Polymersomes in Drug Delivery─From Experiment to Computational Modeling.

Polymersomes, composed of amphiphilic block copolymers, are self-assembled vesicles that have gained attention as potential drug delivery systems due to their good biocompatibility, stability, and versatility. Various experimental techniques have been employed to characterize the self-assembly behaviors and properties of polymersomes. However, they have limitations in revealing molecular details and underlying mechanisms. Computational modeling techniques have emerged as powerful tools to complement experimental studies and enabled researchers to examine drug delivery mechanisms at molecular resolution. This review aims to provide a comprehensive overview of the state of the art in the field of polymersome-based drug delivery systems, with an emphasis on insights gained from both experimental and computational studies. Specifically, we focus on polymersome morphologies, self-assembly kinetics, fusion and fission, behaviors in flow, as well as drug encapsulation and release mechanisms. Furthermore, we also identify existing challenges and limitations in this rapidly evolving field and suggest possible directions for future research.

Self-Assembly of Poly(Amino Acid)s Mediated by Secondary Conformations.

Self-assembly of block copolymers has recently drawn great attention due to its remarkable performance and wide variety of applications in biomedicine, biomaterials, microelectronics, photoelectric materials, catalysts, etc. Poly(amino acid)s (PAAs), formed by introducing synthetic amino acids into copolymer backbones, are able to fold into different secondary conformations when compared with traditional amphiphilic copolymers. Apart from changing the chemical composition and degree of polymerization of copolymers, the self-assembly behaviors of PAAs could be controlled by their secondary conformations, which are more flexible and adjustable for fine structure tailoring. In this article, we summarize the latest findings on the variables that influence secondary conformations, in particular the regulation of order-to-order conformational changes and the approaches used to manage the self-assembly behaviors of PAAs. These strategies include controlling pH, redox reactions, coordination, light, temperature, and so on. Hopefully, we can provide valuable perspectives that will be useful for the future development and use of synthetic PAAs.

Protein-Inspired Polymers with Metal-Site-Regulated Ordered Conformations.

Metal ions play critical roles in facilitating peptide folding and inducing conformational transitions, thereby impacting on the biological activity of many proteins. However, the effect of metal sites on the hierarchical structures of biopolymers is still poorly understood. Herein, inspired by metalloproteins, we report an order-to-order conformational regulation in synthetic polymers mediated by a variety of metal ions. The copolymers are decorated with clinically available desferrioxamine (DFO) as an exogenous ligand template, which presents a geometric constraint toward peptide backbone via short-range hydrogen bonding interactions, thus dramatically altering the secondary conformations and self-assembly behaviors of polypeptides and allowing for a controllable ß-sheet to α-helix transition modulated by metal-ligand interactions. These metallopolymers could form ferritin-inspired hierarchical structures with high stability and membrane activity for efficient brain delivery across the blood-brain barrier (BBB) and long-lasting magnetic resonance imaging (MRI) in vivo.

Antibacterial and Biocompatible Cross-Linked Waterborne Polyurethanes Containing Gemini Quaternary Ammonium Salts.

A cross-linked waterborne polyurethane (CPTMGPU) with long-term stability was developed from poly(ethylene glycol) (PEG), polyoxytetramethylene glycol (PTMG), isophorone diisocyanate (IPDI), l-lysine, and its derivative diamine consisting of gemini quaternary ammonium salt (GQAS), using ethylene glycol diglycidyl ether (EGDE) as a cross-linker. Weight loss test, X-ray photoelectron spectroscopy (XPS) measurements, and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) were performed to prove the surface structure and stability of these CPTMGPU films. Furthermore, the GQAS-bearing CPTMGPUs show repeatable contact-active antibacterial efficacy against both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) bacteria and do not show any inhibition effect against fibroblasts in vitro. After subcutaneous implantation in rats, the CPTMGPU films manifest good biocompatibility in vivo, despite the presence of a typical foreign body reaction toward surrounding tissues and mild systematic inflammation reaction that could be eliminated after a short implantation period, as demonstrated by histology and immunohistochemistry combined with interleukin (IL)-1ß, IL-4, IL-6, IL-10, and TNF-α analysis though enzyme-linked immunosorbent assay (ELISA) and real-time quantitative polymerase chain reaction (qRT-PCR). Therefore, these cross-linked waterborne polyurethanes hold great promise for antibacterial applications in vivo.

Simultaneous Improvement of Oxidative and Hydrolytic Resistance of Polycarbonate Urethanes Based on Polydimethylsiloxane/Poly(hexamethylene carbonate) Mixed Macrodiols.

The degradation behaviors including oxidation and hydrolysis of silicone modified polycarbonate urethanes were thoroughly investigated. These polyurethanes were based on polyhexamethylene carbonate (PHMC)/polydimethylsiloxane (PDMS) mixed macrodiols with molar ratio of PDMS ranging from 5% to 30%. It was proved that PDMS tended to migrate toward surface and even a small amount of PDMS could form a silicone-like surface. Macrophages-mediated oxidation process indicated that the PDMS surface layer was desirable to protect the fragile soft PHMC from the attack of degradative species. Hydrolysis process was probed in detail after immersing in boiling buffered water using combined analytical tools. Hydrolytically stable PDMS could act as protective shields for the bulk to hinder the chain scission of polycarbonate carbonyls whereas the hydrolysis of urethane linkages was less affected. Although the promoted phase separation at higher PDMS fractions lead to possible physical defects and mechanical compromise after degradation, simultaneously enhanced oxidation and hydrolysis resistance could be achieved for the polyurethanes with proper PDMS incorporation.

Cell internalizable and intracellularly degradable cationic polyurethane micelles as a potential platform for efficient imaging and drug delivery.

A cell internalizable and intracellularly degradable micellar system, assembled from multiblock polyurethanes bearing cell-penetrating gemini quaternary ammonium pendent groups in the side chain and redox-responsive disulfide linkages throughout the backbone, was developed for potential magnetic resonance imaging (MRI) and drug delivery. The nanocarrier is featured as a typical "cleavable core-internalizable shell-protective corona" architecture, which exhibits small size, positive surface charge, high loading capacity, and reduction-triggered destabilization. Furthermore, it can rapidly enter tumor cells and release its cargo in response to an intracellular level of glutathione, resulting in enhanced drug efficacy in vitro. The magnetic micelles loaded with superparamagnetic iron oxide (SPIO) nanoparticles demonstrate excellent MRI contrast enhancement, with T2 relaxivity found to be affected by the morphology of SPIO-clustering inside the micelle core. The multifunctional carrier with good cytocompatibility and nontoxic degradation products can serve as a promising theranostic candidate for efficient intracellular delivery of anticancer drugs and real-time monitoring of therapeutic effect.

A Drop-By-Drop Self-Assembled All-Natural Hydrogel as a Desensitizer for Rapid and Enduring Management of Dentin Hypersensitivity.

Dentin hypersensitivity (DH) is a prevalent dental condition arising from the exposure of dentin tubules (DTs), leading to discomfort upon external stimuli. However, achieving swift and profound occlusion of these exposed DTs for immediate and enduring relief remains challenging due to the intricate dentin structure and oral environment. Herein, a pioneering and facile drop-by-drop strategy involving an in situ generated natural supramolecular hydrogel formed by self-assembling silk fibroin (SF) and tannic acid (TA) within the narrow DT space is proposed. When SF and TA aqueous solutions are applied successively to exposed dentin, they penetrate deeply within DTs and coassemble into compact gels, robustly adhering to DT walls. This yields a rapid and compact occlusion effect with an unprecedented depth exceeding 250 µm, maintaining stable occlusion efficacy even under rigorous in vitro and in vivo erosion and friction conditions for no less than 21 days. Furthermore, the biocompatibility and effective occlusion properties are verified through cell studies in simulated oral settings and an in vivo rabbit model. This study, for the first time, demonstrates the translational potential of hydrogel-based desensitizers in treating DH with prompt action, superior occlusion depth and enduring treatment benefits, holding promise as clinical-friendly restorative solutions for delicate-structured biosystems.

Molecular co-assembled strategy tuning protein conformation for cartilage regeneration.

The assembly of oligopeptide and polypeptide molecules can reconstruct various ordered advanced structures through intermolecular interactions to achieve protein-like biofunction. Here, we develop a "molecular velcro"-inspired peptide and gelatin co-assembly strategy, in which amphiphilic supramolecular tripeptides are attached to the molecular chain of gelatin methacryloyl via intra-/intermolecular interactions. We perform molecular docking and dynamics simulations to demonstrate the feasibility of this strategy and reveal the advanced structural transition of the co-assembled hydrogel, which brings more ordered ß-sheet content and 10-fold or more compressive strength improvement. We conduct transcriptome analysis to reveal the role of co-assembled hydrogel in promoting cell proliferation and chondrogenic differentiation. Subcutaneous implantation evaluation confirms considerably reduced inflammatory responses and immunogenicity in comparison with type I collagen. We demonstrate that bone mesenchymal stem cells-laden co-assembled hydrogel can be stably fixed in rabbit knee joint defects by photocuring, which significantly facilitates hyaline cartilage regeneration after three months. This co-assembly strategy provides an approach for developing cartilage regenerative biomaterials.

Construction of targeting-clickable and tumor-cleavable polyurethane nanomicelles for multifunctional intracellular drug delivery.

New strategies for the construction of versatile nanovehicles to overcome the multiple challenges of targeted delivery are urgently needed for cancer therapy. To address these needs, we developed a novel targeting-clickable and tumor-cleavable polyurethane nanomicelle for multifunctional delivery of antitumor drugs. The polyurethane was synthesized from biodegradable poly(ε-caprolactone) (PCL) and L-lysine ethyl ester diisocyanate (LDI), further extended by a new designed L-cystine-derivatized chain extender bearing a redox-responsive disulfide bond and clickable alkynyl groups (Cys-PA), and finally terminated by a detachable methoxyl-poly(ethylene glycol) with a highly pH-sensitive benzoic-imine linkage (BPEG). The obtained polymers show attractive self-assembly characteristics and stimuli-responsiveness, good cytocompatibility, and high loading capacity for doxorubicin (DOX). Furthermore, folic acid (FA) as a model targeting ligand was conjugated to the polyurethane micelles via an efficient click reaction. The decoration of FA results in an enhanced cellular uptake and improved drug efficacy toward FA-receptor positive HeLa cancer cells in vitro. As a proof-of-concept, this work provides a facile approach to the design of extracellularly activatable nanocarriers for tumor-targeted and programmed intracellular drug delivery.

Redox-dual-sensitive multiblock copolymer vesicles with disulfide-enabled sequential drug delivery.

Based on disulfide-enriched multiblock copolymer vesicles, we present a straightforward sequential drug delivery system with dual-redox response that releases hydrophilic doxorubicin hydrochloride (DOX·HCl) and hydrophobic paclitaxel (PTX) under oxidative and reductive conditions, respectively. When compared to concurrent therapeutic delivery, the spatiotemporal control of drug release allows for an improved combination antitumor effect. The simple and smart nanocarrier has promising applications in the field of cancer therapy.

Photoallosteric Polymersomes toward On-Demand Drug Delivery and Multimodal Cancer Immunotherapy.

Allosteric transitions can modulate the self-assembly and biological function of proteins. It remains, however, tremendously challenging to design synthetic allosteric polymeric assemblies with spatiotemporally switchable hierarchical structures and functionalities. Here, a photoallosteric polymersome is constructed that undergoes a rapid conformational transition from ß-sheet to α-helix upon exposure to near-infrared light irradiation. In addition to improving nanoparticle cell penetration and lysosome escape, photoinduced allosteric behavior reconstructs the vesicular membrane structure, which stimulates the release of hydrophilic cytolytic peptide melittin and hydrophobic kinase inhibitor sorafenib. Combining on-demand delivery of multiple therapeutics with phototherapy results in apoptosis and immunogenic death of tumor cells, remold the immune microenvironment and achieve an excellent synergistic anticancer efficacy in vivo without tumor recurrence and metastasis. Such a light-modulated allosteric transition in non-photosensitive polymers provides new insight into the development of smart nanomaterials for biosensing and drug delivery applications.

Intrinsically fluorescent polyureas toward conformation-assisted metamorphosis, discoloration and intracellular drug delivery.

Peptidomimetic polymers have attracted increasing interest because of the advantages of facile synthesis, high molecular tunability, resistance to degradation, and low immunogenicity. However, the presence of non-native linkages compromises their ability to form higher ordered structures and protein-inspired functions. Here we report a class of amino acid-constructed polyureas with molecular weight- and solvent-dependent helical and sheet-like conformations as well as green fluorescent protein-mimic autofluorescence with aggregation-induced emission characteristics. The copolymers self-assemble into vesicles and nanotubes and exhibit H-bonding-mediated metamorphosis and discoloration behaviors. We show that these polymeric vehicles with ultrahigh stability, superfast responsivity and conformation-assisted cell internalization efficiency could act as an "on-off" switchable nanocarrier for specific intracellular drug delivery and effective cancer theranosis in vitro and in vivo. This work provides insights into the folding and hierarchical assembly of biomacromolecules, and a new generation of bioresponsive polymers and nonconventional luminescent aliphatic materials for diverse applications.

Quantitative grafting of peptide onto the nontoxic biodegradable waterborne polyurethanes to fabricate peptide modified scaffold for soft tissue engineering.

Gly-Arg-Gly-Asp-Ser-Pro (GRGDSP) peptide has frequently been used in the biomedical materials to enhance adhesion and proliferation of cells. In this work, we modified the nontoxic biodegradable waterborne polyurethanes (WBPU) with GRGDSP peptide and fabricated 3-D porous scaffold with the modified WBPU to investigate the effect of the immobilized GRGDSP peptide on human umbilical vein endothelial cells (HUVECs) adhesion and proliferation. A facile and reliable approach was first developed to quantitative grafting of GRGDSP onto the WBPU molecular backbone using ethylene glycol diglycidyl ether (EX810) as a connector. Then 3-D porous WBPU scaffolds with various GRGDSP content were fabricated by freeze-drying the emulsion. In both of the HUVECs adhesion and proliferation tests, enhanced cell performance was observed on the GRGDSP grafted scaffolds compared with the unmodified scaffolds and the tissue culture plate (TCP). The adhesion rate and proliferation rate increased with the increase of GRGDSP content in the scaffold and reached a maximum with peptide concentration of 0.85 µmol/g based on the weight of the polyurethanes. These results illustrate the necessity of the effective control of the GRGDSP content in the modified WBPU and support the potential utility of these 3-D porous modified WBPU scaffolds in the soft tissue engineering to guide cell adhesion, proliferation and tissue regeneration.

Improved in vivo stability of silicon-containing polyurethane by fluorocarbon side chain modulation of the surface structure.

As a class of widely used biomedical materials, polyurethanes suffer from their insufficient stability in vivo. Although the commercialized silicone-polyetherurethanes (SiPEUs) have demonstrated excellent biostability compared with polyetherurethanes (PEUs) for long-term implantation, the usage of polydimethylsiloxane (PDMS) inevitably decreased the mechanical properties and unexpected breaches were observed. In this study, we introduced a fluorinated diol (FDO) into SiPEU to modulate the molecular interactions and micro-separated morphology. The fluorinated silicon-containing polyurethane (FSiPEU) was achieved with desirable silicone- and fluorine-enriched surfaces and mechanical properties at a low silicon content. As evidenced by in vitro culture of macrophages and in vivo hematoxylin-eosin (H&E) staining, FSiPEU demonstrated a minimized inflammatory response. After implantation in mice for 6 months, the material was devoid of significant surface degradation and had the least chain cleavage of soft segments. The results indicate that FSiPEU could be promising candidates for long-term implantation considering the combination of biostability, biocompatibility and mechanical performances.

Synthesis, degradation, and cytotoxicity of multiblock poly(epsilon-caprolactone urethane)s containing gemini quaternary ammonium cationic groups.

Novel cationic biodegradable multiblock poly(epsilon-caprolactone urethane)s that contain gemini quaternary ammonium side groups on the hard segments were developed. To obtain these polyurethanes, a new L-lysine-derivatized diamine containing gemini quaternary ammonium side groups (GA8) was first synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectra (NMR), mass spectrometry (MS), and high-resolution mass spectra (HRMS). Then a series of gemini poly(epsilon-caprolactone urethane)s were designed and prepared using L-lysine ethyl ester diisocyanate (LDI), poly(epsilon-caprolactone) (PCL) diols, 1,4-butandiol (BDO), and GA8 and were terminated by methoxyl-poly(ethylene glycol) (m-PEG). The obtained polyurethanes were fully characterized by (1)H NMR, gel permeation chromatograph (GPC), differential scanning calorimetry (DSC), FTIR, and water contact angle (WCA) measurement. The gemini polyurethane shows a rapid rate of hydrolytic and enzymatic degradation, as demonstrated by weight loss and polarizing light microscopy (PLM) observations. In vitro cytotoxicity analysis suggests that both the polyurethanes and their degradation products do not show significant inhibition effect against fibroblasts. Our work provides a new way to synthesize nontoxic and amphiphilic multiblock polyurethanes with rapid degradation rate, and these new materials could be good candidates as biodegradable carriers for drug and gene delivery.

A novel strategy to graft RGD peptide on biomaterials surfaces for endothelization of small-diamater vascular grafts and tissue engineering blood vessel.

To improve the performance of small-diamater vascular grafts, endothelization of biomaterials surfaces and tissue engineering are more promising strategies to fabricate small-diamater vascular grafts. In this study, a Gly-Arg-Gly-Asp-Ser-Pro (GRGDSP) peptide was grafted on the surfaces of poly(carbonate urethane)s (PCUs), with photoactive 4-benzoylbenzoic acid (BBA) by UV irradiation. The photoactive peptides (BBM-GRGDSP) were synthesized with classical active ester of peptide synthesis. The modified surfaces of PCU with the photoactive RGD peptides were characterized by water contact angle measurement and X-ray Photoelectron Spectroscopy (XPS), which results suggested that the peptides were successfully grafted on the PCU surfaces. The effect of these modified surfaces on endothelial cells (ECs) adhesion and proliferation was examined over 72 h. PCU surfaces coupled with the synthetic photoactive RGD peptides, as characterized with phase contrast microscope and the metabolic activity (MTT) assay enhanced ECs proliferation and spreading with increasing concentration of RGD peptides grafted on their surfaces. Increased retention of ECs was also observed on the polymers surfaces under flow shear stress conditions. The results demonstrated that GRGDSP peptides grafted on the surfaces of polymers with photoactive 4-benzoylbenzoic acids could be an efficient method of fabrication for artificial small-diamater blood vessels. The modified polymer is expected to be used for small-diamater vascular grafts and functional tissue engineered blood vessels to improve ECs adhesion and retention on the polymer surfaces under flow shear stress conditions.

[Analysis on SNPs linked with wood properties of Populus nigra L. gene resources].

In this study, 115 Populus nigra L. collected from Europe were used as materials. They were detected for SNPs of genes linked with lignin and holocellulose (4CL, PAL and CesA2) by TaqMan technology and correlations between SNPs and wood properties (the wood speciely gravity, fiber length, fiber width, microfibre angle, lignin, holocellulose content and a-Cellulose content) were also studied. results showed that (1) 27 SNPs were obtained in the genes, such as 4CL, PAL and CesA2 associated with lignin synthesis. Among them, 17 SNPs were transition (A-G, C-T), 10 SNPs were transversion (A-C, G-C, G-T, and A-T). (2) Three of the SNPs were discriminated, a significant negative correlation between holocellulose content of four-year old P. nigra and SNP1 was detected, and contribution ratio was 11.11%. SNP2 and SNP3 had no significant correlation with wood properties. (3) Wood properties of various genotypes of SNP1 were significantly different. CC and CT genotype relative to TT genotype had larger holocellulose content. SNP1 would be an efficient marker to choose P. nigra gene resources that have larger holocellulose content.

"Click" chemistry in polymeric scaffolds: Bioactive materials for tissue engineering.

Polymeric scaffolds have attracted great interests in recent years, due to their fascination with a large variety of examples with promising utilization. Recently, extensive efforts have been devoted to the exploitation of robust and functional polymer-based biomaterial scaffolds with high efficiency. The recent entry of so-called "click" reactions that include kinds of selective and orthogonal reactions under mild conditions have generated real stimulus not only in preparing elegant bioactive materials of choice but also in making the leap to industrial scale build-up of multifunctional products. In this review paper, we account several kinds of polymeric scaffolds prepared/modified via "click" reactions, with emphasis on their synthetic/functionalized strategies, tunable properties, and biomedical applications.

Understanding the effect of alkyl chains of gemini cations on the physicochemical and cellular properties of polyurethane micelles.

Cationic gemini quaternary ammonium (GQA) has been used as a cell internalization promoter to improve the permeability of the cell membrane and enhance the cellular uptake. However, the effect of the alkyl chain length on the cellular properties of nanocarriers has not been elucidated yet. In this study, we developed a series of polyurethane micelles containing GQAs with various alkyl chain lengths. The alteration of the gemini alkyl chain length was found to change the distribution of GQA surfactants in the micellar structure and affect the surface charge exposure, stability, and the protein absorption properties of nanocarriers. Moreover, we also clarified the role of the alkyl chain length in tumor cell internalization and macrophage uptake of polyurethane micelles. This work provides a new understanding on the effect of the GQA alkyl chain length on the physicochemical and biological properties of nanomedicines, and offers guidance on the rational design of effective drug delivery systems where the issue of functional group exposure at the micellar surface should be considered.

Clickable and imageable multiblock polymer micelles with magnetically guided and PEG-switched targeting and release property for precise tumor theranosis.

Targeted delivery of therapeutics and diagnostics using nanotechnology holds great promise to minimize the side effects of conventional chemotherapy and enable specific and real-time detection of diseases. To realize this goal, we report a clickable and imageable nanovehicle assembled from multiblock polyurethanes (MPUs). The soft segments of the polymers are based on detachable poly(ethylene glycol) (PEG) and degradable poly(ε-caprolactone) (PCL), and the hard segments are constructed from lysine- and cystine-derivatives bearing reduction-responsive disulfide linkages and click-active alkynyl moieties, allowing for post-conjugation of targeting ligands via a click chemistry. It was found that the cleavage of PEG corona bearing a pH-sensitive benzoic-imine linkage (BPEG) could act as an on-off switch, which is capable of activating the clicked targeting ligands under extracellular acidic condition, followed by triggering the core degradation and payload release within tumor cells. In combination with superparamagnetic iron oxide nanoparticles (SPION) clustered within the micellar core, the MPUs exhibit excellent magnetic resonance imaging (MRI) contrast effects and T2 relaxation in vitro, as well as magnetically guided MR imaging and multimodal targeting of therapeutics to tumor precisely, leading to significant inhibition of cancer with minimal side effect. This work provides a safe and versatile platform for the further development of smart theranostic systems for potential magnetically-targeted and imaging-guided personalized medicine.