Phenylboronic acid-functionalized polymeric micelles with a HepG2 cell targetability

Recent Advances in Polycaprolactones for Anticancer Drug Delivery

Poly(ε-Caprolactone)s are biodegradable and biocompatible polyesters that have gained considerable attention for drug delivery applications due to their slow degradation and ease of functionalization. One of the significant advantages of polycaprolactone is its ability to attach various functionalities to its backbone, which is commonly accomplished through ring-opening polymerization (ROP) of functionalized caprolactone monomer. In this review, we aim to summarize some of the most recent advances in polycaprolactones and their potential application in drug delivery. We will discuss different types of polycaprolactone-based drug delivery systems and their behavior in response to different stimuli, their ability to target specific locations, morphology, as well as their drug loading and release capabilities.

Innovations in Biomaterial Design toward Successful RNA Interference Therapy for Cancer Treatment

Gene regulation using RNA interference (RNAi) therapy has been developed as one of the frontiers in cancer treatment. The ability to tailor the expression of genes by delivering synthetic oligonucleotides to tumor cells has transformed the way scientists think about treating cancer. However, its clinical application has been limited due to the need to deliver synthetic RNAi oligonucleotides efficiently and effectively to target cells. Advances in nanotechnology and biomaterials have begun to address the limitations to RNAi therapeutic delivery, increasing the likelihood of RNAi therapeutics for cancer treatment in clinical settings. Herein, innovations in the design of nanocarriers for the delivery of oligonucleotides for successful RNAi therapy are discussed.

Non-isotope enriched phenylboronic acid-decorated dual-functional nano-assembles for an actively targeting BNCT drug

The feasibility of boron neutron capture therapy (BNCT) greatly depends on the selective accumulation of ¹⁰B in tumors. The p-boronophenylalanine-fructose (BPA-f) complex has been established as a conventional BNCT agent due to its preferential uptake into tumors, which is driven by amino acid transporters. However, the retention of BPA-f in tumors is highly limited because of an antiport mechanism, which is regulated by a gradient of amino acid concentration across the cancer cell membrane. Thus, to preserve a high ¹⁰B concentration in tumors, patients are inevitably subjected to a constant intravenous infusion. To this end, we employed a phenylboronic acid (PBA)-decorated polymeric nanoparticle (Nano^PBA) as a sialic acid-targeting BNCT agent. In this manner, the PBA can exhibit dual functionalities, i.e., exhibiting a neutron capture capacity and hypersialyated cancer cell targeting effect. Our developed Nano^PBA possesses a supramolecular structure composed of a core and shell comprised of poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG) segments, respectively. The PBA moiety is installed at the PEG end, providing an unusually strong targeting effect, supposedly via multivalent binding onto the cancer cell membrane. As in BNCT, we verified the feasibility of Nano^PBA against a B16 melanoma-bearing mouse model. By virtue of efficient tumor targeting, even at a 100-fold lower dose than BPA-f, the Nano^PBA achieved a potent antitumor effect.

Multi-transformable nanocarrier with tumor extracellular acidity-activated charge reversal, size reduction and ligand reemergence for in vitro efficient doxorubicin loading and delivery

Various nanoparticles as drug delivery system provide significant improvements in the cancer treatment. However, their clinical success remains elusive in large part due to their inability to overcome both systemic and tumor tissue barriers. The nanosystems with nanoproperty-transformability (surface, size, stability and target) hold great promise for achieving enhanced delivery efficacy. However, currently available systems that are mainly polymer-based assemblies usually suffer from the intrinsic drawbacks of poor stability, premature leakage and low drug loading as well as limited transformability. In this study, we designed a facile strategy to build a novel multi-transformable MSNs@GO nanosystem for efficient doxorubicin (DOX) loading and delivery. This novel nanosystem was well characterized and investigated in vitro. The results indicated that the MSNs@GO can realize a very high drug loading ability due to the large pore surface area of MSNs and the demonstrated donor-acceptor (boron‑nitrogen) coordination interactions between phenylboronic acid-containing nanocarriers and electron donor-containing DOX. More importantly, the novel nanocarriers can simultaneously achieve charge reversal, size reduction and ligand reemergence by shielding/deshielding transition via acid-cleavable dynamic boronate bonds under in vitro simulated acidic microenvironment of tumor tissues, opening a new avenue for improving delivery efficiency of chemotherapeutics.

Redox dual-stimuli responsive drug delivery systems for improving tumor-targeting ability and reducing adverse side effects

Cancer is a big challenge that has plagued the human beings for ages and one of the most effective treatments is chemotherapy. However, the low tumor-targeting ability limits the wide clinical application of chemotherapy. The microenvironment plays a critical role in many aspects of tumor genesis. It generates the tumor vasculature and it is highly implicated in the progression to metastasis. To maintain a suitable environment for tumor progression, there are special microenvironment in tumor cell, such as low pH, high level of glutathione (GSH) and reactive oxygen species (ROS), and more special enzymes, which is different to normal cell. Microenvironment-targeted therapy strategy could create new opportunities for therapeutic targeting. Compared to other targeting strategies, microenvironment-targeted therapy strategy will control the drug release into tumor cells more accurately. Redox responsive drug delivery systems (DDSs) are developed based on the high level of GSH in tumor cells. However, there are also GSH in normal cell though its level is lower. In order to control the release of drugs more accurately and reduce side effects, other drug release stimuli have been introduced to redox responsive DDSs. Under the synergistic reaction of two stimuli, redox dual-stimuli responsive DDSs will control the release of drugs more accurately and quickly and even increase the accumulation. This review summarizes strategies of redox dual-stimuli responsive DDSs such as pH, light, enzyme, ROS, and magnetic guide to delivery chemotherapeutic agents more accurately, aiming at providing new ideas for further promoting the drug release, enhancing tumor-targeting and improving anticancer effects. To better illustrate the redox dual-stimuli responsive DDS, preparations of carriers are also briefly described in the review.

Synthesis, Formulation, and Characterization of Doxorubicin-Loaded Laponite/Oligomeric Hyaluronic Acid-Aminophenylboronic Acid Nanohybrids and Cytological Evaluation against MCF-7 Breast Cancer Cells

As a synthetic clay material, laponite RDS (LR) was investigated as an effective drug carrier as a result of the special nanodisk structure together with the negative-charged surface to achieve enhanced cellular uptake and targeted delivery. In this research work, the synthesized oligomeric hyaluronic acid-aminophenylboronic acid (oHA-APBA) was entangled onto LR nanodisks to fabricate a valid targeted platform for breast cancer therapy. Briefly, through the formation of amide bonds, 3-APBA was connected to the chain of oHA with a substituted ratio of 4.0 ± 0.2% to synthesize oHA-APBA copolymer. Thereafter, doxorubicin (DOX) was inserted into the interlayer space of LR by the way of the ion exchange process, followed by an assembly with oHA-APBA as a targeted protection layer. The satisfactory drug encapsulation efficiency (> 80%) and narrow size distribution were achieved. The in vitro drug release study demonstrated the release of DOX from DOX@LR/oHA-APBA was sustained and acid dependent. In addition, after fitting the drug cumulative release of DOX@LR/oHA-APBA under different pH conditions with several kinetic models, it was identified that drug release from DOX@LR/oHA-APBA nanohybrids at pH 5.0 was mainly dependent on both diffusion and ion exchange effects. However, under the condition of pH 7.4, the drug was most efficiently released by diffusion effect. Importantly, DOX@LR/oHA-APBA showed remarkable cellular uptake and intracellular drug distribution in MCF-7 cells, which were consistent with inhibitory ability against MCF-7 cells. Hence, the high DOX loading capacity and enhanced cellular tracking can enlighten LR/oHA-APBA as an effective drug delivery carrier for breast cancer therapy.

Phenylboronic acid-functionalized polyamidoamine-mediated miR-34a delivery for the treatment of gastric cancer

In the present research, a tumor-targeted gene carrier, PPP, was constructed through the modification of phenylboronic acid onto the surface of a polyamidoamine dendrimer, and then miR-34a delivery was employed as a model to evaluate its anti-tumor efficacy.

Cationic polycarbonates via ring-opening polymerization: design, synthesis, and applications

The synthetic methods and applications of cationic polycarbonates via ring-opening polymerization are highlighted.

Phenylboronic acid-modified polyamidoamine-mediated delivery of short GC rich DNA for hepatocarcinoma gene therapy

Phenylboronic acid was introduced on the surface of polyamidoamine to construct a derivative PP, which was further used as a tumor-targeting carrier for realizing the delivery of short GC rich DNA (GCD).

Protein-Polymer Microcapsules for PCR Technology

Protein-polymer microcapsules have attracted much attention, due to their special features and potential in biological use. How to make the most of this type of bio-abiotic hybrid material is an intriguing question. Nevertheless, several unsatisfactory technical issues significantly limited the application of these materials. For instance, introducing various biomolecules and crosslinking for the capsules remains challenging and problematic. In this report, recombinant mCherry protein was covalently linked with poly(N-isopropylacrylamide) (PNIPAAm) to form amphiphilic protein-polymer conjugates, which assembled into microcapsules. These microcapsules are thermoresistant and can be used in the polymerase chain reaction (PCR). In this setting, the reactant molecules can be readily and easily introduced into the microcapsules, and crosslinking and water-oil phase transition are not necessary. This protein-polymer microcapsule PCR system has potential in various biological applications.

Magnetic Mesoporous Silica Gated with Doped Carbon Dot for Site-Specific Drug Delivery, Fluorescence, and MR Imaging

Construction of a theranostic agent which integrates multiple modalities with different functions into one entity is challenging from a molecular design and synthesis perspective. In this context, the present paper reports the fabrication of a novel type of multifunctional hybrid nanoparticle composed of magnetic gadolinium oxide-iron oxide core, mesoporous silica shell gated with boronic acid functionalized highly luminescent carbon quantum dot (BNSCQD). The porous silica shell acts as an excellent reservoir for anticancer drug 5-fluorouracil, whereas the BNSCQD cap impressively controls the drug transport under simulated intracellular environment. Furthermore, recognition and fluorescence turn on response of BNSCQD toward cell surface glycan sialyl Lewis^a (SL^a) enables targeted drug release and excellent fluorescence imaging of SL^a overexpressed HePG2 cancer cells. The r₁ and r₂ relaxivities of the material are found to be 10 and 165 mM^-1 s^-1 which is comparable to commercially available magnetic resonance imaging contrast agents. Benefiting from the combined advantages of dual stimuli-responsive drug release, excellent optical imaging, and MR imaging, this novel construct can be a promising theranostic material.

Convergent Approach to Boronic Acid Functionalized Polycarbonates: Accessing New Dynamic Material Platforms

Polycarbonates are routinely utilized for diverse medicinal applications and are highly efficacious scaffolds for drug delivery and antimicrobial treatments. In order to provide for robust, dynamic platforms for biomedical applications, we have developed new routes for the incorporation of boronic acids into the polycarbonate backbone. These routes take advantage of straightforward postsynthesis modification of established polycarbonate backbones, enabling the preparation of a diverse array of boronic acid functionalized polycarbonates from readily accessible polycarbonates. In particular, this approach circumvents the need for de novo monomer synthesis, functional group incompatibilities, and deprotection steps that often limit other methods. This strategy has been demonstrated using a broad array of unprotected boronic acids to produce both neutral and cationic boronic acid functionalized polycarbonates.

Controllably Switched Drug Release from Successively Dual-Targeted Nanoreservoirs

The development of a nanocarrier with a capacity of releasing therapeutic agent "on demand" is of great importance for enhancing drug efficacy and reducing its side effect. Here, a multifunctional mesoporous silica nanoparticle is presented for cancer therapy. This nanoparticle can not only successively target tumor tissue and tumor cells but also has a function of controllably switching the drug release. Low molecular weight poly(ethyleneimine) segments, which are decorated on the surface of magnetic mesoporous silica nanoparticle with disulfide bonds, are chemically cross-linked, leading to the mesopores being "closed" in blood circulation but being "open" via taking off the coating in cytoplasm. As a result, the encapsulated drug can be kept in nanoparticles in the normal conditions, while be rapidly released in a reduction condition. In vivo antitumor activity demonstrates that this nanoparticle has the highest safety to body and the best therapeutic efficacy against tumors. Therefore, this work presents a good example of rational design of nanocarriers for highly effective cancer therapy.

Enzyme and Redox Dual-Triggered Intracellular Release from Actively Targeted Polymeric Micelles

Highly effective delivery of therapeutic agents into target cells using nanocarriers and subsequently rapid intracellular release are of great importance in cancer treatment. Here, we developed an enzyme and redox dual-responsive polymeric micelle with active targeting abilities to achieve rapid intracellular drug release. To overcome both its poor solubility in water and instability in the blood circulation, camptothecin (CPT) was chemically conjugated to monomethyl poly(ethylene glycol) (mPEG) via a redox-responsive linker to form polymeric prodrugs. The enzyme-responsive function is achieved by connecting hydrophobic polycaprolactone segments and hydrophilic PEG segments with azo bonds. Additionally, the end of the PEG segment was decorated with phenylboronic acid (PBA), endowing the nanocarriers with active targeting abilities. The dual-responsive targeting polymeric micelles can be generated by self-assembly of a mixture of the polymeric prodrug and enzyme-responsive copolymer. The in vitro drug release profile revealed that CPT was rapidly released from the micelles under a simulated condition similar to the tumor cell microenvironment. In vivo and ex vivo fluorescence imaging indicated that these micelles possess excellent specificity to target hepatoma carcinoma cells. The antitumor effect in mice liver cancer cells (H22) in tumor-bearing Kunming (KM) mice demonstrated that this nanocarrier exhibits high therapeutic efficiency in artificial solid tumors and low toxicity to normal tissues, with a survival rate of approximately 100% after 160 days of treatment.

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).

Phenylboronic acid-incorporated elastin-like polypeptide nanoparticle drug delivery systems

Packaging hydrophobic drugs into nanoparticles can improve their aqueous solubility, tumor-specific accumulation and therapeutic effect.

Expanding the Cationic Polycarbonate Platform: Attachment of Sulfonium Moieties by Postpolymerization Ring Opening of Epoxides

Postpolymerization modification is a critical strategy for the development of functional polycarbonate scaffolds for medicinal applications. To expand the scope of available postpolymerization functionalization methods, polycarbonates containing pendant thioether groups were synthesized by organocatalyzed ring-opening polymerization. The thioether group allowed for the postpolymerization ring-opening of functional epoxides, affording a wide variety of sulfonium-functionalized A-B diblock and A-B-A triblock polycarbonate copolymers. The pendant thioether groups were found to be compatible with previously developed postsynthesis functionalization methods allowing for selective and orthogonal modifications of the polycarbonates.

Redox-responsive star-shaped magnetic micelles with active-targeted and magnetic-guided functions for cancer therapy

Highly efficient delivery of therapeutic agents to target sites is of great importance for achieving excellent therapeutic efficacy in cancer treatment. Here, we report a redox-responsive star-shaped magnetic micelle with both active-targeted and magnetic-guided functions. The magnetic star-shaped micelles are formed by self-assembly of four-arm poly(ethylene glycol) (PEG)-poly(ε-caprolactone) (PCL) copolymers with disulfide bonds as intermediate linkers. Anticancer drug doxorubicin (DOX) and magnetic iron oxide nanoparticles (Fe3O4) are simultaneously encapsulated into the hydrophobic cores. PBA ligands are chemically conjugated to the end of the hydrophilic PEG segments, endowing the active targeting of nanocarriers. Both qualitative and quantitative analyses of the intracellular uptake of these micelles with active-targeting and dual-targeting are performed in vitro by cultured with salic acid (SA)-positive tumor cells (human liver carcinoma cell line HepG2, human cervical cancer cell line HeLa) and SA-negative tumor cells (human breast adenocarcinoma cell line MCF-7, human non-small cell lung cancer cell line A549) in the presence or absence of a permanent magnetic field. In vivo biodistribution studies with active-targeting and dual-targeting and in vivo anti-tumor effect are carried out in detail after being applied to the BALB/c mice bearing mouse H22 hepatocarcinoma cells tumor model. These in vivo results demonstrate that a great amount of dual-targeted magnetic micelles accumulate around the tumor tissues by the magnetic-guiding and in turn are taken up by the tumor cells through SA-mediated endocytosis, leading to a high therapeutic efficacy to the artificial solid tumor.

STATEMENT OF SIGNIFICANCE

A redox-responsive star-shaped magnetic micelle with both active-targeted and magnetic-guided functions was developed. Both qualitative and quantitative analysis of the intracellular uptake with dual-targeting of these micelles were performed in vitro by salic acid (SA)-positive tumor cells. The in vivo results demonstrate that a great amount of dual-targeted magnetic micelles accumulated around the tumor tissues, leading to a high therapeutic efficacy to artificial solid tumor.

Phenylboronic acid-functionalized polyamidoamine-mediated Bcl-2 siRNA delivery for inhibiting the cell proliferation

In this study, the conjugation of phenylboronic acid (PBA) to amine-terminated polyamidoamine (PAMAM) was successfully conducted to prepare a tumor-targeted gene carrier PBA-functionalized PAMAM (PPP) for Bcl-2 siRNA delivery, using a heterobifunctional crosslinker NHS-PEG5k-Mal. The carrier possessed favorable capacity for siRNA condensation and could protect siRNA from the degradation against RNase and serum. The introduction of PBA could facilitate the cellular uptake and further transfection of Bcl-2 siRNA demonstrated by confocal laser scanning microscopy and flow cytometry. Meanwhile, PPP-mediated transfection of Bcl-2 siRNA could significantly inhibit the expression of Bcl-2 gene at both mRNA and protein levels. Furthermore, owing to the knock-down of Bcl-2, PPP/siRNA could significantly inhibit the cell proliferation by inducing the cell apoptosis, and also enhance the antitumor efficiency of doxorubicin by suppressing the resistance of tumor cells to chemotherapeutics. In conclusion, the PPP-mediated Bcl-2 siRNA delivery could potentially be an effective platform for solving the drug resistance and further achieving the combined chemotherapy and gene therapy in tumor treatment.

pH-Activated Targeting Drug Delivery System Based on the Selective Binding of Phenylboronic Acid

Phenylboronic acid (PBA) is a tumor-targeting molecule, but its nonspecific interaction with normal cells or other components containing cis-diol residues undoubtedly limits its potential application in tumor-targeting drug delivery. Herein, we developed fructose-coated mixed micelles via PBA-terminated polyethylene glycol monostearate (PBA-PEG-C18) and Pluronic P123 (PEG20-PPG70-PEG20) to solve this problem, as the stability of borate formed by PBA and fructose was dramatically dependent on pH. The fluorescence spectroscopic results indicated that the borate formed by PBA and fructose decomposed at a decreased pH, and better binding between PBA and sialic acid (SA) was observed at a low pH. These results implied that the fructose groups decorated on the surface of the micelles could be out-competed by SA at a low pH. In vitro uptake and cytotoxicity studies demonstrated that the fructose coating on the mixed micelles improved the endocytosis and enhanced the cytotoxicity of drug-loaded mixed micelles in HepG2 cells but reduced the cytotoxicity in normal cells. These results demonstrate that a simple decorating strategy may facilitate PBA-targeted nanoparticles for tumor-specific drug delivery.

Clustering Small Dendrimers into Nanoaggregates for Efficient DNA and siRNA Delivery with Minimal Toxicity

Cationic dendrimers are widely used as nonviral gene vectors, however, current gene materials based on dendrimers are either little effective or too toxic on the transfected cells. Here, a facile strategy is presented to prepare high efficient dendrimers with low transfection toxicity. Small dendrimers with 2 nm are clustered into nanoaggregates (≈100 nm) via phenylboronic acid modification and the self-assembled materials enable efficient DNA and siRNA delivery on several cell lines. The clustered nanostructures can disassemble into small dendrimers in acidic conditions thus exerting significantly less toxicity on the transfected cells. Further structure-function relationship studies reveal that both the phenyl group and boronic acid group play essential roles in the self-assembly and gene delivery processes. The transfection efficacy of phenylboronic acid-modified dendrimers can be down-regulated by blocking the boronic acid groups on dendrimers with diols or degrading the groups with hydrogen peroxide. This study provides a facile strategy in the development of efficient and biocompatible gene vectors based on low molecular weight polymers and clearly demonstrates the structure-function relationship of phenylboronic acid-modified polymers in gene delivery.

A Nanoplatform with Precise Control over Release of Cargo for Enhanced Cancer Therapy

The development of a nanocarrier delivery system having both sufficient stability in blood circulation and a rapid drug release profile at target sites remains a major challenge in cancer therapy. Here, a multifunctional star-shaped micellar system with a precisely spatiotemporal control of releasing encapsulated agents is developed by mixing a photoinitiated crosslinking amphiphilic copolymer with a phenylboronic acid (PBA)-functionalized redox-sensitive amphiphilic copolymer for the first time. The combination of the functional polymers effectively resolves the contradiction that the micellar system cannot release the rapid drug release in cells when it possesses an extreme stability that is often required in blood circulation. In this system, the inner core polymers are photo-crosslinked, endowing a stable micelle matrix structure; the end groups of the hydrophilic segments are decorated with PBA ligands, providing an active targeting ability; disulfide bonds in the micellar matrix impart a redox-responsive trigger for the prompt intracellular release of drugs. As a result, with a relatively low DOX dosage (2 mg kg(-1) per injection) the in vivo antitumor effect on H22-bearing BALB/c mice shows that the micelles have a high therapeutic efficacy against solid tumors while minimal side effects against normal tissues.

Development of phenylboronic acid-functionalized nanoparticles for emodin delivery

Stable and monodisperse phenylboronic acid-functionalized nanoparticles (PBA-NPs) were fabricated using 3-((acrylamido)methyl)phenylboronic acid homopolymer (PBAH) via solvent displacement technique. The effect of operating parameters, including stirring time, initial polymer concentration and the proportion of methanol on the self-assembly process were systematically investigated. The diameters of the PBA-NPs were increased as increasing the initial PBAH concentration and the proportion of methanol. Likewise, there was a linear dependence between the size of self-assembled nanoparticles and the polymer concentration. Moreover, the dissipative particle dynamics (DPD) simulation technique was used to investigate the mechanism of self-assembly behavior of PBAH, which indicated that the interior of PBA-NPs was hydrophobic and compact, and the boronic acid groups were displayed on both the outermost and interior of PBA-NPs. The resulting PBA-NPs could successfully encapsulate emodin through PBA-diol interaction and the encapsulation efficiency (EE%) and drug loading content (DLC%) of drug-loaded PBA-NPs were 78% and 2.1%, respectively. Owing to the acid-labile feature of the boronate linkage, a reduction in environmental pH from pH 7.4 to 5.0 could trigger the disassociation of the boronate ester bonds, which could accelerate the drug release from PBA-Emodin-NPs. Besides, PBA-Emodin-NPs showed a much higher cytotoxicity to HepG2 cells (cancer cells) than that to MC-3T3-E1 cells (normal cells). These results imply that PBA-NPs would be a promising scaffold for the delivery of polyphenolic drugs.

Enzyme responsive mesoporous silica nanoparticles for targeted tumor therapy in vitro and in vivo

This study reports a biocompatible controlled drug release system based on mesoporous silica nanoparticles (MSNs) for tumor microenvironment responsive drug delivery. It was fabricated by grafting phenylboronic acid conjugated human serum albumin (PBA-HSA) onto the surfaces of MSNs as a sealing agent, via an intermediate linker of a functional polypeptide, which was composed of two functional units: the polycation cell penetrating peptide (CPP) polyarginine, and matrix metalloproteinase 2 (MMP-2) substrate peptide. A series of characterizations confirmed that the system had been successfully constructed. In vitro tests proved that the anticancer drug loading system could efficiently induce cell apoptosis in vitro. More importantly, the in vivo tumor experiments confirmed that the anticancer loading system could efficiently inhibit tumor growth with minimal side effects.

A numerical study of the phase behaviors of drug particle/star triblock copolymer mixtures in dilute solutions for drug carrier application

The complex microstructures of drug particle/ABA star triblock copolymer in dilute solutions have been investigated by a theoretical approach which combines the self-consistent field theory and the hybrid particle-field theory. Simulation results reveal that, when the volume fraction of drug particles is smaller than the saturation concentration, the drug particle encapsulation efficiency is 100%, and micelle loading capacity increases with increasing particle volume fraction. When the volume fraction of drug particles is equal to the saturation concentration, the micelles attain the biggest size, and micelle loading capacity reaches a maximum value which is independent of the copolymer volume fraction. When the volume fraction of drug particles is more than the saturation concentration, drug particle encapsulation efficiency decreases with increasing volume fraction of drug particles. Furthermore, it is found that the saturation concentration scales linearly with the copolymer volume fraction. The above simulation results are in good agreement with experimental results.