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Special Issue "Stimuli-Responsive Polymeric Materials"

A special issue of Molecules (ISSN 1420-3049).

Deadline for manuscript submissions: closed (28 February 2019).

Special Issue Editor

Prof. Dr. Il Kim
Website
Guest Editor
Department of Polymer Science and Engineering, Pusan National University, Busan, South Korea
Interests: Polymer synthesis; Polymerization catalysis; Bionanotechnology; Hyperbranched polymers; Polypeptides; Thermoplastic elastomers
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Special Issue Information

Dear Colleagues,

The rapidly-growing field of polymer science has come up with many advances in stimuli-responsive nanomaterials by the design and development of multi-functional polymers, novel architectures, and new synthetic approaches for various targeted applications. The nano-assemblies of polymers with a broad range of stimuli, such as pH, temperature, enzyme, light, redox, electric field, magnetic field, etc., have proven to be promising as adaptive shape memory materials, responsive coatings, controlled release materials, self-healing materials and catalysts. The response is evident by the change in conformation or change in solubility of the polymer, resulting in a change in the properties that translated into macroscopic behaviors. Contemporary synthetic protocols coupled with facile characterization and rigorous theoretical advances have conspired to continuously generate stimuli-responsive polymeric nanomaterials that target applications spanning drug delivery, tissue engineering, bio separation, medical diagnostics and biosensors. This Special Issue, entitled “Stimuli-Responsive Polymeric Materials” will cover synthesis of stimuli responsive copolymers with different polymeric architectures like block copolymers, star, graft, dendritic copolymers, etc., their self-assembly, physio-chemical properties in solution, gels and solid state and various applications. Reviews articles by experts in the field will also be welcome.

Prof. Dr. Il Kim
Guest Editor

Manuscript Submission Information

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Keywords

  • stimulus-responsive (co)polymer
  • smart/intelligent materials
  • shape memory materials
  • self-healing materials
  • sensors and biosensors
  • controlled drug delivery
  • artificial muscles and actuators
  • polymer synthesis
  • computer modelling
  • testing methods

Published Papers (12 papers)

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Research

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Open AccessArticle
Fabrication and Characterisation of Stimuli Responsive Piezoelectric PVDF and Hydroxyapatite-Filled PVDF Fibrous Membranes
Molecules 2019, 24(10), 1903; https://doi.org/10.3390/molecules24101903 - 17 May 2019
Cited by 3
Abstract
Poly(vinylidene fluoride) has attracted interest from the biomaterials community owing to its stimuli responsive piezoelectric property and promising results for application in the field of tissue engineering. Here, solution blow spinning and electrospinning were employed to fabricate PVDF fibres and the variation in [...] Read more.
Poly(vinylidene fluoride) has attracted interest from the biomaterials community owing to its stimuli responsive piezoelectric property and promising results for application in the field of tissue engineering. Here, solution blow spinning and electrospinning were employed to fabricate PVDF fibres and the variation in resultant fibre properties assessed. The proportion of piezoelectric β-phase in the solution blow spun fibres was higher than electrospun fibres. Fibre production rate was circa three times higher for solution blow spinning compared to electrospinning for the conditions explored. However, the solution blow spinning method resulted in higher fibre variability between fabricated batches. Fibrous membranes are capable of generating different cellular response depending on fibre diameter. For this reason, electrospun fibres with micron and sub-micron diameters were fabricated, along with successful inclusion of hydroxyapatite particles to fabricate stimuli responsive bioactive fibres. Full article
(This article belongs to the Special Issue Stimuli-Responsive Polymeric Materials)
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Open AccessCommunication
Synthesis and Acid-Responsiveness of an Insulated π-Conjugated Polymer Containing Spiropyrans in Its Backbone
Molecules 2019, 24(7), 1301; https://doi.org/10.3390/molecules24071301 - 03 Apr 2019
Cited by 3
Abstract
A π-conjugated polymer containing spiropyrans (SPs), which could be almost completely converted to protonated merocyanines (MCH+) and back to the SP form by adding an acid and a base, respectively, was developed. The insulation of the π-conjugated polymer, referred to as [...] Read more.
A π-conjugated polymer containing spiropyrans (SPs), which could be almost completely converted to protonated merocyanines (MCH+) and back to the SP form by adding an acid and a base, respectively, was developed. The insulation of the π-conjugated polymer, referred to as insulated spiropyran-containing poly(p-phenylene ethynylene) (ins-SP-PPE), using permethylated α-cyclodextrins (PM α-CD) suppressed the π-π interaction between the polymer chains containing MCH+, and the installation of PM α-CD improved the switching ability of SPs. The polymer exhibited repeatable acidochromism with almost complete conversion between the SP and MCH+ forms. Photoluminescence measurements were conducted and the acid-induced luminescence quenching of the polymer in the solution was observed, which stemmed from energy transfer from the PPE to MCH+ moieties. In the solid state, the quantum yield of ins-SP-PPE was more than twice that of the uninsulated polymer, which derived from the insulation effects. The acid-induced luminescence quenching was also observed in the solid state. Full article
(This article belongs to the Special Issue Stimuli-Responsive Polymeric Materials)
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Open AccessArticle
Synthesis of AMPSA Polymeric Derivatives Monitored by Electrical Conductivity and Evaluation of Thermosensitive Properties of Resulting Microspheres
Molecules 2019, 24(6), 1164; https://doi.org/10.3390/molecules24061164 - 23 Mar 2019
Cited by 1
Abstract
Four stimuli-responsive polymers of N-isopropylacrylamide (NIPA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) and crosslinked derivatives by N,N′-methylene bisacrylamide (MBA) were synthesized: PNA, PAMPSA, PNAM, PAMPSAM. The effect of the cross-linker and methyl sulphonic acid (-CH3-SO3H) group on particle size, [...] Read more.
Four stimuli-responsive polymers of N-isopropylacrylamide (NIPA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) and crosslinked derivatives by N,N′-methylene bisacrylamide (MBA) were synthesized: PNA, PAMPSA, PNAM, PAMPSAM. The effect of the cross-linker and methyl sulphonic acid (-CH3-SO3H) group on particle size, aggregation and volume phase transition temperature (VPTT) was investigated. Polymeric particles were synthesized via the surfactant free precipitation polymerization (SFPP) at 70 °C in the presence of cationic initiator 2,2′-azobis[2-methylpropionamidine] dihydrochloride (AMP) system. Chemical composition and morphology of investigated samples were evaluated using ATR-FTIR spectroscopy, 1H-NMR spectrometry and SEM-EDS techniques. The hydrodynamic diameters (HD), zeta potential (ZP), and polydispersity index (PDI) in aqueous dispersions were assessed by dynamic light scattering (DLS) between 18–42 °C. HD values at 18 °C for PNA, PAMPSA, PNAM, PAMPSAM polymers were approx. 32, 730, 715, 665 nm, and ZP values were −1.36, −0.01, 8.90, −0.09 mV, respectively. The VPTT range was observed between 29 and 41 °C. PDI’s for PNA and PNAM were low and varied between 0.276 and 0.460, and between 0.119 and 0.056, respectively. PAMPSA and PAMPSAM were characterized by higher PDI in the range 0.728–0.959 and 0.658–0.836, respectively. The results confirmed the thermal sensitivity of the synthesized polymers and indicated a significant polydispersity and aggregation tendency of the resulting molecules. The conductivity results were applied for the interpretation of the polymerization process. Full article
(This article belongs to the Special Issue Stimuli-Responsive Polymeric Materials)
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Open AccessArticle
Ultrasonic Generation of Pulsatile and Sequential Therapeutic Delivery Profiles from Calcium-Crosslinked Alginate Hydrogels
Molecules 2019, 24(6), 1048; https://doi.org/10.3390/molecules24061048 - 16 Mar 2019
Cited by 2
Abstract
Control over of biological processes can potentially be therapeutically regulated through localized biomolecular deliveries. While implantable hydrogels can provide localized therapeutic deliveries, they do not traditionally provide the temporally complex therapeutic delivery profiles required to regulate complex biological processes. Ionically crosslinked alginate hydrogels [...] Read more.
Control over of biological processes can potentially be therapeutically regulated through localized biomolecular deliveries. While implantable hydrogels can provide localized therapeutic deliveries, they do not traditionally provide the temporally complex therapeutic delivery profiles required to regulate complex biological processes. Ionically crosslinked alginate hydrogels have been shown to release encapsulated payloads in response to a remotely applied ultrasonic stimulus, thus potentially enabling more temporally complex therapeutic delivery profiles. However, thorough characterizations of how different types of therapeutic payloads are retained and ultrasonically released need to be performed. Additionally, the impact of potentially disruptive ultrasonic stimulations on hydrogel structure and temperature need to be characterized to better understand what range of ultrasonic signals can be used to trigger release. To perform these characterizations, calcium-crosslinked alginate hydrogels were loaded with various model macromolecules (dextrans), chemotherapeutics, and protein signaling factors and exposed to a variety of single-pulse and multi-pulse ultrasonic signals at various amplitudes and durations. In response to single-pulsed ultrasonic exposures, quantifications of molecular release, degree of gel erosion, and increase in hydrogel temperature revealed that the ultrasonic stimulations required for statistically significant therapeutic deliveries often eroded and heated the gels to unacceptable levels. However, multi-pulse ultrasonic exposures were shown to achieve significant amounts of therapeutic release while keeping gel erosion and temperature increase at modest levels. Finally, experiments were performed demonstrating that ultrasonic stimulation could be used to generate drug release profiles shown to have potential therapeutic benefits (e.g., pulsatile and sequential anticancer delivery profiles). This work underscores the potential of using ultrasonically responsive polymeric hydrogels for providing on-demand control over more complex therapeutic deliver profiles and enhancing drug delivery strategies in cancer therapies and beyond. Full article
(This article belongs to the Special Issue Stimuli-Responsive Polymeric Materials)
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Open AccessArticle
Spatial Frequency Response of Epoxy-Based Volume Holographic Recording Material
Molecules 2019, 24(6), 1018; https://doi.org/10.3390/molecules24061018 - 14 Mar 2019
Abstract
Holographic volume phase gratings are recorded in an epoxy-based, free-surface, volume holographic recording material. Light-induced gratings are formed by photo-triggered mass migration caused by component diffusion. The material resolution enables a wide range of pattern spacings, to record both transmission and reflection holograms [...] Read more.
Holographic volume phase gratings are recorded in an epoxy-based, free-surface, volume holographic recording material. Light-induced gratings are formed by photo-triggered mass migration caused by component diffusion. The material resolution enables a wide range of pattern spacings, to record both transmission and reflection holograms with many different spatial frequencies. An optimum spatial frequency response is found between the low spatial frequency roll-off and the high spatial frequency cut-off. The influence of the energy density of exposure on the spatial frequency response is investigated. Secondary volume holographic gratings (parasitic gratings) are observed in the high frequency range. The possibility of distinguishing the regular grating from the secondary grating is discussed in the form of probe wavelength detuning. Full article
(This article belongs to the Special Issue Stimuli-Responsive Polymeric Materials)
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Open AccessArticle
Application of pH-Responsive Fucoidan/Chitosan Nanoparticles to Improve Oral Quercetin Delivery
Molecules 2019, 24(2), 346; https://doi.org/10.3390/molecules24020346 - 18 Jan 2019
Cited by 13
Abstract
Polymeric nanoparticles based on fucoidan and chitosan were developed to deliver quercetin as a novel functional food. Through the polyelectrolyte self-assembly method, fucoidan/chitosan (F/C) nanoparticles were obtained with three different weight ratios (1/1, 3/1, and 5/1). The content of quercetin in the fucoidan/chitosan [...] Read more.
Polymeric nanoparticles based on fucoidan and chitosan were developed to deliver quercetin as a novel functional food. Through the polyelectrolyte self-assembly method, fucoidan/chitosan (F/C) nanoparticles were obtained with three different weight ratios (1/1, 3/1, and 5/1). The content of quercetin in the fucoidan/chitosan nanoparticles was in the range 110 ± 3 to 335 ± 4 mg·mL−1, with the increase of weight ratio of fucoidan to chitosan in the nanoparticle. Physicochemically stable nanoparticles were obtained with a particle size within the 300–400 nm range and surface potential higher than +30 mV for the 1F/1C ratio nanoparticle and around −30 mV for the 3F/1C and 5F/1C ratios nanoparticles. The 1F/1C ratio nanoparticle became larger and more unstable as the pH increased from 2.5 to 7.4, while the 3F/1C and 5F/1C nanoparticles retained their initial characteristics. This result indicates that the latter nanoparticles were stable along the gastrointestinal tract. The quercetin-loaded fucoidan/chitosan nanoparticles showed strong antioxidant activity and controlled release under simulated gastrointestinal environments (in particular for the 3F/1C and 5F/1C ratios), preventing quercetin degradation and increasing its oral bioavailability. Full article
(This article belongs to the Special Issue Stimuli-Responsive Polymeric Materials)
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Open AccessArticle
Design of Azomethine Diols for Efficient Self-Healing of Strong Polyurethane Elastomers
Molecules 2018, 23(11), 2928; https://doi.org/10.3390/molecules23112928 - 09 Nov 2018
Cited by 2
Abstract
Azomethine diols (AMDs) were synthesized by condensation between a terephthalic aldehyde, polyether diamine, and ethanol amine. The synthesized AMDs were employed to introduce azomethine groups into the backbones of polyurethane elastomers (PUEs). Different AMDs were designed to control the concentration and distribution of [...] Read more.
Azomethine diols (AMDs) were synthesized by condensation between a terephthalic aldehyde, polyether diamine, and ethanol amine. The synthesized AMDs were employed to introduce azomethine groups into the backbones of polyurethane elastomers (PUEs). Different AMDs were designed to control the concentration and distribution of azomethine groups in PUEs. In this study, we explored the intrinsic self-healing of AMD-based PUEs by azomethine metathesis. Particularly, the effects of the concentration and distribution of the azomethine groups on the AMD-based PUEs were considered. Consequently, as the azomethine group concentration increased and the distribution became denser, the self-healing properties improved. With AMD3-40, the self-healing efficiency reached 86% at 130 °C after 30 min. This represents a 150% improvement over the control PUE. Additionally, as the AMD content increased, the mechanical properties improved. With AMD3-40, the tensile strength reached 50 MPa. Therefore, we concluded that the self-healing and mechanical properties of PUEs can potentially be tailored for applications by adjusting the concentration and design of AMD structure for PUEs. Full article
(This article belongs to the Special Issue Stimuli-Responsive Polymeric Materials)
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Open AccessArticle
Dexamethasone-Loaded, PEGylated, Vertically Aligned, Multiwalled Carbon Nanotubes for Potential Ischemic Stroke Intervention
Molecules 2018, 23(6), 1406; https://doi.org/10.3390/molecules23061406 - 10 Jun 2018
Cited by 3
Abstract
The complete synthesis, optimization, purification, functionalization and evaluation of vertically aligned multiwalled carbon nanotubes (VA-MWCNTs) was reported for potential application in dexamethasone delivery to the ischemic brain tissue. The conditions for high yield were optimized and carbon nanotubes functionalized and PEGylated prior to [...] Read more.
The complete synthesis, optimization, purification, functionalization and evaluation of vertically aligned multiwalled carbon nanotubes (VA-MWCNTs) was reported for potential application in dexamethasone delivery to the ischemic brain tissue. The conditions for high yield were optimized and carbon nanotubes functionalized and PEGylated prior to dexamethasone loading. Morphological changes were confirmed by SEM and TEM. Addition of functional groups to MWCNTs was demonstrated by FTIR. Thermal stability reduced following MWCNTs functionalization as demonstrated in TGA. The presence of carbon at 2θ of 25° and iron at 2θ of 45° in MWCNTs was illustrated by XRD. Polydispersive index and zeta potential were found to be 0.261 and −15.0 mV, respectively. Dexamethasone release increased by 55%, 65% and 95% in pH of 7.4, 6.5 and 5.5 respectively as evaluated by UV-VIS. The functionalized VA-MWCNTs were demonstrated to be less toxic in PC-12 cells in the concentration range from 20 to 20,000 µg/mL. These findings have demonstrated the potential of VA-MWCNTs in the enhancement of fast and prolonged release of dexamethasone which could lead to the effective treatment of ischemic stroke. More work is under way for targeting ischemic sites using atrial natriuretic peptide antibody in stroke rats. Full article
(This article belongs to the Special Issue Stimuli-Responsive Polymeric Materials)
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Open AccessArticle
Gold Nanoparticles Grafted with PLL-b-PNIPAM: Interplay on Thermal/pH Dual-Response and Optical Properties
Molecules 2018, 23(4), 921; https://doi.org/10.3390/molecules23040921 - 16 Apr 2018
Cited by 3
Abstract
Narrowly distributed poly(l-lysine-b-N-isopropylacrylamide) (PLL-b-PNIPAM) was prepared through ring-opening polymerization of ε-benzyloxycarbonyl-l-lysine N-carboxy-α-amino anhydride and atom transfer radical polymerization of NIPAM, followed with the removal of ε-benzyloxycarbonyl group. Then gold nanoparticles (AuNPs) grafted [...] Read more.
Narrowly distributed poly(l-lysine-b-N-isopropylacrylamide) (PLL-b-PNIPAM) was prepared through ring-opening polymerization of ε-benzyloxycarbonyl-l-lysine N-carboxy-α-amino anhydride and atom transfer radical polymerization of NIPAM, followed with the removal of ε-benzyloxycarbonyl group. Then gold nanoparticles (AuNPs) grafted with PLL-b-PNIPAM (PNIPAM-PLL-AuNPs) were obtained by the reduction of chloroauric acid with sodium citrate in the presence of PLL-b-PNIPAM. PNIPAM-PLL-AuNPs and its precursors were thoroughly characterized by proton magnetic resonance spectroscope, Fourier transform infrared spectroscope, UV-vis spectroscope, transmission electron microscopy, dynamic light scattering, thermogravimetric analysis, and circular dichroism. The obtained PNIPAM-PLL-AuNPs exhibited high colloid stability even at strong alkaline (pH = 12) and acidic (pH = 2) conditions. The thermal and pH dual-responsive behaviors of the grafting PLL-b-PNIPAM chains was observed to be affected by AuNPs, while not for the secondary structure of PLL chains. Correspondingly, the surface plasmon resonance (SPR) of AuNPs was found to be sensitive to both pH value and temperature. A blue shift in the SPR happened both with increasing pH value and increasing temperature. The stimuli-response was reversible in heating-cooling cycles. The gold nanoparticles with both pH and temperature response may have potential applications in biomedical areas and biosensors. Full article
(This article belongs to the Special Issue Stimuli-Responsive Polymeric Materials)
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Open AccessArticle
An Injectable, Dual Responsive, and Self-Healing Hydrogel Based on Oxidized Sodium Alginate and Hydrazide-Modified Poly(ethyleneglycol)
Molecules 2018, 23(3), 546; https://doi.org/10.3390/molecules23030546 - 01 Mar 2018
Cited by 10
Abstract
Oxidized sodium alginate is a handily modifiable polysaccharide owing to the pendant aldehyde groups which can form dynamic covalent bonds with amines, acylhydrazines, etc., providing oxidized sodium alginate-based hydrogels with stimuli-responsive properties. However, due to the stiffness and, in particular, the hydrophobicity of [...] Read more.
Oxidized sodium alginate is a handily modifiable polysaccharide owing to the pendant aldehyde groups which can form dynamic covalent bonds with amines, acylhydrazines, etc., providing oxidized sodium alginate-based hydrogels with stimuli-responsive properties. However, due to the stiffness and, in particular, the hydrophobicity of sodium alginate dialdehyde at low pH, the mechanical performance and pH stimuli responsiveness of oxidized sodium alginate-based hydrogels are still strictly limited. Herein, we report a new strategy to build an injectable, dual responsive, and self-healing hydrogel based on oxidized sodium alginate and hydrazide-modified poly(ethyleneglycol) (PEG). The hydrazide-modified PEG, referred to as PEG-DTP, acts as a macromolecule crosslinker. We found that the presence of PEG-DTP reduces the hydrophobicity of oxidized sodium alginate at low pH so effectively that even a pH-induced reversible sol-gel transitions can be realized. Meanwhile, the disulfide bonds in PEG-DTP endows the hydrogel with the other reversible sol-gel transitions by redox stimuli. In particular, due to the softness of PEG-DTP chains, mechanical performance was also enhanced significantly. Our results indicate we can easily integrate multi-stimuli responsiveness, injectability, and self-healing behavior together into an oxidized sodium alginate-based hydrogel merely by mixing an oxidized sodium alginate solution with PEG-DTP solution in certain proportions. Full article
(This article belongs to the Special Issue Stimuli-Responsive Polymeric Materials)
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Review

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Open AccessReview
pH-Responsive Polypeptide-Based Smart Nano-Carriers for Theranostic Applications
Molecules 2019, 24(16), 2961; https://doi.org/10.3390/molecules24162961 - 15 Aug 2019
Cited by 2
Abstract
Smart nano-carriers have attained great significance in the biomedical field due to their versatile and interesting designs with different functionalities. The initial stages of the development of nanocarriers mainly focused on the guest loading efficiency, biocompatibility of the host and the circulation time. [...] Read more.
Smart nano-carriers have attained great significance in the biomedical field due to their versatile and interesting designs with different functionalities. The initial stages of the development of nanocarriers mainly focused on the guest loading efficiency, biocompatibility of the host and the circulation time. Later the requirements of less side effects with more efficacy arose by attributing targetability and stimuli-responsive characteristics to nano-carriers along with their bio- compatibility. Researchers are utilizing many stimuli-responsive polymers for the better release of the guest molecules at the targeted sites. Among these, pH-triggered release achieves increasing importance because of the pH variation in different organ and cancer cells of acidic pH. This specific feature is utilized to release the guest molecules more precisely in the targeted site by designing polymers having specific functionality with the pH dependent morphology change characteristics. In this review, we mainly concert on the pH-responsive polypeptides and some interesting nano-carrier designs for the effective theranostic applications. Also, emphasis is made on pharmaceutical application of the different nano-carriers with respect to the organ, tissue and cellular level pH environment. Full article
(This article belongs to the Special Issue Stimuli-Responsive Polymeric Materials)
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Open AccessReview
Endogenous and Exogenous Stimuli-Responsive Drug Delivery Systems for Programmed Site-Specific Release
Molecules 2019, 24(6), 1117; https://doi.org/10.3390/molecules24061117 - 21 Mar 2019
Cited by 10
Abstract
In this study, we reviewed state-of-the-art endogenous-based and exogenous-based stimuli-responsive drug delivery systems (DDS) for programmed site-specific release to overcome the drawbacks of conventional therapeutic modalities. This particular work focuses on the smart chemistry and mechanism of action aspects of several types of [...] Read more.
In this study, we reviewed state-of-the-art endogenous-based and exogenous-based stimuli-responsive drug delivery systems (DDS) for programmed site-specific release to overcome the drawbacks of conventional therapeutic modalities. This particular work focuses on the smart chemistry and mechanism of action aspects of several types of stimuli-responsive polymeric carriers that play a crucial role in extracellular and intracellular sections of diseased tissues or cells. With ever increasing scientific knowledge and awareness, research is underway around the globe to design new types of stimuli (external/internal) responsive polymeric carriers for biotechnological applications at large and biomedical and/or pharmaceutical applications, in particular. Both external/internal and even dual/multi-responsive behavior of polymeric carriers is considered an essential element of engineering so-called ‘smart’ DDS, which controls the effective and efficient dose loading, sustained release, individual variability, and targeted permeability in a sophisticated manner. So far, an array of DDS has been proposed, developed, and implemented. For instance, redox, pH, temperature, photo/light, magnetic, ultrasound, and electrical responsive DDS and/or all in all dual/dual/multi-responsive DDS (combination or two or more from any of the above). Despite the massive advancement in DDS arena, there are still many challenging concerns that remain to be addressed to cover the research gap. In this context, herein, an effort has been made to highlight those concerning issues to cover up the literature gap. Thus, the emphasis was given to the drug release mechanism and applications of endogenous and exogenous based stimuli-responsive DDS in the clinical settings. Full article
(This article belongs to the Special Issue Stimuli-Responsive Polymeric Materials)
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