Synthesis approaches of amphiphilic copolymers for spherical micelle preparation: application in drug delivery

The formation of polymeric micelles in aqueous environments through the self-assembly of amphiphilic polymers can provide a versatile platform to increase the solubility and permeability of hydrophobic drugs and pave the way for their administration. In comparison to various self-assembly-based vehicles, polymeric micelles commonly have a smaller size, spherical morphology, and simpler scale up process. The use of polymer-based micelles for the encapsulation and carrying of therapeutics to the site of action triggered a line of research on the synthesis of various amphiphilic polymers in the past few decades. The extended knowledge on polymers includes biocompatible smart amphiphilic copolymers for the formation of micelles, therapeutics loading and response to external stimuli, micelles with a tunable drug release pattern, etc. Different strategies such as ring-opening polymerization, atom transfer radical polymerization, reversible addition-fragmentation chain-transfer, nitroxide mediated polymerization, and a combination of these methods were employed to synthesize copolymers with diverse compositions and topologies with the proficiency of self-assembly into well-defined micellar structures. The current review provides a summary of the important polymerization techniques and recent achievements in the field of drug delivery using micellar systems. This review proposes new visions for the design and synthesis of innovative potent amphiphilic polymers in order to benefit from their application in drug delivery fields.

Polymerization-Induced Self-Assembly for Efficient Fabrication of Biomedical Nanoplatforms

Amphiphilic copolymers can self-assemble into nano-objects in aqueous solution. However, the self-assembly process is usually performed in a diluted solution (<1 wt%), which greatly limits scale-up production and further biomedical applications. With recent development of controlled polymerization techniques, polymerization-induced self-assembly (PISA) has emerged as an efficient approach for facile fabrication of nano-sized structures with a high concentration as high as 50 wt%. In this review, after the introduction, various polymerization method-mediated PISAs that include nitroxide-mediated polymerization-mediated PISA (NMP-PISA), reversible addition-fragmentation chain transfer polymerization-mediated PISA (RAFT-PISA), atom transfer radical polymerization-mediated PISA (ATRP-PISA), and ring-opening polymerization-mediated PISA (ROP-PISA) are discussed carefully. Afterward, recent biomedical applications of PISA are illustrated from the following aspects, i.e., bioimaging, disease treatment, biocatalysis, and antimicrobial. In the end, current achievements and future perspectives of PISA are given. It is envisioned that PISA strategy can bring great chance for future design and construction of functional nano-vehicles.

Triggered Polymersome Fusion

The contents of biological cells are retained within compartments formed of phospholipid membranes. The movement of material within and between cells is often mediated by the fusion of phospholipid membranes, which allows mixing of contents or excretion of material into the surrounding environment. Biological membrane fusion is a highly regulated process that is catalyzed by proteins and often triggered by cellular signaling. In contrast, the controlled fusion of polymer-based membranes is largely unexplored, despite the potential application of this process in nanomedicine, smart materials, and reagent trafficking. Here, we demonstrate triggered polymersome fusion. Out-of-equilibrium polymersomes were formed by ring-opening metathesis polymerization-induced self-assembly and persist until a specific chemical signal (pH change) triggers their fusion. Characterization of polymersomes was performed by a variety of techniques, including dynamic light scattering, dry-state/cryogenic-transmission electron microscopy, and small-angle X-ray scattering (SAXS). The fusion process was followed by time-resolved SAXS analysis. Developing elementary methods of communication between polymersomes, such as fusion, will prove essential for emulating life-like behaviors in synthetic nanotechnology.

Recent Advances in Drug Release, Sensing, and Cellular Uptake of Ring-Opening Metathesis Polymerization (ROMP) Derived Poly(olefins)

The synthesis and applications of ring-opening metathesis polymerization (ROMP) derived poly(olefins) have emerged as an exciting area of great interest in the field of biomaterials science. The major focus of this mini-review is to present recent advances in the synthesis of functional materials using ROMP-derived poly(olefins) utilized for drug release, sensing, and cellular uptake in the past seven years (2015-2022). This review reveals that materials synthesized by ROMP-derived well-defined functional poly(olefins) stand to be highly promising systems for medical as well as biological studies. Thus, this review may prove to be beneficial for the design and development of new smart and flexible-functionality ROMP-based polymeric materials for various biological applications.

(Bio)degradable and Biocompatible Nano-Objects from Polymerization-Induced and Crystallization-Driven Self-Assembly

Polymerization-induced self-assembly (PISA) and crystallization-driven self-assembly (CDSA) techniques have emerged as powerful approaches to produce a broad range of advanced synthetic nano-objects with high potential in biomedical applications. PISA produces nano-objects of different morphologies (e.g., spheres, vesicles and worms), with high solids content (∼10-50 wt %) and without additional surfactant. CDSA can finely control the self-assembly of block copolymers and readily forms nonspherical crystalline nano-objects and more complex, hierarchical assemblies, with spatial and dimensional control over particle length or surface area, which is typically difficult to achieve by PISA. Considering the importance of these two assembly techniques in the current scientific landscape of block copolymer self-assembly and the craze for their use in the biomedical field, this review will focus on the advances in PISA and CDSA to produce nano-objects suitable for biomedical applications in terms of (bio)degradability and biocompatibility. This review will therefore discuss these two aspects in order to guide the future design of block copolymer nanoparticles for future translation toward clinical applications.

Biomimetic Redox-Responsive Mesoporous Organosilica Nanoparticles Enhance Cisplatin-Based Chemotherapy

Cisplatin-based chemotherapy is dominated in several cancers; however, insufficient therapeutic outcomes and systemic toxicity hamper their clinical applications. Controlled release of cisplatin and reducing inactivation remains an urgent challenge to overcome. Herein, diselenide-bridged mesoporous organosilica nanoparticles (MON) coated with biomimetic cancer cell membrane were tailored for coordination responsive controlled cisplatin delivery and GSH depletion to strengthen Pt-based chemotherapy. Cisplatin-loaded MON (MON-Pt) showed high loading capacity due to robust coordination between selenium and platinum atoms and preventing premature leakage in normal tissue. MON-Pt exhibited a controlled release of activated cisplatin in response to the redox tumor microenvironment. Meanwhile, MON-Pt containing redox-responsive diselenide bonds could efficiently scavenge intracellular inactivation agents, such as GSH, to enhance Pt-based chemotherapy. 4T1 breast cancer cell membranes cloaked MON-Pt (MON-Pt@CM) performed efficient anticancer performance and low in vivo system toxicity due to long blood circulation time and high tumor accumulation benefiting from the tumor targeting and immune-invasion properties of the homologic cancer cell membrane. These results suggest a biomimetic nanocarrier to control release and reduce the inactivation of cisplatin for efficient and safe Pt-based chemotherapy by responding and regulating the tumor microenvironment.

Influence of Solvent on RAFT-mediated Polymerization of Benzyl Methacrylate (BzMA) and How to Overcome the Thermodynamic/Kinetic Limitation of Morphology Evolution during Polymerization-Induced Self-Assembly

Polymerization-induced self-assembly (PISA) has been demonstrated to be a powerful strategy to produce polymeric nano-objects of various morphologies. Dependent on the solubility of monomers, PISA is usually classified into two...

Post-functionalization of drug-loaded nanoparticles prepared by polymerization-induced self-assembly (PISA) with mitochondria targeting ligands

Herein, the postfunctionalization of different non-fouling PISA particles, prepared from either poly(oligo ethylene glycol methyl ether methacrylate) (pPEGMA) and the anticancer drug PENAO (4-(N-(S-penicillaminylacetyl)amino)phenylarsenonous acid) or zwitterionic 2-methacryloyloxyethyl phosphorylcholine (MPC) and PENAO were reported. Both PISA particles were reacted with triphenylphosphonium (TPP) as mitochondria targeting units in order to evaluate the changes in cellular uptake or the toxicity of the conjugated arsenic drug. Attachment of TPP onto the PISA particles however was found not to enhance the mitochondrial accumulation, but it did influence overall the biological activity of pMPC-based particles in 2D and 3D cultured sarcoma SW982 cells. When TPP was conjugated to the pMPC PISA particles more cellular uptake as well as better spheroid penetration were observed, while TPP on PEG-based PISA had only little effect. It was hypothesized that TPP on the micelle surface may not be accessible enough to allow mitochondria targeting, but more structural investigations are required to elucidate this.

Crosslinked Polydicyclopentadiene Nanoparticles via Ring-Opening Metathesis Polymerization-Induced Self-Assembly Approach

In this communication, the preparation of crosslinked polydicyclopentadiene (PDCPD) nanoparticles via ring-opening metathesis polymerization (ROMP)-induced self-assembly approach is reported. For the ROMPs, the macromolecular chain transfer agents (Macro-CTAs) are synthesized via the ring-opening polymerization (ROP) of ε-caprolactone (CL) with cis-2-butene-1,4-diol as the initiator. The ROMPs are performed with chloroform, tetrahydrofuran, toluene, 1,4-dioxane, and N,N-dimethylacetamide as the solvents, respectively, which are catalyzed with Grubbs second generation catalyst. It is found that the crosslinked PDCPD nanoparticles are obtained with spherical, cylindrical to planar morphologies, depending on the molecular weights of Macro-CTAs, the concentrations of DCPD and the natures of solvents. The polymerization induced self-assembly (ROMPISA) by the use of a non-norbornene-based macromolecular chain transfer agent provides a new and efficient approach to prepare crosslinked polymer nanoparticles.

Polymerisation-induced self-assembly (PISA) as a straightforward formulation strategy for stimuli-responsive drug delivery systems and biomaterials: recent advances

Stimuli-responsive amphiphilic block copolymers have emerged as promising nanocarriers for enhancing site-specific and on-demand drug release in response to a range of stimuli such as pH, the presence of redox agents, and temperature. The formulation of amphiphilic block copolymers into polymeric drug-loaded nanoparticles is typically achieved by various methods (e.g. oil-in-water emulsion solvent evaporation, solid dispersion, microphase separation, dialysis or microfluidic separation). Despite much progress that has been made, there remain many challenges to overcome to produce reliable polymeric systems. The main drawbacks of the above methods are that they produce very low solid contents (<1 wt%) and involve multiple-step procedures, thus limiting their scope. Recently, a new self-assembly methodology, polymerisation-induced self-assembly (PISA), has shown great promise in the production of polymer-derived particles using a straightforward one-pot approach, whilst facilitating high yield, scalability, and cost-effectiveness for pharmaceutical industry protocols. We therefore focus this review primarily on the most recent studies involved in the design and preparation of PISA-generated nano-objects which are responsive to specific stimuli, thus providing insight into how PISA may become an effective formulation strategy for the preparation of precisely tailored drug delivery systems and biomaterials, while some of the current challenges and limitations are also critically discussed.

It is Better with Salt: Aqueous Ring-Opening Metathesis Polymerization at Neutral pH

Aqueous ring-opening metathesis polymerization (ROMP) is a powerful tool for polymer synthesis under environmentally friendly conditions, functionalization of biomacromolecules, and preparation of polymeric nanoparticles via ROMP-induced self-assembly (ROMPISA). Although new water-soluble Ru-based metathesis catalysts have been developed and evaluated for their efficiency in mediating cross metathesis (CM) and ring-closing metathesis (RCM) reactions, little is known with regards to their catalytic activity and stability during aqueous ROMP. Here, we investigate the influence of solution pH, the presence of salt additives, and catalyst loading on ROMP monomer conversion and catalyst lifetime. We find that ROMP in aqueous media is particularly sensitive to chloride ion concentration and propose that this sensitivity originates from chloride ligand displacement by hydroxide or H2O at the Ru center, which reversibly generates an unstable and metathesis inactive complex. The formation of this Ru-(OH)n complex not only reduces monomer conversion and catalyst lifetime but also influences polymer microstructure. However, we find that the addition of chloride salts dramatically improves ROMP conversion and control. By carrying out aqueous ROMP in the presence of various chloride sources such as NaCl, KCl, or tetrabutylammonium chloride, we show that diblock copolymers can be readily synthesized via ROMPISA in solutions with high concentrations of neutral H2O (i.e., 90 v/v%) and relatively low concentrations of catalyst (i.e., 1 mol %). The capability to conduct aqueous ROMP at neutral pH is anticipated to enable new research avenues, particularly for applications in biological media, where the unique characteristics of ROMP provide distinct advantages over other polymerization strategies.

Drug-Directed Morphology Changes in Polymerization-Induced Self-Assembly (PISA) Influence the Biological Behavior of Nanoparticles

The effect of the hydrophobic block length on the morphologies of polymerization-induced self-assembled (PISA) nanoparticles is well understood. However, the influence of drug loading on the phase morphology of the nanoparticles during the PISA process, and the resulting biological function of PISA nanoparticles, has barely been investigated. In this work, we show that the addition of a drug, curcumin, during the PISA process shifts the phase diagram toward different morphologies. The PISA system was based on hydrophilic poly(2-(methacryloyloxy)ethylphosphorylcholine) (PMPC), which was chain extended with hydrophobic methyl methacrylate (MMA) in various concentrations of curcumin. According to transmission electron microscopy, the presence of curcumin led to the transition of, for example, worms to polymersome and micelles to worms analysis. To understand the interaction between polymer particles and drug, small-angle X-ray scattering (SAXS), small-angle neutron scattering (SANS), and fluorescence lifetime measurements were carried out. These measurements show that curcumin is predominantly located in the core in the case of micelles and worms while it is found in the shell of polymersomes. The change in morphology influences the cellular uptake by MCF-7 cells and the movement of the particles in multicellular cancer spheroids (3D model). With the increasing amount of drug, the cellular uptake of micelles and worms was enhanced with the increasing grafting density of MPC chains, which contrasts the decreasing cellular uptake in the higher drug-loaded polymersomes due to the lower shell hydration.

Poly(peptide): Synthesis, Structure, and Function of Peptide-Polymer Amphiphiles and Protein-like Polymers

In this Account, we describe the organization of functional peptides as densely arrayed side chains on polymer scaffolds which we introduce as a new class of material called poly(peptide). We describe two general classes of poly(peptide): (1) Peptide-Polymer Amphiphiles (PPAs), which consist of block copolymers with a dense grouping of peptides arrayed as the side chains of the hydrophilic block and connected to a hydrophobic block that drives micelle assembly, and (2) Protein-like Polymers (PLPs), wherein peptide-brush polymers are composed from monomers, each containing a peptide side chain. Peptides organized in this manner imbue polymers or polymeric nanoparticles with a range of functional qualities inherent to their specific sequence. Therefore, polymers or nanoparticles otherwise lacking bioactivity or responsiveness to stimuli, once linked to a peptide of choice, can now bind proteins, enter cells and tissues, have controlled and switchable biodistribution patterns, and be enzyme substrates (e.g., for kinases, phosphatases, proteases). Indeed, where peptide substrates are incorporated, kinetically or thermodynamically driven morphological transitions can be enzymatically induced in the polymeric material. Synergistically, the polymer enforces changes in peptide activity and function by virtue of packing and constraining the peptide. The scaffold can protect peptides from proteolysis, change the pharmacokinetic profile of an intravenously injected peptide, increase the cellular uptake of an otherwise cell impermeable therapeutic peptide, or change peptide substrate activity entirely. Moreover, in addition to the sequence-controlled peptides (generated by solid phase synthesis), the polymer can carry its own sequence-dependent information, especially through living polymerization strategies allowing well-defined blocks and terminal labels (e.g., dyes, contrast agents, charged moieties). Hence, the two elements, peptide and polymer, cooperate to yield materials with unique function and properties quite apart from each alone. Herein, we describe the development of synthetic strategies for accessing these classes of biomolecule polymer conjugates. We discuss the utility of poly(peptide)-based materials in a range of biomedical applications, including imaging of diseased tissues (myocardial infarction and cancer), delivering small molecule drugs to tumors with high specificity, imparting cell permeability to otherwise impermeable peptides, protecting bioactive peptides from proteolysis in harsh conditions (e.g., stomach acid and whole blood), and transporting proteins into traditionally difficult-to-transfect cell types, including stem cells. Poly(peptide) materials offer new properties to both the constituent peptides and to the polymers, which can be tuned by the design of the oligopeptide sequence, degree of polymerization, peptide arrangement on the polymer backbone, and polymer backbone chemistry. These properties establish this approach as valuable for the development of peptides as medicines and materials in a range of settings.

Polymerization techniques in polymerization-induced self-assembly (PISA)

The development of controlled/“living” polymerization greatly stimulated the prosperity of the fabrication and application of block copolymer nano-objects.

Ring-opening metathesis polymerization-induced self-assembly (ROMPISA)

Ring-opening metathesis polymerization-induced self-assembly (ROMPISA) has expanded the preparation of PISA nano-objects beyond radical polymerization approaches. In this highlight article, we summarize current advances and existing challenges in ROMPISA methodologies.