Special Issue on “Function of Polymers in Encapsulation Process”

Encapsulation technology comprises enclosing active agents (core materials) within a homogeneous/heterogeneous matrix (wall material) at the micro/nano scale. In the last few years encapsulation has gained a lot of interest. Using this process, a physical barrier is developed between the inner substance and the environment which on one hand prevents its degradation and facilitates its handling and transportation and on the other hand allows the controlled release of the core material in a certain ambiance [1]. Polymers may be used to trap the material of interest inside the micro/nano-capsules. Such encapsulated systems have many applications in the fields of the food industry, drug delivery, agriculture, cosmetics, coatings, adhesives and so forth. Various biopolymers, such as alginate, chitosan, carrageenan, gums, gelatin, whey protein or starch, act as a barrier against external conditions. Encapsulation in biodegradable polymers can also enhance the permeability and stability of the active agent and thus its bioavailability. Choosing the right polymer is very important in this process due to its impact on target delivery and controlled release, and therefore, on the bioavailability of active agents. It should have the necessary properties, such as being non-reactive with the active agent, flexibility, stability, strength, and impermeability. If the active agent has application in the food industry, the used polymer should be “generally recognized as safe” (GRAS), biodegradable, and capable of preserving the encapsulated material from the atmospher

Silica-Supported Styrene-Co-Divinylbenzene Pickering Emulsion Polymerization: Tuning Surface Charge and Hydrophobicity by pH and Co-Aid Adsorption

In this work, polymerizations of styrene (St) in the presence of divinylbenzene (DVB) as a crosslinking agent and sodium 4-vinylbenzenesulfonate (VBS) have been performed in Pickering emulsions, using silica nanoparticles (SNps) as stabilizing agents and ammonium persulfate as a hydrophilic initiator. In oil-in-water Pickering emulsions with alkaline continuous phase (pH = 9) at 1, 2, and 3 wt% DVB (relative to St), polydisperse spheroid copolymer submicronic nanoparticles were obtained. Comparatively, polymerizations performed in Pickering emulsions with acidic continuous phase (pH = 5) allowed preparing St-co-DVB microspheres with core–shell structures at 1 wt% DVB and St-co-DVB hybrid monoliths with bi-continuous morphologies at 2 and 3 wt% DVB. It is noteworthy that this work reports Pickering emulsion polymerization as a new strategy for preparing hybrid percolated scaffolds with bi-continuous porosity. The proposed mechanisms originated by pH, DVB, and VBS and the drastic impact caused on the final morphology obtained, either hybrid particles or monoliths, are discussed herein

Hybrid hydrogels based on agarose, halloysite nanotubes and polyvinyl alcohol: An excellent nanocarrier for controlled release of 5-fluorouracil

Nanotechnology, rather than traditional medicinal procedures like chemotherapy, now helps to reduce adverse effects. There is a great demand for a biocompatible nanocarrier with a long half-life, high bioavailability, and capable of imaging cells and targeting them selectively. A procedure known as water-in-oil-in-water (W/O/W) emulsification was employed to produce hybrid nanohydrogels containing agarose, polyvinyl alcohol, halloysite nanotubes, and 5-fluorouracil (AGA-PVA-HNT@5-Fu) which can be highly effective for decreasing the particle size of nanohydrogels and improving their uniformity. These hydrogels were produced to specifically target and administer the 5-Fu anti-cancer drug for the treatment of breast cancer. Following the evaluation of physicochemical characteristics, both a substantial drug loading and efficient trapping were accomplished. The nanohydrogels displayed a zeta potential of −38.4 mV indicative of a good stability due to the usage of span 80. Based on the drug release profile conducted in vitro, it was observed that AGA-PVA-HNT@5-Fu released the medication in a regulated way. By using MTT and flow cytometry analysis, it was found that AGA-PVA-HNT@5-Fu could effectively eliminate tumor cells, while the blank nanoparticles proved to be biocompatible. The results indicate that hybrid nanohydrogels based on AGA-PVA-HNT@5-Fu can be utilized as nanohydrogels for treating breast cancer

Cyclic polyethylene glycol as nanoparticle surface ligand

Cyclic polymers behave different than linear polymers due to the lack of end groups and smaller coil dimensions. Herein, we demonstrate that cyclic polyethylene glycol (PEG) can be used as an alternative of classical linear PEG ligands for gold nanoparticle (AuNP) stabilization. We observed that the brush height of cyclic PEG on AuNPs of diameter 4.4 and 13.2 nm increases identically as that of linear brushes with (Nσ1/2)0.7 (N, number of monomers in a chain and σ, grafting density) and that cyclic brushes are more stretched than their linear analogues when compared to their unperturbed dimensions. Such structural effect and the reduced footprint diameter in cyclic brushes with the entire chain in a concentrated polymer brush regime explains the distinct response of NPs to ionic strength and temperature, respectively, compared to linear analogues. These experiments are an important step in understanding the effect of polymer brush topology on colloidal properties.We gratefully acknowledge support from the Spanish Ministry “Ministerio de Ciencia, Innovación y Universidades” (PGC2018-094548-B-I00, MICIU/AEI/FEDER, UE), Basque Government (IT-1175-19 and PIBA 2018-34) and Diputación Foral de Guipúzcoa (RED 2018).Peer reviewe

Ionic conductivity and molecular dynamic behavior in supramolecular ionic networks; the effect of lithium salt addition

Supramolecular ionic networks combine singular properties such as self-healing behaviour and ionic conductivity. In this work we present an insight into the ionic conductivity and molecular dynamic behaviour of an amorphous and semicrystalline supramolecular ionic networks (iNets) that were synthesised by self-assembly of difunctional imidazolium dicationic molecules coupled with (trifluoromethane-sulfonyl) imide dianionic molecules. Relatively low ionic conductivity values were obtained for the semicrystalline iNet below its melting point (Tm =101°C) in comparison with the amorphous iNet for which the conductivity significantly increased (~3 orders of magnitude) above 100°C. Upon LiTFSI doping, the semicrystalline iNet reached conductivity values ~ 10-3 Scm-1 due to enhanced mobility of the network which was supported by solid-state static NMR. Furthermore, the overlapping of 19F and 7Li resonance lines from both the semicrystalline network and the LiTFSI suggests fast molecular motions

Microwave irradiation versus conventional heating assisted free-radical copolymerization in solution

Microwave (MW) irradiation has arisen as a more sustainable alternative to conventional heating (CH) for chemical reactions because it provides non-contact, volumetric equal and fast heating. However, in free-radical polymerization, the MW effect is still quite controversial, probably due to the lack of reliable, comparable experimental data of both CH and MW assisted polymerization processes. In this work, taking advantage of technically superior MW reactor design, similar temperature profiles and conditions of CH and MW assisted polymerization reactions were enabled. Copolymerization of various monomer couples with different polarity and dielectric properties was studied in solution of different organic solvents in the presence of different initiators. As a result, it was concluded that the interaction of the reaction components with the MW irradiation is essential and will determine if any effect of MW irradiation on the reaction and products occurs. On the contrary to some reported studies, for the typical monomers used in free radical polymerization studied here (acrylates, methacrylates, styrene) no difference in reaction rates, copolymer composition and properties were observed between the MWH and CH processes, independently of the solvent and initiator used. However, in the case of the presence of an organometallic monomer within the monomer couple, an observable reaction rate enhancement was obtained under MW irradiation, along with changes in the reactivity ratios and differences in the copolymer composition. This effect is considered a specific microwave effect, for the first time demonstrated in free-radical solution polymerization process and was explained by the principles of selective heating of the organometallic reaction components in solution.The authors gratefully acknowledge the financial support by NATO (SfP project G4255), Spanish Government (CTQ2016-80886-R), and Basque Government (GV IT999-16). Bertha Pérez-Martínez acknowledges the PhD fellowship No. 410922 provided by The National Council of Science and Technology (CONACyT-México).Peer reviewe

Mesoscale morphologies of Nafion-based blend membranes by dissipative particle dynamics

This article belongs to the Special Issue Multifunctional Hybrid Materials Based on Polymers: Design and Performance.Polymer electrolyte membrane (PEM) composed of polymer or polymer blend is a vital element in PEM fuel cell that allows proton transport and serves as a barrier between fuel and oxygen. Understanding the microscopic phase behavior in polymer blends is very crucial to design alternative cost-effective proton-conducting materials. In this study, the mesoscale morphologies of Nafion/poly(1-vinyl-1,2,4-triazole) (Nafion-PVTri) and Nafion/poly(vinyl phosphonic acid) (Nafion-PVPA) blend membranes were studied by dissipative particle dynamics (DPD) simulation technique. Simulation results indicate that both blend membranes can form a phase-separated microstructure due to the different hydrophobic and hydrophilic character of different polymer chains and different segments in the same polymer chain. There is a strong, attractive interaction between the phosphonic acid and sulfonic acid groups and a very strong repulsive interaction between the fluorinated and phosphonic acid groups in the Nafion-PVPA blend membrane. By increasing the PVPA content in the blend membrane, the PVPA clusters’ size gradually increases and forms a continuous phase. On the other hand, repulsive interaction between fluorinated and triazole units in the Nafion-PVTri blend is not very strong compared to the Nafion-PVPA blend, which results in different phase behavior in Nafion-PVTri blend membrane. This relatively lower repulsive interaction causes Nafion-PVTri blend membrane to have non-continuous phases regardless of the composition.U. Sen was supported by JSPS RONPAKU (Dissertation PhD) program with ID No. TUR 11008.Peer reviewe

Gold nanoparticles endowed with low-temperature colloidal stability by cyclic polyethylene glycol in ethanol

The colloidal stability of metal nanoparticles is tremendously dependent on the thermal behavior of polymer brushes. Neat polyethylene glycol (PEG) presents an unconventional upper critical solution temperature in ethanol, where phase segregation and crystallization coexist. This thermal behavior translated to a PEG brush has serious consequences on the colloidal stability in ethanol of gold nanoparticles (AuNPs) modified with PEG brushes upon cooling. We observed that AuNPs (13 nm diameter) stabilized with conventional linear PEG brushes (Mn = 6 and 11 kg mol−1) in ethanol suffer from reversible phase separation upon a temperature drop over the course of a few hours. However, the use of a polymer brush with cyclic topology as a stabilizer prevents sedimentation, ensuring the colloidal stability in ethanol at −25 °C for, at least, four months. We postulate that temperature-driven collapse of chain brushes promotes the interpenetration of linear chains, causing progressive AuNP sedimentation, a process that is unfavorable for cyclic polymer brushes whose topology prevents chain interpenetration. This study reinforces the notion about the importance of polymer topology on the colloidal stability of AuNPs.We gratefully acknowledge support from the Spanish Ministry “Ministerio de Ciencia, Innovación y Universidades” (PGC2018-094548-B-I00, MICINN/FEDER, UE, and PID2019-111772RB-I00), Basque Government (IT-1175-19 and PIBA 2018-34) and Diputación Foral de Guipúzcoa (RED 2018).Peer reviewe

Development of Sustained Release Baricitinib Loaded Lipid-Polymer Hybrid Nanoparticles with Improved Oral Bioavailability

Baricitinib (BTB) is an orally administered Janus kinase inhibitor, therapeutically used for the treatment of rheumatoid arthritis. Recently it has also been approved for the treatment of COVID-19 infection. In this study, four different BTB-loaded lipids (stearin)-polymer (Poly(d,l-lactide-co-glycolide)) hybrid nanoparticles (B-PLN1 to B-PLN4) were prepared by the single-step nanoprecipitation method. Next, they were characterised in terms of physicochemical properties such as particle size, zeta potential (ζP), polydispersity index (PDI), entrapment efficiency (EE) and drug loading (DL). Based on preliminary evaluation, the B-PLN4 was regarded as the optimised formulation with particle size (272 ± 7.6 nm), PDI (0.225), ζP (−36.5 ± 3.1 mV), %EE (71.6 ± 1.5%) and %DL (2.87 ± 0.42%). This formulation (B-PLN4) was further assessed concerning morphology, in vitro release, and in vivo pharmacokinetic studies in rats. The in vitro release profile exhibited a sustained release pattern well-fitted by the Korsmeyer–Peppas kinetic model (R2 = 0.879). The in vivo pharmacokinetic data showed an enhancement (2.92 times more) in bioavailability in comparison to the normal suspension of pure BTB. These data concluded that the formulated lipid-polymer hybrid nanoparticles could be a promising drug delivery option to enhance the bioavailability of BTB. Overall, this study provides a scientific basis for future studies on the entrapment efficiency of lipid-polymer hybrid systems as promising carriers for overcoming pharmacokinetic limitations