Amphiphilic polymeric micelles as the nanocarrier for peroral delivery of poorly soluble anticancer drugs

Introduction: Many amphiphilic copolymers have recently been synthesized as novel promising micellar carriers for the delivery of poorly water-soluble anticancer drugs. Studies on the formulation and oral delivery of such micelles have demonstrated their efficacy in enhancing drug uptake and absorption, and exhibit prolonged circulation time in vitro and in vivo.

Areas covered: In this review, literature on hydrophobic modifications of several hydrophilic polymers, including polyethylene glycol, chitosan, hyaluronic acid, pluronic and tocopheryl polyethylene glycol succinate, is summarized. Parameters influencing the properties of polymeric micelles for oral chemotherapy are discussed and strategies to overcome main barriers for polymeric micelles peroral absorption are proposed.

Expert opinion: During the design of polymeric micelles for peroral chemotherapy, selecting or synthesizing copolymers with good compatibility with the drug is an effective strategy to increase drug loading and encapsulation efficiency. Stability of the micelles can be improved in different ways. It is recommended to take permeability, mucoadhesion, sustained release, and P-glycoprotein inhibition into consideration during copolymer preparation or to consider adding some excipients in the formulation. Furthermore, both the copolymer structure and drug loading methods should be controlled in order to get micelles with appropriate particle size for better absorption.     

Construction and characterization of intestinal oligopeptide transporter PepT1-targeted polymeric micelles for enhanced intestinal absorption of poorly water-soluble agents

To overcome the main barrier of intestinal epithelium for the oral absorption of poorly water-soluble drugs and further improve their oral absorption, Gly-Sar, the substrate of the oligopeptide transporter PepT1 widely distributed in the small intestine,conjugated poly(ethylene glycol)-block-poly(D,L-lactide) (Gly-Sar-PEG-b-PLA) was designed and synthesized, and PepT1-targetedpolymeric micelles were prepared and characterized. The structure of the synthesized Gly-Sar-PEG-b-PLA was confirmed by use of TLC and ¹H-NMR. The average molecular weight measured by GPC was 5954 g/mol with PDI of 1.34. The DiI-loaded polymeric micelles from Gly-Sar-PEG-b-PLA with drug loading content of 0.076% were characterized to exhibit 40.36 nm in diameter with PDI of 0.294, and well-defined spherical shape observed by TEM. Furthermore, the PepT1-targeted polymeric micelles profoundly enhanced intestinal absorption of poorly water-soluble drug. Therefore, the designed PepT1-targeted polymeric micelles might have a promising potential for oral delivery of water-insoluble drugs.     

Polymeric micelles for oral drug administration enabling locoregional and systemic treatments

Introduction: Amphiphilic block copolymers are recognized components of parenteral drug nanocarriers. However, their performance in oral administration has barely been evaluated to any great extent.

Areas covered: This review provides an overview of the methods used to prepare drug-loaded polymeric micelles and to evaluate their stability in gastrointestinal (GI) fluids, and then analyzes in detail recent in vitro and in vivo results about their performance in oral drug delivery. Oral administration of polymeric micelles has been tested for a variety of therapeutic purposes, namely, to increase apparent drug solubility in the GI fluids and facilitate absorption, to penetrate in pathological regions of the GI tract for locoregional treatment, to carry the drug directly toward the blood stream minimizing presystemic loses, and to target the drug after oral absorption to specific tissue or cells in the body.

Expert opinion: Each therapeutic purpose demands micelles with different performance regarding stability in the GI tract, ability to overcome physiological barriers and drug release patterns. Depending on the block copolymer composition and structure, a wealth of self-assembled micelles with different morphologies and stability can be prepared. Moreover, copolymer unimers can play a role in improving drug absorption through the GI mucosa, either by increasing membrane permeability to the drug and/or the carrier or by inhibiting drug efflux transporters or first-pass metabolism. Therefore, polymeric micelles can be pointed out as versatile vehicles to increase oral bioavailability of drugs that exhibit poor solubility or permeability and may even be an alternative to parenteral carriers when targeting is pursued.     

Enhanced blood–brain barrier transport of vinpocetine by oral delivery of mixed micelles in combination with a message guider

The blood–brain barrier represents an insurmountable obstacle for the therapy of central nervous system related diseases. Polymeric micelles have many desirable properties for brain targeting by oral delivery, but the stability and targeting efficiency needs to be improved. In this study, it was demonstrated that binary micelle system can compensate the drawbacks of mono system by preparing mixed micelles in combination with PEG-based copolymers. Here, we explored a brain targeting drug delivery system via facile approaches using P123 based mixed micelles in combination with a message guider from traditional Chinese medicine, borneol, for oral delivery. With higher drug-loading, improved stability, prolonged in vitro release profile, increased bioavailability and enhanced brain targeting effect was achieved after peroral delivery of the mixed micelles. More importantly, without extra structure modification for active targeting, it was demonstrated for the first time that oral delivery of vinpocetine loaded mixed micelles together with borneol is an effective way to increase drug concentration in the brain and the targeting efficiency is borneol dose dependent. Such a “simple but effective” modality may shed light on the potential use of polymeric micelles in combination with a message drug to achieve drug brain targeting or other targeting sites via oral delivery.     

Synthesis of a novel PEG-block-poly(aspartic acid-stat-phenylalanine) copolymer shows potential for formation of a micellar drug carrier

A novel functionalised copolymer with three polymeric components, poly(ethylene glycol)-block-poly(aspartic acid-stat-phenylalanine), PEG-P(asp-phe), was synthesised and investigated for its potential to form micelles via ionic interactions with a model water-soluble drug, diminazene aceturate. Drug-free solutions of structurally related PEG-P(asp-phe) 5:6:4 and PEG-P(asp-phe) 5:4:6 copolymers indicated polymeric aggregation into micellar-type constructs. The size of PEG-P(asp-phe) 5:6:4 micelles was found to be pH and drug content-dependent. The drug-loaded systems existed as discreet units and were fairly uniform in size and shape. More drug could be included in the PEG-P(asp-phe) 5:6:4 micelles as compared to if only interaction with carboxyl groups from aspartic acid units was responsible for micelle formation, indicating the augmentative role of phenylalanine moieties in drug-incorporation. The slower in vitro drug release from PEG-P(asp-phe) 5:6:4 micelles as compared to PEG-Pasp (AB) micelles indicated the role of the phenylalanine moiety in controlling drug release. This study, therefore, confirmed the potential of a novel tri-component copolymer structure, PEG-P(asp-phe), for the formation of polyionic micelles for drug delivery.     

Optimization of self-assembling properties of fatty acids grafted to methoxy poly(ethylene glycol) as nanocarriers for etoposide

The objective of this work was to study the effect of fatty acid chain length grafted to methoxy poly(ethylene glycol) (mPEG) on self assembling properties of micelles for etoposide delivery. Three amphiphilic copolymers were synthesized using mPEG, myristic acid, stearic acid and behenic acid through an esteric linkage. The particle size and zeta potential of the micelles were determined by the dynamic light scattering method. Etoposide was loaded into micelles by film casting using various drug/polymer ratios. Drug release was studied by the dialysis method. The structure of copolymers was confirmed by (1)H NMR and FTIR. Central micellar concentration (CMC) measurements showed that the longer hydrophobic chains formed more thermodynamically stable micelles. Among the prepared copolymers, etoposide showed the highest solubility in the mPEG-behenic copolymer. Drug loading efficiency depended on the hydrophobic chain length and drug/polymer ratio. The highest drug loading efficiency was found in mPEG-myristic micelles with 1:20 drug/polymer ratio. Micelles released 80 % of loaded drug within about 5 h.     

Pharmaceutical evaluation of genistein-loaded pluronic micelles for oral delivery

The purpose of the present study was to determine whether Pluronic F127 polymeric micelles could improve the oral bioavailability of a poor water-soluble drug, such as genistein. Genistein is a phytoestrogen that has estrogenic activity. F127 triblock copolymer consists of PEO100-PPO65-PEO100. Genistein was incorporated in the Pluronic F127 polymeric micelles by a solid dispersion method. The genistein release of genistein-loaded polymeric micelles was studied in vitro (in pH 1.2 and pH 6.8). And the oral bioavailabilities of genistein powder and genistein-loaded micelles were estimated at a dose of 4.0 mg/kg as genistein in rats. Drug loading amount and drug loading efficiency were 11.18% and 97.41%, respectively. The average size of the genistein-loaded polymeric micelles was 27.76 nm. And genistein release of the genistein-loaded polymeric micelles in vitro was 58% (pH 1.2) and 82% (pH 6.8). The bioavailability of genistein-loaded polymeric micelles was better than genistein powder. Consequently, Pluronic F127 polymeric micelles are an effective delivery system for the oral administration of genistein.     

Preparation of Tacrolimus loaded micelles based on poly(ɛ-caprolactone)-poly(ethylene glycol)-poly(ɛ-caprolactone)

Self-assembled polymeric micelles are widely applied in drug delivery system. In this study, Tacrolimus (FK506) loaded micelles were prepared based on biodegradable poly(?-caprolactone)-poly(ethylene glycol)-poly(?-caprolactone) (PCEC) copolymers. Micelles were prepared by self-assembly of triblock copolymer PCEC in distilled water triggered by its amphiphilic characteristics. Drug loading and encapsulation efficiency were determined by adjusting the weight ratio of FK506 and PCEC. The particle size distribution and variation of obtained micelles were determined using Malvern laser particle size analyzer, while the spherical geometry was observed on transmission electron microscope (TEM), and the crystallographic assays were fulfilled by X-ray diffractometer (XRD). Besides, in vitro release profile demonstrated a significant difference between rapid release of free Tacrolimus and much slower and sustained release of FK506 loaded micelles. These results suggested that we have successfully prepared Tacrolimus loaded micelles in an improved method which is safer and more efficient. The prepared micelles might be potential carriers for Tacrolimus delivery in immunosuppressive therapy.     

Antitumor activity of adriamycin-incorporated polymeric micelles of poly(gamma-benzyl L-glutamate)/poly(ethylene oxide)

The multiblock copolymer composed of poly(gamma-benzyl L-glutamate) (PBLG) and poly(ethylene oxide) (PEO) was synthesized to prepare polymeric micelles as an anticancer drug carrier. Adriamycin (ADR) used as an anticancer drug was incorporated into the polymeric micelles prepared by the multiblock copolymer. The higher the drug feeding ratio, the higher the drug loading contents and the lower the drug loading efficiency. The increased drug feeding ratio resulted in increased particle sizes. At all of the formulations, particle sizes were less than 150 nm. The particles were observed as spherical shapes. ADR release from ADR-loaded polymeric micelles in vitro was decreased with an increased drug loading contents. In in vitro antitumor activity test using CT 26 tumor cells, polymeric micelles showed almost similar cytotoxicity when compared to ADR itself while polymeric micelles themselves did not affect cytotoxicity. In in vivo antitumor activity test using mice tumor xenograft model, the polymeric micelles showed improved survivability of mice with minimized weight changes and excellent tumor growth suppression efficacy. Polymeric micelles of the multiblock copolymer suggested to be a good candidate for anticancer drug delivery carrier.     

Renewable poly(δ-decalactone) based block copolymer micelles as drug delivery vehicle: in vitro and in vivo evaluation

Polymers from natural resources are attracting much attention in various fields including drug delivery as green alternatives to fossil fuel based polymers. In this quest, novel block copolymers based on renewable poly(δ-decalactone) (PDL) were evaluated for their drug delivery capabilities and compared with a fossil fuel based polymer i.e. methoxy-poly(ethylene glycol)-b-poly(ε-caprolactone) (mPEG-b-PCL). Using curcumin as a hydrophobic drug model, micelles of PDL block copolymers with different orientation i.e. AB (mPEG-b-PDL), ABA (PDL-b-PEG-b-PDL), ABC (mPEG-b-PDL-b-poly(pentadecalactone) and (mPEG-b-PCL) were prepared by nanoprecipitation method. The size, drug loading and curcumin stability studies results indicated that mPEG-b-PDL micelles was comparable to its counterpart mPEG-b-PCL micelles towards improved delivery of curcumin. Therefore, mixed micelles using these two copolymers were also evaluated to see any change in size, loading and drug release. Drug release studies proposed that sustained release can be obtained using poly(pentadecalactone) as crystalline core whereas rapid release can be achieved using amorphous PDL core. Further, mPEG-b-PDL micelles were found to be non-haemolytic, up to the concentration of 40?mg/mL. In vivo toxicity studies on rats advised low-toxic behaviour of these micelles up to 400?mg/kg dose, as evident by histopathological and biochemical analysis. In summary, it is anticipated that mPEG-b-PDL block copolymer micelles could serve as a renewable alternative for mPEG-b-PCL copolymers in drug delivery applications.     

Formulation of drugs in block copolymer micelles: drug loading and release

Block copolymer micelles have become accepted as a viable strategy for drug formulation and delivery. Block copolymer micelles may serve as solubilizers and/or true drug carriers depending on their drug retention properties in vivo. Indeed the formulation of hydrophobic drugs in these micelle systems has been shown to provide up to a 30,000 fold increase in the water solubility of some compounds. In addition, the administration of drugs in copolymer micelles has been shown to reduce their toxicity and improve their therapeutic efficacy. The present review is focused on the drug loading and release properties of block copolymer micelles. Specifically, the properties of the drug, properties of the micelle core and the presence of interactions between the drug and the core-forming block are discussed in terms of their influence on the drug loading and release properties of the micelles. The various methods employed to prepare drug-loaded micelles are reviewed and the in vitro release assays used to predict the in vivo release characteristics of the formulations are discussed. The balance between drug loading and micelle stability is highlighted as a critical factor in the optimization of micelle-based formulations. The in vivo performance of micelles as delivery systems is evaluated by comparing the pharmacokinetics of free drug and drug administered in micelle-based formulations. Overall, the composition-property and property-performance relationships outlined in this review may aid in guiding the rational design of block copolymer micelles for drug delivery. In addition, suggestions for future research in this area are provided as a means to assist in furthering block copolymer micelles as one of the leading advanced drug delivery technologies for the systemic administration of drugs.     

Paclitaxel-loaded polymeric micelles based on poly(ɛ-caprolactone)-poly(ethylene glycol)-poly(ɛ-caprolactone) triblock copolymers: in vitro and in vivo evaluation

The purpose of this study was to develop polymeric nanoscale drug-delivery system (nano-DDS) for paclitaxel (PTX) from poly(?-caprolactone)-poly(ethylene glycol)-poly(?-caprolactone) (PCL-PEG-PCL, PCEC) copolymers, intended to be intravenously administered, able to improve the therapeutic efficacy of the drug and devoid of the adverse effects of Cremophor EL. Both of the PTX-loaded polymeric micelles and polymersomes were successfully prepared from PCEC copolymers. The obtained PTX-loaded micelles exhibited core-shell morphology with satisfactory size (93 nm), and were favorable for intravenous injection. In vitro cytotoxicity demonstrated that the cytotoxic effect of PTX-loaded micelles was lower than that of Taxol (Bristol-Myers Squibb, Princeton, New Jersey). Pharmacokinetic results indicated that the PTX-loaded micelles had longer systemic circulation time and slower plasma elimination rate than those of Taxol. Furthermore, PTX-loaded micelles showed greater tumor growth-inhibition effect in vivo on EMT6 breast tumor, in comparison with Taxol. Therefore, the prepared polymeric micelles might be potential nano-DDS for PTX delivery in cancer chemotherapy.From the Clinical EditorIn this paper, a paclitaxel- loaded polymeric micelle system is demonstrated to provide optimized intravenous delivery method of this anti-cancer agent. While the study is early preclinical, this approach may have the potential to eventually be studied in clinical trials as well.     

Intelligent polymeric micelles from functional poly(ethylene glycol)-poly(amino acid) block copolymers

This review describes our recent efforts on the design and preparation of intelligent polymeric micelles from functional poly(ethylene glycol)-poly(amino acid) (PEG-PAA) block copolymers. The polymeric micelles feature a spherical sub-100 nm core-shell structure in which anticancer drugs are loaded avoiding undesirable interactions in vivo. Chemical modification of the core-forming block of PEG-PAA with a hydrazone linkage allows the polymeric micelles to release drugs selectively at acidic pH (4-6). Installation of folic acids on the micelle surface improves cancer cell-specific drug delivery efficiency along with pH-controlled drug release. These intelligent micelles appear to be superior over classical micelles that physically incorporate drugs. Studies showed both controlled drug release and targeted delivery features of the micelles reduced toxicity and improved efficacy significantly. Further developments potentiate combination delivery of multiple drugs using mixed micelles. Therefore clinically relevant performance of the polymeric micelles provides a promising approach for more efficient and patient-friendly cancer therapy.     

Enhanced oral bioavailability of paclitaxel in pluronic/LHR mixed polymeric micelles: preparation, in vitro and in vivo evaluation

In order to enhance paclitaxel oral bioavailability, mixed polymeric micelles that comprised of pluronic copolymers and low molecular weight heparin-all-trans-retinoid acid (LHR) conjugate were developed. PTX-loaded mixed polymeric micelles (MPMs) were prepared by dialysis method with high drug loading 26.92 ± 2.08% and 25.82 ± 1.9% for F127/LHR and P188/LHR MPMs respectively, and were found to be spherical in shape with an average size of around 140 nm and a narrow size distribution. In vitro release study showed that pluronic/LHR MPMs exhibited delayed release characteristics compared to Taxol and faster drug release profile compared to LHR plain polymeric micelles (PPMs). The cytotoxic activity of PTX-loaded pluronic/LHR MPMs was slightly higher than LHR PPMs in MCF-7 cells (p<0.01). In situ effective permeability of PTX through rat small intestine was 5- to 6-fold higher with mixed micelles than that of Taxol. Moreover, pluronic/LHR MPMs achieved significantly higher AUC and C(max) level than both of LHR PPMs and Taxol. This enhancement might be due to the inhibition of both P-glycoprotein efflux system and cytochrome P450 metabolism by pluronic copolymers. The current results encourage further development of paclitaxel mixed polymeric micelles as an oral drug delivery system.     

PEGylated nanoparticles for biological and pharmaceutical applications

The utility of polymeric micelles formed through the multimolecular assembly of block copolymer was comprehensively described as novel core–shell typed colloidal carriers for drug and gene targeting. Particularly, novel approaches for the formation of functionalized poly(ethylene glycol) (PEG) layers as hydrophilic outer shell were focused to attain receptor-mediated drug and gene delivery through PEG-conjugated ligands with a minimal non-specific interaction with other proteins. Surface organization of block copolymer micelles with cross-linking core was also described from a standpoint of the preparation of a new functional surface-coating with a unique macromolecular architecture. The micelle-attached surface and the thin hydrogel layer made by layered micelles exhibited nonfouling properties and worked as the reservoir for hydrophobic reagents. Furthermore, the potential utility of multimolecular assembly derived from heterobifunctional PEGs and block copolymers were explored to systematically modify the properties of metal and semiconductor nanostructures by controlling their structure and their surface properties, making them extremely attractive for use in biological and biomedical applications.     

PEGylated nanoparticles for biological and pharmaceutical applications

The utility of polymeric micelles formed through the multimolecular assembly of block copolymer was comprehensively described as novel core-shell typed colloidal carriers for drug and gene targeting. Particularly, novel approaches for the formation of functionalized poly(ethylene glycol) (PEG) layers as hydrophilic outer shell were focused to attain receptor-mediated drug and gene delivery through PEG-conjugated ligands with a minimal non-specific interaction with other proteins. Surface organization of block copolymer micelles with cross-linking core was also described from a standpoint of the preparation of a new functional surface-coating with a unique macromolecular architecture. The micelle-attached surface and the thin hydrogel layer made by layered micelles exhibited nonfouling properties and worked as the reservoir for hydrophobic reagents. Furthermore, the potential utility of multimolecular assembly derived from heterobifunctional PEGs and block copolymers were explored to systematically modify the properties of metal and semiconductor nanostructures by controlling their structure and their surface properties, making them extremely attractive for use in biological and biomedical applications.     

Local Delivery of Indomethacin to Arthritis-Bearing Rats through Polymeric Micelles Based on Amphiphilic Polyphosphazenes

Purpose Preparation, in vitro and in vivo evaluation of indomethacin-loaded polymeric micelles based on amphiphilic polyphosphazene. Methods Amphiphilic polyphosphazenes (PNIPAAm/EAB-PPPs) with poly (N-isopropylacrylamide) (PNIPAAm) and ethyl 4-aminobenzoate (EAB) as side groups were synthesized through thermal ring-opening polymerization and subsequent substitution reactions. Indomethacin (IND) loaded polymeric micelles based on PNIPAAm/EAB-PPPs were prepared by dialysis procedure. In vitro IND release kinetics was investigated in 0.1 M PBS (pH 7.4), while in vivo pharmacokinetics was performed in Sprague–Dawley rats. In vivo pharmacodynamic study was carried out based on two animal models, i.e. carrageenan-induced acute paw edema and complete Freund’s adjuvant (CFA) induced ankle arthritis model. Results Drug loading capacity of micelles based on this type of amphiphilic copolymers was mainly determined by copolymer composition and the chemical structure of drug. In addition to the compatibility between drug and micellar core, hydrogen bonding interaction between drug and hydrophilic corona may significantly influence drug loading as well. In vitro drug release in PBS suggested that there was no significant difference in release rate between micelles based on copolymers with various EAB content. Compared with the rats administered with free IND aqueous solution, IND concentration in rats’ plasma showed a prolonged maintenance in experimental group treated with IND-loaded polymeric micelles. In vivo pharmacodynamic study indicated that sustained therapeutic efficacy could be achieved through topical injection of the aqueous solution of IND-loaded micelles. Local delivery of IND can avoid the severe gastrointestinal stimulation, which was frequently associated with oral administration as evidenced by ulceration evaluation. Conclusions The promising results of current preliminary study suggest that this type of amphiphilic copolymers could be used as injectable drug carriers for hydrophobic drugs.     

Micelles in anticancer drug delivery

In recent years, the development of micelle-based carriers for cancer chemotherapy has been the object of growing scientific interest, both in academia and the pharmaceutical industry. Micelles have attracted attention in drug formulation and targeting, given that they provide a set of unique features. The core/shell structure accounts for their qualities as efficient drug delivery systems. The core provides a reservoir where hydrophobic drugs can be dissolved, and the corona confers hydrophilicity to the overall system. Sequestration of anticancer drugs in the inner core can protect them from premature degradation and allow their accumulation at tumoral sites. Micelles can be subdivided into two different groups according to their molecular weights: low-molecular-weight surfactant micelles and polymeric micelles. Although surfactant micelles such as polyethoxylated castor oil (e.g. Cremophor® EL) are commonly used to solubilize hydrophobic anticancer drugs such as paclitaxel, they have often been associated with serious adverse effects. Polymeric micelles may offer several advantages over surfactant micelles in terms of drug loading, adverse effects, stability, and targeting of tumors. Indeed, polymeric micelles can increase the circulation time of cytostatics and induce substantial changes in their biodistribution, including tumor accumulation via the enhanced permeation and retention effect. In addition, some recent studies have demonstrated that amphiphilic block copolymers (e.g. poloxamers) used for the preparation of polymeric micelles could increase the activity of several cytostatics by reversing multidrug resistance. This review first describes and compares surfactant micelle and polymeric micelle systems, already commercialized or under investigation, used to administer cytostatics. Secondly, their in vitro interactions with neoplastic cells and tissues are discussed in terms of cellular uptake and pharmacologic activity. In particular, the pharmacokinetics and biodistribution of micelles, along with the factors affecting their delivery to tumoral sites, are thoroughly discussed. Finally, in vivo studies reporting the anticancer activity and toxicity of drugs associated with micelles are reviewed.     

Synthesis and evaluation of biotin-conjugated pH-responsive polymeric micelles as drug carriers

pH-Responsive polymeric micelles have been investigated as drug carriers for chemotherapy. Ligand-mediated polymeric micelles, which can penetrate the target tumors due to their high binding affinity to a specific receptor on the surface of tumors, were developed to achieve targeted drug delivery. In this study, biotin-conjugated methoxypoly(ethylene glycol)-grafted-poly(β-amino ester) was prepared for active and pH-sensitive tumor targeting. These polymers were modified by cholesteryl chloroformate to improve the hydrophobicity of the micelle core. The structure of the biotin-conjugated polymer was confirmed by (1)H NMR spectroscopy, and the existence of biotin at the surface of the polymeric micelles was evaluated by an 4'-hydroxyazobenzene-2-carboxylic acid/avidin (HABA/avidin) binding assay at different pHs. The micelle properties were determined by dynamic light scattering and the result showed that the mean size of the polymeric micelles was approximately 20 nm. For cancer therapy, doxorubicin (DOX) was loaded into the polymeric micelles with a high loading efficiency. From the in vitro cellular uptake results, the biotin-conjugated polymeric micelles can effectively release doxorubicin at acidic tumor cells compared to the micelles without biotin. Overall, biotin-conjugated pH-responsive polymeric micelles have great potential to be used as drug carriers.