Synthesis and Characterisation of Novel Temperature and pH Sensitive Physically Cross-Linked Poly (N-vinylcaprolactam-co-itaconic Acid) Hydrogels for Drug Delivery

Green Synthesis and the Evaluation of a Functional Amphiphilic Block Copolymer as a Micellar Curcumin Delivery System

Polymer micelles represent one of the most attractive drug delivery systems due to their design flexibility based on a variety of macromolecular synthetic methods. The environmentally safe chemistry in which the use or generation of hazardous materials is minimized has an increasing impact on polymer-based drug delivery nanosystems. In this work, a solvent-free green synthetic procedure was applied for the preparation of an amphiphilic diblock copolymer consisting of biodegradable hydrophobic poly(acetylene-functional carbonate) and biocompatible hydrophilic polyethylene glycol (PEG) blocks. The cyclic functional carbonate monomer 5-methyl-5-propargyloxycarbonyl-1,3-dioxane-2-one (MPC) was polymerized in bulk using methoxy PEG-5K as a macroinitiator by applying the metal-free organocatalyzed controlled ring-opening polymerization at a relatively low temperature of 60 °C. The functional amphiphilic block copolymer self-associated in aqueous media into stable micelles with an average diameter of 44 nm. The copolymer micelles were physico-chemically characterized and loaded with the plant-derived anticancer drug curcumin. Preliminary in vitro evaluations indicate that the functional copolymer micelles are non-toxic and promising candidates for further investigation as nanocarriers for biomedical applications.

Synthesis and Characterisation of Hydrogels Based on Poly (N-Vinylcaprolactam) with Diethylene Glycol Diacrylate

Poly (N-vinylcaprolactam) is a polymer that is biocompatible, water-soluble, thermally sensitive, non-toxic, and nonionic. In this study, the preparation of hydrogels based on Poly (N-vinylcaprolactam) with diethylene glycol diacrylate is presented. The N-Vinylcaprolactam-based hydrogels are synthesised by using a photopolymerisation technique using diethylene glycol diacrylate as a crosslinking agent, and Diphenyl (2, 4, 6-trimethylbenzoyl) phosphine oxide as a photoinitiator. The structure of the polymers is investigated via Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy. The polymers are further characterised using differential scanning calorimetry and swelling analysis. This study is conducted to determine the characteristics of P (N-vinylcaprolactam) with diethylene glycol diacrylate, including the addition of Vinylacetate or N-Vinylpyrrolidone, and to examine the effects on the phase transition. Although various methods of free-radical polymerisation have synthesised the homopolymer, this is the first study to report the synthesis of Poly (N-vinylcaprolactam) with diethylene glycol diacrylate by using free-radical photopolymerisation, using Diphenyl (2, 4, 6-trimethylbenzoyl) phosphine oxide to initiate the reaction. FTIR analysis shows that the NVCL-based copolymers are successfully polymerised through UV photopolymerisation. DSC analysis indicates that increasing the concentration of crosslinker results in a decrease in the glass transition temperature. Swelling analysis displays that the lower the concentration of crosslinker present in the hydrogel, the quicker the hydrogels reach their maximum swelling ratio.

Development and evaluation of pH sensitive semi-interpenetrating networks: assessing the impact of itaconic acid and aloe vera on network swelling and cetirizine release

Hydrogels are crosslinked three-dimensional networks, and their properties can be easily tuned to target the various segments of the gastrointestinal tract (GIT). Cetirizine HCl (CTZ HCl) is an antihistaminic drug, which when given orally can upset the stomach. Moreover, this molecule has shown maximum absorption in the intestine. To address these issues, we developed a pH-responsive semi-interpenetrating polymer network (semi-IPN) for the delivery of CTZ HCl to the lower part of the GIT. Initially, 10 different formulations of itaconic acid-grafted-poly (acrylamide)/aloe vera [IA-g-poly (AAm)/aloe vera] semi-IPN were developed by varying the concentration of IA and aloe vera using the free radical polymerization technique. Based on swelling and sol-gel analysis, formulation F5 containing 0.3%w/w aloe vera and 6%w/w IA was chosen as the optimum formulation. The solid-state characterization of the optimized formulation (F5) revealed a successful incorporation of CTZ HCl in semi-IPN without any drug-destabilizing interaction. The in vitro drug release from F5 showed limited release in acidic media followed by a controlled release in the intestinal environment for over 72 h. Furthermore, during the in vivo evaluation, formulation F5 did not affect the hematological parameters, kidney, and liver functions. Clinical observations did not reveal any signs of illness in rabbits treated with hydrogels. Histopathological images of vital organs of treated animals showed normal cellular architecture. Thus, the results suggest a non-toxic nature and overall potential of the developed formulation as a targeted drug carrier.

Modulation of the Lower Critical Solution Temperature of Thermoresponsive Poly(N-vinylcaprolactam) Utilizing Hydrophilic and Hydrophobic Monomers

Four-dimensional printing is primarily based on the concept of 3D printing technology. However, it requires additional stimulus and stimulus-responsive materials. Poly-N-vinylcaprolactam is a temperature-sensitive polymer. Unique characteristics of poly-N-vinylcaprolactam -based hydrogels offer the possibility of employing them in 4D printing. The main aim of this study is to alter the phase transition temperature of poly-N-vinylcaprolactam hydrogels. This research focuses primarily on incorporating two additional monomers with poly-N-vinylcaprolactam: Vinylacetate and N-vinylpyrrolidone. This work contributes to this growing area of research by altering (increasing and decreasing) the lower critical solution temperature of N-vinylcaprolactam through photopolymerisation. Poly-N-vinylcaprolactam exhibits a lower critical solution temperature close to the physiological temperature range of 34-37 °C. The copolymers were analysed using various characterisation techniques, such as FTIR, DSC, and UV-spectrometry. The main findings show that the inclusion of N-vinylpyrrolidone into poly-N-vinylcaprolactam increased the lower critical solution temperature above the physiological temperature. By incorporating vinylacetate, the lower critical solution temperature dropped to 21 °C, allowing for potential self-assembly of 4D-printed objects at room temperature. In this case, altering the lower critical solution temperature of the material can potentially permit the transformation of the 4D-printed object at a particular temperature.

Cytotoxicity and Biomineralization Potential of Flavonoids Incorporated into PNVCL Hydrogels

This study aimed to evaluate the effects of flavonoids incorporated into poly(N-vinylcaprolactam) (PNVCL) hydrogel on cell viability and mineralization markers of odontoblast-like cells. MDPC-23 cells were exposed to ampelopsin (AMP), isoquercitrin (ISO), rutin (RUT) and control calcium hydroxide (CH) for evaluation of cell viability, total protein (TP) production, alkaline phosphatase (ALP) activity and mineralized nodule deposition by colorimetric assays. Based on an initial screening, AMP and CH were loaded into PNVCL hydrogels and had their cytotoxicity and effect on mineralization markers determined. Cell viability was above 70% when MDPC-23 cells were treated with AMP, ISO and RUT. AMP showed the highest ALP activity and mineralized nodule deposition. Extracts of PNVCL+AMP and PNVCL+CH in culture medium (at the dilutions of 1/16 and 1/32) did not affect cell viability and stimulated ALP activity and mineralized nodules’ deposition, which were statistically higher than the control in osteogenic medium. In conclusion, AMP and AMP-loaded PNVCL hydrogels were cytocompatible and able to induce bio-mineralization markers in odontoblast-cells.

Microbiological Properties and Cytotoxicity of PNVCL Hydrogels Containing Flavonoids as Intracanal Medication for Endodontic Therapy

This study aimed to evaluate the cytotoxicity and microbiological properties of poly (N-vinylcaprolactam)-PNVCL hydrogels containing flavonoids as intracanal medication for endodontic therapy. Antimicrobial activity of ampelopsin (AMP), isoquercitrin and rutin was determined against Enterococcus faecalis, Actinomyces israelii, Lactobacillus casei, Streptococcus mutans, and Fusobacterium nucleatum by the microdilution method. After synthesis and characterization by rheology, PNVCL hydrogels were loaded with AMP and controls calcium hydroxide (CH) and chlorhexidine (CHX), and determined the compounds release profile. PNVCL+AMP, PNVCL+CH, PNVCL+CHX were evaluated on multi-species biofilms and analyzed by Scanning Electron Microscopy (SEM) and Confocal Laser Scanning Microscopy (CLSM). Cytotoxicity was determined after fibroblasts exposure to serial dilutions of AMP and PNVCL hydrogel extracts. AMP was effective against all of the bacteria tested, especially against S. mutans, A. israelli and F. nucleatum. SEM and CLSM analysis showed that PNVCL + AMP caused a significant decrease and disorganization of multi-species biofilms and reduction of intracanal viable cells, superior to the other groups. AMP affected fibroblast viability at concentrations above 0.125 mg/mL, and extracts of PNVCL+AMP showed low cytotoxicity. In conclusion, PNVCL containing AMP demonstrated cytocompatibility and potent effect against multi-species biofilms and could be potential intracanal medication for endodontic purposes.

Synthesis and Characterization of a Novel Dual-Responsive Nanogel for Anticancer Drug Delivery

In this study, to reduce the side effects of anticancer drugs and also to increase the efficiency of current drug delivery systems, a pH and temperature-responsive polymeric nanogel was synthesized by copolymerization of N-vinylcaprolactam (VCL) and acrylic acid (AA) monomers (P(VCL-co-AA)) with a novel cross-linker, triethylene glycol dimethacrylate (TEGDMA), as a biocompatible and nontoxic component. The structural and physicochemical features of the P(VCL-co-AA) nanogel were characterized by FT-IR, DLS/Zeta potential, FE-SEM, and 1HNMR techniques. The results indicated that spherical polymeric nanogel was successfully synthesized with a 182 nm diameter. The results showed that the polymerization process continues with the opening of the carbon-carbon double bond of monomers, which was approved by C-C band removing located at 1600 cm-1. Doxorubicin (Dox) as a chemotherapeutic agent was loaded into the P(VCL-co-AA), whit a significant loading of Dox (83%), and the drug release profile was investigated in the physiological and cancerous site simulated conditions. P(VCL-co-AA) exhibited a pH and temperature-responsive behavior, with an enhanced release rate in the cancerous site condition. The biocompatibility and nontoxicity of P(VCL-co-AA) were approved by MTT assay on the normal human foreskin fibroblasts-2 (HFF-2) cell line. Also, Dox-loaded P(VCL-co-AA) had excellent toxic behavior on the Michigan Cancer Foundation-7 (MCF-7) cell line as model cancerous cells. Moreover, Dox-loaded P(VCL-co-AA) had higher toxicity in comparison with free Dox, which would be a vast advantage in reducing Dox side effects in the clinical cancer treatment applications.

Synthesis and characterization of dual-responsive poly(N-vinylcaprolactam-co-N-methylolacrylamide) nanogels

This article reports the synthesis of poly(N-vinylcaprolactam-co-N-methylolacrylamide) (P(NVCL-co-NMA)) nanogels and investigates their thermo-/pH-responsive behavior. The formation of nanogels was synthesized using free radical emulsion polymerization by varying the monomer composition of NVCL:NMA, and their molecular structure was characterized by ¹H-NMR and FTIR. It was found that the nanogels were successfully prepared, and the nanogels exhibited LCST-type phase transition behavior. Cloud point transition temperature (T_c) was studied as a function of copolymer composition, MBA concentration, and pH of the solution by exploring their changes in turbidity using UV-vis spectrophotometer. Our studies reveal that T_c nanogels increased with increasing concentration of NMA, which is due to the hydrophilicity of NMA. Our research also demonstrated that the increase in MBA percentage could decrease the T_c of the synthesized nanogels. Interestingly, P(NVCL-co-NMA) nanogels showed not only a thermoresponsive behavior but also a pH response with increasing T_c in a strong acidic environment owing to the H-bonds within the polymer chains. The results show that nanogels with initial monomer composition of NVCL and NMA of 75% and 25%, respectively, and using 4% of MBA showed T_c around 35°C at pH 7.4. In addition, DLS studies also confirmed this result since the particle sizes became much larger after surpassing the temperature of 35°C. Due to this founding, such nanogels might have potential application in controlled release. Nevertheless, further studies regarding the adjustment of T_c are still needed.

Methacrylic acid based microgels and hybrid microgels

Methacrylic acid based microgels have got much consideration in the last two decades because of their potential uses in different fields owing to their responsive behaviour towards external stimuli. Synthesis, properties and uses of methacrylic acid based microgels and their hybrids have been critically reviewed in this article. With minute change in external stimuli such as pH and ionic strength of medium, these microgels show quick swelling/deswelling reversibly. The methacrylic acid based microgels have been widely reported for applications in the area of nanotechnology, drug delivery, sensing and catalysis due to their responsive behaviour. A critical review of current research development in this field along with upcoming perception is presented here. This discussion is concluded with proposed probable future studies for additional growth in this field of research.

Preparation and application of pH-responsive drug delivery systems

Microenvironment-responsive drug delivery systems (DDSs) can achieve targeted drug delivery, reduce drug side effects and improve drug efficacies. Among them, pH-responsive DDSs have gained popularity since the pH in the diseased tissues such as cancer, bacterial infection and inflammation differs from a physiological pH of 7.4 and this difference could be harnessed for DDSs to release encapsulated drugs specifically to these diseased tissues. A variety of synthetic approaches have been developed to prepare pH-sensitive DDSs, including introduction of a variety of pH-sensitive chemical bonds or protonated/deprotonated chemical groups. A myriad of nano DDSs have been explored to be pH-responsive, including liposomes, micelles, hydrogels, dendritic macromolecules and organic-inorganic hybrid nanoparticles, and micron level microspheres. The prodrugs from drug-loaded pH-sensitive nano DDSs have been applied in research on anticancer therapy and diagnosis of cancer, inflammation, antibacterial infection, and neurological diseases. We have systematically summarized synthesis strategies of pH-stimulating DDSs, illustrated commonly used and recently developed nanocarriers for these DDSs and covered their potential in different biomedical applications, which may spark new ideas for the development and application of pH-sensitive nano DDSs.

NVCL-Based Hydrogels and Composites for Biomedical Applications: Progress in the Last Ten Years

Hydrogels consist of three-dimensionally crosslinked polymeric chains, are hydrophilic, have the ability to absorb other molecules in their structure and are relatively easy to obtain. However, in order to improve some of their properties, usually mechanical, or to provide them with some physical, chemical or biological characteristics, hydrogels have been synthesized combined with other synthetic or natural polymers, filled with inorganic nanoparticles, metals, and even polymeric nanoparticles, giving rise to composite hydrogels. In general, different types of hydrogels have been synthesized; however, in this review, we refer to those obtained from the thermosensitive polymer poly(N-vinylcaprolactam) (PNVCL) and we focus on the definition, properties, synthesis techniques, nanomaterials used as fillers in composites and mainly applications of PNVCL-based hydrogels in the biomedical area. This type of material has great potential in biomedical applications such as drug delivery systems, tissue engineering, as antimicrobials and in diagnostic and bioimaging.

Comparative study of oral and intranasal puerarin for prevention of brain injury induced by acute high-altitude hypoxia

Human activities in the areas of high altitude have increased significantly recently. Brain is highly sensitive to changing of oxygen pressure due to high altitude, and this physiological response may lead to serious brain injury, such as learning and memory disabilities. Puerarin is a phytoestrogen with many pharmacological activities, such as treatment of neurological disorders. However, most of current drugs can not easily enter brain through the blood-brain barrier (BBB). The nose-to-brain route can bypass BBB for brain-targeting. Here, thermosensitive in situ hydrogels (TISGs) of puerarin were prepared with poloxamers 407, poloxamers 188 and propylene glycol to improve bioavailability and brain targeting. In vitro drug release in simulated nasal fluids, rheological properties and cilia toxicity of puerarin TISGs were explored. The pharmacodynamics and pharmacokinetics of puerarin by intranasal (i.n.) and oral (p.o.) administrations were also evaluated. The viscosity of puerarin TISGs tended to increase obviously with increased temperature. The puerarin release profile and transmucosal process of puerarin TISGs could be described with the first-order kinetics equation, depending on drug diffusion. The cilia toxicity of puerarin TISGs was not obvious. Rat models of hypobarism/hypoxia-induced brain injury were established with a hypobaric simulation chamber. Morris water maze and open filed tests indicated that puerarin TISGs improved the spatial memory and spontaneous exploratory behavior of the rats suffering from hypoxia-induced brain injury. Furthermore, puerarin TISGs decreased the level of oxidative stress cytokines (malondialdehyde (MDA) and glutathione (GSH)) in the peripheral circulation, alleviated the cerebral histological lesions, and relieved the expression of hypoxia-inducible factor-1α (HIF-1α). Intranasal puerarin TISGs were absorbed quickly with a shorter T_max (10.0 ± 5.7 min) compared to that of oral puerarin (36 ± 13.4 min). In addition, the relative bioavailability of i.n. puerarin TISGs was high to 300% compared to oral administration of puerarin. The area under the curve (AUC) of brain after i.n. administration of puerarin TISGs was 954.5 ± 335.1 h.ng/mL, while no puerarin was detected in the brain after oral administration. Therefore, i.n. puerarin TISGs led to excellent brain targeting effect. Puerarin TISGs are an effective neuroprotector formulation for prevention of brain injury induced by acute high-altitude hypoxia.

Formulation and Characterization of Gelatin-Based Hydrogels for the Encapsulation of Kluyveromyces lactis-Applications in Packed-Bed Reactors and Probiotics Delivery in Humans

One of the main issues when orally administering microorganism-based probiotics is the significant loss of bioactivity as they pass through the gastrointestinal (GI) tract. To overcome these issues, here, we propose to encapsulate the probiotic yeast Kluyveromyces lactis on chemically crosslinked gelatin hydrogels as a means to protect the bioactive agents in different environments. Hydrogels were prepared by the chemical crosslinking of gelatin, which is commercially available and inexpensive. This is crucial to ensure scalability and cost-effectiveness. To explore changes in key physicochemical parameters and their impact on cell viability, we varied the concentration of the crosslinking agent (glutaraldehyde) and the gelatin. The synthesized hydrogels were characterized in terms of morphological, physical-chemical, mechanical, thermal and rheological properties. This comprehensive characterization allowed us to identify critical parameters to facilitate encapsulation and enhance cell survival. Mainly due to pore size in the range of 5-10 μm, sufficient rigidity (breaking forces of about 1 N), low brittleness and structural stability under swelling and relatively high shear conditions, we selected hydrogels with a high concentration of gelatin (7.5% (w/v)) and concentrations of the crosslinking agent of 3.0% and 5.0% (w/w) for cell encapsulation. Yeasts were encapsulated with an efficiency of about 10% and subsequently tested in bioreactor operation and GI tract simulated media, thereby leading to cell viability levels that approached 95% and 50%, respectively. After testing, the hydrogels' firmness was only reduced to half of the initial value and maintained resistance to shear even under extreme pH conditions. The mechanisms underlying the observed mechanical response will require further investigation. These encouraging results, added to the superior structural stability after the treatments, indicate that the proposed encapsulates are suitable to overcome most of the major issues of oral administration of probiotics and open the possibility to explore additional biotech applications further.

Synthesis and Self-Assembly of Poly(N-Vinylcaprolactam)-b-Poly(ε-Caprolactone) Block Copolymers via the Combination of RAFT/MADIX and Ring-Opening Polymerizations

Well-defined amphiphilic, biocompatible and partially biodegradable, thermo-responsive poly(N-vinylcaprolactam)-b-poly(ε-caprolactone) (PNVCL-b-PCL) block copolymers were synthesized by combining reversible addition-fragmentation chain transfer (RAFT) and ring-opening polymerizations (ROP). Poly(N-vinylcaprolactam) containing xanthate and hydroxyl end groups (X–PNVCL–OH) was first synthesized by RAFT/macromolecular design by the interchange of xanthates (RAFT/MADIX) polymerization of NVCL mediated by a chain transfer agent containing a hydroxyl function. The xanthate-end group was then removed from PNVCL by a radical-induced process. Finally, the hydroxyl end-capped PNVCL homopolymer was used as a macroinitiator in the ROP of ε-caprolactone (ε-CL) to obtain PNVCL-b-PCL block copolymers. These (co)polymers were characterized by Size Exclusion Chromatography (SEC), Fourier-Transform Infrared spectroscopy (FTIR), Proton Nuclear Magnetic Resonance spectroscopy (¹H NMR), UV–vis and Differential Scanning Calorimetry (DSC) measurements. The critical micelle concentration (CMC) of the block copolymers in aqueous solution measured by the fluorescence probe technique decreased with increasing the length of the hydrophobic block. However, dynamic light scattering (DLS) demonstrated that the size of the micelles increased with increasing the proportion of hydrophobic segments. The morphology observed by cryo-TEM demonstrated that the micelles have a pointed-oval-shape. UV–vis and DLS analyses showed that these block copolymers have a temperature-responsive behavior with a lower critical solution temperature (LCST) that could be tuned by varying the block copolymer composition.