pH-Sensitive Vesicles Formed by Amphiphilic Grafted Copolymers with Tunable Membrane Permeability for Drug Loading/Release: A Multiscale Simulation Study

Coarse-grained modeling and dynamics tracking of nanoparticles diffusion in human gut mucus

The gastrointestinal (GI) tract's mucus layer serves as a critical barrier and a mediator in drug nanoparticle delivery. The mucus layer's diverse molecular structures and spatial complexity complicates the mechanistic study of the diffusion dynamics of particulate materials. In response, we developed a bi-component coarse-grained mucus model, specifically tailored for the colorectal cancer environment, that contained the two most abundant glycoproteins in GI mucus: Muc2 and Muc5AC. This model demonstrated the effects of molecular composition and concentration on mucus pore size, a key determinant in the permeability of nanoparticles. Using this computational model, we investigated the diffusion rate of polyethylene glycol (PEG) coated nanoparticles, a widely used muco-penetrating nanoparticle. We validated our model with experimentally characterized mucus pore sizes and the diffusional coefficients of PEG-coated nanoparticles in the mucus collected from cultured human colorectal goblet cells. Machine learning fingerprints were then employed to provide a mechanistic understanding of nanoparticle diffusional behavior. We found that larger nanoparticles tended to be trapped in mucus over longer durations but exhibited more ballistic diffusion over shorter time spans. Through these discoveries, our model provides a promising platform to study pharmacokinetics in the GI mucus layer.

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.

Co-assembly of Amphiphilic Triblock Copolymers with Nanodrugs and Drug Release Kinetics in Solution

Polymeric vesicles present great potential in disease treatment as they can be featured as a structurally stable and easily functionalized drug carrier that can simultaneously encapsulate multiple drugs and release them on-demand. Based on the dissipative particle dynamics (DPD) simulation, the drug-loaded vesicles were designed by the co-assembly process of linear amphiphilic triblock copolymers and hydrophobic nanodrugs in solvents, and most importantly, the drug release behavior of drug-loaded vesicles were intensively investigated. The drug-loaded aggregates, such as vesicles, spherical micelles, and disk-like micelles, were observed by varying the size and concentration of nanodrugs and the length of the hydrophobic block. The distribution of nanodrugs in the vesicles was intensively analyzed. As the size of the nanodrugs increases, the localization of nanodrugs change from being unable to fully wrap in the vesicle wall to the uniform distribution and finally to the aggregation in the vesicles at the fixed concentration of nanodrugs. The membrane thickness of the drug-loaded polymeric vesicle can be increased, and the nanodrugs localized closer to the center of the vesicle by increasing the length of the hydrophobic block. The nanodrugs will be released from vesicles by varying the interactions between the nanodrug and the solvent or the hydrophobic block and the solvent, respectively. We found that the release kinetics conforms to the first-order kinetic model, which can be used to fit the cumulative release rate of nanodrugs over time. The results showed that increasing the size of nanodrugs, the length of hydrophobic block, and the interaction parameters between the hydrophobic block and the solvent will slow down the release rate of the nanodrug and change the drug release process from monophasic to biphasic release model.

A dissipative particle dynamics simulation of controlled loading and responsive release of theranostic agents from reversible crosslinked triblock copolymer vesicles

To control the transport stability and release efficiency of loaded theranostic drugs in triblock copolymer carriers, the reversible crosslinking ability is of great significance. A molecular level exploration of such a function is needed to extend existing stabilizing and responsive dissociation mechanisms of carriers. Here, dissipative particle dynamics simulations were used to first demonstrate the formation of triblock copolymer vesicular carriers. Chemical crosslinking was used to strengthen the structural stability of the vesicle shell to avoid drug leakage. Reversible decrosslinking along with dissociation of the vesicle and release of loaded drugs were then explored. The structural, energetic and dynamical properties of the system were discussed at the molecular level. The regulation mechanism of drug release patterns was revealed by systematically exploring the effect of intra and intermolecular repulsive interactions. The results indicate that the chemical crosslinking of copolymers enhanced the compactness of the vesicle shell with a strengthened microstructure, increased binding energy, and limited chain migration, thus achieving more stable delivery of drugs. In terms of drug release, we clarified how the pairwise interactions of beads in the solution system affect the responsive dissociation of the vesicle and associated release patterns (speed and amount) of drugs. More efficient delivery and smart release of theranostic drugs are achieved using such reversible crosslinked triblock copolymer vesicles.

Functional insulin aspart/insulin degludec-based microneedles for promoting postprandial glycemic control

Insulin aspart (IAsp) and insulin degludec (IDeg), as the third generation of insulin, have a faster onset time or a more durable action period, which may simulate the secretion of insulin under physiological conditions. Microneedles (MNs) are transdermal delivery devices that may allow diabetic patients to easily deploy transdermal insulin therapy while considerably reducing injection pain. In this study, we investigated the combination of dissolving MNs with IAsp or IDeg therapy as an alternative to daily multiple insulin injections, aiming to improve glycemic control and patient compliance. Mechanical properties of the MNs, structural stability of insulin encapsulated in the MNs, and transdermal application characteristics were studied to assess the practicality of insulin-loaded MNs for diabetes therapy. In vivo experiments conducted on diabetic rats demonstrated that the IAsp- and IDeg-loaded MNs have comparable blood glucose control abilities to that of subcutaneous injections. In addition, the therapeutic properties of insulin-loaded MNs under diverse dietary conditions and application strategies were further investigated to provide new information to support future clinical trials. Taken together, the proposed MNs have the potential to improve balances between glycemic control, hypoglycemia risk, and convenience, providing patients with simpler regimens. STATEMENT OF SIGNIFICANCE: 1. The fabricated functional insulin-loaded dissolving microneedles closely matched the glucose rise that occurs in response to meals, demonstrating promising alternatives for multiple daily insulin injections. 2. The hypoglycemic properties of insulin microneedles were investigated under diverse dietary conditions and application strategies, yielding new information to support future clinical trials. 3. Molecular dynamics simulations were utilized to study the interactions between the insulin and microneedle matrix materials, providing a strategy for theoretically understanding drug stability as well as the release mechanism of drug-loaded microneedles.

Exploring conformations of comb-like polymers with varying grafting density in dilute solutions

Comb-like polymers have shown potential as advanced materials for a diverse palette of applications due to the tunability of their polymer architecture. To date, however, it still remains a challenge to understand how the conformational properties of these polymers arise from the interplay of their architectural parameters. In this work, extensive simulations were performed using dissipative particle dynamics to investigate the effect of grafting density, backbone length, and sidechain length on the conformations of comb-like polymers immersed in a good solvent. To quantify the effect of these architectural parameters on polymer conformations, we computed the asphericity, radius of gyration, and backbone and sidechain end-to-end distances. Bond-bond correlation functions and effective Kuhn lengths were computed to quantify the topological stiffness induced by sidechain-sidechain interactions. Simulation results reveal that the effective Kuhn length increases as grafting density and sidechain length increase, in agreement with previous experimental and theoretical studies. This increase in stiffness results in comb-like polymers adopting extended conformations as grafting density and sidechain length increase. Simulation results regarding the radius of gyration of comb-like polymers as a function of grafting density are compared with scaling theory predictions based on a free energy proposed by Morozova and Lodge [ACS Macro Lett. 6, 1274-1279 (2017)] and scaling arguments by Tang et al. [Macromolecules 55, 8668-8675 (2022)].

Redox-Responsive Polymersomes as Smart Doxorubicin Delivery Systems

Stimuli-responsive polymersomes have emerged as smart drug delivery systems for programmed release of highly cytotoxic anticancer agents such as doxorubicin hydrochloride (Dox·HCl). Recently, a biodegradable redox-responsive triblock copolymer (mPEG–PDH–mPEG) was synthesized with a central hydrophobic block containing disulfide linkages and two hydrophilic segments of poly(ethylene glycol) methyl ether. Taking advantage of the self-assembly of this amphiphilic copolymer in aqueous solution, in the present investigation we introduce a solvent-exchange method that simultaneously achieves polymersome formation and drug loading in phosphate buffer saline (10 mM, pH 7.4). Blank and drug-loaded polymersomes (5 and 10 wt.% feeding ratios) were prepared and characterized for morphology, particle size, surface charge, encapsulation efficiency and drug release behavior. Spherical vesicles of uniform size (120–190 nm) and negative zeta potentials were obtained. Dox·HCl was encapsulated into polymersomes with a remarkably high efficiency (up to 98 wt.%). In vitro drug release studies demonstrated a prolonged and diffusion-driven release at physiological conditions (~34% after 48 h). Cleavage of the disulfide bonds in the presence of 50 mM glutathione (GSH) enhanced drug release (~77%) due to the contribution of the erosion mechanism. Therefore, the designed polymersomes are promising candidates for selective drug release in the reductive environment of cancer cells.

Using Amphiphilic Polymer Micelles as the Templates of Antisolvent Crystallization to Produce Drug Nanocrystals

Biocompatible and biodegradable amphiphilic polymeric micelles (PLA-CMCS-g-OA) were prepared by surface grafting of oleic acid and polylactic acid onto carboxymethyl chitosan and were used as templates for the crystallization of camptothecin. The camptothecin (CPT) nanocrystals prepared by the novel micelle-templated antisolvent crystallization (mt-ASC) method demonstrated higher crystallinity, narrower particle size distribution, and slower release characteristic than those prepared by conventional antisolvent crystallization (c-ASC) using a high initial concentration and fast addition rate. In particular, the CPT release behavior of mt-ASC products in phosphate buffer solutions presented a pH-responsive characteristic with the increasing release rate of CPT under lower pH conditions. This work confirmed that amphiphilic nanomicelle-templated crystallization was an effective method for preparing drug nanocrystals.

Mesoscale Modeling of Agglomeration of Molecular Bottlebrushes: Focus on Conformations and Clustering Criteria

Using dissipative particle dynamics, we characterize dynamics of aggregation of molecular bottlebrushes in solvents of various qualities by tracking the number of clusters, the size of the largest cluster, and an average aggregation number. We focus on a low volume fraction of bottlebrushes in a range of solvents and probe three different cutoff criteria to identify bottlebrushes belonging to the same cluster. We demonstrate that the cutoff criteria which depend on both the coordination number and the length of the side chain allows one to correlate the agglomeration status with the structural characteristics of bottlebrushes in solvents of various qualities. We characterize conformational changes of the bottlebrush within the agglomerates with respect to those of an isolated bottlebrush in the same solvents. The characterization of bottlebrush conformations within the agglomerates is an important step in understanding the relationship between the bottlebrush architecture and material properties. An analysis of three distinct cutoff criteria to identify bottlebrushes belonging to the same cluster introduces a framework to identify both short-lived transient and long-lived agglomerates; the same approach could be further extended to characterize agglomerates of various macromolecules with complex architectures beyond the specific bottlebrush architecture considered herein.

DPD Modelling of the Self- and Co-Assembly of Polymers and Polyelectrolytes in Aqueous Media: Impact on Polymer Science

This review article is addressed to a broad community of polymer scientists. We outline and analyse the fundamentals of the dissipative particle dynamics (DPD) simulation method from the point of view of polymer physics and review the articles on polymer systems published in approximately the last two decades, focusing on their impact on macromolecular science. Special attention is devoted to polymer and polyelectrolyte self- and co-assembly and self-organisation and to the problems connected with the implementation of explicit electrostatics in DPD numerical machinery. Critical analysis of the results of a number of successful DPD studies of complex polymer systems published recently documents the importance and suitability of this coarse-grained method for studying polymer systems.

Interplay of distributions of multiple guest molecules in block copolymer micelles: A dissipative particle dynamics study

HYPOTHESIS

Delivery of multiple payloads using the same micelle is of significance to achieve multifunctional or synergistic effects. The interacting distribution of different payloads in micelles is expected to influence the loading stability and capacity. It is highly desirable to explore how intermolecular interactions affect the joint distribution of multi-payloads.

EXPERIMENTS

Dissipative Particle Dynamics simulations were performed to probe the loading of three payloads: decane with a linear carbon chain, butylbenzene with an aromatic ring connected to carbon chain, and naphthalene with double aromatic rings, within poly(β-amino ester)-b-poly(ethylene glycol) micelles. Properties of core-shell micelles, e.g., morphological evolution, radial density distribution, mean square displacement, and contact statistics, were analyzed to reveal payloads loading stability and capacity. Explorations were extended to vesicular, multi-compartment, double helix, and layer-by-layer micelles with more complex inner structures.

FINDINGS

Different payloads have their own preferred locations. Decane locates at the hydrophilic/hydrophobic interface, butylbenzene occupies both the hydrophilic/hydrophobic interface and the hydrophobic core, while naphthalene enters the hydrophobic core. More efficient delivery of multi-payloads is achieved since the competition of payloads occupying preferred locations is minimized. The fusion of micelles encapsulating different payloads suggests that specific payloads will move to their preferred positions without interfering other payloads.

Poly(amino ester)-Based Polymers for Gene and Drug Delivery Systems and Further Application toward Cell Culture System

Various synthetic polymers based on poly(amino ester) (PAE) are suggested as candidates for gene and drug delivery owing to their pH-responsiveness, which contributes to efficient delivery performance. PAE-based pH-responsive polymers are more biodegradable and hydrophilic than other types of pH-responsive polymers. The functionality of PAE-based polymers can be reinforced by using different chemical modifications to improve the efficiency of gene and drug delivery. Additionally, PAE-based polymers are used in many ways in the biomedical field, such as in transdermal delivery and stem cell culture systems. Here, the recent novel PAE-based polymers designed for gene and drug delivery systems along with their further applications toward adult stem cell culture systems are reviewed. The synthetic tactics are contemplated and pros and cons of each type of polymer are analyzed, and detailed examples of the different types are analyzed.

Computer Simulations on a pH-Responsive Anticancer Drug Delivery System Using Zwitterion-Grafted Polyamidoamine Dendrimer Unimolecular Micelles

Unimolecular micelles have attracted wide attention in the field of drug delivery because of their thermodynamic stability and uniform size distribution. However, their drug loading/release mechanisms at the molecular level have been poorly understood. In this work, the stability and drug loading/release behaviors of unimolecular micelles formed using generation-5 polyamidoamine-graft-poly(carboxybetaine methacrylate) (PAMAM(G5)-PCBMA) were studied by dissipative particle dynamics simulations. In addition, the unimolecular micelles formed using generation-5 polyamidoamine-graft-poly(ethyleneglycol methacrylate) (PAMAM(G5)-PEGMA) were used as a comparison. The simulation results showed that PAMAM(G5)-PCBMA can spontaneously form core-shell unimolecular micelles. The PAMAM(G5) dendrimer constitutes a hydrophobic core to load the doxorubicin (DOX), while the zwitterionic PCBMA serves as a protective shell to improve the stability of the unimolecular micelle. The DOX can be encapsulated into the cavity of PAMAM(G5) at the physiological pH 7.4. The drug loading efficiency and drug loading content showed some regularities with the increase in the drug concentration. At the acidic pH 5.0, the loaded DOX can be released gradually from the hydrophobic core. The comparison of DOX-loaded morphologies between the PAMAM(G5)-PCBMA system and PAMAM(G5)-PEGMA system showed that the former has better monodisperse stability. This work could offer theoretical guidance for the design and development of promising unimolecular micelles for drug delivery.

Using reactive dissipative particle dynamics to understand local shape manipulation of polymer vesicles

Biological cells have long been of interest to researchers due to their capacity to actively control their shape. Accordingly, there is significant interest in generating simplified synthetic protocells that can alter their shape based on an externally or internally generated stimulus. To date, most progress has been made towards controlling the global shape of a protocell, whereas less is known about generating a local shape change. Here, we seek to better understand the possible mechanisms for producing local morphological changes in a popular protocell system, the block copolymer vesicle. Accordingly, we have combined Dissipative Particle Dynamics (DPD) and the Split Reactive Brownian Dynamics algorithm (SRBD) to produce a simulation tool that is capable of modeling the dynamics of self-assembled polymer structures as they undergo chemical reactions. Using this Reactive DPD or RDPD method, we investigate local morphological change driven by either the microinjection of a stimulus or an enzymatically-produced stimulus. We find that sub-vesicle-scale morphological change can be induced by either a solvent stimulus that swells the vesicle membrane, or by a reactant stimulus that alters the chemistry of the block polymer in the membrane corona. Notably, the latter method results in a more persistent local deformation than the former, which we attribute to the slower diffusion of polymer chains relative to the solvent. We quantify this deformation and show that it can be modulated by altering the interaction parameter of the parts of the polymer chain that are affected by the stimulus.

Mechanistic Understanding From Molecular Dynamics Simulation in Pharmaceutical Research 1: Drug Delivery

In this review, we outline the growing role that molecular dynamics simulation is able to play as a design tool in drug delivery. We cover both the pharmaceutical and computational backgrounds, in a pedagogical fashion, as this review is designed to be equally accessible to pharmaceutical researchers interested in what this new computational tool is capable of and experts in molecular modeling who wish to pursue pharmaceutical applications as a context for their research. The field has become too broad for us to concisely describe all work that has been carried out; many comprehensive reviews on subtopics of this area are cited. We discuss the insight molecular dynamics modeling has provided in dissolution and solubility, however, the majority of the discussion is focused on nanomedicine: the development of nanoscale drug delivery vehicles. Here we focus on three areas where molecular dynamics modeling has had a particularly strong impact: (1) behavior in the bloodstream and protective polymer corona, (2) Drug loading and controlled release, and (3) Nanoparticle interaction with both model and biological membranes. We conclude with some thoughts on the role that molecular dynamics simulation can grow to play in the development of new drug delivery systems.

Precise Mesoscopic Model Providing Insights into Polymerization-Induced Self-Assembly

Self-assembly of copolymer is an important approach to obtain multifarious nanostructures. Polymerization-induced self-assembly (PISA) is a recently developed and powerful copolymer self-assembly strategy. However, some researchers have reported a different morphology prepared by PISA and the traditional copolymer self-assembly using the same copolymer system. In this work, to explore the mystery, we develop a precise mesoscopic dissipative particle dynamics (DPD) model to reveal insights into the PISA of poly(4-vinylpyridine)-b-polystyrene (P4VP-b-PS). It is observed that P4VP-b-PS nanotubes can be obtained via TSA rather than PISA, which is consistent with reported experimental results. By carefully investigating the dynamics of PISA under specific solvent and monomer conditions and different polymerization rates, we propose that combining excessive monomers with multistep PISA can help to enhance the morphological regulation ability of PISA and retain a high solid content simultaneously. The findings in this study not only provide a precise modeling method for investigating copolymer self-assembly but also serve as a rational guide for future studies toward optimization of the PISA strategy.

Dual responsive PMEEECL–PAE block copolymers: a computational self-assembly and doxorubicin uptake study

The self-assembly behaviour of dual-responsive block copolymers and their ability to solubilize the anticancer drug doxorubicin (DOX) has been investigated using all-atom molecular dynamics (MD) simulations, MARTINI coarse-grained (CG) force field simulation and Scheutjens–Fleer self-consistent field (SCF) computations. These diblock copolymers, composed of poly{γ-2-[2-(2-methoxyethoxy)ethoxy]ethoxy-ε-caprolactone} (PMEEECL) and poly(β-amino ester) (PAE) are dual-responsive: the PMEEECL block is thermoresponsive (becomes insoluble above a certain temperature), while the PAE block is pH-responsive (becomes soluble below a certain pH). Three MEEECL₂₀–AE_M compositions with M = 5, 10, and 15, have been studied. All-atom MD simulations have been performed to calculate the coil-to-globule transition temperature (T_cg) of these copolymers and finding appropriate CG mapping for both PMEEECL–PAE and DOX. The output of the MARTINI CG simulations is in agreement with SCF predictions. The results show that DOX is solubilized with high efficiency (75–80%) at different concentrations inside the PMEEECL–PAE micelles, although, interestingly, the loading efficiency is reduced by increasing the drug concentration. The non-bonded interaction energy and the RDF between DOX and water beads confirm this result. Finally, MD simulations and SCF computations reveal that the responsive behaviour of PMEEECL–PAE self-assembled structures take place at temperature and pH ranges appropriate for drug delivery.

The self-assembly behaviour of dual-responsive block copolymers and their ability to solubilize the drug doxorubicin is demonstrated using molecular dynamics simulations, coarse-grained force field simulations and self-consistent field theory.

Computer-assisted engineering of programmed drug releasing multilayer nanomedicine via indomethacin-mediated ternary complex for therapy against a multidrug resistant tumor

Nanomedicine with programmed drug release can give full play to the synergistic effect of multi-component system in complicated tumor environment. However, the construction of these programmed drug delivery systems often depends on the sophisticated materials design and synthesis. In this study, we successfully designed an indomethacin (IND)-mediated ternary complex system based on a PEG cleavable polyethyleneimine (PEI), indomethacin (IND) and benzene ring containing chemotherapeutic drugs (such as paclitaxel (PTX), doxorubicin and docetaxel). Based on the difference of hydrophobicity in these components, these components were one-pot self-assembled into drug-loaded IND mediated PEGylation cleavable nanoassemblies (IPCNs) in multilayer structure. In drug-loaded IPCNs, PEG fragments, PEI/IND, and chemotherapeutic drug were respectively distributed from the out layer to core of nanomedicine. When drug-loaded IPCNs reached tumor site through EPR effect, the PEG fragment would firstly responsively release to the acidic tumor microenvironment to expose the intermediate layer of drug-loaded IPCNs that composed by mixture of PEI and IND for increasing the surface potential to promote the uptake by tumor cells. After entering cells, IND would be released faster than chemotherapeutic drug encapsulated in core to efficiently inhibit the expression of multidrug resistance protein 1 to reverse MDR of tumor cells before chemotherapeutic drug releasing. Contributed by the staged responsively releasing of PEG fragments, IND and encapsulated chemotherapeutic drug, the drug-loaded IPCNs exhibited a superior antitumor efficacy against A549/MDR tumor cells both in vitro and in vivo. STATEMENT OF SIGNIFICANCE: The way to develop programmed released drug delivery system is commonly relied on complicated material design and synthesis. Herein, under the computer-assist design, we successfully designed a ternary complex derived from indomethacin (IND), paclitaxel (PTX) and a pH-responsive PEGylated polyethyleneimine (PEG-s-PEI), and employed this ternary complex to successfully prepare a high drug loading and multilayer structured nanomedicine of PTX (PTX IPCNs). Contribute by the different location of PTX, IND and PEG-s-PEI in PTX IPCNs, PEG fragments, IND and PTX molecules could programmed release after reaching tumor for perfectly realizing the synergistic anti-tumor effect of tumor targeting, reversal of MDR and chemotherapy. Based on a fusion of these multiple mechanisms, PTX IPCNs showed a superior antitumor efficacy in mice loading A549/MDR tumor.

Composite Nanotube Ring Structures Formed by Two-Step Self-Assembly for Drug Loading/Release

Nanotube rings are barely reported novel structures formed by the self-assembly of soft matter, as compared with nanotube structures and ring structures. The two-step self-assembly of amphiphilic copolymer AB and solvophobic copolymer CDC was studied. We found that nanotube rings can be formed from a certain mass ratio of copolymer CDC to copolymer AB and block D of certain rigidity. More interestingly, we discovered a new strategy for drug loading and release, which is different from the usual strategies reported in the literature. The present study provides a new rationale for the self-assembly of copolymers.

Zwitterionic Membrane via Nonsolvent Induced Phase Separation: A Computer Simulation Study

Dissipative particle dynamics (DPD) was adopted to study the nonsolvent induced phase separation (NIPS) process during a pH-responsive poly(ether sulfone) membrane preparation with a zwitterionic copolymer poly(ether sulfone)- block-polycarboxybetaine methacrylate (PES-b-PCBMA) as the blending additive. The membrane formation process and final morphology were analyzed. Simulation results show that the hydrophilic PCBMA segments enrich on the membrane surface by surface segregation and exhibit pH-responsive behavior, which is attributed to the deprotonation of the carboxylic acid group. With the polymer concentration increasing, both the shrinkage of the membrane and the flexibility of the system decrease, which also reduce the effect of surface segregation. By adjusting the blend ratio of PES-b-PCBMA with PES from 5% to 15%, the surface coverage of PCBMA segments on the membrane can be regulated. This work contributes to a better understanding on the mechanism of NIPS and can serve as a guide for the design of the polymer blend membrane.

pH-Responsive Zwitterionic Copolymer DHA-PBLG-PCB for Targeted Drug Delivery: A Computer Simulation Study

In this work, the self-assembled behaviors of zwitterionic copolymer docosahexaenoic acid- b-poly(γ-benzyl-l-glutamate)- b-poly(carboxybetaine methacrylate) (DHA-PBLG-PCB) and the loading and release mechanism of the anticancer drug doxorubicin (DOX) was investigated via computer simulations. The effects of polymer concentration, drug content, and pH on polymeric micelles were explored by dissipative particle dynamics (DPD) simulations. Simulation results show that DHA-PBLG₁₅-PCB₁₀ can self-assemble into core-shell micelles; in addition, the drug-loaded micelles have a pH-responsive feature. DOX can be encapsulated into the core-shell micelle under normal physiological pH conditions, whereas it can be released under acidic pH conditions. The self-assembled behaviors of copolymer DHA-PBLG-PEG were also studied to have a comparison with those of DHA-PBLG-PCB. The DHA-PBLG₁₅-PCB₁₀ system has a stable structure and it has a great potential to serve as drug delivery vehicles for targeted drug delivery.

Hyaluronic Acid-Decorated Laponite® Nanocomposites for Targeted Anticancer Drug Delivery

In this study, hyaluronic acid (HA), a natural polysaccharide that can specifically bind to CD44 receptors, was conjugated onto laponite® (LAP) nanodisks for the encapsulation and specific delivery of the anti-cancer drug doxorubicin (DOX) to CD44-overexpressed cancer cells. The prepared LM-HA could encapsulate DOX efficiently and release drug in a continuous manner with pH-responsiveness. In vitro cell viability assay proved that LM-HA had good biocompatibility, and drug-loaded LM-HA/DOX exhibited targeted anti-tumor effects against HeLa cells with CD44 receptors overexpressed. In addition, the flow cytometric detection and confocal laser scanning microscope results confirmed that LM-HA/DOX could be specifically internalized by HeLa cells via CD44-mediated endocytosis. Therefore, the HA-modified LAP nanodisks with high drug loading efficiency, pH-sensitive drug release properties and CD44 targetability might be an efficient nanoplatform for cancer chemotherapy.

4/6-Herto-arm and 4/6-mikto-arm star-shaped block polymeric drug-loaded micelles and their pH-responsive controlled release properties: a dissipative particle dynamics simulation

Star-shaped polymers have received significant attention and have been widely developed for prospective applications in drug delivery owing to their topological structure and unique physiochemical characteristics.

Redox-Responsive Core-Cross-Linked Block Copolymer Micelles for Overcoming Multidrug Resistance in Cancer Cells

Success of chemotherapy as a treatment for cancer has been often inhibited by multidrug resistance (MDR) of the cancer cells. There is a clear need to generate strategies to overcome this resistance. In this work, we have developed redox-responsive and core-cross-linked micellar nanocarriers using poly(ethylene glycol)-block-poly(2-(methacryloyloxy)ethyl 5-(1,2-dithiolan-3-yl)pentanoate) diblock copolymers (PEG-b-PLAHEMA) with tunable swelling properties for the delivery of drugs toward drug-sensitive MDA-MB-231 and drug-resistant MDA-MB-231 (231R) cancer cells. PEG-b-PLAHEMA containing varying number of 2-(methacryloyloxy)ethyl 5-(1,2-dithiolan-3-yl)pentanoate (LAHEMA) units were synthesized by employing the reversible addition-fragmentation chain transfer polymerization technique. The block copolymer self-assembly, cross-linking induced by reduction, and de-cross-linking triggered time-dependent controlled swelling of micelles were studied using dynamic light scattering, fluorescence spectroscopy, and transmission electron microscopy. In vitro cytotoxicity, cellular uptake efficiency, and glutathione-responsive anticancer activity of doxorubicin (DOX) encapsulated in core-cross-linked block copolymer micelles (CCMs) toward both drug-sensitive and drug-resistant cancer cell lines were evaluated. Significant reduction in IC₅₀ was observed by DOX-loaded CCMs toward drug-resistant 231R cancer cell lines, which was further improved by coencapsulating DOX and verapamil (a P-glycoprotein inhibitor) in CCMs. Thus, these reduction-sensitive biocompatible CCMs with tunable swelling property are very promising in overcoming MDR in cancer cells.

One-pot production of porous assemblies by PISA of star architecture copolymers: a simulation study

Porous vesicles can be produced in one-pot by the PISA of star architecture copolymers.

Computational approaches to cell-nanomaterial interactions: keeping balance between therapeutic efficiency and cytotoxicity

Owing to their unique properties, nanomaterials have been widely used in biomedicine since they have obvious inherent advantages over traditional ones. However, nanomaterials may also cause dysfunction in proteins, genes and cells, resulting in cytotoxic and genotoxic responses. Recently, more and more attention has been paid to these potential toxicities of nanomaterials, especially to the risks of nanomaterials to human health and safety. Therefore, when using nanomaterials for biomedical applications, it is of great importance to keep the balance between therapeutic efficiency and cytotoxicity (i.e., increase the therapeutic efficiency as well as decrease the potential toxicity). This requires a deeper understanding of the interactions between various types of nanomaterials and biological systems at the nano/bio interface. In this review, from the point of view of theoretical researchers, we will present the current status regarding the physical mechanism of cytotoxicity caused by nanomaterials, mainly based on recent simulation results. In addition, the strategies for minimizing the nanotoxicity naturally and artificially will also be discussed in detail. Furthermore, we should notice that toxicity is not always bad for clinical use since causing the death of specific cells is the main way of treating disease. Enhancing the targeting ability of nanomaterials to diseased cells and minimizing their side effects on normal cells will always be hugely challenging issues in nanomedicine. By combining the latest computational studies with some experimental verifications, we will provide special insights into recent advances regarding these problems, especially for the design of novel environment-responsive nanomaterials.

Compact Vesicles Self-Assembled from Binary Graft Copolymers with High Hydrophilic Fraction for Potential Drug/Protein Delivery

Hollow vesicles self-assembled from amphiphilic copolymers are of great interest in biomedicine field as drug and protein carriers. Efficient preparation of polymeric vesicles with high stability in vivo is highly desirable. Herein, a novel cooperative self-assembly of two graft copolymers (GCPs) with reversed hydrophilic-hydrophobic segments is investigated to achieve morphology control for biomedical application. Interestingly, nanosized vesicles are obtained for the binary system with relatively high hydrophilic fraction (f_hydrophilic, ∼60%), contrary to what is found in its single-component counterpart. The cooperative self-assembly endowed the hybrid vesicles with excellent resistance to protein adsorption, prolonged blood circulation time, as well as low leakage of hydrophilic drugs/proteins. Furthermore, the biological activity of the protein is well preserved inside the cooperative vesicles, making it a promising candidate as the protein carrier.

Energy-Transfer Phenomena in Thermoresponsive and pH- Switchable Fluorescent Diblock Copolymer Vesicles

We describe the development of a polymeric vesicle that not only selectively fluoresces at low pH, a condition prevailing in cancer cells, but also can potentially monitor the thermoresponsive release of a drug even if the drug is nonfluorescent. The developed fluorescence resonance energy transfer (FRET)-based thermoresponsive vesicular nanocarriers are composed of a new poly(PEGMA)-b-poly(NIPA-r-R6GMED) block copolymer, which undergoes pH-switchable superior turn on-off fluorescence characteristics. The block copolymer was synthesized using the RAFT technique, and its solution properties and self-assembly behavior were investigated by turbidity measurements, fluorescence spectroscopy, ¹H NMR, dynamic light scattering, and transmission electron microscopy. The block copolymer self-assembled to form nanostructured vesicles above the critical aggregation temperature under physiologically relevant conditions. Steady-state and time-resolved fluorescence spectroscopy were utilized to study the FRET process between encapsulated hydrophobic guest C-153 (donor) and polymer-bound R6GMED units (acceptor) in the thermoresponsive vesicles. The FRET rate and efficiency were found to vary as a result of the pH-dependent changes in the quantum yield of the acceptor molecules. The occurrence of a highly efficient FRET in this polymeric vesicular nanocarrier at acidic pH, a condition similar to the cytoplasm and cell nucleus in leukemic tissues, and the ability to encapsulate hydrophilic and hydrophobic molecules and their temperature-controlled release make it potentially useful in imaging guided real-time monitoring of drug-delivery vehicles.

Controllable multicompartment morphologies from cooperative self-assembly of copolymer-copolymer blends

Multicompartment nanostructures, such as microcapsules with clearly separated shell and core, are not easily accessible by conventional block copolymer self-assembly. We assess a versatile computational strategy through cooperative assembly of diblock copolymer blends to generate spherical and cylindrical compartmentalized micelles with intricate structures and morphologies. The co-assembly strategy combines the advantages of polymer blending and incompatibility-induced phase separation. Following this strategy, various nanoassemblies of pure AB, binary AB/AC and ternary AB/AC/AD systems such as compartmentalized micelles with sponge-like, Janus, capsule-like and onion-like morphologies can be obtained. The formation and structural adjustment of microcapsule micelles, in which the shell or core can be occupied by either pure or mixed diblock copolymers, were explored. The mechanism involving the separation of shell and core copolymers is attributed to the stretching force differences of copolymers which drive the arrangement of different copolymers in a pathway to minimize the total interfacial energy. Moreover, by adjusting block interactions, an efficient approach is exhibited for regulating the shell or core composition and morphology in microcapsule micelles, such as the transition from the "pure shell/mixed core" morphology to the "mixed shell/pure core" morphology in the AB/AC/AD micelle. This mesoscale simulation study identifies the key factors governing co-assembly of diblock copolymer blends and provides bottom-up insights towards the design and optimization of new multicompartment micelles.

Tunable Permeability of Cross-Linked Microcapsules from pH-Responsive Amphiphilic Diblock Copolymers: A Dissipative Particle Dynamics Study

Using dissipative particle dynamics simulation, we probe the tunable permeability of cross-linked microcapsules made from pH-sensitive diblock copolymers poly(ethylene oxide)-b-poly(N,N-diethylamino-2-ethyl methacrylate) (PEO-b-PDEAEMA). We first examine the self-assembly of non-cross-linked microcapsules and their pH-responsive collapse and then explore the effects of cross-linking and block interaction on the swelling or deswelling of cross-linked microcapsules. Our results reveal a preferential loading of hydrophobic dicyclopentadiene (DCPD) molecules in PEO-b-PDEAEMA copolymers. Upon reduction of pH, non-cross-linked microcapsules fully decompose into small wormlike clusters as a result of large self-repulsions of protonated copolymers. With increasing degree of cross-linking, the morphology of the microcapsule becomes more stable to pH change. The highly cross-linked microcapsule shell undergoes significant local polymer rearrangement in acidic solution, which eliminates the amphiphilicility and therefore enlarges the permeability of the shell. The responsive cross-linked shell experiences a disperse-to-buckle configurational transition upon reduction of pH, which is effective for the steady or pulsatile regulation of shell permeability. The swelling rate of the cross-linked shell is dependent on both electrostatic and nonelectrostatic interactions between the pH-sensitive groups as well as the other groups. Our study highlights the combination of cross-linking structure and block interactions in stabilizing microcapsules and tuning their selective permeability.

Nanoarchitectures by hierarchical self-assembly of ursolic acid: entrapment and release of fluorophores including anticancer drug doxorubicin

Ursolic acid, a naturally occurring 6-6-6-6-6 monohydroxy triterpenic acid, extractable from the leaves ofPlumeria rubra, spontaneously self-assemble in aqueous liquids yielding nanoarchitectures capable of entrapping guest molecules including anticancer drug.