Polyacrylamide-g-alginate-based electrically responsive hydrogel for drug delivery application: Synthesis, characterization, and formulation development

Porosity Engineering of Dried Smart Poly(N-isopropylacrylamide) Hydrogels for Gas Sensing

A recent study unveiled the potential of acrylamide-based stimulus-responsive hydrogels for volatile organic compound detection in gaseous environments. However, for gas sensing, a large surface area, that is, a highly porous material, offering many adsorption sites is crucial. The large humidity variation in the gaseous environment constitutes a significant challenge for preserving an initially porous structure, as the pores tend to be unstable and irreversibly collapse. Therefore, the present investigation focuses on enhancing the porosity of smart PNiPAAm hydrogels under the conditions of a gaseous environment and the preservation of the structural integrity for long-term use. We have studied the influence of polyethylene glycol (PEG) as a porogen and the application of different drying methods and posttreatment. The investigations lead to the conclusion that only the combination of PEG addition, freeze-drying, and subsequent conditioning in high relative humidity enables a long-term stable formation of a porous surface and inner structure of the material. The significantly enhanced swelling response in a gaseous environment and in the test gas acetone is confirmed by gravimetric experiments of bulk samples and continuous measurements of thin films on piezoresistive pressure sensor chips. These measurements are furthermore complemented by an in-depth analysis of the morphology and microstructure. While the study was conducted for PNiPAAm, the insights and developed processes are general in nature and can be applied for porosity engineering of other smart hydrogel materials for VOC detection in gaseous environments.

Alginate-Based Smart Materials and Their Application: Recent Advances and Perspectives

Nature produces materials using available molecular building blocks following a bottom-up approach. These materials are formed with great precision and flexibility in a controlled manner. This approach offers the inspiration for manufacturing new artificial materials and devices. Synthetic artificial materials can find many important applications ranging from personalized therapeutics to solutions for environmental problems. Among these materials, responsive synthetic materials are capable of changing their structure and/or properties in response to external stimuli, and hence are termed "smart" materials. Herein, this review focuses on alginate-based smart materials and their stimuli-responsive preparation, fragmentation, and applications in diverse fields from drug delivery and tissue engineering to water purification and environmental remediation. In the first part of this report, we review stimuli-induced preparation of alginate-based materials. Stimuli-triggered decomposition of alginate materials in a controlled fashion is documented in the second part, followed by the application of smart alginate materials in diverse fields. Because of their biocompatibility, easy accessibility, and simple techniques of material formation, alginates can provide solutions for several present and future problems of humankind. However, new research is needed for novel alginate-based materials with new functionalities and well-defined properties for targeted applications.

Correlative Light and Electron Microscopy for Nanoparticle-Cell Interaction and Protein Localization

Various silica-based fluorescent nanoparticles ((Si-FNP)) with magnetic or metal cores represent a standard class of nanoparticles offering new opportunities for high-resolution cellular imaging and biomedicine applications, such as drug delivery. Their high solubility, homogeneity, biocompatibility, and chemical inertness Si-FNPs make them attractive probes for correlative light and electron microscopy (CLEM) studies, offering novel insights into nanoparticle-cell interactions in detail. In the present chapter, we present a procedure for imaging silica-based fluorescent magnetic core-shell nanoparticles (Si-FMNP) at the single-particle scale in cells. Our method facilitates the acquisition of information on the extracellular and intercellular distribution of nanoparticles and their various interactions with various cellular organelles when cells are cultured and electroporated by NPs. In addition, such information could facilitate the evaluation of the efficacy of nanocarriers designed for drug delivery.

Tunable Hydrogels: Introduction to the World of Smart Materials for Biomedical Applications

Hydrogels are hydrated polymers that are able to mimic many of the properties of living tissues. For this reason, they have become a popular choice of biomaterial in many biomedical applications including tissue engineering, drug delivery, and biosensing. The physical and biological requirements placed on hydrogels in these contexts are numerous and require a tunable material, which can be adapted to meet these demands. Tunability is defined as the use of knowledge-based tools to manipulate material properties in the desired direction. Engineering of suitable mechanical properties and integrating bioactivity are two major aspects of modern hydrogel design. Beyond these basic features, hydrogels can be tuned to respond to specific environmental cues and external stimuli, which are provided by surrounding cells or by the end user (patient, clinician, or researcher). This turns tunable hydrogels into stimulus-responsive smart materials, which are able to display adaptable and dynamic properties. In this book chapter, we will first shortly cover the foundation of hydrogel tunability, related to mechanical properties and biological functionality. Then, we will move on to stimulus-responsive hydrogel systems and describe their basic design, as well as give examples of their application in diverse biomedical fields. As both the understanding of underlying biological mechanisms and our engineering capacity mature, even more sophisticated tunable hydrogels addressing specific therapeutic goals will be developed.

Functionally Tailored Electro-Sensitive Poly(Acrylamide)-g-Pectin Copolymer Hydrogel for Transdermal Drug Delivery Application: Synthesis, Characterization, In-vitro and Ex-vivo Evaluation

Background and Objectives:

To develop electro-sensitive transdermal drug delivery systems (ETDDS) using polyacrylamide-grafted-pectin (PAAm-g-PCT) copolymer hydrogel for rivastigmine delivery.

Methods:

Free radical polymerization and alkaline hydrolysis technique was employed to synthesize PAAm-g-PCT copolymer hydrogel. The PAAm-g-PCT copolymeric hydrogel was used as a reservoir and cross-linked blend films of PCT and poly(vinyl alcohol) as rate-controlling membranes (RCMs) to prepare ETDDS.

Results:

The pH of the hydrogel reservoir was found to be in the range of 6.81 to 6.93 and drug content was 89.05 to 96.29%. The thickness of RCMs was in the range of 51 to 99 μ and RCMs showed permeability behavior against water vapors. There was a reduction in the water vapor transmission rate as the glutaraldehyde (GA) concentration was increased. The drug permeation rate from the ETDDS was enhanced under the influence of electric stimulus against the absence of an electric stimulus. The increase in flux by 1.5 fold was recorded with applied electric stimulus. The reduction in drug permeability observed when the concentration of GA was increased. Whereas, the permeability of the drug was augmented as an electric current was changed from 2 to 8 mA. The pulsatile drug release under “on– off” cycle of electric stimulus witnessed a faster drug release under ‘on’ condition and it was slow under ‘off’ condition. The alteration in skin composition after electrical stimulation was confirmed through histopathology studies.

Conclusion:

The PAAm-g-PCT copolymer hydrogel is a useful carrier for transdermal drug delivery activated by an electric signal to provide on-demand release of rivastigmine.

Electrically Triggered Transdermal Drug Delivery Utilizing Poly(Acrylamide)-graft-Guar Gum: Synthesis, Characterization and Formulation Development

Objective:

The study aimed to prepare electrically-triggered transdermal drug delivery systems (ETDS) using electrically responsive polyacrylamide-graft-gaur gum (PAAm-g-GaG) copolymer.

Methods:

The PAAm-g-GaG copolymer was synthesized by adopting free radical polymerization grafting method. This PAAm-g-GaG copolymer hydrogel acts as a drug reservoir and blend films of Guar Gum (GaG) and Polyvinyl Alcohol (PVA) were included as Rate Controlling Membranes (RCM) in the system. The PAAm-g-GaG copolymer was characterized by FTIR, neutralization equivalent values, thermogravimetric analysis and elemental analysis.

Results:

On the basis of results obtained, it is implicit that the drug permeation decreased with an increase in the concentration of glutaraldehyde and RCM thickness; while drug permeation rate was increased with increasing applied electric current strength from 2 to 8 mA. A two fold increase in flux values was observed with the application of DC electric current. An increase in drug permeation was witnessed under on condition of electric stimulus and permeation was decreased when electric stimulus was "off". The skin histopathology study confirmed the changes in skin structure when electrical stimulus was applied.

Conclusion:

The electrically-sensitive PAAm-g-GaG copolymer is a useful biomaterial for transdermal drug delivery application.

Dual stimulus responsive drug release under the interaction of pH value and pulsatile electric field for a bacterial cellulose/sodium alginate/multi-walled carbon nanotube hybrid hydrogel

Hydrogels synthesized by SA, BC and MWCNTs was a pH and electric responsive drug delivery system. The combination stimuli-releasing had selectivity for the pH value. Pulsatile releasing pattern was also had selectivity for the pH value.

pH- and electro-response characteristics of bacterial cellulose nanofiber/sodium alginate hybrid hydrogels for dual controlled drug delivery

An ionic crosslinking nanocellulose/sodium alginate (BC/SA) hybrid hydrogel was prepared as a dual-stimuli responsive release system. The drug release rate of BC/SA hybrid hydrogels in vitro not only depend on pH value but also depend on the presence of electric stimulus.

Crosslinked ionic polysaccharides for stimuli-sensitive drug delivery

Polysaccharides are gaining increasing attention as components of stimuli-responsive drug delivery systems, particularly since they can be obtained in a well characterized and reproducible way from the natural sources. Ionic polysaccharides can be readily crosslinked to render hydrogel networks sensitive to a variety of internal and external variables, and thus suitable for switching drug release on-off through diverse mechanisms. Hybrids, composites and grafted polymers can reinforce the responsiveness and widen the range of stimuli to which polysaccharide-based systems can respond. This review analyzes the state of the art of crosslinked ionic polysaccharides as components of delivery systems that can regulate drug release as a function of changes in pH, ion nature and concentration, electric and magnetic field intensity, light wavelength, temperature, redox potential, and certain molecules (enzymes, illness markers, and so on). Examples of specific applications are provided. The information compiled demonstrates that crosslinked networks of ionic polysaccharides are suitable building blocks for developing advanced externally activated and feed-back modulated drug delivery systems.

pH-responsive interpenetrating network hydrogel beads of poly(acrylamide)-g-carrageenan and sodium alginate for intestinal targeted drug delivery: synthesis, in vitro and in vivo evaluation

In the present work, we synthesized pH-responsive interpenetrating network (IPN) hydrogel beads of polyacrylamide grafted κ-carrageenan (PAAm-g-CG) and sodium alginate (SA) for targeting ketoprofen to the intestine. The PAAm-g-CG was synthesized by free radical polymerization followed by alkaline hydrolysis under nitrogen gas. The PAAm-g-CG was characterized by elemental analysis, FTIR spectroscopy and thermogravimetric analysis (TGA). The drug-loaded IPN hydrogel beads were prepared by simple ionotropic gelation/covalent crosslinking method. The amorphous nature of drug in the beads was confirmed by differential scanning calorimetry and X-ray diffraction studies. The spherical shape of the beads was confirmed by scanning electron microscopic analysis. The beads exhibited ample pH-responsive behavior in the pulsatile swelling study. The ketoprofen release was significantly increased when pH of the medium was changed from acidic to alkaline. The beads showed maximum of 10% drug release in acidic medium of pH 1.2, and about 90% drug release was recorded in alkaline medium of pH 7.4. Stomach histopathology of albino rats indicated that the prepared beads were able to retard the drug release in stomach leading to the reduced ulceration, hemorrhage and erosion of gastric mucosa.

Alginate graft copolymers and alginate-co-excipient physical mixture in oral drug delivery

OBJECTIVES

Use of alginate graft copolymers in oral drug delivery reduces dosage form manufacture complexity with reference to mixing or coating processes. It is deemed to give constant or approximately steady weight ratio of alginate to covalently attached co-excipient in copolymers, thereby leading to controllable matrix processing and drug release. This review describes various grafting approaches and their outcome on oral drug release behaviour of alginate graft copolymeric matrices. It examines drug release modulation mechanism of alginate graft copolymers against that of co-excipients in non-grafted formulations.

KEY FINDINGS

Drug release from alginate matrices can be modulated through using either co-excipients or graft copolymers via changing their swelling, erosion, hydrophobicity/hydrophilicity, porosity and/or drug adsorption capacity. However, it is not known if the drug delivery performance of formulations prepared using alginate graft copolymers is superior to those incorporating graft-equivalent co-excipient physically in a dosage form without grafting but at the corresponding graft weight, owing to limited studies being available.

CONCLUSIONS

The value of alginate graft copolymers as the potential alternative to alginate-co-excipient physical mixture in oral drug delivery cannot be entirely defined by past and present research. Such an issue is complicated by the lack of green chemistry graft copolymer synthesis approach, high grafting process cost, complications and hazards, and the formed graft copolymers having unknown toxicity. Future research will need to address these matters to achieve a widespread commercialization and industrial application of alginate graft copolymers in oral drug delivery.