Amphiphilic Polyphosphazene for Fluorocarbon Emulsion Stabilization

High internal phase emulsions (HIPEs) have been of great interest for fabricating fluorinated porous polymers having controlled pore structures and excellent physicochemical properties. However, it remains a challenge to prepare stable fluorocarbon HIPEs, due to the lack of suitable surfactants. By randomly grating hydrophilic and fluorophilic side chains to polyphosphazene (PPZ), a comb-like amphiphilic PPZ surfactant with biodegradability is designed and synthesized for stabilizing water/fluorocarbon oil-based emulsions. The hydrophilic-lipophilic balance of PPZs can be controlled by tuning the grating ratio of the two side chains, leading to the preparation of stable water-in-oil HIPEs and oil-in-water emulsions, and the production of fluorinated porous polymers and particles by polymerizing the oil phase. These fluorinated porous polymers show excellent thermal stability and, due to the hydrophobicity and porous structure, applications in the field of oil/water separation can be achieved.

Conformal Conversion of Polyphosphazene@Sb2MoO6 Nanowires to N/S-Doped/Carbon-Coated SbPO4/MoOx for High-performance Lithium Storage

Alloy-type antimony (Sb) and conversion-type molybdenum (Mo) anodes have attracted extensive attention in the application of lithium-ion batteries (LIBs) owing to their high theoretical capacity. In this study, Sb2MoO6 nanowires are prepared via a hydrothermal method and assessed their thermal behavior upon heat treatment, observing an intriguing transformation from nanowire to Sb2O3/MoOx nanosheets. To enhance structure stability, the Sb2MoO6 nanowires are successfully coated with a polyphosphazene layer (referred to as PZS@Sb2MoO6), which not only preserved the nanowires form but also yielded N/S co-doped carbon-coated SbPO4/MoOx (NS-C@SbPO4/MoOx) nanowires following annealing in an inert environment. This composite benefits from the stable PO4 3- anion that serve as a buffer against volume expansion and form a Li3PO4 matrix during cycling, both of which substantially bolster ion transport and cycle endurance. Doping with heteroatoms introduces numerous oxygen vacancies, augmenting the number of electrochemically active sites, and carbon integration considerably enhances the electronic conductivity of the electrode and alleviates the volume-change-induced electrode pulverization. Employed as anode materials in LIBs, the NS-C@SbPO4/MoOx electrode exhibits remarkable cycling performance (449.8 mA h g-1 at 1000 mA g-1 over 700 cycles) along with superior rate capability (394.2 mA h g-1 at 2000 mA g-1).

A Biodegradable "One-For-All" Nanoparticle for Multimodality Imaging and Enhanced Photothermal Treatment of Breast Cancer

Silver sulfide nanoparticles (Ag2S-NP) hold promise for various optical-based biomedical applications, such as near-infrared fluorescence (NIRF) imaging, photoacoustics (PA), and photothermal therapy (PTT). However, their NIR absorbance is relatively low, and previous formulations are synthesized using toxic precursors under harsh conditions and are not effectively cleared due to their large size. Herein, sub-5 nm Ag2S-NP are synthesized and encapsulated in biodegradable, polymeric nanoparticles (AgPCPP). All syntheses are conducted using biocompatible, aqueous reagents under ambient conditions. The encapsulation of Ag2S-NP in polymeric nanospheres greatly increases their NIR absorbance, resulting in enhanced optical imaging and PTT effects. AgPCPP nanoparticles exhibit potent contrast properties suitable for PA and NIRF imaging, as well as for computed tomography (CT). Furthermore, AgPCPP nanoparticles readily improve the conspicuity of breast tumors in vivo. Under NIR laser irradiation, AgPCPP nanoparticles significantly reduce breast tumor growth, leading to prolonged survival compared to free Ag2S-NP. Over time, AgPCPP retention in tissues gradually decreases, without any signs of acute toxicity, providing strong evidence of their safety and biodegradability. Therefore, AgPCPP may serve as a "one-for-all" theranostic agent that degrades into small components for excretion after fulfilling diagnostic and therapeutic tasks, offering good prospects for clinical translation.

In Situ Growth Strategy to Construct "Four-In-One" Separators with Functionalized Polyphosphazene Coatings for Safe and Stable Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) are facing many challenges, such as the inadequate conductivity of sulfur, the shuttle effect caused by lithium polysulfide (LiPSs), lithium dendrites, and the flammability, which have hindered their commercial applications. Herein, a "four-in-one" functionalized coating is fabricated on the surface of polypropylene (PP) separator by using a novel flame-retardant namely InC-HCTB to meet these challenges. InC-HCTB is obtained by cultivating polyphosphazene on the surface of carbon nanotubes with an in situ growth strategy. First, this unique architecture fosters an enhanced conductive network, bolstering the bidirectional enhancement of both ionic and electronic conductivities. Furthermore, InC-HCTB effectively inhibits the shuttle effect of LiPSs. LSBs exhibit a remarkable capacity of 1170.7 mA h g-1 at 0.2 C, and the capacity degradation is a mere 0.0436% over 800 cycles at 1 C. Third, InC-HCTB coating serves as an ion migration network, hindering the growth of lithium dendrites. More importantly, InC-HCTB exhibits notable flame retardancy. The radical trapping action in the gas phase and the protective effect of the shielded char layer in the condensed phase are simulated and verified. This facile in situ growth strategy constructs a "four-in-one" functional separator coating, rendering InC-HCTB a promising additive for the large-scale production of safe and stable LSBs.

Superfluorinated, Highly Water-Soluble Polyphosphazenes as Potential 19F Magnetic Resonance Imaging (MRI) Contrast Agents

"Hot spot" 19F magnetic resonance imaging (MRI) has garnered significant attention recently for its ability to image various disease markers quantitatively. Unlike conventional gadolinium-based MRI contrast agents, which rely on proton signal modulation, 19F-MRI's direct detection has a unique advantage in vivo, as the human body exhibits a negligible background 19F-signal. However, existing perfluorocarbon (PFC) or PFC-based contrast materials suffer from several limitations, including low longitudinal relaxation rates and relatively low imaging efficiency. Hence, we designed a macromolecular contrast agent featuring a high number of magnetically equivalent 19F-nuclei in a single macromolecule, adequate fluorine nucleus mobility, and excellent water solubility. This design utilizes superfluorinated polyphosphazene (PPz) polymers as the 19F-source; these are modified with sodium mercaptoethanesulfonate (MESNa) to achieve water solubility exceeding 360 mg/mL, which is a similar solubility to that of sodium chloride. We observed substantial signal enhancement in MRI with these novel macromolecular carriers compared to non-enhanced surroundings and aqueous trifluoroacetic acid (TFA) used as a positive control. In conclusion, these novel water-soluble macromolecular carriers represent a promising platform for future MRI contrast agents.

Antimicrobial, Antioxidant, and Anti-Inflammatory Nanoplatform for Effective Management of Infected Wounds

Burn wound healing continues to pose significant challenges due to excessive inflammation, the risk of infection, and impaired tissue regeneration. In this regard, an antibacterial, antioxidant, and anti-inflammatory nanocomposite (called HPA) that combines a nanosystem using hexachlorocyclotriphosphazene and the natural polyphenol of Phloretin with silver nanoparticles (AgNPs) is developed. HPA effectively disperses AgNPs to mitigate any toxicity caused by aggregation while also showing the pharmacological activities of Phloretin. During the initial stage of wound healing, HPA rapidly releases silver ions from its surface to suppress bacterial activity. Moreover, these nanoparticles are pH-sensitive and degrade efficiently in the acidic infection microenvironment, gradually releasing Phloretin. This sustained release of Phloretin helps scavenge overexpressed reactive oxygen species in the infected microenvironment area, thus reducing the upregulation of pro-inflammatory cytokines. The antibacterial activity, free radical clearance, and regulation of inflammatory factors of HPA through in vitro experiments are validated. Additionally, its effects using an infectious burn mouse model in vivo are evaluated. HPA is found to promote collagen deposition and epithelialization in the wound area. With its synergistic antibacterial, antioxidant, and anti-inflammatory activities, as well as favorable biocompatibilities, HPA shows great promise as a safe and effective multifunctional nanoplatform for burn injury wound dressings.

Barnacle-Inspired Wet Tissue Adhesive Hydrogels with Inherent Antibacterial Properties for Infected Wound Treatment

Currently, antibiotics are the most common treatment for bacterial infections in clinical practice. However, with the abuse of antibiotics and the emergence of drug-resistant bacteria, the use of antibiotics has faced an unprecedented challenge. It is imminent to develop nonantibiotic antimicrobial agents. Based on the cation-π structure of barnacle cement protein, a polyphosphazene-based polymer poly[(N,N-dimethylethylenediamine)-g-(N,N,N,N-dimethylaminoethyl p-ammonium bromide (ammonium bromide)-g-(N,N,N,N-dimethylaminoethyl acetate ethylammonium bromide)] (PZBA) with potential adhesion and inherent antibacterial properties was synthesized, and a series of injectable antibacterial adhesive hydrogels (PZBA-PVA) were prepared by cross-linking with poly(vinyl alcohol) (PVA). PZBA-PVA hydrogels showed good biocompatibility, and the antibacterial rate of the best-performed hydrogel reached 99.81 ± 0.04% and 98.80 ± 2.16% against Staphylococcus aureus and Escherichia coli within 0.5 h in vitro, respectively. In the infected wound model, the healing rate of the PZBA-PVA-treated group was significantly higher than that of the Tegaderm film group due to the fact that the hydrogel suppressed inflammatory responses and modulated the infiltration of immune cells. Moreover, the wound healing mechanism of the PZBA-PVA hydrogel was further evaluated by real-time polymerase chain reaction and total RNA sequencing. The results indicated that the process of hemostasis and tissue development was prompted and the inflammatory and immune responses were suppressed to accelerate wound healing. Overall, the PZBA-PVA hydrogel is shown to have the potential for infected wound healing application.

Nonaqueous Interfacial Polymerization-Derived Polyphosphazene Films for Sieving or Blocking Hydrogen Gas

A series of cyclomatrix polyphosphazene films have been prepared by nonaqueous interfacial polymerization (IP) of small aromatic hydroxyl compounds in a potassium hydroxide dimethylsulfoxide solution and hexachlorocyclotriphosphazene in cyclohexane on top of ceramic supports. Via the amount of dissolved potassium hydroxide, the extent of deprotonation of the aromatic hydroxyl compounds can be changed, in turn affecting the molecular structure and permselective properties of the thin polymer networks ranging from hydrogen/oxygen barriers to membranes with persisting hydrogen permselectivities at high temperatures. Barrier films are obtained with a high potassium hydroxide concentration, revealing permeabilities as low as 9.4 × 10^-17 cm³ cm cm^-2 s^-1 Pa^-1 for hydrogen and 1.1 × 10^-16 cm³ cm cm^-2 s^-1 Pa^-1 for oxygen. For films obtained with a lower concentration of potassium hydroxide, single gas permeation experiments reveal a molecular sieving behavior, with a hydrogen permeance of around 10^-8 mol m^-2 s^-1 Pa^-1 and permselectivities of H₂/N₂ (52.8), H₂/CH₄ (100), and H₂/CO₂ (10.1) at 200 °C.

Thermal Stabilities and Flame Retardancy of Polyamide 66 Prepared by In Situ Loading of Amino-Functionalized Polyphosphazene Microspheres

The flame-retardant polyamide 66 composites (FR-PA66) were prepared by in situ loading of amino-functionalized polyphosphazene microspheres (HCNP), which were synthesized in the laboratory and confirmed by a Fourier transform infrared spectrometer (FTIR), scanning electron microscope (SEM), and transmission electron microscope (TEM). The thermal stabilities and flame retardancy of FR-PA66 were measured using thermogravimetric analysis (TGA), a thermogravimetric infrared instrument (TG-IR), the limiting oxygen index (LOI), the horizontal and vertical combustion method (UL-94), and a cone calorimeter. The results illustrate that the volatile matter of FR-PA66 mainly contains carbon dioxide, methane₄, and water vapor under heating, accompanied by the char residue raising to 14.1 wt% at 600 °C and the value of the LOI and UL-94 rating reaching 30% and V-0, respectively. Moreover, the addition of HCNP decreases the peak of the heat release rate (pHRR), total heat release (THR), mass loss (ML), and total smoke release (TSR) of FR-PA66 to 373.7 kW/m², 106.7 MJ/m², 92.5 wt%, and 944.8 m²/m², respectively, verifying a significant improvement in the flame retardancy of PA66.

Skin Vaccination with Ebola Virus Glycoprotein Using a Polyphosphazene-Based Microneedle Patch Protects Mice against Lethal Challenge

Ebolavirus (EBOV) infection in humans is a severe and often fatal disease, which demands effective interventional strategies for its prevention and treatment. The available vaccines, which are authorized under exceptional circumstances, use viral vector platforms and have serious disadvantages, such as difficulties in adapting to new virus variants, reliance on cold chain supply networks, and administration by hypodermic injection. Microneedle (MN) patches, which are made of an array of micron-scale, solid needles that painlessly penetrate into the upper layers of the skin and dissolve to deliver vaccines intradermally, simplify vaccination and can thereby increase vaccine access, especially in resource-constrained or emergency settings. The present study describes a novel MN technology, which combines EBOV glycoprotein (GP) antigen with a polyphosphazene-based immunoadjuvant and vaccine delivery system (poly[di(carboxylatophenoxy)phosphazene], PCPP). The protein-stabilizing effect of PCPP in the microfabrication process enabled preparation of a dissolvable EBOV GP MN patch vaccine with superior antigenicity compared to a non-polyphosphazene polymer-based analog. Intradermal immunization of mice with polyphosphazene-based MN patches induced strong, long-lasting antibody responses against EBOV GP, which was comparable to intramuscular injection. Moreover, mice vaccinated with the MN patches were completely protected against a lethal challenge using mouse-adapted EBOV and had no histologic lesions associated with ebolavirus disease.

Research Progress in Energy Based on Polyphosphazene Materials in the Past Ten Years

With the rapid development of electronic devices, the corresponding energy storage equipment has also been continuously developed. As important components, including electrodes and diaphragms, in energy storage device and energy storage and conversion devices, they all face huge challenges. Polyphosphazene polymers are widely used in various fields, such as biomedicine, energy storage, etc., due to their unique properties. Due to its unique design variability, adjustable characteristics and high chemical stability, they can solve many related problems of energy storage equipment. They are expected to become a new generation of energy materials. This article briefly introduces the research progress in energy based on polyphosphazene materials in the past ten years, on topics such as fuel cells, solar cells, lithium batteries and supercapacitors, etc. The main focus of this work is on the defects of different types of batteries. Scholars have introduced different functional group modification that solves the corresponding problem, thus increasing the battery performance.

Multistage ROS-Responsive and Natural Polyphenol-Driven Prodrug Hydrogels for Diabetic Wound Healing

The high level of reactive oxygen species (ROS) and bacterial infection impede wound healing of the diabetic wound. Here, benefiting from the antioxidation effects of tannic acid (TA) and ROS-responsive phenylborate ester (PBAE), a series of ROS-responsive anti-inflammatory TA-conjugated nanoparticle hydrogels (PPBA-TA-PVA) can be obtained by conveniently mixing TA, phenylboric acid modified polyphosphazene (PPBA), and poly(vinyl alcohol) (PVA). The obtained PPBA-TA-PVA hydrogels could effectively inhibit the growth of Escherichia coli (antibacterial rate = 93.1 ± 1.1%) within 4 h and effectively scavenge both 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals and •OH radicals in vitro. Besides, the cell migration rate of HDFa cells treated with PPBA-TA-PVA hydrogels (84.2 ± 4.6%) was twice the rate of normal cells (43.8 ± 8.1%) after 24 h of cocultivation. The clinical relevance was demonstrated further by assessing the PPBA-TA-PVA hydrogels in full-thickness excisional wounds in a streptozotocin (STZ)-induced diabetic rat model. The PPBA-TA-PVA hydrogels could act as effective ROS-scavenging agents to alleviate inflammation and accelerate wound closure by decreasing the proinflammatory cytokines (IL-6, IL-1β) and increasing the gene expression of TGF-β1, COL-1, and COL-3, which resulted in faster re-epithelialization and increased formation of granulation tissue.

Nanohybrid of Co3O4 Nanoparticles and Polyphosphazene-Decorated Ultra-Thin Boron Nitride Nanosheets for Simultaneous Enhancement in Fire Safety and Smoke Suppression of Thermoplastic Polyurethane

Thermoplastic polyurethane (TPU) is widely used in daily life due to its characteristics of light weight, high impact strength, and compression resistance. However, TPU products are extremely flammable and will generate toxic fumes under fire attack, threatening human life and safety. In this article, a nanohybrid flame retardant was designed for the fire safety of TPU. Herein, Co₃O₄ was anchored on the surface of exfoliated ultra-thin boron nitride nanosheets (BNNO@Co₃O₄) via coprecipitation and subsequent calcination. Then, a polyphosphazene (PPZ) layer was coated onto BNNO@Co₃O₄ by high temperature polymerization to generate a nanohybrid flame retardant named BNNO@Co₃O₄@PPZ. The cone calorimeter results exhibited that the heat release and smoke production during TPU combustion were remarkably restrained after the incorporation of the nanohybrid flame retardant. Compared with pure TPU, the peak heat release rate (PHRR) decreased by 44.1%, the peak smoke production rate (PSPR) decreased by 51.2%, and the peak CO production rate (PCOPR) decreased by 72.5%. Based on the analysis of carbon residues after combustion, the significant improvement in fire resistance of TPU by BNNO@Co3O4@PPZ was attributed to the combination of quenching effect, catalytic carbonization effect, and barrier effect. In addition, the intrinsic mechanical properties of TPU were well maintained due to the existence of the PPZ organic layer.

Polyphosphazene: A New Adjuvant Platform for Cocaine Vaccine Development

Cocaine is a highly addictive drug that has seen a steady uptrend causing severe health problems worldwide. Currently, there are no approved therapeutics for treating cocaine use disorder; hence, there is an urgent need to identify new medications. Immunopharmacotherapeutics is a promising approach utilizing endogenous antibodies generated through active vaccination, and if properly programmed, can blunt a drug's psychoactive and addictive effects. However, drug vaccine efficacy has largely been limited by the modest levels of antibodies induced. Herein, we explored an adjuvant system consisting of a polyphosphazene macromolecule, specifically poly[di(carboxylatoethylphenoxy)-phosphazene] (PCEP), a biocompatible synthetic polymer that was solicited for improved cocaine conjugate vaccine delivery performance. Our results demonstrated PCEP's superior assembling efficiency with a cocaine hapten as well as with the combined adjuvant CpG oligodeoxynucleotide (ODN). Importantly, this combination led to a higher titer response, balanced immunity, successful sequestering of cocaine in the blood, and a reduction in the drug in the brain. Moreover, a PCEP-cocaine conjugate vaccine was also found to function well via intranasal administration, where its efficacy was demonstrated through the antibody titer, affinity, mucosal IgA production, and a reduction in cocaine's locomotor activity. Overall, a comprehensive evaluation of PCEP integrated within a cocaine vaccine established an advance in the use of synthetic adjuvants in the drugs of abuse vaccine field.

Preparation and Properties of Novel Crosslinked Polyphosphazene-Aromatic Ethers Organic-Inorganic Hybrid Microspheres

A series of novel crosslinked polyphosphazene-aromatic ether organic-inorganic hybrid microspheres with different structures were prepared via precipitation polycondensation between hexachlorocyclotriphosphazene (HCCP) and bisphenol monomers. The bisphenol monomers have different numbers of -CF₃ in the side group, which correspond to distinct oligomeric species-absorbing mechanisms. The wetting behavior of the microsphere surface was evaluated using a water contact angle (CA) measurement, which increased with the increase in the content of -CF₃ in polyphosphazene. We also investigated the effects of HCCP concentration and ultrasonic power on the morphology of the microspheres.

Polyphosphazene-Based Nanocarriers for the Release of Camptothecin and Epirubicin

The design and study of efficient polymer-based drug delivery systems for the controlled release of anticancer drugs is one of the pillars of nanomedicine. The fight against metastatic and invasive cancers demands therapeutic candidates with increased and selective toxicity towards malignant cells, long-term activity and reduced side effects. In this sense, polyphosphazene nanocarriers were synthesized for the sustained release of the anticancer drugs camptothecin (CPT) and epirubicin (EPI). Linear poly(dichloro)phosphazene was modified with lipophilic tocopherol or testosterone glycinate, with antioxidant and antitumor activity, and with hydrophilic Jeffamine M1000 to obtain different polyphosphazene nanocarriers. It allowed us to encapsulate the lipophilic CPT and the more hydrophilic EPI. The encapsulation process was carried out via solvent exchange/precipitation, attaining a 9.2-13.6 wt% of CPT and 0.3-2.4 wt% of EPI. CPT-loaded polyphosphazenes formed 140-200 nm aggregates in simulated body physiological conditions (PBS, pH 7.4), resulting in an 80-100-fold increase of CPT solubility. EPI-loaded polyphosphazenes formed 250 nm aggregates in an aqueous medium. CPT and EPI release (PBS, pH 7.4, 37 °C) was monitored for 202 h, being almost linear during the first 8 h. The slow release of testosterone and tocopherol was also sustained for 150 h in PBS (pH 7.4 and 6.0) at 37 °C. The co-delivery of testosterone or tocopherol and the anticancer drugs from the nanocarriers was expected. Cells of the human breast cancer cell line MCF-7 demonstrated good uptake of anticancer-drug-loaded nanocarriers after 6 h. Similarly, MCF-7 spheroids showed good uptake of the anticancer-drug-loaded aggregates after 72 h. Almost all anticancer-drug-loaded polyphosphazenes exhibited similar or superior toxicity against MCF-7 cells and spheroids when compared to raw anticancer drugs. Additionally, cell-cycle arrest in the G2/M phase was increased in response to the drug-loaded nanocarriers. Almost no toxicity of anticancer-drug-loaded aggregates against primary human lung fibroblasts was observed. Furthermore, the aggregates displayed no hemolytic activity, which is in contrast to the parent anticancer drugs. Consequently, synthesized polyphosphazene-based nanocarriers might be potential nanomedicines for chemotherapy.

Polyphosphazene and Non-Catechol-Based Antibacterial Injectable Hydrogel for Adhesion of Wet Tissues as Wound Dressing

Wound dressings with excellent adhesiveness, antibacterial, self-healing, hemostasis properties, and therapeutic effects have great significance for the treatment of acute trauma. So far, numerous mussel-inspired catechol-based wet adhesives have been reported, opening a pathway for the treatment of acute trauma. However, catechol-based hydrogels are easily oxidized, which limits their applications. Here, the design of a polyphosphazene and non-catechol based antibacterial injectable hydrogel is reported as a multifunctional first aid bandage. Inspired by barnacle cement proteins, a series of dynamic phenylborate ester based adhesive hydrogels are prepared by combining the cation-π structure modified polyphosphazene with polyvinyl alcohol. The inherent antibacterial property (4 h antibacterial rate 99.6 ± 0.2%), anti-mechanical damage, and hemostatic behavior are investigated to confirm multi-functions of wound dressings. In water, the hydrogels firmly adhere to tissue surfaces through cation-π and π-π interactions as well as hydrogen bonding (adhesion strength = 45 kPa). Moreover, in vivo experiments indicate the hydrogels can shorten the bleeding time and reduce the amount of bleeding by 88%, and significantly accelerate the wound healing rate. These hydrogels have a promising application in the treatment of acute trauma, which is in urgent need of anti-infection and hemostasis.

The Adjuvants Polyphosphazene (PCEP) and a Combination of Curdlan Plus Leptin Promote a Th17-Type Immune Response to an Intramuscular Vaccine in Mice

Our aim was to determine whether polyphosphazene (PCEP), Curdlan (β-glucan, a dectin-1 agonist), and Leptin could act as adjuvants to promote a Th17-type adaptive immune response in mice. Mice were vaccinated via the intramuscular route then boosted three weeks later with Ovalbumin plus: PCEP, Leptin, Curdlan, PCEP+Curdlan, Curdlan+Leptin, or saline. Mice vaccinated with OVA+PCEP and OVA+Curdlan+Leptin showed significantly higher frequency of antigen-specific CD4+ T cells secreting IL-17 relative to OVA-vaccinated mice. No formulation increased the frequency of CD4+ T cells secreting IL-4 or IFNγ. Since activation of innate immunity precedes the development of adaptive immunity, we wished to establish whether induction of Th17-type immunity could be predicted from in vitro experiments and/or from the local cytokine environment after immunization with adjuvants alone. Elevated IL-6 and TGFβ with reduced secretion of IL-12 is a cytokine milieu known to promote differentiation of Th17-type immunity. We injected the immunostimulants or saline buffer into murine thigh muscles and measured acute local cytokine production. PCEP induced significant production of IL-6 and reduced IL-12 production in muscle but it did not lead to elevated TGFβ production. Curdlan+Leptin injected into muscle induced significant production of TGFβ and IL-17 but not IL-6 or IL-12. We also stimulated splenocytes with media or PCEP, Leptin, Curdlan, PCEP+Curdlan, Curdlan+Leptin, PCEP+Leptin, and PCEP+Curdlan+Leptin and measured cytokine production. PCEP stimulation of splenocytes failed to induce significant production of IL-6, IL-12, TGFβ, or IL-17 and therefore ex vivo splenocyte stimulation failed to predict the increased frequency of Th17-type T cells in response to the vaccine. Curdlan-stimulated splenocytes produced Th1-type, inducing cytokine, IL-12. Curdlan+/-PCEP stimulated TGF-β production and Curdlan+Leptin+/- PCEP induced secretion of IL-17. We conclude that PCEP as well as Curdlan+Leptin are Th17-type vaccine adjuvants in mice but that cytokines produced in response to these adjuvants in muscle after injection or in ex vivo cultured splenocytes did not predict their role as a Th17-type adjuvant. Together, these data suggest that the cytokine environments induced by these immunostimulants did not predict induction of an antigen-specific Th17-type adaptive immune response. This is the first report of these adjuvants inducing a Th17-type adaptive immune response.

Strong Chemical Interaction between Lithium Polysulfides and Flame-Retardant Polyphosphazene for Lithium-Sulfur Batteries with Enhanced Safety and Electrochemical Performance

The shuttle effect of lithium polysulfides (LiPS) and potential safety hazard caused by the burning of flammable organic electrolytes, sulfur cathode, and lithium anode seriously limit the practical application of lithium-sulfur (Li-S) batteries. Here, a flame-retardant polyphosphazene (PPZ) covalently modified holey graphene/carbonized cellulose paper is reported as a multifunctional interlayer in Li-S batteries. During the discharge/charge process, once the LiPS are generated, the as-obtained flame-retardant interlayer traps them immediately through the nucleophilic substitution reaction between PPZ and LiPS, effectively inhibiting the shuttling effect of LiPS to enhance the cycle stability of Li-S batteries. Meanwhile, this strong chemical interaction increases the diffusion coefficient for lithium ions, accelerating the lithiation reaction with complete inversion. Moreover, the as-obtained interlayer can be used as a fresh 3D current collector to establish a flame-retardant "vice-electrode," which can trap dissolved sulfur and absorb a large amount of electrolyte, prominently bringing down the flammability of the sulfur cathode and electrolyte to improve the safety of Li-S batteries. This work provides a viable strategy for using PPZ-based materials as strong chemical scavengers for LiPS and a flame-retardant interlayer toward next-generation Li-S batteries with enhanced safety and electrochemical performance.

Polyoctahedral Silsesquioxane Hexachlorocyclotriphosphazene Membranes for Hot Gas Separation

There is a need for gas separation membranes that can perform at high temperatures, for example, for CO₂ capture in industrial processes. Polyphosphazenes classify as interesting materials for use under these conditions because of their high thermal stability, hybrid nature, and postfunctionalization options. In this work, thin-film composite cyclomatrix polyphosphazene membranes are prepared via the interfacial polymerization reaction between polyhedral oligomeric silsesquioxane and hexachlorocyclotriphosphazene on top of a ceramic support. The prepared polyphosphazene networks are highly crosslinked and show excellent thermal stability until 340 °C. Single gas permeation experiments at temperatures ranging from 50 to 250 °C reveal a molecular sieving behavior, with permselectivities as high as 130 for H₂/CH₄ at the low temperatures. The permselectivities of the membranes persist at the higher temperatures; at 250 °C H₂/N₂ (40), H₂/CH₄ (31) H₂/CO₂ (7), and CO₂/CH₄ (4), respectively, while maintaining permeances in the order of 10^-7 to 10^-8 mol m^-2 s^-1 Pa^-1. Compared to other types of polymer-based membranes, especially the H₂/N₂ and H₂/CH₄ selectivities are high, with similar permeances. Consequently, the hybrid polyphosphazene membranes have great potential for use in high-temperature gas separation applications.

Flexible All-Solid-State Li-Ion Battery Manufacturable in Ambient Atmosphere

The rational design and exploration of safe, robust, and inexpensive energy storage systems with high flexibility are greatly desired for integrated wearable electronic devices. Herein, a flexible all-solid-state battery possessing competitive electrochemical performance and mechanical stability has been realized by easy manufacture processes using carbon nanotube enhanced phosphate electrodes of LiTi₂(PO₄)₃ and Li₃V₂(PO₄)₃ and a highly conductive solid polymer electrolyte made of polyphosphazene/PVDF-HFP/LiBOB [PVDF-HFP, poly(vinylidene fluoride-co-hexafluoropropylene)]. The components were chosen based on their low toxicity, systematic manufacturability, and (electro-)chemical matching in order to ensure ambient atmosphere battery assembly and to reach high flexibility, good safety, effective interfacial contacts, and high chemical and mechanical stability for the battery while in operation. The high energy density of the electrodes was enabled by a novel design of the self-standing anode and cathode in a way that a large amount of active particles are embedded in the carbon nanotube (CNT) bunches and on the surface of CNT fabric, without binder additive, additional carbon, or a large metallic current collector. The electrodes showed outstanding performance individually in half-cells with liquid and polymer electrolyte, respectively. The prepared flexible all-solid-state battery exhibited good rate capability, and more than half of its theoretical capacity can be delivered even at 1C at 30 °C. Moreover, the capacity retentions are higher than 75% after 200 cycles at different current rates, and the battery showed smaller capacity fading after cycling at 50 °C. Furthermore, the promising practical possibilities of the battery concept and fabrication method were demonstrated by a prototype laminated flexible cell.

Cross-Linked Polyphosphazene Blends as Robust CO2 Separation Membranes

An effective cross-linking technique allows a viscous and highly gas-permeable hydrophilic polyphosphazene to be cast as solid membrane films. By judicious blending with other polyphosphazenes to improve the mechanical properties, a membrane exhibiting the highest CO₂ permeability (610 barrer) among polyphosphazenes combined with a good CO₂/N₂ selectivity (35) was synthesized and described here. The material demonstrates performance stability after 500 h of exposure to a coal-fired power plant flue gas, making it attractive for use in carbon capture applications. Its CO₂/N₂ selectivity under conditions up to full humidity is also stable, and although the gas permeability does decline, the performance is fully recovered upon drying. The high molecular weight of these heteropolymers also allows them to be cast as a thin selective layer on an asymmetric porous membrane, yielding a CO₂ permeance of 1200 GPU and a CO₂/N₂ pure gas selectivity of 31, which does not decline over 2000 h. In addition to gas separation membranes, this cross-linked polyphosphazene can potentially be extended to other applications, such as drug delivery or proton exchange membranes, which take advantage of the polyphosphazene's versatile chemistry.

New cross-linkable poly[bis(octafluoropentoxy) phosphazene] biomaterials: Synthesis, surface characterization, bacterial adhesion, and plasma coagulation responses

Biomaterial-associated microbial infection and thrombosis represent major issues to the success of long-term use of implantable blood-contacting medical devices. The development of new poly[bis(octafluoropentoxy) phosphazene (OFP) biomaterials provides new routes for combatting microbial infection and thrombosis. However, the limited mechanical properties of OFP to date render them unsuitable for application in medical devices and inhibit any attempts at subsequent surface topography modification. In this study, we synthesized cross-linkable OFPs (X-OFPs) with the different degrees of cross-linking in an effort to improve the mechanical properties. The results showed that the surface chemistry and surface topography of X-OFPs do not change significantly, but the surface mechanical stiffness increased after cross-linking. Atomic force microscopic phase images showed that the polymer phase separation structures changed due to cross-linking. Experiments with three bacterial strains: Staphylococcal epidermidis, Staphylococcal aureus, and Pseudomonas aeruginosa showed that bacterial adhesion was significantly decreased on the OFP and X-OFPs for both the pre-cross-linked and cross-linked as compared to polyurethane biomaterials. Furthermore, bacterial adhesions were lower on X-OFP surfaces than on pre-cross-linked materials, suggesting that mechanical stiffness is an important parameter influencing bacterial adhesion. Blood plasma coagulation responses revealed longer coagulation times for OFP and X-OFP materials than on polyurethanes, indicating that the new cross-linked OFPs are resistant to plasma coagulation compared to currently used polyurethane biomaterials.

Acid-Responsive and Biologically Degradable Polyphosphazene Nanodrugs for Efficient Drug Delivery

To enhance the therapeutic effects and reduce the damage to normal tissues in cancer chemotherapy, it is indispensable to develop drug delivery carriers with controllable release and good biocompatibility. In this work, acid-responsive and degradable polyphosphazene (PPZ) nanoparticles were synthesized by the reaction of hexachlorotripolyphosphonitrile (HCCP) with 4-hydroxy-benzoic acid (4-hydroxy-benzylidene)-hydrazide (HBHBH) and anticancer drug doxorubicin (DOX). The controlled release of DOX could be realized based on the acid responsiveness of acylhydrazone in HBHBH. Experimental results showed that polyphosphazene nanoparticles remained stable in the body's normal fluids (pH ∼ 7.4), while they were degraded and controllable release of DOX in an acidic environment such as tumors (pH ∼ 6.8) and lysosome and endosome (∼5.0) in cancer cells In particular, the doxorubicin (DOX)-loading ratio was fair high and could be tuned from 10.6 to 52.6% by changing the dosing ratio of DOX to HBHBH. Meanwhile, the polyphosphazene nanodrugs showed excellent toxicity to tumor cells and reduced the side effect to normal cells both in vitro and in vivo due to their enhanced permeability and retention (EPR) effect and pH-sensitive degradation properties. Therefore, the constructed pH-sensitive drug delivery system has great potential for cancer chemotherapy.

Experimental PCEP-Adjuvanted Swine Influenza H1N1 Vaccine Induced Strong Immune Responses but Did Not Protect Piglets against Heterologous H3N2 Virus Challenge

Vaccination is the most efficient method of protection against influenza infections. However, the rapidly mutating viruses and development of new strains make it necessary to develop new influenza vaccines annually. Hence, vaccines that stimulate cross-protection against multiple influenza subtypes are highly sought. Recent evidence suggests that adjuvants such as PCEP that promote Th1-type T cell and Th2-type T cell immune responses and broad-spectrum immune responses may confer cross-protection against heterologous influenza strains. In this study, we evaluated whether the immunogenic and protective potential of PCEP-adjuvanted inactivated swine influenza virus H1N1 vaccine can protect pigs immunized against live H3N2 virus. Piglets were vaccinated via the intradermal route with PCEP-adjuvanted inactivated swine influenza virus (SIV) H1N1 vaccine, boosted at day 21 with the same vaccines then challenged with infectious SIV H3N2 virus at day 35 via the tracheobronchial route. The pigs showed significant anti-H1N1 SIV specific antibody titres and H1N1 SIV neutralizing antibody titres, and these serum titres remained after the challenge with the H3N2 virus. In contrast, vaccination with anti-H1N1 SIV did not trigger anti-H3N2 SIV antibody titres or neutralizing antibody titres and these titres remained low until pigs were challenged with H3N2 SIV. At necropsy (six days after challenge), we collected prescapular lymph nodes and tracheobronchial draining the vaccination sites and challenge site, respectively. ELISPOTs from lymph node cells restimulated ex vivo with inactivated SIV H1N1 showed significant production of IFN-γ in the tracheobronchial cells, but not the prescapular lymph nodes. In contrast, lymph node cells restimulated ex vivo with inactivated SIV H1N1 showed significantly higher IL-13 and IL-17A in the prescapular lymph nodes draining the vaccination sites relative to unchallenged animals. Lung lesion scores show that intradermal vaccination with H1N1 SIV plus PCEP did not prevent lesions when the animals were challenged with H3N2. These results confirm previous findings that PCEP is effective as a vaccine adjuvant in that it induces strong immune responses and protects against homologous swine influenza H1N1 virus, but the experimental H1N1 vaccine failed to cross-protect against heterologous H3N2 virus.

Main-Chain Phosphorus-Containing Polymers for Therapeutic Applications

Polymers in which phosphorus is an integral part of the main chain, including polyphosphazenes and polyphosphoesters, have been widely investigated in recent years for their potential in a number of therapeutic applications. Phosphorus, as the central feature of these polymers, endears the chemical functionalization, and in some cases (bio)degradability, to facilitate their use in such therapeutic formulations. Recent advances in the synthetic polymer chemistry have allowed for controlled synthesis methods in order to prepare the complex macromolecular structures required, alongside the control and reproducibility desired for such medical applications. While the main polymer families described herein, polyphosphazenes and polyphosphoesters and their analogues, as well as phosphorus-based dendrimers, have hitherto predominantly been investigated in isolation from one another, this review aims to highlight and bring together some of this research. In doing so, the focus is placed on the essential, and often mutual, design features and structure-property relationships that allow the preparation of such functional materials. The first part of the review details the relevant features of phosphorus-containing polymers in respect to their use in therapeutic applications, while the second part highlights some recent and innovative applications, offering insights into the most state-of-the-art research on phosphorus-based polymers in a therapeutic context.

Design of a Novel Theranostic Nanomedicine (III): Synthesis and Physicochemical Properties of Tumor-Targeting Cisplatin Conjugated to a Hydrophilic Polyphosphazene

Purpose

A new theranostic nanomedicine involving anticancer-active cisplatin moiety was designed to study its tumor-targeting properties as well as its drug efficacy and toxicity.

Methods

A cisplatin carrier polymer was prepared by grafting equimolar polyethylene glycol of a molecular weight of 550 (PEG550) and aminoethanol to the poly(dichlorophosphazene) backbone. Cisplatin was conjugated to the carrier polymer using cis-aconitic acid as a linker.

Results

The cisplatin-loaded polyphosphazene, named "Polycisplatin" was found to be amphiphilic in aqueous solution and self-assembled into nanoparticles with an average particle size of 18.6 nm in diameter. The time-dependent organ distribution study of Cy5.5-labeled Polycisplatin in the A549-tumor-bearing mice exhibited a high tumor selectivity of Polycisplatin by EPR effect despite the relatively small particle size. In order to compare the in vivo efficacy of Polycisplatin and cisplatin, their xenograft trials were performed using nude mice against the human gastric cell line MKN-28. Polycisplatin exhibited slightly less tumor suppression effect compared with cisplatin at the same dose of 1.95 mg Pt/kg, which is the maximum tolerate dose of cisplatin, but at the higher double dose of 3.9 mg Pt/kg, Polycisplatin exhibited a little better efficacy than cisplatin. Furthermore, mice treated with cisplatin at the dose of 1.95 mg Pt/kg exhibited severe body weight decrease by about 25%, while mice treated with Polycisplatin did not show serious body weight decrease even at its double dose of 3.9 mg Pt/kg. Furthermore, kidney indicators including kidney index, BUN, and creatinine values measured displayed that Polycisplatin is much less nephrotoxic than cisplatin.

Conclusion

Nanoparticular Polycisplatin was successfully prepared by conjugating cisplatin to a hydrophilic polyphosphazene carrier polymer using the acid-cleavable cis-aconitic acid. Polycisplatin nanoparticles exhibit excellent tumor-targeting properties by EPR effect. The xenograft trials exhibited excellent antitumor efficacy and reduced systemic toxicity of Polycisplatin.

131 I-Labeled Multifunctional Polyphosphazene Nanospheres for SPECT Imaging-Guided Radiotherapy of Tumors

Design of theranostic nanoplatforms represents a major topic for current nanomedicine. Here, the preparation of multifunctional poly(cyclotriphosphazene-co-polyethylenimine) nanospheres (PNSs) labeled with radionuclide ¹³¹ I for single photon emission computed tomography (SPECT) imaging-guided radiotherapy of tumors is reported. In this work, PNSs are prepared using hexachlorocyclotriphosphazene as a crosslinker to crosslink branched polyethylenimine (PEI) via a nucleophilic substitution reaction, modified with 3-(4'-hydroxyphenyl) propionic acid-OSu (HPAO) for ¹³¹ I labeling, and reacted with 1,3-propane sulfonate (1,3-PS) to render the particles with antifouling property, followed by acetylation of the remaining surface amines and labeling with ¹³¹ I. The acquired PNS.NHAc-HPAO(¹³¹ I)-PS particles are well characterized. It is shown that the multifunctional PNSs with an average size of 184 ± 29.3 nm exhibit favorable antifouling properties, high ¹³¹ I labeling efficiency (76.05 ± 3.75%), and excellent radiostability and colloidal stability. With these properties owned, the developed PNS.NHAc-HPAO(¹³¹ I)-PS spheres enable much more efficient SPECT imaging and radiotherapy of a xenografted tumor model in vivo than the PEI counterpart material (PEI.NHAc-HPAO(¹³¹ I)-PS). The developed PNSs may be used as a versatile platform for further development of different forms of nanomedicine for various biomedical applications.

Design of Hierarchical NiCo-LDH@PZS Hollow Dodecahedron Architecture and Application in High-Performance Epoxy Resin with Excellent Fire Safety

Developing advanced performance epoxy (EP) resin with low flammability and light smoke has been an increasing focus of its research. Especially, it is crucial to reduce the emission of smoke and toxic gases generated during the burning of EP, so that it meets the green and safe industrial requirement. Therefore, a 3D NiCo-LDH@PZS hollow dodecahedral structure was designed and synthesized by using the ZIF-67 as both the precursor and an in situ sacrificial template and the amino group-containing polyphosphazene (PZS) as interfacial compatibilizer and flame retardant cooperative. The release behaviors of heat, smoke, and poisonous gases were carefully investigated. More precisely, the EP/NiCo-LDH@PZS4.0 is endowed with a decrease of 30.9% and 11.2% of the peak heat release rate and the total heat release, respectively. The emissions of smoke and poisonous gases including nitric oxides, aromatic compounds, carbonyl compounds, oxycarbide, and hydrocarbons are much less as well. Especially, the maximum release concentrations of HCN of EP/NiCo-LDH4.0 are reduced by 87.8%. With regard to styrene, methane, and ethane, the maximum release concentrations of EP/NiCo-LDH@PZS4.0 are reduced by 85.9%, 90.6%, and 93.1%, respectively. The total yield of CO and CO₂ and the consumption of O₂ of EP/NiCo-LDH@PZS4.0 are also reduced by 64.5%, 32.4%, and 33.6%. The fractional effective dose, an index of toxicity smoke, of EP/NiCo-LDH@PZS4.0 is reduced by 20.4%. The DMA tests were performed to study the mechanical properties of EP composites, and the storage modulus and Tg of EP composites are increased with the incorporation of NiCo-LDH@PZS. The possible mechanism of flame retardant was proposed based on the analysis of the condensed and gas phases of EP composites.

Activatable Hybrid Polyphosphazene-AuNP Nanoprobe for ROS Detection by Bimodal PA/CT Imaging

Overproduction of reactive oxygen species (ROS) is often related to inflammation or cancer and can cause tissue damage. Probes that have been previously reported to image ROS typically rely on imaging techniques that have low depth penetration in tissue, thus limiting their use to superficial disease sites. We report herein a novel formulation of hybrid nanogels loaded with gold nanoparticles (AuNP) to produce contrast for computed tomography (CT) and photoacoustics (PA), both being deep-tissue imaging techniques. The polyphosphazene polymer has been designed to selectively degrade upon ROS exposure, which triggers a switch-off of the PA signal by AuNP disassembly. This ROS-triggered degradation of the nanoprobes leads to a significant decrease in the PA contrast, thus allowing ratiometric ROS imaging by comparing the PA to CT signal. Furthermore, ROS imaging using these nanoprobes was applied to an in vitro model of inflammation, that is, LPS-stimulated macrophages, where ROS-triggered disassembly of the nanoprobe was confirmed via reduction of the PA signal. In summary, these hybrid nanoprobes are a novel responsive imaging agent that have the potential to image ROS overproduction by comparing PA to CT contrast.

Stabilization of Gold Nanoparticles

During the last number of years a variety of crystallization-driven self-assembly (CDSA) processes based on semicrystalline block copolymers have been developed to prepare a number of different nanomorphologies in solution (micelles). We herein present a convenient synthetic methodology combining: (i) The anionic polymerization of 2-vinylpyridine initiated by organolithium functionalized phosphane initiators; (ii) the cationic polymerization of iminophosphoranes initiated by –PR₂Cl₂; and (iii) a macromolecular nucleophilic substitution step, to prepare the novel block copolymers poly(bistrifluoroethoxy phosphazene)-b-poly(2-vinylpyridine) (PTFEP-b-P2VP), having semicrystalline PTFEP core forming blocks. The self-assembly of these materials in mixtures of THF (tetrahydrofuran) and 2-propanol (selective solvent to P2VP), lead to a variety of cylindrical micelles of different lengths depending on the amount of 2-propanol added. We demonstrated that the crystallization of the PTFEP at the core of the micelles is the main factor controlling the self-assembly processes. The presence of pyridinyl moieties at the corona of the micelles was exploited to stabilize gold nanoparticles (AuNPs).

Air-Stable Polyphosphazene-Functionalized Few-Layer Black Phosphorene for Flame Retardancy of Epoxy Resins

Similar to graphene, few-layer black phosphorus (BP) features thermal stability, mechanical properties, and characteristic dimension effects, which has potential as a new member of nanofillers for fabricating polymer nanocomposites. Herein, a cross-linked polyphosphazene-functionalized BP (BP-PZN) is developed with abundant -NH₂ groups via a one-pot polycondensation of 4,4'-diaminodiphenyl ether and hexachlorocyclotriphosphazene on the surface of BP nanosheets. Whereafter, the resulting BP-PZN is incorporated into epoxy resin (EP) to study the flame-retardant property and smoke suppression performance. Cone results show that the introduction of 2 wt% BP-PZN distinctly improves the flame-retardant property of EP, for instance, 59.4% decrease in peak heat release rate and 63.6% reduction in total heat release. The diffusion of pyrolysis products from EP during combustion is obviously suppressed after incorporating the BP-PZN nanosheets. Meanwhile, the EP/BP-PZN nanocomposites exhibit air stability after exposure to ambient conditions for four months. The air stability of the BP nanosheets in EP matrix is assigned to surface wrapping by PZN and embedded in the polymer matrix as dual protection. As a new member of the 2D nanomaterials, BP nanosheets have potential to be a new choice for fabricating high-performance nanocomposites.

Cyclomatrix Polyphosphazene Porous Networks with J-Aggregated Multiphthalocyanine Arrays for Dual-Modality Near-Infrared Photosensitizers

Here, we have developed a kind of cyclomatrix polyphosphazene with excellent photophysical properties and pursued their potential of being organic photosensitizers for dual-modality phototherapy. Briefly, hexachlorocyclophosphazene (HCCP) with D_{3 h} symmetry is adopted as a synthon to attach Zn(II) phthalocyanine (ZnPc) to form dendritic units that are covalently expanded into a soluble porous network through the nucleophilic substitution reaction. Molecular simulation reveals that the multi-ZnPc units around HCCP can be oriented in a side-by-side manner, leading to the remarkably red-shifted and intense absorbance in the near-infrared (NIR) region. To validate the potential in bioapplication, such ZnPc-based polyphosphazenes are assembled by incorporation of polyvinylpyrrolidone (PVP) to produce the uniform nanoparticles with aqueous dispersibility and biocompatibility. From the in vitro results, the PVP-stabilized photosensitizing nanoparticles can undergo the photothermal/photodynamic processes to concurrently generate heat and singlet oxygen for efficiently killing cancer cells upon exposure to a single-bandwidth NIR laser (785 nm). Compared with the known organic photosensitizers, cyclomatrix polyphosphazene would be a promising platform to configure a diversity of reticular arrays with dense and oriented arrangement of dye molecules, leading to their largely enhanced photophysical and photochemical properties.

Biodegradable Cyclomatrix Polyphosphazene Nanoparticles: A Novel pH-Responsive Drug Self-Framed Delivery System

Traditional drug delivery systems suffer from low drug-loading and relatively weak therapeutic efficacy, therefore, development of new drug delivery systems with high-efficiency has become more urgent. In this report, a novel-innovative drug delivery strategy, namely drug self-framed delivery system (DSFDS), is prepared via using anticancer drugs as polymer frame without using any carriers. The drug molecules (exemplified by doxorubicin) containing more than two nucleophilic functional groups (diols/diamines) directly reacted with hexachlorocyclotriphosphazene via mild precipitation polycondensation under ambient conditions, forming biocompatible drug self-framed delivery nanoparticles. Because of the covalent bonding of the drug molecules, DSFD nanoparticles (DSFDs) with super high drug-loading were stable in the circulation during delivery. However, sustained release of drug in the acidic environment within cells endowed DSFDs with long-term anticancer therapeutic efficacy. This strategy is applicable for diverse hydrophilic and hydrophobic drugs and may be a new platform for designing high drug-loading and release-controllable drug delivery systems.

Design of pH-Sensitive Nanovesicles via Cholesterol Analogue Incorporation for Improving in Vivo Delivery of Chemotherapeutics

pH-responsive polymersomes have emerged as promising nanocarriers for antitumor drugs to realize their fast release and action in a weakly acidic microenvironment of tumor cells. Herein, however, we designed a remarkably pH-responsive polymersome self-assembled from amphiphilic benzimidazole-based polyphosphazenes via the incorporation of cholesteryl hemisuccinate (CholHS), a type of cholesteric molecule, into the polymersome bilayers to inhibit the drug release during blood circulation. Actually, unwanted premature drug leakage before arriving at the acidic tumor site has become a serious problem for polymersomes encapsulating water-soluble drugs, especially when the drug loading is at a high level, thus limiting the therapeutic efficacy. In this study, polymersomes displayed high loading capability of doxorubicin hydrochloride as 12.83%. More importantly, CholHS incorporation decreased the membrane permeability of the polymersome and effectively retarded the cargo release under physiological conditions but induced the fast drug-release rate at pH 5.5, demonstrating a more remarkably acid-responsive release behavior when compared to that of the CholHS-free polymersomes. Further in vivo investigations including pharmacokinetic and antitumor activity studies verified the extended circulation time and enhanced antitumor efficacy of the drug-loaded CholHS-incorporated polymersomes.

Hierarchical Polyphosphazene@Molybdenum Disulfide Hybrid Structure for Enhancing the Flame Retardancy and Mechanical Property of Epoxy Resins

A novel polyphosphazene (PZS) microsphere@molybdenum disulfide nanoflower (MoS₂) hierarchical hybrid architecture was first synthesized and applied for enhancing the mechanical performance and flame retardancy of epoxy (EP) resin via a cooperative effect. Herein, using PZS microsphere as the template, a layer of MoS₂ nanoflowers were anchored to PZS spheres via a hydrothermal strategy. The well-designed PZS@MoS₂ exhibits excellent fire retardancy and a reinforcing effect. The obtained PZS@MoS₂ significantly enhanced the flame-retardant performance of EP composites, which can be proved by thermogravimetric and cone calorimeter results. For instance, the incorporation of 3 wt % PZS@MoS₂ brought about a 41.3% maximum reduction in the peak heat-release rate and decreased by 30.3% maximum in the total heat release, accompanying the higher graphitized char layer. With regard to mechanical property, the storage modulus of EP/PZS@MoS₂3.0 in the glassy state was dramatically increased to 22.4 GPa in comparison with that of pure EP (11.15 GPa). It is sensible to know that the improved flame-retardant performance for EP composites is primarily assigned to a physical barrier effect of the MoS₂ nanoflowers and the polyphosphazene structure has an positive impact on promoting char formation in the condensed phase.

Design of theranostic nanomedicine (II): synthesis and physicochemical properties of a biocompatible polyphosphazene-docetaxel conjugate

To prepare an efficient theranostic polyphosphazene–docetaxel (DTX) conjugate, a new drug delivery system was designed by grafting a multifunctional lysine ethylester (LysOEt) as a spacer group along with methoxy poly(ethylene glycol) (MPEG) to the polyphosphazene backbone ([NP]_n), and then DTX was conjugated to the carrier polymer using acid-cleavable cis-aconitic acid (AA) as a linker. The resultant polyphosphazene–DTX conjugate, formulated as [NP(MPEG550)₃(Lys-OEt)(AA)(DTX)]_n and named “Polytaxel”, exhibited high water solubility and stability by forming stable polymeric micelles as shown in its transmission electron microscopy image and dynamic light scattering measurements. Another important aspect of Polytaxel is that it can easily be labeled with various imaging agents using the lysine amino group, enabling studies on various aspects, such as its organ distribution, tumor-targeting properties, pharmacokinetics, toxicity, and excretion. The pharmacokinetics of Polytaxel was remarkably improved, with prolonged elimination half-life and enhanced area under the curve. Ex vivo imaging study of cyanine dye-labeled Polytaxel showed that intravenously injected Polytaxel is long circulating in the blood stream and selectively accumulates in tumor tissues. Polytaxel distributed in other organs was cleared from all major organs at ~6 weeks after injection. The in vitro study of DTX release from the carrier polymer showed that >95% of conjugated DTX was released at pH 5.4 over a period of 7 days. Xenograft trials of Polytaxel using nude mice against the human gastric tumor cell line MKN-28 showed complete tumor regression, with low systemic toxicity. Polytaxel is currently in preclinical study.

Biodegradable Polyphosphazene Based Peptide-Polymer Hybrids

A novel series of peptide based hybrid polymers designed to undergo enzymatic degradation is presented, via macrosubstitution of a polyphosphazene backbone with the tetrapeptide Gly-Phe-Leu-Gly. Further co-substitution of the hybrid polymers with hydrophilic polyalkylene oxide Jeffamine M-1000 leads to water soluble and biodegradable hybrid polymers. Detailed degradation studies, via ³¹P NMR spectroscopy, dynamic light scattering and field flow fractionation show the polymers degrade via a combination of enzymatic, as well as hydrolytic pathways. The peptide sequence was chosen due to its known property to undergo lysosomal degradation; hence, these degradable, water soluble polymers could be of significant interest for the use as polymer therapeutics. In this context, we investigated conjugation of the immune response modifier imiquimod to the polymers via the tetrapeptide and report the self-assembly behavior of the conjugate, as well as its enzymatically triggered drug release behavior.

Design of a novel theranostic nanomedicine: synthesis and physicochemical properties of a biocompatible polyphosphazene-platinum(II) conjugate

To develop a theranostic nanomedicine involving the antitumor-active moiety (dach)Pt(II) (dach: trans-(±)-1,2-diaminocyclohexane) of oxaliplatin (OX), a new biocompatible polyphosphazene carrier polymer was designed by grafting with a methoxy poly(ethylene glycol) (MPEG) to increase duration of circulation in the blood and with aminoethanol (AE) as a spacer group. The antitumor (dach)Pt moiety was conjugated to the carrier polymer using cis-aconitic acid (AA) as a linker, resulting in a polymer conjugate formulated as [NP(MPEG550)(AE-AA)Pt(dach)]_n, named “Polyplatin” (PP). PP was found to self-assemble into very stable polymeric nanoparticles with a mean diameter of 55.1 nm and a critical aggregation concentration of 18.5 mg/L in saline. PP could easily be labeled with a fluorescence dye such as Cy5.5 for imaging studies. The time-dependent ex vivo image studies on organ distributions and clearance of Cy-labeled PP have shown that PP accumulated in the tumor with high selectivity by the enhanced permeability and retention effect but was cleared out from all the major organs including the liver in about 4 weeks postinjection. Another time-dependent bioimaging study on distribution and clearance of PP in mouse kidney using laser ablation inductively coupled plasma mass spectroscopy has shown that PP accumulates much less in kidney and is more rapidly excreted than monomeric OX, which is in accord with the very low acute toxicity of PP as shown by its high LD₅₀ value of more than 2000 mg/kg. The pharmacokinetic study of PP has shown that it has a much longer half-life (t_1/2β) of 13.3 hours compared with the 5.21 hours of OX and about a 20 times higher area under the curve value of 42,850.8 ng h/mL compared with the 2,320.4 ng h/mL of OX. The nude mouse xenograft trials of PP against the gastric MKN-28 tumor cell line exhibited remarkably better tumor efficacy compared with OX at the higher tolerated dose, with lower systemic toxicity.

Administration of Poly[di(sodium carboxylatoethylphenoxy)phosphazene] (PCEP) and Avian Beta Defensin as Adjuvants in Inactivated Inclusion Body Hepatitis Virus and its Hexon Protein-Based Experimental Vaccine Formulations in Chickens

Inclusion body hepatitis (IBH) is one of the major infectious diseases adversely affecting the poultry industry of the United States and Canada. Currently, no effective and safe vaccine is available for the control of IBH virus (IBHV) infection in chickens. However, based on the excellent safety and immunogenic profiles of experimental veterinary vaccines developed with the use of new generation adjuvants, we hypothesized that characterization of vaccine formulations containing inactivated IBHV or its capsid protein hexon as antigens, along with poly[di(sodium carboxylatoethylphenoxy)phosphazene] (PCEP) and avian beta defensin 2 (ABD2) as vaccine adjuvants, will be helpful in development of an effective and safe vaccine formulation for IBH. Our data demonstrated that experimental administration of vaccine formulations containing inactivated IBHV and a mixture of PCEP with or without ABD2 as an adjuvant induced significantly higher antibody responses compared with other vaccine formulations, while hexon protein-based vaccine formulations showed relatively lower levels of antibody responses. Thus, a vaccine formulation containing inactivated IBHV with PCEP or a mixture of PCEP and ABD2 (with a reduced dosage of PCEP) as an adjuvant may serve as a potential vaccine candidate. However, in order to overcome the risks associated with whole virus inactivated vaccines, characterization of additional viral capsid proteins, including fiber protein and penton of IBHV along with hexon protein in combination with more new generation adjuvants, will be helpful in further improvements of vaccines against IBHV infection.

Safety and Immunogenicity of a Randomized Phase 1 Prime-Boost Trial With ALVAC-HIV (vCP205) and Oligomeric Glycoprotein 160 From HIV-1 Strains MN and LAI-2 Adjuvanted in Alum or Polyphosphazene

BACKGROUND

Prime-boost regimens comprising ALVAC-HIV (prime) and human immunodeficiency virus type 1 (HIV) Env (boost) induce HIV-specific neutralizing antibody and cell-mediated immune responses, but the impact of boost schedule and adjuvant requires further definition.

METHODS

A phase 1 trial was conducted. In part A (open label), 19 volunteers received oligomeric glycoprotein 160 from HIV strains MN and LAI-2 (ogp160 MN/LAI-2) with dose escalation (25, 50, 100 μg) and either polyphosphazene (pP) or alum adjuvant. In part B, 72 volunteers received either placebo (n=12) or recombinant canarypox virus expressing HIV antigens (ALVAC-HIV [vCP205]) with different doses and schedules of ogp160 MN/LAI-2 in pP or alum (n = 60).

RESULTS

The vaccines were safe and well tolerated, with no vaccine-related serious adverse events. Anti-gp70 V1V2 antibody responses were detected in 17 of 19 part A volunteers (89%) and 10%-100% of part B volunteers. Use of a peripheral blood mononuclear cell-based assay revealed that US-1 primary isolate neutralization was induced in 2 of 19 recipients of ogp160 protein alone (10.5%) and 5 of 49 prime-boost volunteers (10.2%). Among ogp160 recipients, those who received pP were more likely than those who received alum to have serum that neutralized tier 2 viruses (12% vs 0%; P = .015).

CONCLUSIONS

Administration of ogp160 with pP induces primary isolate tier 2 neutralizing antibody responses in a small percentage of volunteers, demonstrating proof of concept and underscoring the importance of further optimization of prime-boost strategies for HIV infection prevention.

CLINICAL TRIALS REGISTRATION

NCT00004579.

Nanodisco balls: control over surface versus core loading of diagnostically active nanocrystals into polymer nanoparticles

Nanoparticles of complex architectures can have unique properties. Self-assembly of spherical nanocrystals is a high yielding route to such systems. In this study, we report the self-assembly of a polymer and nanocrystals into aggregates, where the location of the nanocrystals can be controlled to be either at the surface or in the core. These nanospheres, when surface decorated with nanocrystals, resemble disco balls, thus the term nanodisco balls. We studied the mechanism of this surface loading phenomenon and found it to be Ca(2+) dependent. We also investigated whether excess phospholipids could prevent nanocrystal adherence. We found surface loading to occur with a variety of nanocrystal types including iron oxide nanoparticles, quantum dots, and nanophosphors, as well as sizes (10-30 nm) and shapes. Additionally, surface loading occurred over a range of polymer molecular weights (∼30-3000 kDa) and phospholipid carbon tail length. We also show that nanocrystals remain diagnostically active after loading onto the polymer nanospheres, i.e., providing contrast in the case of magnetic resonance imaging for iron oxide nanoparticles and fluorescence for quantum dots. Last, we demonstrated that a fluorescently labeled protein model drug can be delivered by surface loaded nanospheres. We present a platform for contrast media delivery, with the unusual feature that the payload can be controllably localized to the core or the surface.

Phosphorous-containing polymers for regenerative medicine

Disease and injury have resulted in a large, unmet need for functional tissue replacements. Polymeric scaffolds can be used to deliver cells and bioactive signals to address this need for regenerating damaged tissue. Phosphorous-containing polymers have been implemented to improve and accelerate the formation of native tissue both by mimicking the native role of phosphorous groups in the body and by attachment of other bioactive molecules. This manuscript reviews the synthesis, properties, and performance of phosphorous-containing polymers that can be useful in regenerative medicine applications.

Polyphosphazene/nano-hydroxyapatite composite microsphere scaffolds for bone tissue engineering

The nontoxic, neutral degradation products of amino acid ester polyphosphazenes make them ideal candidates for in vivo orthopedic applications. The quest for new osteocompatible materials for load bearing tissue engineering applications has led us to investigate mechanically competent amino acid ester substituted polyphosphazenes. In this study, we have synthesized three biodegradable polyphosphazenes substituted with side groups, namely, leucine, valine, and phenylalanine ethyl esters. Of these polymers, the phenylalanine ethyl ester substituted polyphosphazene showed the highest glass transition temperature (41.6 degrees C) and, hence, was chosen as a candidate material for forming composite microspheres with 100 nm sized hydroxyapatite (nHAp). The fabricated composite microspheres were sintered into a three-dimensional (3-D) porous scaffold by adopting a dynamic solvent sintering approach. The composite microsphere scaffolds showed compressive moduli of 46-81 MPa with mean pore diameters in the range of 86-145 microm. The 3-D polyphosphazene-nHAp composite microsphere scaffolds showed good osteoblast cell adhesion, proliferation, and alkaline phosphatase expression and are potential suitors for bone tissue engineering applications.