controlled drug release through incorporation of stimuli-responsive components. Despite these features, polymersome nanocarriers frequently suffer from nontargeting delivery and poor membrane permeability. In recent years, polymersomes have been functionalized for more efficient drug delivery. The surface shells were explored to be modified with diverse active targeting groups to improve disease-targeting delivery. The membrane permeability of the polymersomes was adjusted by incorporation of the stimuli-responsive components for smart controlled transportation of the encapsulated drugs. Therefore, being the polymersome-biointerface, tailorable properties can be introduced by its carefully modulated engineering. This review elaborates on the role of polymersome membranes as a platform to incorporate versatile features. First, we discuss how surface functionalization facilitates the directional journey to the targeting sites toward specific diseases, cells, or intracellular organelles via active targeting. Moreover, recent advances in the past decade related to membrane permeability to control drug release are also summarized. We finally discuss future development to promote polymersomes as in vivo drug delivery nanocarriers.

Protein Vesicles with pH-Responsive Disassembly

Protein biomaterials offer several advantages over those made from other components because their amino acid sequence can be precisely controlled with genetic engineering to produce a diverse set of material building blocks. In this work, three different elastin-like polypeptide (ELP) sequences were designed to synthesize pH-responsive protein vesicles. ELPs undergo a thermally induced hydrophobic transition that enables self-assembly of different kinds of protein biomaterials. The transition can be tuned by the composition of the guest residue, X, within the ELP pentapeptide repeat unit, VPGXG. When the guest residue is substituted with an ionizable amino acid, such as histidine, the ELP undergoes a pH-dependent hydrophobic phase transition. We used pH-responsive ELPs with different levels of histidine substitution, in combination with leucine zippers and globular, functional proteins, to fabricate protein vesicles. We demonstrate pH-dependent self-assembly, diameter, and disassembly of the vesicles using a combination of turbidimetry, dynamic light scattering, microscopy, and small angle X-ray scattering. As the ELP transition is dependent on the sequence, the vesicle properties also depend on the histidine content in the ELP building blocks. These results demonstrate the tunability of protein vesicles endowed with pH responsiveness, which expands their potential in drug-delivery applications.

Artificial Organelles with Orthogonal-Responsive Membranes for Protocell Systems: Probing the Intrinsic and Sequential Docking and Diffusion of Cargo into Two Coexisting Avidin-Polymersomes

The challenge of effective integration and use of artificial organelles with orthogonal-responsive membranes and their communication in eukaryotic protocells is to understand the intrinsic membrane characteristics. Here, a novel photo-crosslinked and pH-responsive polymersome (Psome B) with 2-(N,N'-diisopropylamino)ethyl units in the membrane and its respective Avidin-Psome B hybrids, are reported as good candidates for artificial organelles. Biotinylated (macro)molecules are able to dock and diffuse into Avidin-Psome B to carry out biological activity in a pH- and size-dependent manner. Combined with another polymersome (Psome A) with 2-(N,N'-diethylamino)ethyl units in the membrane, two different pH-responsive polymersomes for mimicking different organelles in one protocell system are reported. The different intrinsic docking and diffusion processes of cargo (macro)molecules through the membranes of coexisting Psome A and B are pH-dependent as confirmed using pH titration-dynamic light scattering (DLS). Psome A and B show separated "open", "closing/opening", and "closed" states at various pH ranges with different membrane permeability. The results pave the way for the construction of multicompartmentalized protocells with controlled communications between different artificial organelles.

pH-responsive polymeric micelles self-assembled from benzoic-imine-containing alkyl-modified PEGylated chitosan for delivery of amphiphilic drugs

In order to efficiently promote loading efficiency and aqueous photostability of indocyanine green (ICG), an amphiphilic tricarbocyanine dye, the polysaccharide-based nanomicelles utilized as a vehicle for ICG were fabricated by self-assembly of the amphiphilic benzoic-imine-containing PEGylated chitosan/4-(dodecyloxy)benzaldehyde (DBA) conjugates in aqueous solution of pH 7.4. The resulting polymeric micelles were characterized to have a hydrophobic hybrid chitosan/DBA core surrounded by hydrophilic PEG shells. Importantly, the encapsulation of ICG into the hybrid chitosan/DBA core of polymeric micelles by the combined hydrophobic and electrostatic interactions not only promoted the ICG loading but also enhanced its aqueous photostability. With the pH of micelle suspension being reduced from 7.4 to 5.0, upon acid-triggered cleavage of benzoic-imine bonds between chitosan and DBA as well as the extending of the protonated chitosan segments from hybrid cores toward aqueous phase, the rather hydrophobic DBA-rich core was formed within micelles, thereby leading to shrinking of the polymeric micelles. The robust ICG-loaded polymeric micelles showed several superior properties including the inhibition of ICG leakage under the mimic physiological and acidic conditions, favorable biocompatibility and photo-activated hyperthermia effect. This work suggests that the pH-responsive ICG-carrying chitosan-based micelles display great potential in cancer theranostic.

The chemistry of cross-linked polymeric vesicles and their functionalization towards biocatalytic nanoreactors

Self-assembly of amphiphilic block copolymers into polymersomes continues to be a hot topic in modern research on biomimetics. Their well-known and valued mechanical strength can be increased even further if they are cross-linked. These additional bonds prevent a collapse or disassembly of the polymersomes and open the way towards smart nanoreactors. A variety of chemistries have been applied to obtain the desired cross-linked polymersomes, and therefore, the chemical approaches performed over time will be highlighted in this mini-review. Due to the large number of studies, a selected set of photo-cross-linked and pH-sensitive polymersomes will be specifically highlighted. This system has proven to be a very potent candidate for the formation of nanoreactors and drug delivery systems, and even for the formation of functional multicompartment cell mimics.

pH-Responsive polymeric nanocarriers for efficient killing of cariogenic bacteria in biofilms

Traditional antibacterial treatments, such as chlorhexidine (CHX), destroy cariogenic biofilms. However, they exert negative effects in clinical applications, for example, teeth staining, taste disturbance and harm to oral tissue after a long-term exposure. Therefore, biocompatible strategies for efficient antibacterial drug delivery are in high demand. In this study, aimed at dental caries therapy enhancement, we designed a pH-responsive nanocarrier system, capable of releasing CHX in an acidic environment within cariogenic biofilms. Cationic poly(ethylene glycol)-block-poly(2-(((2-aminoethyl)carbamoyl)oxy)ethyl methacrylate) (PEG-b-PAECOEMA) was synthesized first. Modification of PAECOEMA by citraconic anhydride (CA) forms negatively charged PEG-b-PAECOEMA/CA, which could assemble into core-shell polyionic complex micelles (PICMs) when mixed with cationic CHX via electrostatic interactions. PICMs are stable in healthy neutral oral microenvironments with CHX encapsulated in the core and PEG shell exposed. Once in acidic milieu within caries-producing biofilms, they rapidly disassemble and release CHX cargo owing to degradation of citraconic amide groups. Molecular structures of the above copolymers were confirmed using 1H NMR and gel permeation chromatography (GPC) analysis. The pH-dependent degradation rates of citraconic amide in PEG-b-PAECOEMA/CA copolymer were measured by fluorescamine method. Atomic force microscopy (AFM) studies confirmed successful assembly of well-defined spherical PICMs in aqueous solution. The disassembly of PICMs in acidic microenvironment was observed using dynamic light scattering (DLS). PICMs showed an obvious pH-dependent drug release profile when the pH changed from 7.4 to 5.5. More importantly, the micellar system could reduce drug toxicity of CHX and exhibited outstanding antibacterial capability in the biofilm of Streptococcus mutans. Micelles constructed from pH-sensitive PEG-b-PAECOEMA/CA are highly promising for dental caries therapy and provide guidelines for drug-delivery system design in other acidic pathologic systems.

Bioinspired Smart Nanosystems in Advanced Therapeutic Applications

BACKGROUND

Nanoparticle technologies used for human administration must be designed to interact with a living host environment. The idea about bioinspired smart drug delivery carriers includes the development of biocompatible nanomaterials which can be further loaded with the drug for specific targeted drug delivery applications.

OBJECTIVE

Biosmart nanosystems are used for several applications in the delivery of drugs and pharmaceuticals for their therapeutic applications like biological markers, diagnostic purposes such as imaging applications and also for gene therapy. Thus, the bioinspired nanocarriers are capable of carrying biologically active molecules to the target sites. This bioinspired nanosystem constitutes of lipids, polymers and biomaterials which utilizes various responsive sensors for targeted drug delivery systems. However, external conditions such as heat, light, magnetic or electric field and ultrasounds, along with temperature, altered pH and ionic strength can affect the bioinspired smart nanosystem for drug delivery.

CONCLUSION

The present review focuses on challenges for the development of bioinspired smart nanocarriers for the management of various disorders.

Rapid conjugation of nanoparticles, proteins and siRNAs to microbubbles by strain-promoted click chemistry for ultrasound imaging and drug delivery

A new strategy using catalyst-free strain-promoted alkyne-azide cycloaddition (SPAAC) "click" chemistry for the ligation of anti-cancer drug-loaded nanoparticles, functionalized proteins, and siRNA conjugated micelles to microbubbles (MB) was established. The results showed fast ligation within 5 min without sacrificing microbubble size and density. The ultrasound test showed good imaging abilities of the microbubbles after functionalization. This microbubble-therapeutic SPAAC "click" conjugation developed in the current study involves no toxic catalyst or initiator, has ultra-fast reaction speed, and is versatile for the ligation of various anti-cancer or therapeutic agents to microbubbles. These advantages render the SPAAC click strategy promising for broad applications in ultrasound-guided imaging and therapeutic delivery.

Red blood cell-derived nanovesicles for safe and efficient macrophage-targeted drug delivery in vivo

RBC-derived nanovesicles are effective hydrophilic drug carriers and can effectively deliver drugs into macrophages both in vitro and in vivo.

Engineering Polymersomes for Diagnostics and Therapy

Engineered polymer vesicles, termed as polymersomes, confer a flexibility to control their structure, properties, and functionality. Self-assembly of amphiphilic copolymers leads to vesicles consisting of a hydrophobic bilayer membrane and hydrophilic core, each of which is loaded with a wide array of small and large molecules of interests. As such, polymersomes are increasingly being studied as carriers of imaging probes and therapeutic drugs. Effective delivery of polymersomes necessitates careful design of polymersomes. Therefore, this review article discusses the design strategies of polymersomes developed for enhanced transport and efficacy of imaging probes and therapeutic drugs. In particular, the article focuses on overviewing technologies to regulate the size, structure, shape, surface activity, and stimuli- responsiveness of polymersomes and discussing the extent to which these properties and structure of polymersomes influence the efficacy of cargo molecules. Taken together with future considerations, this article will serve to improve the controllability of polymersome functions and accelerate the use of polymersomes in biomedical applications.

Selective cancer treatment via photodynamic sensitization of hypoxia-responsive drug delivery

The precise and selective delivery of chemodrugs into tumors represents a critical requirement for anti-cancer therapy. Intelligent delivery systems that are responsive to a single internal or external stimulus often lack sufficient cancer selectivity, which compromises the drug efficacy and induces undesired side effects. To overcome this dilemma, we herein report a cancer-targeting vehicle which allows highly cancer-selective drug release in response to cascaded external (light) and internal (hypoxia) dual triggers. In particular, doxorubicin (DOX)-loaded, hypoxia-dissociable nanoparticles (NPs) were prepared from self-assembled polyethylenimine-nitroimidazole (PEI-NI) micelles that were further co-assembled with hyaluronic acid-Ce6 (HC). Upon accumulation in tumor cells, tumor site-specific light irradiation (660 nm, 10 mW cm^-2) generated high levels of reactive oxygen species (ROS) and greatly enhanced the hypoxic levels to induce NP dissociation and accordingly DOX release. A synergistic anti-cancer efficacy between DOX-mediated chemotherapy and Ce6-mediated photodynamic therapy (PDT) was thus achieved, resulting in reduced side effects to normal tissues/cells. This study therefore provides an effective method to control the cancer-specific drug delivery by responding to cascaded multiple triggers, and it renders promising applications for the programmed combination of chemotherapy and PDT toward cancer treatment.

Hollow polymer nanocapsules: synthesis, properties, and applications

Hollow polymer nanocapsules (HPNs) have gained tremendous interest in recent years due to their numerous desirable properties compared to their solid counterparts.

Dynamic Docking and Undocking Processes Addressing Selectively the Outside and Inside of Polymersomes

Increasing complexity and diversity of polymersomes and their compartments is a key issue for mimicking cellular functions and protocells. Thus, new challenges arise in terms of achieving tunable membrane permeability and combining it with control over the membrane diffusion process, and thus enabling a localized and dynamic control of functionality and docking possibilities within or on the surface of polymeric compartments. This study reports the concept of polymersomes with pH-tunable membrane permeability for controlling sequential docking and undocking processes of small molecules and nanometer-sized protein mimics selectively on the inside and outside of the polymersome membrane as a further step toward the design of intelligent multifunctional compartments for use in synthetic biology and as protocells. Host-guest interactions between adamantane and β-cyclodextrin as well as noncovalent interactions between poly(ethylene glycol) tails and β-cyclodextrin are used to achieve selective and dynamic functionalization of the inner and outer spheres of the polymersome membrane.

Polyphenolic Polymersomes of Temperature-Sensitive Poly(N-vinylcaprolactam)-block-Poly(N-vinylpyrrolidone) for Anticancer Therapy

We report a versatile synthesis for polyphenolic polymersomes of controlled submicron (<500 nm) size for intracellular delivery of high and low molecular weight compounds. The nanoparticles are synthesized by stabilizing the vesicular morphology of thermally responsive poly(N-vinylcaprolactam)_n-b-poly(N-vinylpyrrolidone)_m (PVCL_n-PVPON_m) diblock copolymers with tannic acid (TA), a hydrolyzable polyphenol, via hydrogen bonding at a temperature above the copolymer's lower critical solution temperature (LCST). The PVCL₁₇₉-PVPON_m diblock copolymers are produced by controlled reversible addition-fragmentation chain transfer (RAFT) polymerization of PVPON using PVCL as a macro-chain transfer agent. The size of the TA-locked (PVCL₁₇₉-PVPON_m) polymersomes at room temperature and upon temperature variations are controlled by the PVPON chain length and TA:PVPON molar unit ratio. The particle diameter decreases from 1000 to 950, 770, and 250 nm with increasing PVPON chain length (m = 107, 166, 205, 234), and it further decreases to 710, 460, 290, and 190 nm, respectively, upon hydrogen bonding with TA at 50 °C. Lowering the solution temperature to 25 °C results in a slight size increase for vesicles with longer PVPON. We also show that TA-locked polymersomes can encapsulate and store the anticancer drug doxorubicin (DOX) and higher molecular weight fluorescein isothiocyanate (FITC)-dextran in a physiologically relevant pH and temperature range. Encapsulated DOX is released in the nuclei of human alveolar adenocarcinoma tumor cells after 6 h incubation via biodegradation of the TA shell with the cytotoxicity of DOX-loaded polymersomes being concentration-dependent. Our approach offers biocompatible and intracellular degradable nanovesicles of controllable size for delivery of a variety of encapsulated materials. Considering the particle monodispersity, high loading capacity, and a facile two-step aqueous assembly based on the reversible temperature-responsiveness of PVCL, these polymeric vesicles have significant potential as novel drug nanocarriers and provide a new perspective for fundamental studies on thermo-triggered polymer assemblies in solutions.

Lymph cancer chemotherapy: delivery of doxorubicin-gemcitabine prodrug and vincristine by nanostructured lipid carriers

PURPOSE

Radiation and chemotherapy are the most common course of treatment for B-cell lymphoma. Doxorubicin (DOX), gemcitabine (GEM), and vincristine (VCR) are the commonly used antilymphoma chemotherapeutic drugs. The aim of this study is to construct a novel drug delivery system for the combination delivery of the three drugs on lymphoma.

MATERIALS AND METHODS

DOX-GEM prodrug was synthesized. Novel nanostructured lipid carriers (NLCs) containing DOX-GEM prodrug and VCR were prepared and used to treat B-cell lymphoma through in vivo treatment to a lymph cancer animal model. The systemic toxicity of the nanomedicine was also evaluated during the treatment.

RESULTS

DOX-GEM prodrug and VCR-loaded NLCs (DOX-GEM VCR NLCs) exhibited the highest antitumor effect in B-cell lymphoma cells and lymphoma animal xenografts when compared with the single drug-loaded NLCs and the drug solutions.

CONCLUSION

It could be concluded that the highest antitumor effect can be achieved by the system due to the stable drug-loading capacity, attractive anticancer therapeutic effects, and reduced toxicities in human Burkitt's lymphoma cell line and mice-bearing cancer model. The resulting DOX-GEM VCR NLCs could be an efficient antilymph cancer agent and could be developed further for the treatment of other tumors.

Fine-tuning the pH response of polymersomes for mimicking and controlling the cell membrane functionality

To expand the biomedical applications of pH responsive polymersomes a concept is presented for precisely adjusting the pH triggered transition of the membrane permeability.

Covalent crosslinking of graphene oxide and carbon nanotube into hydrogels enhances nerve cell responses

Healing of nerve injuries is a critical medical issue. Biodegradable polymeric conduits are a promising therapeutic solution to provide guidance for axon growth in a given space, thus helping nerve heal. Extensive studies in the past decade reported that conductive materials could effectively increase neurite and axon extension in vitro and nerve regeneration in vivo. In this study, graphene oxide and carbon nanotubes were covalently functionalized with double bonds to obtain crosslinkable graphene oxide acrylate (GOa) sheets and carbon nanotube poly(ethylene glycol) acrylate (CNTpega). An electrically conductive reduced GOa-CNTpega-oligo(polyethylene glycol fumarate) (OPF) hydrogel (rGOa-CNTpega-OPF) was successfully fabricated by chemically crosslinking GOa sheets and CNTpega with OPF chains followed by in situ chemical reduction in l-ascorbic acid solution. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) imaging showed homogenous distribution of GOa/CNTpega carbon content in the rGOa-CNTpega-OPF composite hydrogel, resulting in a significant increase of electrical conductivity compared with neutral OPF without carbon content. Cell studies showed excellent biocompatibility and distinguished PC12 cell proliferation and spreading on the rGOa-CNTpega-OPF composite hydrogel. Fluorescent microscopy imaging demonstrated robustly stimulated neurite development in these cells on a conductive rGOa-CNTpega-OPF composite hydrogel compared with that on neutral OPF hydrogels. These results illustrated a promising potential for the rGOa-CNTpega-OPF composite hydrogel to serve as conduits for neural tissue engineering.