Synthesis and characterization of amphiphilic block copolymers with allyl side-groups

Tuning Net Charge in Aliphatic Polycarbonates Alters Solubility and Protein Complexation Behavior

A synthetic strategy yielded polyelectrolytes and polyampholytes with tunable net charge for complexation and protein binding. Organocatalytic ring-opening polymerizations yielded aliphatic polycarbonates that were functionalized with both carboxylate and ammonium side chains in a post-polymerization, radical-mediated thiol-ene reaction. Incorporating net charge into the polymer architecture altered the chain dimensions in phosphate buffered solution in a manner consistent with self-complexation and complexation behavior with model proteins. A net cationic polyampholyte with 5% of carboxylate side chains formed large clusters rather than small complexes with bovine serum albumin, while 50% carboxylate polyampholyte was insoluble. Overall, the aliphatic polycarbonates with varying net charge exhibited different macrophase solution behaviors when mixed with protein, where self-complexation appears to compete with protein binding and larger-scale complexation.

2,2-Bis(hydroxymethyl) propionic acid based cyclic carbonate monomers and their (co)polymers as advanced materials for biomedical applications

Designing grafted biodegradable polymers with tailored multi-functional properties is one of the most researched fields with extensive biomedical applications. Among many biodegradable polymers, polycarbonates have gained much attention due to their ease of synthesis, high drug loading, and excellent biocompatibility profiles. Among various monomers, 2,2-bis(hydroxymethyl) propionic acid (bis-MPA) derived cyclic carbonate monomers have been extensively explored in terms of their synthesis as well as their polymerization. Since the late 90s, significant advancements have been made in the design of bis-MPA derived cyclic carbonate monomers as well as in their reaction schemes. Currently, bis-MPA derived polycarbonates have taken a form of an entire platform with a multitude of applications, the latest being in the field of nanotechnology, targeted drug, and nucleic acid delivery. The present review outlines an up to date developments that have taken place in the last two decades in the design, synthesis, and biomedical applications of bis-MPA derived cyclic carbonates and their (co)polymers.

Polycarbonate-based ultra-pH sensitive nanoparticles improve therapeutic window

Stimuli-sensitive nanomaterials with cooperative response are capable of converting subtle and gradual biological variations into robust outputs to improve the precision of diagnostic or therapeutic outcomes. In this study, we report the design, synthesis and characterization of a series of degradable ultra-pH sensitive (dUPS) polymers that amplify small acidic pH changes to efficacious therapeutic outputs. A hydrolytically active polycarbonate backbone is used to construct the polymer with pH-dependent degradation kinetics. One dUPS polymer, PSC7A, can achieve activation of the stimulator of interferon genes and antigen delivery upon endosomal pH activation, leading to T cell-mediated antitumor immunity. While a non-degradable UPS polymer induces granulomatous inflammation that persists over months at the injection site, degradable PSC7A primes a transient acute inflammatory response followed by polymer degradation and complete tissue healing. The improved therapeutic window of the dUPS polymers opens up opportunities in pH-targeted drug and protein therapy.

Synthesis of Zwitterionic and Trehalose Polymers with Variable Degradation Rates and Stabilization of Insulin

Polymers that stabilize biomolecules are important as excipients in protein formulation. Herein, we describe a class of degradable polymers that have tunable degradation rates depending on the polymer backbone and can stabilize proteins to aggregation. Specifically, zwitterion- and trehalose-substituted polycaprolactone, polyvalerolactone, polycarbonate, and polylactide were prepared and characterized with regards to their hydrolytic degradation and ability to stabilize insulin to mechanical agitation during heat. Ring-opening polymerization (ROP) of allyl-substituted monomers was performed by using organocatalysis, resulting in well-defined alkene-substituted polymers with good control over molecular weight and dispersity. The polymers were then modified by using photocatalyzed thiol-ene reactions to install protein-stabilizing carboxybetaine and trehalose side chains. The resulting polymers were water-soluble and exhibited a wide range of half-lives, from 12 h to more than 3 months. The polymers maintained the ability to stabilize the therapeutic protein insulin from activity loss due to aggregation, demonstrating their potential as degradable excipients for protein formulation.

Leveraging a polycationic polymer to direct tunable loading of an anticancer agent and photosensitizer with opposite charges for chemo-photodynamic therapy

Herein, we reported a primary amine containing polycationic polymer to load an oppositely charged anticancer drug (doxorubicin, DOX) and a photosensitizer (chlorin e6, Ce6) for combinational chemo-photodynamic therapy. The electrostatic interactions as well as other multiple interactions between the polymer and payloads endowed the drug-loaded nanoparticles with excellent stability. Moreover, the electrostatic attraction between the cationic polymer and anionic Ce6 dictated that Ce6 had higher loading efficiency than DOX. DOX showed pH-responsive drug release owing to the increased solubility of protonated DOX and reduced interaction with the partially protonated polymer under acidic conditions. In contrast, Ce6 showed pH-insensitive release because of the smaller change in solubility and the intense interactions between Ce6 and the polymer. Synergistic chemo/photodynamic therapy of 4T1 cancer cells was achieved by light-triggered reactive oxygen species (ROS)-mediated enhanced cellular uptake and effective endo/lysosomal escape of drug-loaded nanoparticles. Our study demonstrated that the polycationic polymer could act as a robust carrier for differential loading and release of oppositely charged cargos for combinational therapy.

Sequence controlled copolymerization of lactide and a functional cyclic carbonate using stereoselective aluminum catalysts

Stereoselective aluminum complexes were applied for the ROP of LA and MAC producing functional copolyesters with quasi-diblock, tapered, gradient and random sequence distributions.

Recent development of functional aliphatic polycarbonates for the construction of amphiphilic polymers

Functional aliphatic polycarbonates in the construction of amphiphilic polymers are summarized in seven categories (hydrophobic, hydrophilic, or/and functional unit).

Postpolymerization Modifications of Alkene-Functional Polycarbonates for the Development of Advanced Materials Biomaterials

Functional aliphatic polycarbonates have attracted significant attention as materials for use as biomedical polymers in recent years. The incorporation of pendent functionality offers a facile method of modifying materials postpolymerization, thus enabling functionalities not compatible with ring-opening polymerization (ROP) to be introduced into the polymer. In particular, polycarbonates bearing alkene-terminated functional groups have generated considerable interest as a result of their ease of synthesis, and the wide range of materials that can be obtained by performing simple postpolymerization modifications on this functionality, for example, through radical thiol-ene addition, Michael addition, and epoxidation reactions. This review presents an in-depth appraisal of the methods used to modify alkene-functional polycarbonates postpolymerization, and the diversity of practical applications for which these materials and their derivatives have been used.

Self-assembly of pH-responsive biodegradable mixed micelles based on anionic and cationic polycarbonates for doxorubicin delivery

Poly(5-propyl-1,3-dioxan-2-one)-b-dimethylamine modified polycarbonate (PC(MPpC-MMA)) and poly(ethylene glycol)-b-carboxylated polycarbonate (PEG-PCCOOH) diblock copolymers were prepared to construct a pH responsive, highly stable and biodegradable mixed micelle. The two copolymers self-assembled into the mixed micelle in pH 7.4 PBS driven by electrostatic and hydrophobic interactions. PC(MPpC-MMA) with hydrophobic inner core was used for carrying drug and the dimethylamine part was designed as a trigger to disassemble the mixed micelle. PEG-PCCOOH could shield the positive character of the micelle which might show disadvantage to normal tissue. In addition, the free carboxyl groups could further increase the loading efficiency of positive charged drugs. The size and zeta potential of the micelle gradually decreased with increasing the molar ratio of PEG-PCCOOH to PC(MPpC-MMA). These mixed micelles could withstand high ionic strength of plasma and were rather stable for long time storage. However, via decrease of pH value from 7.4 to 5.0, they could undergo dissociation into smaller nanoparticles which were in a diameter of 20nm and showed positive surface nature. In vitro drug delivery studies showed a faster release rate at pH 5.0 than that at pH 7.4. The MTT assays demonstrated potent cytotoxic activity against HepG2 cells. All these results indicate that the newly mixed polycarbonate micelle can show great potential in biomedical field.

Core functionalization of semi-crystalline polymeric cylindrical nanoparticles using photo-initiated thiol-ene radical reactions

Sequential ring-opening and reversible addition-fragmentation chain transfer (RAFT) polymerization was used to form a triblock copolymer of tetrahydropyran acrylate (THPA), 5-methyl-5-allyloxycarbonyl-1,3-dioxan-2-one (MAC) and l-lactide. Concurrent deprotection of the THPA block and crystallization-driven self-assembly (CDSA) was undertaken and allowed for the formation of cylindrical micelles bearing allyl handles in a short outer core segment. These handles were further functionalized by different thiols using photo-initiated thiol-ene radical reactions to demonstrate that the incorporation of an amorphous PMAC block within the core does not disrupt CDSA and can be used to load the cylindrical nanoparticles with cargo.

Redox-responsive, core-crosslinked degradable micelles for controlled drug release

We developed novel redox-responsive, core-crosslinked micelles (CCLMs) via a simple, one-step click chemistry reaction.

Poly(2-ethyl-2-oxazoline)-block-polycarbonate block copolymers: from improved end-group control in poly(2-oxazoline)s to chain extension with aliphatic polycarbonate through a fully metal-free ring-opening polymerisation process

This work reports on defining optimal conditions to achieve tailored P(EtOx-co-PC) copolymers in an efficient and metal-free ring-opening polymerisation process.

Synthesis and AIE properties of PEG–PLA–PMPC based triblock amphiphilic biodegradable polymers

The synthesis of a novel AIE-active micelle based on living immortal polymerization of cyclic esters and a “click” reaction of azide functionalized TPE is described.

Aldehyde-functional polycarbonates as reactive platforms

Ozonolysis of allyl-functional polycarbonates provides aldehyde-functional polycarbonates that have potential to be reactive platforms for transformation into diverse active materials.

A microstereolithography resin based on thiol-ene chemistry: towards biocompatible 3D extracellular constructs for tissue engineering

A new class of degradable aliphatic poly(carbonate) resins for use in microstereolithographic process is described.

Transferrin-conjugated micelles: enhanced accumulation and antitumor effect for transferrin-receptor-overexpressing cancer models

As the transport protein for iron, transferrin can trigger cellular endocytosis once binding to its receptor (TfR) on the cell membrane. Using this property, we conjugated transferrin onto the surface of biodegradable polymeric micelles constructed from amphiphilic block copolymers. The core of micelle was either labeled with a near-infrared dye (NIR) or conjugated with a chemotherapeutic drug paclitaxel (PTX) to study the biodistribution or antitumor effect in nude mice bearing subcutaneous TfR-overexpressing cancers. DLS and TEM showed that the sizes of Tf-conjugated and Tf-free micelles were in the range of 85-110 nm. Confocal laser scanning microscopy and flow cytometry experiments indicated that the uptake efficiency of the micelles by the TfR-overexpressing cells was enhanced by Tf conjugation. Semiquantitative analysis of the NIR signals collected from the tumor site showed that the maximum accumulation was achieved at 28 h in the M(NIR) group, while at 22 h in Tf-M(NIR) groups; and the area under the intensity curve in the Tf-M(NIR) groups was more than that in M(NIR) group. Finally, the tumor inhibition effects of targeting micelles were studied with the gastric carcinoma model which overexpressed TfR. The analysis of tumor volumes and the observation of H&E-stained tumor sections showed that Tf-M(PTX) had the best antitumor effect compared with the control groups (saline, PTX, and M(PTX)). The results of this study demonstrated the potential application of Tf-conjugated polymeric micelles in the treatment of TfR-overexpressing cancers.

Biodegradable, multi-layered coatings for controlled release of small molecules

Incorporation of orthogonal functional groups into biodegradable polymers permits the fabrication of multi-layered thin films with improved adhesion and tunable degradation profiles. The bi-layer structure also allows for accurate control over small molecule release.

A Versatile Monomer for Preparing Well-Defined Functional Polycarbonates and Poly(ester-carbonates)

Despite the increasing demands for functional degradable biomaterials, strategies for generating materials with modular compositions and well-defined functionalities from common building blocks are still lacking. Here we report an azido-functionalized cyclic carbonate monomer, AzDXO, that exhibited controlled/"living" ring-opening polymerization kinetics under the catalysis of 1,8-diazabicyclo[5.4.0]-undec-7-ene. Homopolymerization of AzDXO and copolymerization of AzDXO with lactide resulted in polycarbonate and poly(ester-carbonates) with well-defined composition and narrow polydispersity. Further side-chain functionalizations of these polymers were accomplished under facile conditions via copper-catalyzed or copper-free strain-promoted azido-alkyne cyclcoaddition. This versatile monomer building block, obtainable in two steps without tedious purifications, provides a practical solution to the preparation of well-defined functional polycarbonates and poly(ester-carbonates).

Micellar carrier based on methoxy poly(ethylene glycol)-block-poly(epsilon-caprolactone) block copolymers bearing ketone groups on the polyester block for doxorubicin delivery

Block copolymers of Methoxy poly(ethylene glycol)-block-poly(epsilon-caprolactone) bearing ketone groups (MPEG-b-P(CL-co-OPD)) are synthesized and evaluated for its potential to form micelles containing doxorubicin (DOX), a representative anticancer drug, by using an in vitro method based on membrane dialysis to emulate drug release in vivo. The (1)H NMR spectra of the prepared block copolymers in D(2)O solution exhibit peaks due to the P(OPD-co-CL) in decreased intensity, indicates that the polymers form micelle particles containing the hydrophilic segments in their external parts. The CMC of the copolymer decrease with an increase in the content of ketone groups in the hydrophobic chain. Drug-free and drug-loaded solutions of structurally related copolymers indicate the polymeric aggregation into micellar-type constructs. The size of the drug-loaded micelles is found to be larger than corresponding drug-free micelles. The release rate of MPEG-b-PCL micelles is faster than MPEG-b-P(OPD-co-CL) micelles in pH 7.4 buffered solution and they have a similar release rate in pH 5.0 buffered solution. This study, therefore, confirms the potential of a novel functional block copolymers, Methoxy poly(ethylene glycol)-block-poly(epsilon-caprolactone) bearing ketone Groups, for the formation of polymeric micelles for drug delivery.