Novel Thermoresponsive Polymers Having Biodegradable Phosphoester Backbones

Advanced Biomaterials Derived from Functional Polyphosphoesters: Synthesis, Properties, and Biomedical Applications

Polyphosphoesters (PPEs) represent an innovative class of biodegradable polymers, with the phosphate ester serving as the core repeating unit of their polymeric backbone. Recently, biomaterials derived from functionalized PPEs have garnered significant interest in biomedical applications because of their commendable biocompatibility, biodegradability, and the capacity for functional modification. This review commences with a brief overview of synthesis methodologies and the distinctive properties of PPEs, including thermoresponsiveness, degradability, stealth effect, and biocompatibility. Subsequently, the review delves into the latest applications of PPEs-based nanocarriers for drug or gene delivery and PPEs-based polymeric prodrugs and scaffolds in the biomedical field, presenting several illustrative examples for each application. By encapsulating the advancements of recent years, this review aims to offer an enhanced understanding and serve as a reference for the synthesis and biomedical applications of functional PPEs.

Fully Degradable Polyphosphoester Cubosomes for Sustainable Agrochemical Delivery

Microplastic pollution and the urgent need for sustainable agriculture have raised interest in developing degradable carriers for controlled agrochemical release. Porous polymeric particles are particularly promising due to their unique release profiles compared to solid or core-shell carriers. However, creating degradable, mesoporous (2-50 nm) microparticles is challenging, and their potential for agrochemical delivery is largely unexplored. A straightforward self-assembly method is demonstrated for fully degradable porous polymer cubosomes (PCs), showcasing their ability to load and release agrochemicals. Using fully degradable block copolymers (BCPs), poly(ethyl ethylene phosphate)-b-polylactide (PEEP-b-PLA), PCs are synthesized in water with high inner order and open pores averaging 19 ± 3 nm in diameter. During the self-assembly process in the presence of the hydrophobic fungicide tebuconazole, polymersomes transform into PCs by enriching the hydrophobic polymer domain and altering the BCP packing parameter. After self-assemby, highly porous and fungicide-loaded PCs are obtained. Fungicide-loaded PCs show high antimycotic activity against Botrytis cinerea (grey mold), adhere to Vitis vinifera Riesling leaves even after simulated rain, and release the fungicide continuously over several days with different release-kinetics compared to solid particles. PCs hydrolyze completely into lactic acid and phosphate derivatives, highlighting their potential as microplastic-free agrochemical delivery systems for sustainable agriculture.

Thermoresponsive Polyphosphoester via Polycondensation Reactions: Synthesis, Characterization, and Self-Assembly

Using a novel strategy, amphiphilic polyphosphoesters based on poly(oxyethylene H-phosphonate)s (POEHP) with different poly(ethylene glycol) segment lengths and aliphatic alcohols with various alkyl chain lengths were synthesized using polycondensation reactions. They were characterized by ¹H NMR, ¹³C {H} NMR ³¹P NMR, IR, and size exclusion chromatography (SEC). The effects of the polymer structure on micelle formation and stability, micelle size, and critical micelle temperature were studied via dynamic light scattering (DLS). The hydrophilic/hydrophobic balance of these polymers can be controlled by changing the chain lengths of hydrophilic PEG and hydrophobic alcohols. A solubilizing test, using Sudan III, revealed that hydrophobic substances can be incorporated inside the hydrophobic core of polymer associates. Loading capacity depends on the length of alkyl side chains. The results obtained indicate that these structurally flexible polymers have the potential as drug carriers.

DBU and TU synergistically induced ring-opening polymerization of phosphate esters: a mechanism study

Biocompatible and biodegradable polyphosphoesters derived from the ring-opening polymerization (ROP) of phosphate esters have drawn increasing attention because of their potential applications in clinical and therapeutic fields.

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.

Surface Grafting Polyphosphoesters on Cellulose Nanocrystals To Improve the Emulsification Efficacy

Particle-stabilized emulsion systems have been developed to address the problematic properties of conventional surfactants. However, the nature and properties of the fine particles used in such systems remain a critical issue for stability enhancement. Herein, we describe a thermoswitchable oil-in-water (O/W) particle-stabilized emulsion that exhibits improved stability due to the addition of cellulose nanocrystals (CNCs) modified with poly[2-isopropoxy-2-oxo-1,3,2-dioxaphospholane] (PIPP), which exhibits relatively good biocompatibility and biodegradability. Various parameters, such as surface activity, concentration of particles, polarity of solvents, and temperatures, on the formation of emulsions with CNCs grafted with PIPP (CNC-g-PIPP) were investigated. Results showed that the surface activity of CNC-g-PIPP was significantly improved compared with the unmodified material. Heptane-in-water particle-stabilized emulsions with CNC-g-PIPP were stably formed, and the effect of temperature on the stability of the emulsions was characterized. CNC-g-PIPP exhibited function as an effective particulate emulsifier at 4 °C because of the strong adsorption at the oil-water interface. However, the emulsions rapidly disintegrated at 45 °C, which is above the low critical solution temperature of PIPP on CNC, as the hydrophobized CNC-g-PIPP desorbed from the oil-water interface. Based on these findings, a thermally induced reversible emulsification/demulsification was presented. The resulting switchable particle-stabilized emulsion based on CNC-g-PIPP shows promise for the ability to control the stability of an emulsion in response to temperature, which is attractive for use in biological applications.

Phosphodiester Hydrogels for Cell Scaffolding and Drug Release Applications

Given the major structural role phosphodiesters play in the organism it is surprising they have not been more widely adopted as a building block in sophisticated biomimetic hydrogels and other biomaterials. The potential benefits are substantial: phosphoester-based materials show excellent compatibility with blood, cells, and a remarkable resistance to protein adsorption that may trigger a foreign-body response. In this work, a novel class of phosphodiester-based ionic hydrogels is presented which are crosslinked via a phosphodiester moiety. The material shows good compatibility with blood, supports the growth and proliferation of tissue and presents opportunities for use as a drug release matrix as shown with fluorescent model compounds. The final gel is produced via base-induced elimination from a phosphotriester precursor, which is made by the free-radical polymerization of a phosphotriester crosslinker. This crosslinker is easily synthesized via multigram one-pot procedures out of common laboratory chemicals. Via the addition of various comonomers the properties of the final gel may be tuned leading to a wide range of novel applications for this exciting class of materials.

Stimuli-Responsive Phosphorus-Based Polymers

This microreview details recent developments in stimuli-responsive polymers with phosphorus in the main-chain, in particular polyphosphazenes and polyphosphoesters. The presence of phosphorus in the polymers endows unique properties onto the macromolecules, which can be utilized for the preparation of materials capable of physically responding to specific stimuli. Achieving the desired responsiveness has been much facilitated by recent developments in synthetic polymer chemistry, in particular controlled synthesis and backbone functionalization phosphorus-based polymers, in order to achieve the required properties and hence responsiveness of the materials. The development of phosphorus-based polymers which respond to the most important stimuli are discussed, namely, pH, oxidation, reduction, temperature and biological triggers. The polymers are placed in the context not just of each other but also with reference to state-of-the-art organic polymers.

Thermo-Responsive Graphene Oxide/Poly(Ethyl Ethylene Phosphate) Nanocomposite via Ring Opening Polymerization

An efficient strategy for growing thermo-sensitive polymers from the surface of exfoliated graphene oxide (GO) is reported in this article. GO sheets with hydroxyls and epoxy groups on the surface were first prepared by modified Hummer's method. Epoxy groups on GO sheets can be easily modified through ring-opening reactions, involving nucleophilic attack by tris(hydroxymethyl) aminomethane (TRIS). The resulting GO-TRIS sheets became a more versatile precursor for next ring opening polymerization (ROP) of ethyl ethylene phosphate (EEP), leading to GO-TRIS/poly(ethyl ethylene phosphate) (GO-TRIS-PEEP) nanocomposite. The nanocomposite was characterized by ¹H NMR, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), differential thermal gravity (DTG), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Since hydrophilic PEEP chains make the composite separate into single layers through hydrogen bonding interaction, the dispersity of the functionalized GO sheets in water is significantly improved. Meanwhile, the aqueous dispersion of GO-TRIS-PEEP nanocomposite shows reversible temperature switching self-assembly and disassembly behavior. Such a smart graphene oxide-based hybrid material is promising for applications in the biomedical field.

Bone-targeting poly(ethylene sodium phosphate)

Poly(ethylene sodium phosphate) (PEP·Na) showed excellent cytocompatibility and in vivo bone affinity. Moreover, PEP·Na did not interact with thrombin, which is a coagulation-related protein. Because immobilization of therapeutic agents and imaging probes on PEP·Na is easily performed, PEP·Na is a promising polymer for bone-targeted therapies.

Transiently thermoresponsive polymers and their applications in biomedicine

The focus of this review is on the class of transiently thermoresponsive polymers. These polymers are thermoresponsive, but gradually lose this property upon chemical transformation - often a hydrolysis reaction - in the polymer side chain or backbone. An overview of the different approaches used for the design of these polymers along with their physicochemical properties is given. Their amphiphilic properties and degradability into fully soluble compounds make this class of responsive polymers attractive for drug delivery and tissue engineering applications. Examples of these are also provided in this review.

High definition polyphosphoesters: between nucleic acids and plastics

Nucleic acids and synthetic polyphosphoester materials have been distinct fields – this review shows how these areas now comprise a continuum.

Synthesis of multi-arm star thermo-responsive polymers and topology effects on phase transition

Linear and star thermo-responsive polymers of poly(N-acryloylsarcosine methyl ester) [(PNASME)_n] and poly(N-isopropylacrylamide) [(PNIPAM)_n] with arm number n = 1, 2, 3 and 4 were synthesized following a core-first method via solution RAFT polymerization employing a series of mono- and multi-functional chain transfer agents.

Dipicolylamine Functionalized Polyfluorene Based Gel with Lower Critical Solution Temperature: Preparation, Characterization, and Application

A thermoresponsive fluorescent polymer gel with lower critical solution temperature (LCST) phase transition has been prepared by cooperating conjugated fluorene homopolymer poly(2,7-(9,9-di(8-di(2-picolyl)aminooctyl))fluorene) (PPAOF) and small organic dye sulforhodamine B (SRB) or its sodium salt (SRB-Na). The sol-gel phase transition originates from the electrostatic interactions between the protonated pyridyl/amino groups in PPAOF and the sulfonic groups in the organic dye molecules, as revealed by FTIR, variable-temperature ¹H NMR spectroscopies, and cyclic voltammetry measurements. Consequently, the LCST value can be finely controlled by simply tuning the component concentrations. Moreover, due to the inefficient energy transfer, the resulting fluorescent polymer gel exhibits two independent emission bands at 440 and 577 nm, assigned to the characteristic emissions from fluorene homopolymer and organic dye, respectively. Furthermore, this fluorescent polymer gel exhibits a reversible electrofluorochromic (EFC) property with high fluorescence contrast when it is assembled in a single-layer supporting electrolyte-free EFC device. Most interestingly, different fluorescence colors can be achieved from the two electrodes of the device. Our findings may present a new way to design conjugated polymer based LCST gels and EFC materials.

Controlled ring-opening polymerisation of cyclic phosphates, phosphonates and phosphoramidates catalysed by heteroleptic BHT-alkoxy magnesium complexes

BHT-Mg-alkoxides are readily available and effective ROP catalysts for cyclic ethylene phosphate monomers and outperform conventional organocatalysts in versatility.

Treatment of otitis media by transtympanic delivery of antibiotics

Otitis media is the most common reason U.S. children receive antibiotics. The requisite 7- to 10-day course of oral antibiotics can be challenging to deliver in children, entails potential systemic toxicity, and encourages selection of antimicrobial-resistant bacteria. We developed a drug delivery system that, when applied once to the tympanic membrane through the external auditory canal, delivers an entire course of antimicrobial therapy to the middle ear. A pentablock copolymer poloxamer 407-polybutylphosphoester (P407-PBP) was designed to flow easily during application and then to form a mechanically strong hydrogel on the tympanic membrane. U.S. Food and Drug Administration-approved chemical permeation enhancers within the hydrogel assisted flux of the antibiotic ciprofloxacin across the membrane. This drug delivery system completely eradicated otitis media from nontypable Haemophilus influenzae (NTHi) in 10 of 10 chinchillas, whereas only 62.5% of animals receiving 1% ciprofloxacin alone had cleared the infection by day 7. The hydrogel system was biocompatible in the ear, and ciprofloxacin was undetectable systemically (in blood), confirming local drug delivery and activity. This fast-gelling hydrogel could improve compliance, minimize side effects, and prevent systemic distribution of antibiotics in one of the most common pediatric illnesses, possibly minimizing the development of antibiotic resistance.

Anti-Resorptive Functions of Poly(ethylene sodium phosphate) on Human Osteoclasts

Osteoporosis involves hyperactive osteoclasts. A large number of current drugs result in side effects affecting their efficacy in the clinic. Polyphosphoesters are unique polymeric biomaterials because of their biocompatibility, biodegradability, and bone affinity. We studied the viability and ability of human osteoclasts to resorb bone when dosed with poly(ethylene sodium phosphate) (PEP·Na). This did not trigger any change in osteoblast cell viability, however the polymer diminished human osteoclasts and their ability to resorb bone at concentrations as low as 10(-4) m · mL(-1). This is the first report to validate the possibility of using polyphosphoesters for selective inhibition of human osteoclast functions, indicating its potential to be used as an effective polymer prodrug for treatment of osteoporosis.

Synthesis, characterization and micellization of amphiphilic polyethylene-b-polyphosphoester block copolymers

Amphiphilic polyethylene-block-polyphosphoester (PE-b-PPE) copolymers can self-assemble into spherical micelles in aqueous solution and efficiently carry paclitaxel (PTX) drug.

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.

Water-Soluble Poly(phosphonate)s via Living Ring-Opening Polymerization

A small difference brings high control: In poly(phosphonate)s a stable carbon-phosphorus linkage attaches a side chain to a degradable poly(phosphoester)-backbone. A novel cyclic phosphonate monomer was developed to generate water-soluble aliphatic poly(ethylene methylphospho-nate)s. The monomer is accessible via a robust three-step protocol that can be easily scaled-up. Polymerization was initiated by a primary alcohol, mediated by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in less than 2 h at 0 °C. The molecular weight distributions were monomodal and very narrow (below 1.1) in all cases and molecular weights up to about 20000 g/mol have been prepared, proving the living nature of this polymerization. The resulting polymers were characterized in detail via NMR spectroscopy, size exclusion chromatography, and differential scanning calorimetry. Also, the reaction kinetics have been evaluated for several monomer/initiator ratios and found to guarantee a living behavior in all cases superior to other poly(phosphate)s reported earlier. The polymers are all highly water-soluble without a lower critical solution temperature and are nontoxic against HeLa cells.