Synthesis, characterization, and in vitro evaluation of the starch-based α-amylase responsive hydrogels

Controlled-release drug delivery systems are promising platforms in medicine. Among various types of material in drug delivery, hydrogels are interesting ones. They are water-soluble and tissue compatible polymers with a high capacity to carry and release drugs in a controllable manner. In this study, we introduce the synthesis, characterization, and application of an α-amylase responsive hydrogel in controlled drug delivery. The newly synthesized starch-based hydrogels structurally characterized by means of Fourier-transform infrared spectroscopy and scanning electron microscopy. A proapoptotic drug, doxorubicin, was loaded into the hydrogels and the controlled release of the drug was assessed in the presence of α-amylase and ultimately it was evaluated to controlled-drug release in vitro and subsequently in killing cancer cells. Our results highlight the effectiveness of temporal drug delivery using α-amylase responsive hydrogels in killing cancer cells.

Process Strategies for the Transition of 1G to Advanced Bioethanol Production

Nowadays, the transport sector is one of the main sources of greenhouse gas (GHG) emissions and air pollution in cities. The use of renewable energies is therefore imperative to improve the environmental sustainability of this sector. In this regard, biofuels play an important role as they can be blended directly with fossil fuels and used in traditional vehicles’ engines. Bioethanol is the most used biofuel worldwide and can replace gasoline or form different gasoline-ethanol blends. Additionally, it is an important building block to obtain different high added-value compounds (e.g., acetaldehyde, ethylene, 1,3-butadiene, ethyl acetate). Today, bioethanol is mainly produced from food crops (first-generation (1G) biofuels), and a transition to the production of the so-called advanced ethanol (obtained from lignocellulosic feedstocks, non-food crops, or industrial waste and residue streams) is needed to meet sustainability criteria and to have a better GHG balance. This work gives an overview of the current production, use, and regulation rules of bioethanol as a fuel, as well as the advanced processes and the co-products that can be produced together with bioethanol in a biorefinery context. Special attention is given to the opportunities for making a sustainable transition from bioethanol 1G to advanced bioethanol.

Localized Interleukin-12 for Cancer Immunotherapy

Interleukin-12 (IL-12) is a potent, pro-inflammatory type 1 cytokine that has long been studied as a potential immunotherapy for cancer. Unfortunately, IL-12's remarkable antitumor efficacy in preclinical models has yet to be replicated in humans. Early clinical trials in the mid-1990's showed that systemic delivery of IL-12 incurred dose-limiting toxicities. Nevertheless, IL-12's pleiotropic activity, i.e., its ability to engage multiple effector mechanisms and reverse tumor-induced immunosuppression, continues to entice cancer researchers. The development of strategies which maximize IL-12 delivery to the tumor microenvironment while minimizing systemic exposure are of increasing interest. Diverse IL-12 delivery systems, from immunocytokine fusions to polymeric nanoparticles, have demonstrated robust antitumor immunity with reduced adverse events in preclinical studies. Several localized IL-12 delivery approaches have recently reached the clinical stage with several more at the precipice of translation. Taken together, localized delivery systems are supporting an IL-12 renaissance which may finally allow this potent cytokine to fulfill its considerable clinical potential. This review begins with a brief historical account of cytokine monotherapies and describes how IL-12 went from promising new cure to ostracized black sheep following multiple on-study deaths. The bulk of this comprehensive review focuses on developments in diverse localized delivery strategies for IL-12-based cancer immunotherapies. Advantages and limitations of different delivery technologies are highlighted. Finally, perspectives on how IL-12-based immunotherapies may be utilized for widespread clinical application in the very near future are offered.

Sono-Assembly of the [Arg-Phe]4 Octapeptide into Biofunctional Nanoparticles

High-frequency ultrasound treatment is found to be a one-pot green technique to produce peptide-based nanostructures by ultrasound assisted self-assembly of oligopeptides. [Arg-Phe]₄ octapeptides, consisting of alternating arginine (Arg/R) and phenylalanine (Phe/F) sequences, were subjected to 430 kHz ultrasound in aqueous solution in the absence of any external agents, to form [RF]₄ nanoparticles ([RF]₄-NPs), ~220 nm in diameter. A comprehensive analysis of the obtained nanoparticles demonstrated that the aromatic moieties of the oligopeptides can undergo oxidative coupling to form multiple oligomeric species, which then self-assemble into well-defined fluorescent nanoparticles. [RF]₄-NPs were functionalized with polyethylene glycol (PEGylated) to improve their colloidal stability. Unlike the parent peptide, the PEGylated [RF]₄-NPs showed limited cytotoxicity towards MDA-MB-231 cells. Furthermore, the intracellular trafficking of PEGylated [RF]₄-NPs was investigated after incubation with MDA-MB-231 cells to demonstrate their efficient endo-lysosomal escape. This work highlights that the combined use of ultrasonic technologies and peptides enables easy fabrication of nanoparticles, with potential application in drug delivery.

PLCL/Silk fibroin based antibacterial nano wound dressing encapsulating oregano essential oil: Fabrication, characterization and biological evaluation

The use of natural biocompatible drugs is highly desirable in wound dressing compared to synthetic chemicals. Oregano essential oil (OEO) is a promising natural compound with marked antibacterial, antioxidant and anti-inflammatory activities. The topical delivery of OEO may result in lower therapeutic efficacy and irritation to the skin. Moreover, OEO is a volatile compound results in instability as well. To overcome these drawbacks, we successfully encapsulated OEO in Poly (L-lactide-co-caprolactone) (PLCL)/ Silk fibroin (SF) nanofibers membrane (NF) and achieved the encapsulation efficiency (%) up to 59.14 ± 0.58. The fabricated membranes were undergone through physicochemical as well as biological evaluation. SEM characterization revealed that OEO could be successfully encapsulated maintaining a smooth profile of nanofibers. The biocompatibility of the NF membrane was confirmed by cytotoxicity assay. Antibacterial results indicated that OEO containing nanofibrous membranes are highly active against both gram-positive and gram-negative bacteria. The result revealed that 5% is the optimized concentration of OEO capable to completely inhibit bacterial growth. Moreover, the NF membranes were evaluated for their in vivo wound healing potential. The results confirmed that OEO containing NF membrane is not only capable to accelerate the wound contraction but also enhances the quality of wound healing confirmed through histology analysis. H&E and Masson's trichrome staining indicated the neo-epithelialization, granulation tissue formation, angiogenesis, and collagen deposition in a group treated with PLCL/SF/5% OEO. Based on the physicochemical and biological evaluation, PLCL/SF/5% OEO NF membrane can be considered as a potential wound dressing candidate.

Nanocomposite hydrogel with NIR/magnet/enzyme multiple responsiveness to accurately manipulate local drugs for on-demand tumor therapy

Chemotherapy is one of the most commonly utilized approaches to treat malignant tumor. However, the well-controlled chemotherapy able to accurately manipulate local drugs for on-demand tumor treatment is still a challenge. Herein, a magnet and light dual-responsive hydrogel combining thermosensitive poly(N-acryloyl glycinamide) (PNAGA), doxorubicin (DOX) loaded and polyester (PE) capped mesoporous silica nanocarriers (MSNs) as well as Fe₃O₄ nanoparticles (Fe₃O₄ NPs) grafted graphene oxide (GO) was fabricated to address above issue. The Fe₃O₄ NPs and GO respectively serve as magnetothermal agent and photothermal agent to perform hyperthermia, meanwhile to generate chain motion of PNAGA with varying degrees under different conditions of magnetic field and/or NIR irradiation. This strategy not only allowed the gel-sol transition of the hydrogel by prior heating for tumor injection, but performed controllable release routes of DOX-MSNs-PE (DMP for short) nanocarriers to meet various requirements from different patients and the changing states of tumor. Furthermore, these escaped DMP nanocarriers could be taken by surrounding tumor cells, and then deliver their drug to these cells after rapid hydrolysis of the PE cap triggered by esterase, resulting in accurate chemotherapy. Both in vitro and in vivo results indicated that the PNAGA-DMP-Fe₃O₄@GO hydrogel combining well-controllable chemotherapy and hyperthermia can eliminate more than 90% tumor cells and effectively inhibit the tumor growth in mice model, demonstrating the great candidate of our hydrogel for accurate tumor therapy.

Visible Light-Curable Hydrogel Systems for Tissue Engineering and Drug Delivery

Visible light-curable hydrogels have been investigated as tissue engineering scaffolds and drug delivery carriers due to their physicochemical and biological properties such as porosity, reservoirs for drugs/growth factors, and similarity to living tissue. The physical properties of hydrogels used in biomedical applications can be controlled by polymer concentration, cross-linking density, and light irradiation time. The aim of this review chapter is to outline the results of previous research on visible light-curable hydrogel systems. In the first section, we will introduce photo-initiators and mechanisms for visible light curing. In the next section, hydrogel applications as drug delivery carriers will be emphasized. Finally, cellular interactions and applications in tissue engineering will be discussed.

Engineered Hydrogels for Brain Tumor Culture and Therapy

Brain tumors' severity ranges from benign to highly aggressive and invasive. Bioengineering tools can assist in understanding the pathophysiology of these tumors from outside the body and facilitate development of suitable antitumoral treatments. Here, we first describe the physiology and cellular composition of brain tumors. Then, we discuss the development of three-dimensional tissue models utilizing brain tumor cells. In particular, we highlight the role of hydrogels in providing a biomimetic support for the cells to grow into defined structures. Microscale technologies, such as electrospinning and bioprinting, and advanced cellular models aim to mimic the extracellular matrix and natural cellular localization in engineered tumor tissues. Lastly, we review current applications and prospects of hydrogels for therapeutic purposes, such as drug delivery and co-administration with other therapies. Through further development, hydrogels can serve as a reliable option for in vitro modeling and treatment of brain tumors for translational medicine.

Advances in drug delivery systems: Work in progress still needed?

A new era of science and technology has emerged in pharmaceutical research with focus on developing novel drug delivery systems for oral administration. Conventional dosage forms like tablets and capsules are associated with a low bioavailability, frequent application, side effects and hence patient noncompliance. By developing novel strategies for drug delivery, researchers embraced an alternative to traditional drug delivery systems. Out of those, fast dissolving drug delivery systems are very eminent among pediatrics and geriatrics. Orally disintegrating films are superior over fast dissolving tablets as the latter are assigned with the risk of suffocation. Due to their ability of bypassing the dissolution and the first pass effect after oral administration, self-emulsifying formulations have also become increasingly popular in improving oral bioavailability of hydrophobic drugs. Osmotic devices enable a controlled drug delivery independent upon gastrointestinal conditions using osmosis as driving force. The advances in nanotechnology and the variety of possible materials and formulation factors enable a targeted delivery and triggered release. Vesicular systems can be easily modified as required and provide a controlled and sustained drug delivery to a specific site.

This work provides an insight of the novel approaches in drug delivery covering the critical comparison between traditional and novel “advanced-designed” systems.

Hydrogel Biomaterials for Application in Ocular Drug Delivery

There are many challenges involved in ocular drug delivery. These are a result of the many tissue barriers and defense mechanisms that are present with the eye; such as the cornea, conjunctiva, the blinking reflex, and nasolacrimal drainage system. This leads to many of the conventional ophthalmic preparations, such as eye drops, having low bioavailability profiles, rapid removal from the administration site, and thus ineffective delivery of drugs. Hydrogels have been investigated as a delivery system which is able to overcome some of these challenges. These have been formulated as standalone systems or with the incorporation of other technologies such as nanoparticles. Hydrogels are able to be formulated in such a way that they are able to change from a liquid to gel as a response to a stimulus; known as "smart" or stimuli-responsive biotechnology platforms. Various different stimuli-responsive hydrogel systems are discussed in this article. Hydrogel drug delivery systems are able to be formulated from both synthetic and natural polymers, known as biopolymers. This review focuses on the formulations which incorporate biopolymers. These polymers have a number of benefits such as the fact that they are biodegradable, biocompatible, and non-cytotoxic. The biocompatibility of the polymers is essential for ocular drug delivery systems because the eye is an extremely sensitive organ which is known as an immune privileged site.

Nanotribology of hydrogels with similar stiffness but different polymer and crosslinker concentrations

HYPOTHESIS

The stiffness has been found to regulate hydrogel performances and applications. However, the key interfacial properties of hydrogels, like friction and adhesion are not controlled by the stiffness, but are altered by the structure and composition of hydrogels, like polymer volume fraction and crosslinking degree.

EXPERIMENTS

Colloidal probe atomic force microscopy has been use to investigate the relationship between tribological properties (friction and adhesion) and composition of hydrogels with similar stiffness, but different polymer volume fractions and crosslinking degrees.

FINDINGS

The interfacial normal and lateral (friction) forces of hydrogels are not directly correlated to the stiffness, but altered by the hydrogel structure and composition. For normal force measurements, the adhesion increases with polymer volume fraction but decreases with crosslinking degree. For lateral force measurements, friction increases with polymer volume fraction, but decreases with crosslinking degree. In the low normal force regime, friction is mainly adhesion-controlled and increases significantly with the adhesion and polymer volume fraction. In the high normal force regime, friction is predominantly load-controlled and shows slow increase with normal force.

Synthesis and Applications of Hydrogels in Cancer Therapy

Hydrogels are water-insoluble, hydrophilic, cross-linked, three-dimensional networks of polymer chains having the ability to swell and absorb water but do not dissolve in it, that comprise the major difference between gels and hydrogels. The mechanical strength, physical integrity and solubility are offered by the crosslinks. The different applications of hydrogels can be derived based on the methods of their synthesis, response to different stimuli, and their different kinds. Hydrogels are highly biocompatible and have properties similar to human tissues that make it suitable to be used in various biomedical applications, including drug delivery and tissue engineering. The role of hydrogels in cancer therapy is highly emerging in recent years. In the present review, we highlighted different methods of synthesis of hydrogels and their classification based on different parameters. Distinctive applications of hydrogels in the treatment of cancer are also discussed.

Development of Chitosan-Based Hydrogel Containing Antibiofilm Agents for the Treatment of Staphylococcus aureus-Infected Burn Wound in Mice

Methicillin-resistant Staphylococcus aureus (MRSA) is considered a common colonizer of burn wound and accounts for high morbidity and mortality all across the globe. Systemic antibiotic therapy which is generally prescribed for these patients has a number of limitations. These include high drug dose, toxicity, and chances of development of drug resistance. However, local delivery of drug not only addresses these limitations but also provides better efficacy at the site of infection. In the present study, hydrogel preparations were developed for the topical delivery of moxifloxacin for the treatment of S. aureus-infected burn wound. Moxifloxacin was characterized by UV, FTIR, DSC, hot-stage microscopy, NMR, and HPLC and loaded into conventional and Boswellia-containing novel gels. Gels were characterized by visual examination, pH, UV spectroscopy, and release assays. In vivo studies showed that both gels were effective in eradicating the bacteria completely from the wound site when treatment was started during the early stage of infection. On the contrary, delayed treatment of planktonic and biofilm cells with novel gel showed better efficacy as compared with conventional gel in S. aureus-infected burn wound. Histopathological analysis also showed better skin healing efficacy of novel gel than conventional gel. Our results show that moxifloxacin can be efficiently used topically in the management of burn wound infections along with other antibacterial agents. Since biofilm-mediated infections are on the rise especially in chronic bacterial disease, therefore, a preparation containing antibiofilm agent-like Boswellia as one of the excipients would be more meaningful.

From design to applications of stimuli-responsive hydrogel strain sensors

Stimuli-responsive hydrogel strain sensors that synergize the advantages of both hydrogel and smart functional materials have attracted increasing interest from material design to emerging applications in health monitors and human–machine interfaces.

Local environment-dependent kinetics of ester hydrolysis revealed by direct 1H NMR measurement of degrading hydrogels

We have demonstrated the use of a simple ¹H NMR spectrometry-based method to directly measure the pseudo first-order hydrolytic cleavage rate constant (k_obs) of methacrylate-derived ester crosslinkers in hydrogels composed of PEG, dextran, carboxymethyl dextran (CM-dextran) and hyaluronic acid (HA). Using this technique, we systematically examined how the local environment in the hydrogel influenced the rate of ester hydrolysis. Within the formulations being studied, the esters in the crosslinked polymer network (gel state) degraded 1.8 times faster than esters of similar chemistry in soluble polymers (solution state). Furthermore, the value of k_obs was independent of the polymer concentration or the hydrogel network structure, although these parameters affected the swelling profiles in response to the hydrolytic degradation. On the other hand, the presence of the negatively charged carboxylate groups in the polymer chains decreased k_obs in gel state, while only minimally affecting k_obs in solution state. Hydrogels composed of negatively charged polymers (HA and CM-dextran) had a k_obs about 30% smaller than hydrogels composed of neutral polymers (dextran and PEG). The reported method provides a reliable tool to resolve conflicting views about hydrogel degradation, and to guide the rational design of degradable hydrogel. STATEMENT OF SIGNIFICANCE: Degradable hydrogels are widely used in biological applications. A common degradation mechanism of the crosslinked polymer is by hydrolytic cleavage. However, the hydrogel micro-milieu do affect the behavior of the hydrolysable bonds, for example esters. There have been several conflicting speculations on how hydrogel composition would affect the macroscopic degradation behavior. In this report, we simply, but innovatively applied ordinary ¹H NMR spectrometry-based method to probe the rate of ester cleavage in the native hydrogel milieu. We tried to answer whether these parameters will have direct influence on ester cleavage, or have indirect effect on the overall network disintegration behavior. This study provides quantitative evidences to assist theoretical modeling and to guide rational formulation design.

Exploring the inner environment of protein hydrogels with fluorescence spectroscopy towards understanding their drug delivery capabilities

Time-resolved fluorescence have used to explore the inner surface and solvation dynamics within protein hydrogels assisting in rationalizing their drug binding and release capabilities.

Non-proteinogenic amino acid based supramolecular hydrogel material for enhanced cell proliferation

Supramolecular gel material built from low-molecular-weight (LMW) gelators finds potential applications in various fields, especially in drug delivery, cell encapsulation and delivery, and tissue engineering. The majority of the LMW gelators in these applications are based on functionalized peptides/amino acids consisting of proteinogenic amino acids which are proteolytically unstable. Herein, we have developed a new LMW gelator containing non-proteinogenic amino acid namely 2,3-diaminopropionic acid (Dap), a key precursor in the synthesis of many antibiotics namely viomycin and capreomycin, by functionalizing with fluorenylmethoxycarbonyl at both amino terminals of Dap [Fm-Dap(Fm)]. Hydrogelation test at different pH indicates that Fm-Dap(Fm) can form a hydrogel in a wide range of pH (4.9 to 9.1) with minimum hydrogelation concentration depends on the pH. The mechanical strength and thermal stability of the Fm-Dap(Fm) hydrogel material are found to decrease with increasing pH (acidic > neural/physiological > basic). The thermal stability of Fm-Dap(Fm) hydrogels is pH-dependent and elicits high stability at acidic pH. Also, Fm-Dap(Fm) hydrogels exhibit strong thixotropic property where regelation (self-healing) occurs upon release of stress. Morphological analysis indicates the formation of fibrils, which are entangled to form three dimensional network structures. Several spectroscopic measurements provided evidence for the self-assembly of Fm-Dap(Fm) molecules through intermolecular aromatic π-π stacking and hydrogen bonding interactions during hydrogelation. Interestingly, Fm-Dap(Fm) not only exhibits hydrogel formation but also shows cell viability and enhanced cell proliferation at physiological pH (7.4). Further, Fm-Dap(Fm) forms a hydrogel upon co-incubation with vitamin B₁₂ and also exhibits release of vitamin B₁₂ over a period. The current study thus demonstrates the development of a new hydrogel material, based on LMW gelator containing the non-proteinogenic amino acid, which can elicit cell viability, enhanced cell proliferation, drug encapsulation, and drug release properties. Hence, Fm-Dap(Fm) hydrogel could be an ideal material for biomedical applications, especially in tissue engineering and drug delivery.

Injectable and fast self-healing protein hydrogels

Injectable hydrogels are adapted to irregularities in the desired location by injection as a liquid and gelation in situ. However, traditional slow-gelling injectable hydrogels may result in loss of cargo (cells/drugs) as well as diffusion at the target site, and extremely rapid gelation may lead to undesired premature coagulation. These practical problems can be solved by using self-healing hydrogels. Herein, through the reduction of disulfide bonds in BSA protein by using a reducing agent, the disulfide bonds between the individual BSA protein molecules are re-matched to form a network structure, thereby forming a protein hydrogel. This hydrogel shows an efficient and rapid self-healing property, and the broken protein hydrogel can be fast repaired within 1-2 minutes in response to H₂O₂ stimulation, and the repair efficiency reached up to 100%. The hydrogel can be extruded using only a pinhole syringe, and cytotoxicity experiments have demonstrated excellent biocompatibility of the protein hydrogel. This non-toxic, injectable, fast self-healing protein hydrogel is expected to be widely used in biomedical, tissue engineering, injectable gel, 3D bioprinting, and other applications.

Periodate-Modified Gum Arabic Cross-linked PVA Hydrogels: A Promising Approach toward Photoprotection and Sustained Delivery of Folic Acid

The chemically oxidized gum arabic was prepared and used as a naturally derived nontoxic and pH-responsive cross-linker to develop smart polyvinyl alcohol (PVA)-based hydrogels for the first time. The formulated hydrogels exhibited high mechanical properties, good porosity, and pH sensitivity, which facilitated their application as promising biomaterials for sustained delivery of folic acid. Further, the synthesized cross-linked PVA hydrogels displayed no cytotoxicity toward the human embryonic kidney cell line and exhibited higher blood compatibility. The hydrolytic degradation study confirmed their biodegradable nature. While the sustained delivery along with photoprotective properties of these hydrogels confirmed their multifunctional characteristics, these results suggest that these hydrogels may act as an efficient photoprotective material and find their application in the field of drug delivery.

Centrifugal Force-Driven Modular Micronozzle System: Generation of Engineered Alginate Microspheres

In this study, we developed a modular micronozzle system that can control the flow of fluid based on centrifugal force and synthesize functional alginate microspheres with various structures and sizes. Our method is to fabricate a programmable microreactor that can be easily manufactured without the conventional soft-lithography process using various sequences of the micronozzles with various inner diameters. To overcome the obstacles of pump-based microfluidic devices that need to be precisely controlled, we designed the programmable microreactor to be driven under centrifugal force with a combination of micronozzles, thus enabling the mass production of various functional alginate microspheres within a few minutes. The programmable microreactor designed through the arrangement of the modular micronozzles enables the formation of various types of alginate microspheres such as core-shell, Janus, and particle mixture. These materials are controlled to a size from 400 µm to 900 µm. In addition, our platform is used to generate pH-responsive smart materials, and to easily control various sizes, shapes, and compositions simultaneously. By evaluating the release process of model drugs according to the pH change, the possibility of drug delivery application is confirmed. We believe that our method can contribute to development of biomaterials engineering that has been limited by the requirement of sophisticated devices, and special skills and/or labor.

Thread-Like Radical-Polymerization via Autonomously Propelled (TRAP) Bots

Micromotor-mediated synthesis of thread-like hydrogel microstructures in an aqueous environment is presented. The study utilizes a catalytic micromotor assembly (owing to the presence of a Pt layer), with an on-board chemical reservoir (i.e., polymerization mixture), toward thread-like radical-polymerization via autonomously propelled bots (i.e., TRAP bots). Synergistic coupling of catalytically active Pt layer, together with radical initiators (H₂ O₂ and FeCl₃ (III)), and PEGDA monomers preloaded into the TRAP bot, results in the polymerization of monomeric units into elongated thread-like hydrogel polymers coupled with self-propulsion. Interestingly, polymer generation via TRAP bots can also be triggered in the absence of hydrogen peroxide for cellular/biomedical application. The resulting polymeric hydrogel microstructures are able to entrap living cells (NIH 3T3 fibroblast cells), and are easily separable via a centrifugation or magnetic separation (owing to the presence of a Ni layer). The cellular biocompatibility of TRAP bots is established via a LIVE/DEAD assay and MTS cell proliferation assay (7 days observation). This is the first study demonstrating real-time in situ hydrogel polymerization via an artificial microswimmer, capable of enmeshing biotic/abiotic microobjects in its reaction environment, and lays a strong foundation for advanced applications in cell/tissue engineering, drug delivery, and cleaner technologies.

Tuning the Structure of Galacturonate Hydrogels: External Gelation by Ca, Zn, or Fe Cationic Cross-Linkers

We show here how the nature of various divalent cations M²⁺ (Ca²⁺, Zn²⁺, or Fe²⁺) influences the structure and mechanical properties of ionotropic polygalacturonate (polyGal) hydrogels designed by the diffusion of cations along one direction (external gelation). All hydrogels exhibit strong gradients of polyGal and cation concentrations, which are similar for all studied cations with a constant ratio R = [M²⁺]/[Gal] equal to 0.25, showing that every M²⁺ cation interacts with four galacturonate (Gal) units all along the gels. The regions of the hydrogels formed in the early stages of the gelation process are also similar for all cations and are homogeneous, with the same characteristic mesh size (75 ± 5 Å, as measured by small angle neutron scattering (SANS)) and the same storage modulus G' (∼5 × 10⁴ Pa). Conversely, in the regions of the gels formed in later stages of the process there exist differences in mechanical properties, turbidity, and local structure from one cation to another. Zn(II)-polyGal and Fe(II)-polyGal hydrogels display mesoscopic heterogeneities, more marked in case of Fe than for Zn, that are not present in Ca(II)-polyGal hydrogels. This comes from the mode and the strength of association between the cation and the Gal unit (bidentate for Ca²⁺ and monodentate "egg-box" for Zn²⁺ and Fe²⁺). Cross-links formed by Zn²⁺ and Fe²⁺ have a higher stability (lower ability to untie and reform) that induces the formation of local heterogeneities in the early stages of the gelation process whose size progressively increases during the gel growth, a mechanism that does not occur for cross-links made by Ca²⁺ that are less stable and enable possible reorganizations between polyGal chains.

Poly[(N-acryloyl glycinamide)-co-(N-acryloyl l-alaninamide)] and Their Ability to Form Thermo-Responsive Hydrogels for Sustained Drug Delivery

In the presence of water, poly(N-acryloyl glycinamide) homopolymers form highly swollen hydrogels that undergo fast and reversible gel↔sol transitions on heating. According to the literature, the transition temperature depends on concentration and average molecular weight, and in the case of copolymers, composition and hydrophilic/hydrophobic character. In this article, we wish to introduce new copolymers made by free radical polymerization of mixtures of N-acryloyl glycinamide and of its analog optically active N-acryloyl l-alaninamide in various proportions. The N-acryloyl l-alaninamide monomer was selected in attempts to introduce hydrophobicity and chirality in addition to thermo-responsiveness of the Upper Critical Solubilization Temperature-type. The characterization of the resulting copolymers included solubility in solvents, dynamic viscosity in solution, Fourrier Transform Infrared, Nuclear Magnetic Resonance, and Circular Dichroism spectra. Gel→sol transition temperatures were determined in phosphate buffer (pH = 7.4, isotonic to 320 mOsm/dm³). The release characteristics of hydrophilic Methylene Blue and hydrophobic Risperidone entrapped in poly(N-acryloyl glycinamide) and in two copolymers containing 50 and 75% of alanine-based units, respectively, were compared. It was found that increasing the content in N-acryloyl-alaninamide-based units increased the gel→sol transition temperature, decreased the gel consistency, and increased the release rate of Risperidone, but not that of Methylene Blue, with respect to homo poly(N-acryloyl glycinamide). The increase observed in the case of Risperidone appeared to be related to the hydrophobicity generated by alanine residues.

Mucoadhesive Hydrogel Nanoparticles as Smart Biomedical Drug Delivery System

Hydrogels are widely used materials which have many medical applications. Their ability to absorb aqueous solutions and biological fluids gives them innovative characterizations resulting in increased compatibility with biological activity. In this sense, they are used extensively for encapsulation of several targets such as biomolecules, viruses, bacteria, and mammalian cells. Indeed, many methods have been published which are used in hydrogel formulation and biomedical encapsulations involving several cross-linkers. This system is still rich with the potential of undiscovered features. The physicochemical properties of polymers, distinguished by their interactions with biological systems into mucoadhesive, gastro-adhesive, and stimuli responsive polymers. Hydrogel systems may be assembled as tablets, patches, gels, ointments, and films. Their potential to be co-formulated as nanoparticles extends the limits of their assembly and application. In this review, mucoadhesive nanoparticles and their importance for biomedical applications are highlighted with a focus on mechanisms of overcoming mucosal resistance.

Thermo-Responsive Nanocomposite Hydrogels Based on PEG-b-PLGA Diblock Copolymer and Laponite

Poly(ethylene glycol)-b-poly(d,l-lactide-co-glycolide) (PEG-b-PLGA) diblock copolymers are widely known as polymeric surfactants for biomedical applications, and exhibit high solubility in water compared to PLGA-b-PEG-b-PLGA triblock copolymers known as gelation agents. In order to overcome the difficulties in the preparation of thermo-responsive hydrogels based on PLGA-b-PEG-b-PLGA due to the low solubility in water, the fabrication of thermo-responsive hydrogels based on PEG-b-PLGA with high solubility in water was attempted by adding laponite to the PEG-b-PLGA solution. In detail, PEG-b-PLGA with high solubility in water (i.e., high PEG/PLGA ratio) were synthesized. Then, the nanocomposite solution based on PEG-b-PLGA and laponite (laponite/PEG-b-PLGA nanocomposite) was fabricated by mixing the PEG-b-PLGA solutions and the laponite suspensions. By using the test tube inversion method and dynamic mechanical analysis (DMA), it was found that thermo-responsive hydrogels could be obtained by using PEG-b-PLGA, generally known as polymeric surfactants, and that the gelation temperature was around the physiological temperature and could be regulated by changing the solution composition. Furthermore, from the structural analysis by small angle neutron scattering (SANS), PEG-b-PLGA was confirmed to be on the surface of the laponite platelets, and the thermosensitive PEG-b-PLGA on the laponite surface could trigger the thermo-responsive connection of the preformed laponite network.