Special Issue "Responsive Polymers for Drug Delivery, Imaging and Theranostic Functions"

A special issue of Polymers (ISSN 2073-4360).

Deadline for manuscript submissions: closed (15 September 2016).

Special Issue Editors

Prof. Dr. Shiyong Liu
Website
Guest Editor
Department of Polymer Science and Engineering, CAS Key Laboratory of Soft Matter Chemistry, Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, 96 Jinzhai Road, Hefei, Anhui Province 230026, China
Interests: responsive polymers; supramolecular functional materials; polymer chemistry; biomaterials; chemosensors and biosensors; kinetics in complex fluids
Prof. Dr. Jinming Hu
Website
Guest Editor
Department of Polymer Science and Engineering, CAS Key Laboratory of Soft Matter Chemistry, University of Science and Technology of China, 96 Jinzhai Road, Hefei, Anhui Province 230026, China
Interests: stimuli-responsive polymers; supramolecular functional materials; hybrid nanomaterials; chemosensors and biosensors; imaging and theranostic agents
Prof. Dr. Ravin Narain
Website
Guest Editor
Department of Chemical and Materials Engineering, Donadeo Innovation Centre for Engineering, Faculty of Engineering, University of Alberta, Edmonton, AB T6G 1H9, Canada
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

Similar to living systems that can nonlinearly respond to external applied stimuli/signals, responsive polymers can undergo drastic changes in chemical and (or) physical properties to adapt to the surrounding environment which made them unique materials for a wide of applications including drug delivery, imaging, theranostic agents, tissue engineering, self-healing/shape-memory materials, as well as smart coatings and textiles. Notably, despite tremendous achievements, emerging outcomes have continuously bloomed from ever-increasing understanding of delicate polymer synthesis, advanced characterization techniques, and versatile functional integrations of responsive polymers.

This Specific Issue entitled “Responsive Polymers for Drug Delivery, Imaging and Theranostic Functions” will cover the recent development of responsive polymers ranging from precise design and synthesis, controlled self-assembly, and functional applications, particularly in the fields of drug and gene delivery, imaging, and theranostics. However, topics may also encompass other fundamental fields, such as kinetic transitions of responsive polymers in equilibrium and non-equilibrium states and theoretical elucidation of responsive behavior and underlying mechanisms. Contributions from both original research studies and comprehensive reviews are welcome.

Prof. Dr. Shiyong Liu
Prof. Dr. Jinming Hu
Prof. Dr. Ravin Narain
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

 

Keywords

  • stimuli-responsive
  • supramolecular assemblies
  • functional applications
  • biomedical and biomimetic materials
  • drug and gene delivery
  • therapeutic agents
  • imaging and theranostic agents
  • self-healing materials
  • shape-memory polymers
  • chemosensors and biosensors

Published Papers (10 papers)

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Research

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Open AccessArticle
Synthesis of Novel Temperature- and pH-Sensitive ABA Triblock Copolymers P(DEAEMA-co-MEO2MA-co-OEGMA)-b-PEG-b-P(DEAEMA-co-MEO2MA-co-OEGMA): Micellization, Sol–Gel Transitions, and Sustained BSA Release
Polymers 2016, 8(11), 367; https://doi.org/10.3390/polym8110367 - 11 Nov 2016
Cited by 2
Abstract
Novel temperature- and pH-responsive ABA-type triblock copolymers, P(DEAEMA-co-MEO2MA-co-OEGMA)-b-PEG-b-P(DEAEMA-co-MEO2MA-co-OEGMA), composed of a poly(ethylene glycol) (PEG) middle block and temperature- and pH-sensitive outer blocks, were synthesized by atom transfer [...] Read more.
Novel temperature- and pH-responsive ABA-type triblock copolymers, P(DEAEMA-co-MEO2MA-co-OEGMA)-b-PEG-b-P(DEAEMA-co-MEO2MA-co-OEGMA), composed of a poly(ethylene glycol) (PEG) middle block and temperature- and pH-sensitive outer blocks, were synthesized by atom transfer radical polymerization (ATRP). The composition and structure of the copolymer were characterized by 1H NMR and gel permeation chromatography (GPC). The temperature- and pH-sensitivity, micellization, and the sol–gel transitions of the triblock copolymers in aqueous solutions were studied using transmittance measurements, surface tension, viscosity, fluorescence probe technique, dynamic light scattering (DLS), zeta-potential measurements, and transmission electron microscopy (TEM). The lower critical solution temperature (LCST) of the triblock copolymer, which contains a small amount of a weak base group, (N,N-diethylamino) ethyl methacrylate (DEAEMA), can be tuned precisely and reversibly by changing the solution pH. When the copolymer concentration was sufficiently high, increasing temperature resulted in the free-flowing solution transformation into a micellar gel. The sol-to-gel transition temperature (Tsol–gel) in aqueous solution will continue to decrease as solution concentration increases. Full article
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Open AccessArticle
Synthesis of Thermo-Responsive Polymer via Radical (Co)polymerization of N,N-Dimethyl-α-(hydroxymethyl)acrylamide with N,N-Diethylacrylamide
Polymers 2016, 8(10), 374; https://doi.org/10.3390/polym8100374 - 20 Oct 2016
Cited by 3
Abstract
α-Functionalized acrylamides have not been considered as an effective monomer design due to their poor polymerizability, although the analogues, α-functionalized acrylates, are attractive monomers of which polymers exhibit characteristic properties. In this article, we report the first example of radical polymerization of α-functionalized [...] Read more.
α-Functionalized acrylamides have not been considered as an effective monomer design due to their poor polymerizability, although the analogues, α-functionalized acrylates, are attractive monomers of which polymers exhibit characteristic properties. In this article, we report the first example of radical polymerization of α-functionalized N,N-disubstituted acrylamide affording thermo-responsive hydrophilic polymers. N,N-dimethyl-α-(hydroxymethyl)acrylamide (DMαHAA) was (co)polymerized with N,N-diethylacrylamide (DEAA). Although the homopolymerization did not afford a polymeric product, the copolymerizations with various feed ratios yielded a series of the copolymers containing 0%–65% of DMαHAA units. The obtained copolymers exhibited a lower critical solution temperature (LCST) in water; the cloud points (Tcs) were linearly elevated as the contents of DMαHAA units from 32 to 64 °C, indicating that DMαHAA functioned as a more hydrophilic monomer than DEAA. The linear relationship between Tc and DMαHAA content suggests that the homopolymer, poly(DMαHAA), should have Tc at ca. 80 °C, although it is not available by direct radical homopolymerization. Full article
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Open AccessFeature PaperArticle
Surface Immobilization of pH-Responsive Polymer Brushes on Mesoporous Silica Nanoparticles by Enzyme Mimetic Catalytic ATRP for Controlled Cargo Release
Polymers 2016, 8(8), 277; https://doi.org/10.3390/polym8080277 - 02 Aug 2016
Cited by 23
Abstract
Peroxidase mimetic catalytic atom transfer radical polymerization (ATRP) was first used to install tertiary amine-functionalized polymer brushes on the surface of mesoporous silica nanoparticles (MSNs) in a facile and highly efficient manner. Poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) brushes-grafted MSNs were fabricated [...] Read more.
Peroxidase mimetic catalytic atom transfer radical polymerization (ATRP) was first used to install tertiary amine-functionalized polymer brushes on the surface of mesoporous silica nanoparticles (MSNs) in a facile and highly efficient manner. Poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) brushes-grafted MSNs were fabricated by biocompatible deuterohemin-β-Ala-His-Thr-Val-Glu-Lys (DhHP-6)-catalyzed surface-initiated ATRP (SI-ATRP). The resulting organic–inorganic hybrid nanocarriers were fully characterized by Fourier transform-infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), SEM, TEM, Elemental analysis, Zeta-potential, and N2 adsorption–desorption isotherms, which demonstrated the successful coating of pH-responsive polymers on the MSN surface. Rhodamine 6G (Rh6G) dyes were further loaded within the mesopores of this nanocarrier, and the release of Rh6G out of MSNs in a controlled fashion was achieved upon lowing the solution pH. The electrostatic repulsion of positively-charged tertiary ammonium of PDMAEMAs in acidic environments induced the stretching out of polymer brushes on MSN surfaces, thus opening the gates to allow cargo diffusion out of the mesopores of MSNs. Full article
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Open AccessArticle
pH-Responsive Tumor-Targetable Theranostic Nanovectors Based on Core Crosslinked (CCL) Micelles with Fluorescence and Magnetic Resonance (MR) Dual Imaging Modalities and Drug Delivery Performance
Polymers 2016, 8(6), 226; https://doi.org/10.3390/polym8060226 - 07 Jun 2016
Cited by 9
Abstract
The development of novel theranostic nanovectors is of particular interest in treating formidable diseases (e.g., cancers). Herein, we report a new tumor-targetable theranostic agent based on core crosslinked (CCL) micelles, possessing tumor targetable moieties and fluorescence and magnetic resonance (MR) dual imaging modalities. [...] Read more.
The development of novel theranostic nanovectors is of particular interest in treating formidable diseases (e.g., cancers). Herein, we report a new tumor-targetable theranostic agent based on core crosslinked (CCL) micelles, possessing tumor targetable moieties and fluorescence and magnetic resonance (MR) dual imaging modalities. An azide-terminated diblock copolymer, N3-POEGMA-b-P(DPA-co-GMA), was synthesized via consecutive atom transfer radical polymerization (ATRP), where OEGMA, DPA, and GMA are oligo(ethylene glycol)methyl ether methacrylate, 2-(diisopropylamino)ethyl methacrylate, and glycidyl methacrylate, respectively. The resulting diblock copolymer was further functionalized with DOTA(Gd) (DOTA is 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakisacetic acid) or benzaldehyde moieties via copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) chemistry, resulting in the formation of DOTA(Gd)-POEGMA-b-P(DPA-co-GMA) and benzaldehyde-POEGMA-b-P(DPA-co-GMA) copolymers. The resultant block copolymers co-assembled into mixed micelles at neutral pH in the presence of tetrakis[4-(2-mercaptoethoxy)phenyl]ethylene (TPE-4SH), which underwent spontaneous crosslinking reactions with GMA residues embedded within the micellar cores, simultaneously switching on TPE fluorescence due to the restriction of intramolecular rotation. Moreover, camptothecin (CPT) was encapsulated into the crosslinked cores at neutral pH, and tumor-targeting pH low insertion peptide (pHLIP, sequence: AEQNPIYWARYADWLFTTPLLLLDLALLVDADEGTCG) moieties were attached to the coronas through the Schiff base chemistry, yielding a theranostic nanovector with fluorescence and MR dual imaging modalities and tumor-targeting capability. The nanovectors can be efficiently taken up by A549 cells, as monitored by TPE fluorescence. After internalization, intracellular acidic pH triggered the release of loaded CPT, killing cancer cells in a selective manner. On the other hand, the nanovectors labeled with DOTA(Gd) contrast agents exhibited increased relaxivity (r1 = 16.97 mM−1·s−1) compared to alkynyl-DOTA(Gd) small molecule precursor (r1 = 3.16 mM−1·s−1). Moreover, in vivo MRI (magnetic resonance imaging) measurements revealed CCL micelles with pHLIP peptides exhibiting better tumor accumulation and MR imaging performance as well. Full article
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Review

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Open AccessReview
Light-Responsive Polymer Micro- and Nano-Capsules
Polymers 2017, 9(1), 8; https://doi.org/10.3390/polym9010008 - 29 Dec 2016
Cited by 31
Abstract
A significant amount of academic and industrial research efforts are devoted to the encapsulation of active substances within micro- or nanocarriers. The ultimate goal of core–shell systems is the protection of the encapsulated substance from the environment, and its controlled and targeted release. [...] Read more.
A significant amount of academic and industrial research efforts are devoted to the encapsulation of active substances within micro- or nanocarriers. The ultimate goal of core–shell systems is the protection of the encapsulated substance from the environment, and its controlled and targeted release. This can be accomplished by employing “stimuli-responsive” materials as constituents of the capsule shell. Among a wide range of factors that induce the release of the core material, we focus herein on the light stimulus. In polymers, this feature can be achieved introducing a photo-sensitive segment, whose activation leads to either rupture or modification of the diffusive properties of the capsule shell, allowing the delivery of the encapsulated material. Micro- and nano-encapsulation techniques are constantly spreading towards wider application fields, and many different active molecules have been encapsulated, such as additives for food-packaging, pesticides, dyes, pharmaceutics, fragrances and flavors or cosmetics. Herein, a review on the latest and most challenging polymer-based micro- and nano-sized hollow carriers exhibiting a light-responsive release behavior is presented. A special focus is put on systems activated by wavelengths less harmful for living organisms (mainly in the ultraviolet, visible and infrared range), as well as on different preparation techniques, namely liposomes, self-assembly, layer-by-layer, and interfacial polymerization. Full article
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Open AccessReview
Recent Advances in Dual Temperature Responsive Block Copolymers and Their Potential as Biomedical Applications
Polymers 2016, 8(11), 380; https://doi.org/10.3390/polym8110380 - 27 Oct 2016
Cited by 50
Abstract
The development of stimuli responsive polymers has progressed significantly with novel preparation techniques, which has allowed access to new materials with unique properties. Dual thermoresponsive (double temperature responsive) block copolymers are particularly of interest as their properties can change depending on the lower [...] Read more.
The development of stimuli responsive polymers has progressed significantly with novel preparation techniques, which has allowed access to new materials with unique properties. Dual thermoresponsive (double temperature responsive) block copolymers are particularly of interest as their properties can change depending on the lower critical solution temperature (LCST) or upper critical solution temperature (UCST) of each segment. For instance, these block copolymers can change from being hydrophilic, to amphiphilic or to hydrophobic simply by changing the solution temperature without any additional chemicals and the block copolymers can change from being fully solubilized to self-assembled structures to macroscopic aggregation/precipitation. Based on the unique solution properties, these dual thermo-responsive block copolymers are expected to be suitable for biomedical applications. This review is divided into three parts; LCST-LCST types of block copolymers, UCST-LCST types of block copolymers, and their potential as biomedical applications. Full article
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Open AccessReview
Emerging Multifunctional NIR Photothermal Therapy Systems Based on Polypyrrole Nanoparticles
Polymers 2016, 8(10), 373; https://doi.org/10.3390/polym8100373 - 20 Oct 2016
Cited by 22
Abstract
Near-infrared (NIR)-light-triggered therapy platforms are now considered as a new and exciting possibility for clinical nanomedicine applications. As a promising photothermal agent, polypyrrole (PPy) nanoparticles have been extensively studied for the hyperthermia in cancer therapy due to their strong NIR light photothermal effect [...] Read more.
Near-infrared (NIR)-light-triggered therapy platforms are now considered as a new and exciting possibility for clinical nanomedicine applications. As a promising photothermal agent, polypyrrole (PPy) nanoparticles have been extensively studied for the hyperthermia in cancer therapy due to their strong NIR light photothermal effect and excellent biocompatibility. However, the photothermal application of PPy based nanomaterials is still in its preliminary stage. Developing PPy based multifunctional nanomaterials for cancer treatment in vivo should be the future trend and object for cancer therapy. In this review, the synthesis of PPy nanoparticles and their NIR photothermal conversion performance were first discussed, followed by a summary of the recent progress in the design and implementation on the mulitifunctionalization of PPy or PPy based therapeutic platforms, as well as the introduction of their exciting biomedical applications based on the synergy between the photothermal conversion effect and other stimulative responsibilities. Full article
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Open AccessReview
A Review of Thermo- and Ultrasound-Responsive Polymeric Systems for Delivery of Chemotherapeutic Agents
Polymers 2016, 8(10), 359; https://doi.org/10.3390/polym8100359 - 18 Oct 2016
Cited by 28
Abstract
There has been an exponential increase in research into the development of thermal- and ultrasound-activated delivery systems for cancer therapy. The majority of researchers employ polymer technology that responds to environmental stimuli some of which are physiologically induced such as temperature, pH, as [...] Read more.
There has been an exponential increase in research into the development of thermal- and ultrasound-activated delivery systems for cancer therapy. The majority of researchers employ polymer technology that responds to environmental stimuli some of which are physiologically induced such as temperature, pH, as well as electrical impulses, which are considered as internal stimuli. External stimuli include ultrasound, light, laser, and magnetic induction. Biodegradable polymers may possess thermoresponsive and/or ultrasound-responsive properties that can complement cancer therapy through sonoporation and hyperthermia by means of High Intensity Focused Ultrasound (HIFU). Thermoresponsive and other stimuli-responsive polymers employed in drug delivery systems can be activated via ultrasound stimulation. Polyethylene oxide/polypropylene oxide co-block or triblock polymers and polymethacrylates are thermal- and pH-responsive polymer groups, respectively but both have proven to have successful activity and contribution in chemotherapy when exposed to ultrasound stimulation. This review focused on collating thermal- and ultrasound-responsive delivery systems, and combined thermo-ultrasonic responsive systems; and elaborating on the advantages, as well as shortcomings, of these systems in cancer chemotherapy. The mechanisms of these systems are explicated through their physical alteration when exposed to the corresponding stimuli. The properties they possess and the modifications that enhance the mechanism of chemotherapeutic drug delivery from systems are discussed, and the concept of pseudo-ultrasound responsive systems is introduced. Full article
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Open AccessReview
Stimuli-Directed Helical Chirality Inversion and Bio-Applications
Polymers 2016, 8(8), 310; https://doi.org/10.3390/polym8080310 - 18 Aug 2016
Cited by 17
Abstract
Helical structure is a sophisticated ubiquitous motif found in nature, in artificial polymers, and in supramolecular assemblies from microscopic to macroscopic points of view. Significant progress has been made in the synthesis and structural elucidation of helical polymers, nevertheless, a new direction for [...] Read more.
Helical structure is a sophisticated ubiquitous motif found in nature, in artificial polymers, and in supramolecular assemblies from microscopic to macroscopic points of view. Significant progress has been made in the synthesis and structural elucidation of helical polymers, nevertheless, a new direction for helical polymeric materials, is how to design smart systems with controllable helical chirality, and further use them to develop chiral functional materials and promote their applications in biology, biochemistry, medicine, and nanotechnology fields. This review summarizes the recent progress in the development of high-performance systems with tunable helical chirality on receiving external stimuli and discusses advances in their applications as drug delivery vesicles, sensors, molecular switches, and liquid crystals. Challenges and opportunities in this emerging area are also presented in the conclusion. Full article
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Open AccessFeature PaperReview
Stimuli-Responsive Block Copolymer-Based Assemblies for Cargo Delivery and Theranostic Applications
Polymers 2016, 8(7), 268; https://doi.org/10.3390/polym8070268 - 22 Jul 2016
Cited by 28
Abstract
Although a number of tactics towards the fabrication and biomedical exploration of stimuli-responsive polymeric assemblies being responsive and adaptive to various factors have appeared, the controlled preparation of assemblies with well-defined physicochemical properties and tailor-made functions are still challenges. These responsive polymeric assemblies, [...] Read more.
Although a number of tactics towards the fabrication and biomedical exploration of stimuli-responsive polymeric assemblies being responsive and adaptive to various factors have appeared, the controlled preparation of assemblies with well-defined physicochemical properties and tailor-made functions are still challenges. These responsive polymeric assemblies, which are triggered by stimuli, always exhibited reversible or irreversible changes in chemical structures and physical properties. However, simple drug/polymer nanocomplexes cannot deliver or release drugs into the diseased sites and cells on-demand due to the inevitable biological barriers. Hence, utilizing therapeutic or imaging agents-loaded stimuli-responsive block copolymer assemblies that are responsive to tumor internal microenvironments (pH, redox, enzyme, and temperature, etc.) or external stimuli (light and electromagnetic field, etc.) have emerged to be an important solution to improve therapeutic efficacy and imaging sensitivity through rationally designing as well as self-assembling approaches. In this review, we summarize a portion of recent progress in tumor and intracellular microenvironment responsive block copolymer assemblies and their applications in anticancer drug delivery and triggered release and enhanced imaging sensitivity. The outlook on future developments is also discussed. We hope that this review can stimulate more revolutionary ideas and novel concepts and meet the significant interest to diverse readers. Full article
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