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Gels
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Hydrogels for Drug Delivery
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Hydrogels for Drug Delivery

A special issue of Gels (ISSN 2310-2861).

Deadline for manuscript submissions: closed (15 December 2017) | Viewed by 60818

Special Issue Editors

Prof. Dr. Alejandro Sosnik

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Guest Editor
Laboratory of Pharmaceutical Nanomaterials Science, Department of Materials Science and Engineering, Technion-Israel Institute of Technology, Haifa 3200003, Israel
Interests: biomaterials; drugs; polymers; small-molecule drug and polymer self-assembly; polymeric nanoparticles; polymeric micelles; hybrid ceramic–polymer nanomaterials; pharmaceutical materials science; drug delivery and targeting; mucosal drug delivery; nanomedicine; pediatric cancer
Special Issues, Collections and Topics in MDPI journals
Dr. Katia Seremeta

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Guest Editor
Institute for Research in Advanced Technological Processes, National Council for Scientific and Technical Research, National University of the Chaco Austral (INIPTA—CONICET—UNCAUS), Chaco 3700, Argentina
Interests: pharmaceutical sciences; microtechnology; nanotechnology; drug delivery systems; polymers gels
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Over the years, water-based gels (hydrogels) have attracted major attention as drug delivery systems. Among the most remarkable applications, it is worth mentioning prolonged drug residence time in the action site and more controlled rate of release and absorption, improved bioavailability, and reduced side-effects. One of the main advantages of hydrogels is their great versatility in terms of compositional features and adjustability to various administration routes, from parenteral to non-parenteral ones. Based on the application envisioned, the design of bioadhesive or mucoadhesive hydrogels may be of benefit. For example, hydrogels are used as wound dressing and dermatological patches for local and systemic therapy. In a similar way, they can be applied in the vaginal tract for local treatment or in the nasal cavity for a similar goal or, conversely, to targeting the central nervous system in the so-called intranasal delivery. Buccal hydrogels provide a high local concentration of the drug that facilitates absorption and surpasses hepatic first-pass metabolism. In this framework, innovative buccal films have been developed for administration of drugs in pediatric and unconscious patients or individuals with swallowing difficulty. More recently, the in situ-forming hydrogel technology in response to changes of the physiological conditions (e.g., pH, temperature, ionic strength) was exploited for the sustained release of active compounds by the subcutaneous and intramuscular routes. For this, hydrogel precursor solutions loaded with therapeutic compounds are injected in body sites deprived of significant fluids flow and stabilized by physical or chemical means. Overall, hydrogels have demonstrated outstanding capabilities to ensure patient compliance, while achieving long-term therapeutic effects. The present Special Issue is dedicated to overview the most relevant applications of hydrogels in drug delivery with special emphasis on mucosal routes.

Assoc. Prof. Alejandro Sosnik
Assist. Prof. Katia Seremeta
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. Gels 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 2100 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

  • hydrogels
  • drug delivery systems
  • administration routes
  • mucosal drug delivery
  • nanomedicine
  • bioavailability

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Published Papers (7 papers)

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Research

Jump to: Review

3423 KiB  
Article
The Influence of Differently Shaped Gold Nanoparticles Functionalized with NIPAM-Based Hydrogels on the Release of Cytochrome C
by Sulalit Bandyopadhyay, Anuvansh Sharma and Wilhelm Robert Glomm
Gels 2017, 3(4), 42; https://doi.org/10.3390/gels3040042 - 8 Nov 2017
Cited by 10 | Viewed by 5852
Abstract
Here, we report the synthesis and functionalization of five different shapes of Au nanoparticles (NPs), namely nanorods, tetrahexahedral, bipyramids, nanomakura, and spheres with PEG and poly (N-isopropylacrylamide)-acrylic acid (pNIPAm-AAc) hydrogels. The anisotropic NPs are synthesized using seed-mediated growth in the presence [...] Read more.
Here, we report the synthesis and functionalization of five different shapes of Au nanoparticles (NPs), namely nanorods, tetrahexahedral, bipyramids, nanomakura, and spheres with PEG and poly (N-isopropylacrylamide)-acrylic acid (pNIPAm-AAc) hydrogels. The anisotropic NPs are synthesized using seed-mediated growth in the presence of silver. The NPs have been characterized using Dynamic Light Scattering (DLS), zeta potential measurements, UV-Visible spectrophotometry (UV-Vis), and Scanning Transmission Electron Microscopy (S(T)EM). Cyt C was loaded into the PEG-hydrogel-coated AuNPs using a modified breathing-in method. Loading efficiencies (up to 80%), dependent on particle geometry, concentration, and hydrogel content, were obtained. Release experiments conducted at high temperature (40 °C) and acidic pH (3) showed higher release for larger sizes of PEG-hydrogel-coated AuNPs, with temporal transition from spherical to thin film release geometry. AuNP shape, size, number density, and hydrogel content are found to influence the loading as well as release kinetics of Cyt C from these systems. Full article
(This article belongs to the Special Issue Hydrogels for Drug Delivery)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>S(T)EM images of (<b>a</b>) AuNR; (<b>b</b>) PEG-hydrogel coated AuNR; (<b>c</b>) AuHex; (<b>d</b>) PEG-hydrogel coated AuHex; (<b>e</b>) AuBP; (<b>f</b>) PEG-hydrogel coated AuBP; (<b>g</b>) AuNM; (<b>h</b>) PEG-hydrogel coated AuNM; (<b>i</b>) AuNS; and (<b>j</b>) PEG-hydrogel coated AuNS.</p> Full article ">Figure 2
<p>(<b>a</b>) Hydrodynamic sizes and (<b>b</b>) zeta potentials of different shapes of AuNPs.</p> Full article ">Figure 3
<p>Variation of (<b>a</b>) hydrodynamic sizes and (<b>b</b>) zeta potentials of AuNPs with different concentrations of PEG. Variation of (<b>c</b>) hydrodynamic sizes and (<b>d</b>) zeta potentials of AuNPs with different concentrations of hydrogel.</p> Full article ">Figure 4
<p>(<b>a</b>) UV-Vis spectra for differently shaped AuNPs. Variation of UV-Vis spectra after coating with PEG followed by hydrogel coating for (<b>b</b>) AuNR; (<b>c</b>) AuHex; (<b>d</b>) AuBP; (<b>e</b>) AuNM; and (<b>f</b>) AuNS; Variation of (<b>g</b>) hydrodynamic sizes and (<b>h</b>) zeta potentials of differently shaped AuNPs measured at base and release conditions, respectively.</p> Full article ">Figure 4 Cont.
<p>(<b>a</b>) UV-Vis spectra for differently shaped AuNPs. Variation of UV-Vis spectra after coating with PEG followed by hydrogel coating for (<b>b</b>) AuNR; (<b>c</b>) AuHex; (<b>d</b>) AuBP; (<b>e</b>) AuNM; and (<b>f</b>) AuNS; Variation of (<b>g</b>) hydrodynamic sizes and (<b>h</b>) zeta potentials of differently shaped AuNPs measured at base and release conditions, respectively.</p> Full article ">Figure 5
<p>(<b>a</b>) Loading and (<b>b</b>) encapsulation efficiencies for differently shaped AuNPs for two different hydrogel concentrations. Release kinetics of Cyt <span class="html-italic">C</span> from differently shaped AuNPs for (<b>c</b>) 1.7 mg/mL and (<b>d</b>) 3.3 mg/mL hydrogel concentrations respectively. (<b>e</b>) Rate constants and (<b>f</b>) release exponents for Cyt <span class="html-italic">C</span> release from differently shaped AuNPs.</p> Full article ">
3957 KiB  
Article
Controlled Release of Vascular Endothelial Growth Factor from Heparin-Functionalized Gelatin Type A and Albumin Hydrogels
by Christiane Claaßen, Lisa Sewald, Günter E. M. Tovar and Kirsten Borchers
Gels 2017, 3(4), 35; https://doi.org/10.3390/gels3040035 - 9 Oct 2017
Cited by 32 | Viewed by 7473
Abstract
Bio-based release systems for pro-angiogenic growth factors are of interest, to overcome insufficient vascularization and bio-integration of implants. In this study, we investigated heparin-functionalized hydrogels based on gelatin type A or albumin as storage and release systems for vascular endothelial growth factor (VEGF). [...] Read more.
Bio-based release systems for pro-angiogenic growth factors are of interest, to overcome insufficient vascularization and bio-integration of implants. In this study, we investigated heparin-functionalized hydrogels based on gelatin type A or albumin as storage and release systems for vascular endothelial growth factor (VEGF). The hydrogels were crosslinked using carbodiimide chemistry in presence of heparin. Heparin-functionalization of the hydrogels was monitored by critical electrolyte concentration (CEC) staining. The hydrogels were characterized in terms of swelling in buffer solution and VEGF-containing solutions, and their loading with and release of VEGF was monitored. The equilibrium degree of swelling (EDS) was lower for albumin-based gels compared to gelatin-based gels. EDS was adjustable with the used carbodiimide concentration for both biopolymers. Furthermore, VEGF-loading and release were dependent on the carbodiimide concentration and loading conditions for both biopolymers. Loading of albumin-based gels was higher compared to gelatin-based gels, and its burst release was lower. Finally, elevated cumulative VEGF release after 21 days was determined for albumin-based hydrogels compared to gelatin A-based hydrogels. We consider the characteristic net charges of the proteins and degradation of albumin during release time as reasons for the observed effects. Both heparin-functionalized biomaterial systems, chemically crosslinked gelatin type A or albumin, had tunable physicochemical properties, and can be considered for controlled delivery of the pro-angiogenic growth factor VEGF. Full article
(This article belongs to the Special Issue Hydrogels for Drug Delivery)
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Graphical abstract
Full article ">Figure 1
<p>Critical electrolyte concentration (CEC) staining of gelatin type A (10 wt %) and albumin (10 wt %) hydrogels without heparin or with heparin (1 wt %) that were crosslinked with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) (0.125 M). Hydrogels were washed for at least 5 h in PBS<sup>+</sup> before staining. Alcian blue solutions (0.05%, pH 5.8) with 0.06 to 0.9 M MgCl<sub>2</sub> were applied for staining. Hydrogels without heparin showed no dependence of staining on electrolyte concentration, indicating that the CEC for albumin and gelatin hydrogels was lower than 0.06 M MgCl<sub>2</sub>. For heparin-functionalized hydrogels, the CEC was 0.5 M MgCl<sub>2</sub>.</p> Full article ">Figure 2
<p>Results of the gravimetric determination of the gel yield of hydrogels. Hydrogels were prepared with gelatin type A or albumin (10 wt %), heparin (1 wt %), and different EDC concentrations. At 0.1 M EDC, no crosslinking was achieved for albumin-based gels. There was no significant influence of EDC concentration or biopolymer type on the gel yield (<span class="html-italic">p</span> &gt; 0.05; <span class="html-italic">n</span> = 3).</p> Full article ">Figure 3
<p>Swelling kinetics of gelatin (10 wt %) or albumin (10 wt %) hydrogels with heparin (1 wt %) crosslinked via EDC (0.125 M). The degree of swelling was determined at different time points and is denoted in % of the degree of swelling of the respective gels after 24 h. Both hydrogel types showed a fast water uptake. Gelatin-based gels passed through a hyper-swollen state after approximately 30 min, while albumin-based gels swelled continuously. Evaluation of the absolute numbers for the degrees of swelling for each gel revealed that after 60 min, no significant variation of degree of swelling (DS) was noticed. (<span class="html-italic">p</span> &gt; 0.05, <span class="html-italic">n</span> = 4).</p> Full article ">Figure 4
<p>Results of the gravimetric characterization of the hydrogels. Hydrogels were prepared with gelatin type A or albumin (10 wt %), heparin (1 wt %), and different EDC concentrations. At 0.1 M EDC, no crosslinking was achieved for albumin-based gels. The EDS decreased with increasing EDC concentration for both biopolymers (asterisks with solid lines: <span class="html-italic">p</span> &lt; 0.05; grey lines refer to gelatin, black line refers to albumin; <span class="html-italic">n</span> = 3), while the EDS of gelatin gels was significantly higher compared to the albumin gels in all cases (asterisk with dotted lines: <span class="html-italic">p</span> &lt; 0.01; <span class="html-italic">n</span> = 3).</p> Full article ">Figure 5
<p>Hydrolytic stability of hydrogels prepared with gelatin (10 wt %) or albumin (10 wt %) and heparin (1 wt %) with 0.125 M EDC. Hydrogels were incubated under the same conditions as for the release of growth factor. Gel yield (<b>A</b>) and DS (<b>B</b>) were determined at different time points and are denoted as percentage of the initial values in the figure. There was no significant decrease in gel yield for both biopolymers (<span class="html-italic">p</span> &gt; 0.05; <span class="html-italic">n</span> = 5); for the EDS a significant increase for albumin-based hydrogels was noticed (<span class="html-italic">p</span> &lt; 0.05; <span class="html-italic">n</span> = 5), while no significant effect for gelatin type A gels was found (<span class="html-italic">p</span> &gt; 0.3; <span class="html-italic">n</span> = 5).</p> Full article ">Figure 6
<p>Cumulative release profiles of hydrogels prepared with gelatin type A (10 wt %) or albumin (10 wt %) with heparin (1 wt %). Loading was achieved by swelling in vascular endothelial growth factor (VEGF)-solution (1 µg VEGF per mL; loading with 0.1 µg VEGF per mg hydrogel dry weight). VEGF concentrations were normalized to the total VEGF amount used for hydrogel loading. Crosslinking and loading conditions: (<b>A</b>) 0.125 M EDC/1 h; (<b>B</b>) 0.125 M EDC/3 h; (<b>C</b>) 0.15 M EDC/1 h; (<b>D</b>) 0.15 M EDC/3 h. Gelatin type A-based hydrogels showed a higher initial release but lower overall release compared to albumin-based gels. Gelatin gels showed a diffusion controlled release curve, while release curves of albumin seemed to be diffusion controlled the first days but were afterwards similar to a zero-order release (<span class="html-italic">n</span> = 3).</p> Full article ">Figure 7
<p>Results of key parameters for the release properties. Hydrogels were prepared with gelatin type A (10 wt %) or albumin (10 wt %) and heparin (1 wt %). For each composition, two EDC concentrations (0.125 M and 0.15 M) were used and hydrogels were loaded by swelling for 1 or 3 h in VEGF solution (1 µg VEGF per mL; loading with 0.1 µg VEGF per mg hydrogel dry weight). VEGF concentrations were normalized to the total VEGF amount used for hydrogel loading (<span class="html-italic">n</span> = 3). (<b>A</b>) Loading efficiency: albumin hydrogels had a higher loading efficiency compared to gelatin type A hydrogels (<span class="html-italic">p</span> &lt; 0.001). For both hydrogel types the loading efficiency showed a negative correlation with the loading time (<span class="html-italic">p</span> &lt; 0.01); (<b>B</b>) Burst release (release within 24 h): gelatin type A hydrogels had a higher burst release compared to albumin gels (<span class="html-italic">p</span> &lt; 0.001). For albumin hydrogels, crosslinker concentration showed a negative correlation with the burst release (<span class="html-italic">p</span> &lt; 0.01); (<b>C</b>) Cumulative overall release after 21 days: was higher for albumin gels compared to gelatin gels (<span class="html-italic">p</span> &lt; 0.001); (<b>D</b>) Average release rate between day 7 and day 21: release rates of all albumin gels were significantly higher compared to the corresponding gelatin type A-based gel (<span class="html-italic">p</span> &lt; 0.001).</p> Full article ">
11010 KiB  
Article
Assembly of a Tripeptide and Anti-Inflammatory Drugs into Supramolecular Hydrogels for Sustained Release
by Marina Kurbasic, Chiara D. Romano, Ana M. Garcia, Slavko Kralj and Silvia Marchesan
Gels 2017, 3(3), 29; https://doi.org/10.3390/gels3030029 - 3 Aug 2017
Cited by 26 | Viewed by 6916
Abstract
Supramolecular hydrogels offer interesting opportunities for co-assembly with drugs towards sustained release over time, which could be achieved given that the drug participates in the hydrogel nanostructure, and it is not simply physically entrapped within the gel matrix. dLeu-Phe-Phe is an attractive [...] Read more.
Supramolecular hydrogels offer interesting opportunities for co-assembly with drugs towards sustained release over time, which could be achieved given that the drug participates in the hydrogel nanostructure, and it is not simply physically entrapped within the gel matrix. dLeu-Phe-Phe is an attractive building block of biomaterials in light of the peptide’s inherent biocompatibility and biodegradability. This study evaluates the assembly of the tripeptide in the presence of either of the anti-inflammatory drugs ketoprofen or naproxen at levels analogous to commercial gel formulations. Fourier-transformed infrared (FT-IR), circular dichroism, Thioflavin T fluorescence, transmission electron microscopy (TEM), and oscillatory rheometry are used. Drug release over time is monitored by means of reverse-phase high performance liquid chromatography, and shows different kinetics for the two drugs. Full article
(This article belongs to the Special Issue Hydrogels for Drug Delivery)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Chemical structures of drug model compounds evaluated for co-assembly with the peptide <sup><span class="html-small-caps">d</span></sup>Leu-Phe-Phe in previous studies (<b>top</b>) and this study (<b>bottom</b>). <b>*</b> denotes the chiral centre of the racemic mixture that composes ketoprofen.</p> Full article ">Figure 2
<p>Oscillatory rheometry analysis of hydrogels (<b>a</b>–<b>c</b>) frequency sweeps; (<b>d</b>–<b>f</b>) time sweeps; (<b>g</b>–<b>i</b>) stress sweeps.</p> Full article ">Figure 3
<p>TEM micrographs of (<b>a</b>) peptide hydrogel, (<b>b</b>) peptide hydrogel with ketoprofen, and (<b>c</b>) peptide hydrogel with naproxen. Scale bar = 50 nm.</p> Full article ">Figure 4
<p>CD spectra of hydrogels; (<b>a</b>–<b>c</b>) kinetics over 60 min, (<b>d</b>–<b>f</b>) heating ramps up to 80 °C.</p> Full article ">Figure 5
<p>Thioflavin T fluorescence assay.</p> Full article ">Figure 6
<p>Drug release study for naproxen (<b>a</b>,<b>b</b>) and ketoprofen (<b>c</b>,<b>d</b>).</p> Full article ">
3506 KiB  
Article
A Controlled Antibiotic Release System for the Development of Single-Application Otitis Externa Therapeutics
by Bogdan A. Serban, Kristian T. Stipe, Jeremy B. Alverson, Erik R. Johnston, Nigel D. Priestley and Monica A. Serban
Gels 2017, 3(2), 19; https://doi.org/10.3390/gels3020019 - 17 May 2017
Cited by 15 | Viewed by 5506
Abstract
Ear infections are a commonly-occurring problem that can affect people of all ages. Treatment of these pathologies usually includes the administration of topical or systemic antibiotics, depending on the location of the infection. In this context, we sought to address the feasibility of [...] Read more.
Ear infections are a commonly-occurring problem that can affect people of all ages. Treatment of these pathologies usually includes the administration of topical or systemic antibiotics, depending on the location of the infection. In this context, we sought to address the feasibility of a single-application slow-releasing therapeutic formulation of an antibiotic for the treatment of otitis externa. Thixotropic hydrogels, which are gels under static conditions but liquefy when shaken, were tested for their ability to act as drug controlled release systems and inhibit Pseudomonas aeruginosa and Staphylococcus aureus, the predominant bacterial strains associated with outer ear infections. Our overall proof of concept, including in vitro evaluations reflective of therapeutic ease of administration, formulation stability, cytocompatibility assessment, antibacterial efficacy, and formulation lifespan, indicate that these thixotropic materials have strong potential for development as otic treatment products. Full article
(This article belongs to the Special Issue Hydrogels for Drug Delivery)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Tetraethyl orthosilicate (TEOS) hydrolysis. (<b>A</b>) Reaction scheme for the formation of the SiO<sub>2</sub> network due to TEOS hydrolysis; (<b>B</b>) Fourier-transformed infrared spectroscopy (FTIR) monitoring of TEOS hydrolysis indicating the apparition of the ethanol peak—a side product of the TEOS hydrolysis reaction; and (<b>C</b>) Proton nuclear magnetic resonance (<sup>1</sup>H-NMR) analysis and confirmation of TEOS hydrolysis. The upper spectrum corresponds to TEOS, while the bottom spectrum shows a shift in the –CH<sub>2</sub>– (methylene) peak from 3.8 to 3.4 ppm and –CH<sub>3</sub> (methyl) peak from 1.1 to 0.9 ppm, indicative of hydrolysis. The 2.0 ppm peak in the hydrolyzed TEOS spectrum corresponds to the methyl groups of the acetic acid used for hydrolysis.</p> Full article ">Figure 2
<p>Physical appearance and optical clarity of thixogels.</p> Full article ">Figure 3
<p>Rheological evaluation of hydrogel thixotropy during three stress cycles. All three formulations show stress-dependent gel-sol transitions. After the first cycle, for all formulations, the storage modulus (G′) values were higher, most likely due to polymeric network consolidation through solvent exclusion.</p> Full article ">Figure 4
<p>Evaluation of the temperature dependent behavior of the thixogels. A slight temperature dependence (approximately 10% increase in G′) is observed at temperatures above 60 °C, probably due to solvent loss.</p> Full article ">Figure 5
<p>Evaluation of the swelling behavior of thixogels in aqueous environments, indicating that the hydrogels minimally change their volumes (approximately 1%) in the presence of physiological fluids (no statistically significant differences were noted between the three formulations).</p> Full article ">Figure 6
<p>Thixogels cytocompatibility assessment. (<b>A</b>) LIVE/DEAD evaluation of cells on TXH indicating the presence of active intracellular esterases, intact cell membranes and some cytoplasmic vacuolation (circled); (<b>B</b>) evaluation of cellular metabolic activity via methyl tetrazolium salt (MTS) Cell-Titer assay, indicating reduced mitochondrial activity on TXL and TXH; (<b>C</b>) improvement of cellular metabolic activity through the addition on polyethylene glycol, molecular weight 600 Da (PEG600) to TXH; and (<b>D</b>) LIVE/DEAD evaluation of cells on TXH/PEG600 75% showing a more physiological spindle-like morphology with some cytoplasmic vacuolation (circled).</p> Full article ">Figure 7
<p>Evaluation of the controlled release capabilities of the thixogels by using fluorescein as a model drug. Lanolin—a compounding wax used for otic ointments—was used as a control. All three thixogels elicited controlled release properties for seven days.</p> Full article ">Figure 8
<p>Fluorescein release from thixogels indicating the controlled release capabilities of the hydrogels. (<b>A</b>) Evaluation of the effects of PEG200 addition, in different amounts, on the fluorescein release properties, compared to TXH; (<b>B</b>) evaluation of the effects of PEG600 addition, in different amounts, on the fluorescein release properties, compared to TXH; (<b>C</b>) comparison of TXH, TXH + PEG200 50%, and TXH + PEG600 50% release rates indicating that longer PEG chains decrease the release rates; and (<b>D</b>) assessment of the loading capacity of the thixogels with four different concentrations of fluorescein, indicating a consistent loading efficiency of ~70%.</p> Full article ">Figure 9
<p>Evaluation of the antibacterial activity of thixogels. (<b>A</b>) Evaluation of the effect of TEOS amounts (TXL versus TXH) on <span class="html-italic">S. aureus</span> growth; (<b>B</b>) evaluation of the effect of TEOS amounts (TXL versus TXH) on <span class="html-italic">P. aeruginosa</span> growth; (<b>C</b>) evaluation of TXH hydrogels with and without PEG on <span class="html-italic">S. aureus</span> growth; and (<b>D</b>) evaluation of TXH hydrogels with and without PEG on <span class="html-italic">P. aeruginosa</span> growth.</p> Full article ">Figure 10
<p>Evaluation of thixogel dehydration rates indicating that all formulations would gradually dry out to a small amount of dry material, and most likely would be naturally eliminated without causing hearing impairment.</p> Full article ">

Review

Jump to: Research

15 pages, 2551 KiB  
Review
Nanocomposite Hydrogels: Advances in Nanofillers Used for Nanomedicine
by Arti Vashist, Ajeet Kaushik, Anujit Ghosal, Jyoti Bala, Roozbeh Nikkhah-Moshaie, Waseem A. Wani, Pandiaraj Manickam and Madhavan Nair
Gels 2018, 4(3), 75; https://doi.org/10.3390/gels4030075 - 6 Sep 2018
Cited by 70 | Viewed by 10388
Abstract
The ongoing progress in the development of hydrogel technology has led to the emergence of materials with unique features and applications in medicine. The innovations behind the invention of nanocomposite hydrogels include new approaches towards synthesizing and modifying the hydrogels using diverse nanofillers [...] Read more.
The ongoing progress in the development of hydrogel technology has led to the emergence of materials with unique features and applications in medicine. The innovations behind the invention of nanocomposite hydrogels include new approaches towards synthesizing and modifying the hydrogels using diverse nanofillers synergistically with conventional polymeric hydrogel matrices. The present review focuses on the unique features of various important nanofillers used to develop nanocomposite hydrogels and the ongoing development of newly hydrogel systems designed using these nanofillers. This article gives an insight in the advancement of nanocomposite hydrogels for nanomedicine. Full article
(This article belongs to the Special Issue Hydrogels for Drug Delivery)
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Graphical abstract
Full article ">Figure 1
<p>Nanocomposite hydrogels gels with various shapes: (<b>a</b>) thin film, (<b>b</b>) sheet, (<b>c</b>) uneven sheet, (<b>d</b>) hollow tube, and (<b>e</b>) bellows. Reprinted with permission from Reference [<a href="#B8-gels-04-00075" class="html-bibr">8</a>]. Copyright 2007 Elsevier.</p> Full article ">Figure 2
<p>Illustration of potential nanofillers such as 0D (fullerene, C60), 1D small-walled carbon nanotubes &amp; Multi-walled carbon nanotubes (SWCNTs &amp; MWCNTs), 2D (graphene, graphene oxide or functionalized graphene), and 3D (graphite, silicate, BaTiO<sub>3</sub>), which are used to synthesize nanocomposite hydrogel networks based on organic-inorganic-organic hybrid nanocomposite chemistry.</p> Full article ">Figure 3
<p>Supramolecular polymer/clay nanocomposite hydrogel scaffold for bone regeneration. Reprinted with permission from Reference [<a href="#B80-gels-04-00075" class="html-bibr">80</a>]. Copyright 2017 American Chemical Society.</p> Full article ">Figure 4
<p>Injectable dopamine-modified poly(ethylene glycol) nanocomposite hydrogel with enhanced adhesive properties and bioactivity. Reprinted from Reference [<a href="#B82-gels-04-00075" class="html-bibr">82</a>]. Copyright 2014 American Chemical Society.</p> Full article ">Figure 5
<p>Fabrication of 3D macroscopic hydrogel with graphene oxide nanosheets (<b>a</b>) and the mechanism of selective detection of antibiotics (<b>b</b>). Reprinted with permission from reference [<a href="#B92-gels-04-00075" class="html-bibr">92</a>]. Copyright 2016 Elsevier.</p> Full article ">
30 pages, 1731 KiB  
Review
Encapsulation of Biological Agents in Hydrogels for Therapeutic Applications
by Víctor H. Pérez-Luna and Orfil González-Reynoso
Gels 2018, 4(3), 61; https://doi.org/10.3390/gels4030061 - 11 Jul 2018
Cited by 77 | Viewed by 8348
Abstract
Hydrogels are materials specially suited for encapsulation of biological elements. Their large water content provides an environment compatible with most biological molecules. Their crosslinked nature also provides an ideal material for the protection of encapsulated biological elements against degradation and/or immune recognition. This [...] Read more.
Hydrogels are materials specially suited for encapsulation of biological elements. Their large water content provides an environment compatible with most biological molecules. Their crosslinked nature also provides an ideal material for the protection of encapsulated biological elements against degradation and/or immune recognition. This makes them attractive not only for controlled drug delivery of proteins, but they can also be used to encapsulate cells that can have therapeutic applications. Thus, hydrogels can be used to create systems that will deliver required therapies in a controlled manner by either encapsulation of proteins or even cells that produce molecules that will be released from these systems. Here, an overview of hydrogel encapsulation strategies of biological elements ranging from molecules to cells is discussed, with special emphasis on therapeutic applications. Full article
(This article belongs to the Special Issue Hydrogels for Drug Delivery)
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Full article ">Figure 1
<p>Hydrogels can present barriers that prevent recognition of encapsulated viruses, bacteria, or cells by the immune system. The hydrogel can also provide an internal environment that allows the encapsulated cells to survive changes in environment.</p> Full article ">Figure 2
<p>IgG molecules entrapped within a degradable hydrogel. (<b>A</b>) The IgG molecules are encapsulated by means of physical entrapment. (<b>B</b>) Entrapped IgG molecules are covalently linked to the hydrogel. (<b>C</b>) Release of encapsulated IgG molecules (physically entrapped) versus time. Burst release (of IgG in this case) occurs when biomolecules are encapsulated within hydrogels (<b>A</b>). (<b>D</b>) Release of encapsulated IgG molecules that were covalently linked to the hydrogel. The burst release was delayed when the antibodies were linked to the hydrogel by means of covalent bonds using bifunctional PEG molecules (<b>B</b>). Adapted and reproduced with permission from [<a href="#B129-gels-04-00061" class="html-bibr">129</a>].</p> Full article ">Figure 3
<p>(<b>Top</b>) Concept of encapsulation of bacteriophages within an ionic hydrogel. At low pH, the carboxylate groups remain protonated, and the hydrogel does not swell with the acidic fluids of the stomach. Once the particles reach the small intestine, the change in pH causes the carboxyl groups to become deprotonated (hence changed and more polar), which causes the hydrogel to swell and release the encapsulated bacteriophages. (<b>Bottom</b>) Number of plaque forming units from a system with encapsulated bacteriophages after 0 h (T0), 6 h (T6), and 24 h (T24) of residence within the hydrogel particles at the given pH values. (* indicates significantly different phage titres using a 2 sample <span class="html-italic">t</span>-test at each condition compared with phage at T0 for each composition (<span class="html-italic">p</span> &lt; 0.05).). (Adapted and reproduced with permission from [<a href="#B206-gels-04-00061" class="html-bibr">206</a>].)</p> Full article ">Figure 4
<p>Fractional release of <span class="html-italic">P. acidilactici</span> from xanthan–chitosan capsules prepared under four different conditions. The release pH conditions are pH = 2.0 for SGF and pH = 6.8 for SIF. (<b>a</b>) Chitosan: 0.7% (<span class="html-italic">w</span>/<span class="html-italic">v</span>), pH = 6.2; Xanthan: 0.7% (<span class="html-italic">w</span>/<span class="html-italic">v</span>) and 1.0% (<span class="html-italic">w</span>/<span class="html-italic">v</span>); (<b>b</b>) Chitosan: 0.7% (<span class="html-italic">w</span>/<span class="html-italic">v</span>), pH = 4.5; Xanthan: 0.7% (<span class="html-italic">w</span>/<span class="html-italic">v</span>) and 1.0% (<span class="html-italic">w</span>/<span class="html-italic">v</span>). (Reproduced and adapted with permission from [<a href="#B218-gels-04-00061" class="html-bibr">218</a>].)</p> Full article ">Figure 5
<p>Porcine islet cells encapsulated with a PEG diacrylate-based hydrogel using interfacial photopolymerization. The thin, outermost zone (labeled A) was presumed to be less crosslinked, and the filamentous nature of this outer zone may be due to the incomplete crosslinking of the hydrogel at the termination of laser illumination. Because the photoinitiator was present only at the islet surface, the thicker inner zone, closer to the islets (labeled B) and thus closer to the eosin Y photoinitiator, was presumably more highly crosslinking and thus had a more dense appearance. (Reproduced and adapted with permission from [<a href="#B20-gels-04-00061" class="html-bibr">20</a>].)</p> Full article ">
18837 KiB  
Review
Polymeric Hydrogels as Technology Platform for Drug Delivery Applications
by Alejandro Sosnik and Katia P. Seremeta
Gels 2017, 3(3), 25; https://doi.org/10.3390/gels3030025 - 3 Jul 2017
Cited by 71 | Viewed by 15159
Abstract
Hydrogels have become key players in the field of drug delivery owing to their great versatility in terms of composition and adjustability to various administration routes, from parenteral (e.g., intravenous) to non-parenteral (e.g., oral, topical) ones. In addition, based on the envisioned application, [...] Read more.
Hydrogels have become key players in the field of drug delivery owing to their great versatility in terms of composition and adjustability to various administration routes, from parenteral (e.g., intravenous) to non-parenteral (e.g., oral, topical) ones. In addition, based on the envisioned application, the design of bioadhesive or mucoadhesive hydrogels with prolonged residence time in the administration site may be beneficial. For example, hydrogels are used as wound dressings and patches for local and systemic therapy. In a similar way, they can be applied in the vaginal tract for local treatment or in the nasal cavity for a similar goal or, conversely, to target the central nervous system by the nose-to-brain pathway. Overall, hydrogels have demonstrated outstanding capabilities to ensure patient compliance, while achieving long-term therapeutic effects. The present work overviews the most relevant and recent applications of hydrogels in drug delivery with special emphasis on mucosal routes. Full article
(This article belongs to the Special Issue Hydrogels for Drug Delivery)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Hydrogels and tissue engineering. Schematic diagram of the use of hydrogels in (<b>A</b>) microencapsulation and (<b>B</b>) tissue-engineering scaffold. (Reprinted with permission from reference [<a href="#B16-gels-03-00025" class="html-bibr">16</a>]. Copyright 2014 Elsevier).</p> Full article ">Figure 2
<p>Preparation of alginate hydrogels coated with chitosan for wound dressing. (Reprinted from reference [<a href="#B20-gels-03-00025" class="html-bibr">20</a>]).</p> Full article ">Figure 3
<p>(<b>a</b>,<b>b</b>) Microscopic images of mesenchymal stromal cells (MSC) cultured for seven days in control culture medium after crystal violet staining; (<b>c</b>,<b>d</b>) microscopic images of MSC cultured for seven days in 0.1% chitosan hydrochloride culture medium after crystal violet staining. (Reprinted from reference [<a href="#B20-gels-03-00025" class="html-bibr">20</a>]).</p> Full article ">Figure 4
<p>Schematic representations of Pluronic<sup>®</sup> F127 micelles: (<b>a</b>) single micelle with spherical core-shell geometry; (<b>b</b>) single 2D hexagonally packed layer of micelles; (<b>c</b>) two 2D hexagonally packed layers of micelles (AB); and (<b>d</b>) three layers with ABC (or Faced Centered Cubic, FCC) stacking sequence structure. (<b>b</b>–<b>d</b>) correspond to the radial geometry. (Reprinted with permission from reference [<a href="#B32-gels-03-00025" class="html-bibr">32</a>]. Copyright 2007 American Chemical Society).</p> Full article ">Figure 5
<p>Tetracycline release profiles from poloxamer (- - -) and monoglyceride (―) based gels. Kinetics were determined by equilibrium dialysis. The reported values represent the average of five independent experiments, bars = S.D. (Reprinted with permission from reference [<a href="#B34-gels-03-00025" class="html-bibr">34</a>]. Copyright 1996 Elsevier).</p> Full article ">Figure 6
<p>Correlation between in vitro pilocarpine release and pupillary constriction obtained in vivo. A linear correlation is evident with an <span class="html-italic">R</span><sup>2</sup> of 0.97. As the amount of pilocarpine available for absorption decreases, a corresponding increase in pupil diameter is observed. Data are reported as mean ± SEM. Solid line indicates the best-fit line and dashed line indicates the 95% confidence interval. (Reprinted with permission from reference [<a href="#B1-gels-03-00025" class="html-bibr">1</a>]. Copyright 2009 Elsevier).</p> Full article ">Figure 7
<p>Hematoxylin and Eosin staining to visualize the histology of CEES and NM-exposed corneas treated for 24 h with doxycycline in solution or in a hydrogel. The damaged area is where the epithelium meets the stroma. The wound-healing efficacy of doxycycline solution was close to the doxycycline hydrogel for CEES exposed corneas, as the extent of damage was comparatively mild. However, a superior wound healing efficacy was observed with hydrogels over solutions when harshly damaged NM-exposed corneas were treated with doxycycline. CEES: half mustard; NM: mustard; DOXY: doxycycline. (Reprinted with permission from reference [<a href="#B45-gels-03-00025" class="html-bibr">45</a>]. Copyright 2010 Elsevier).</p> Full article ">Figure 8
<p>Concept behind hydrogels of poly[(propylenesulfide) (PPS)-(<span class="html-italic">N</span>,<span class="html-italic">N</span>-dimethylacrylamide) (DMA)-(<span class="html-italic">N</span>-isopropylacrylamide) (PNIPAAM) that undergo reversible gelation at 37 °C and degrade upon exposure to ROS. (Reprinted with permission from reference [<a href="#B26-gels-03-00025" class="html-bibr">26</a>]. Copyright 2014 American Chemical Society).</p> Full article ">Figure 9
<p>Schematic of aFGF-heparin (HP) thermo-sensitive hydrogels enhance the recovery of spinal cord injury (SCI). The protection of aFGF-HP containing blood-spinal cord barrier (BSCB) protection, neuroprotection, remyelination, attenuation of astrogliosis, axon elongation in three different stages after SCI, which are the main obstacles to recovery of SCI. (Reprinted with permission from reference [<a href="#B50-gels-03-00025" class="html-bibr">50</a>]. Copyright 2017 American Chemical Society).</p> Full article ">Figure 10
<p>Representative TEM micrographs for the aqueous dried AgNPs (100 μg AgNPs/mL): (<b>A</b>) uncoated AgNPs; (<b>B</b>) SDS-coated AgNPs; (<b>C</b>) PEG-coated AgNPs (×100,000); (<b>D</b>) β-CD-coated AgNPs (×140,000) with sizes = 15.7 ± 4.8, 13 ± 4, 19.2 ± 3.6, and 14 ± 4.4 nm, respectively (<span class="html-italic">n</span> = 50, bar represents 100 nm). Insets indicate histograms of AgNPs size distribution. Abbreviations: TEM, transmission electron microscopy; AgNPs, silver nanoparticles; SDS, sodium dodecyl sulfate; PEG, polyethylene glycol; β-CD, β-cyclodextrin. (Reprinted from reference [<a href="#B52-gels-03-00025" class="html-bibr">52</a>]).</p> Full article ">Figure 11
<p>Successive images of representative mice skin abrasion wounds infected with MRSA at different time intervals. Two groups were treated with 0.1% silver nanoparticles (AgNPs) hydrogel and 1% silver sulfadiazine cream. The two other groups were the blank hydrogel-treated group and control untreated mice. Abbreviations: MRSA, methicillin-resistant <span class="html-italic">Staphylococcus aureus</span>; AgNPs, silver nanoparticles. (Reprinted from reference [<a href="#B52-gels-03-00025" class="html-bibr">52</a>]).</p> Full article ">Figure 12
<p>(<b>A</b>) Schematic illustration of the preparation of pectin/starch hydrogels encapsulated <span class="html-italic">Lactobacillus plantarum</span> (<span class="html-italic">L. plantarum</span>) cells. (<b>B</b>) Release profile of encapsulated cells in buffered solution with pH 1.2 and pH 7.4; Values shown are means ± standard deviations (<span class="html-italic">n</span> = 3). (Reprinted with permission from reference [<a href="#B57-gels-03-00025" class="html-bibr">57</a>]. Copyright 2017 Elsevier).</p> Full article ">Figure 12 Cont.
<p>(<b>A</b>) Schematic illustration of the preparation of pectin/starch hydrogels encapsulated <span class="html-italic">Lactobacillus plantarum</span> (<span class="html-italic">L. plantarum</span>) cells. (<b>B</b>) Release profile of encapsulated cells in buffered solution with pH 1.2 and pH 7.4; Values shown are means ± standard deviations (<span class="html-italic">n</span> = 3). (Reprinted with permission from reference [<a href="#B57-gels-03-00025" class="html-bibr">57</a>]. Copyright 2017 Elsevier).</p> Full article ">Figure 13
<p>Percentages of paracetamol release from the hydroxyethylacryl chitosan (HC)/sodium alginate (SA) hydrogels after immersing in simulated gastric fluid (SGF) for 2 h followed by simulated intestinal fluid (SIF) for 6 h at 37 °C: (<b>a</b>) varying ratios of HC to SA and (<b>b</b>) HC50SA50 with varying cross-linker types). (Reprinted with permission from reference [<a href="#B61-gels-03-00025" class="html-bibr">61</a>]. Copyright 2017 Elsevier).</p> Full article ">
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