Application of Supercritical Solvent Impregnation for Production of Zeolite Modified Starch-Chitosan Polymers with Antibacterial Properties

Synthesis and characterization of chitosan/collagen/polycaprolactone hydrogel films with enhanced biocompatibility and hydrophilicity for artificial tendon applications

Regenerative medicine confronts various obstacles, such as creating and advancing biomaterials. Besides being safe, such materials should promote cellular activity. Polycaprolactone (PCL) has numerous medical applications as an engineering material. However, these polymers lack hydrophilicity. Herein, chitosan (CS)/collagen (COL)/polycaprolactone hydrogel films (CSCPs) were synthesized with different weight ratios of PCL; specifically, CS/COL (CSC): PCL content of 1:3, 1:6, and 1:9. For this purpose, novel COL immobilization on CS was performed via covalent attachment. Following the addition of PCL to CSC hydrogel, the resulting CSCP hydrogel films were characterized using tensile measurements, TGA, XRD, FTIR, and FE-SEM. A greater PCL content increases the elongation at break from 134.8 to 369.5 % and the tensile strength of the hydrogel films from 4.8 to 18.4 MPa. The hydrophobicity of prepared specimens was assessed through water absorption and contact-angle tests. For CSCP3 to CSCP9, the water contact angle increased from 61.03° to 70.82°. After 48 days, CSCP6 and CSCP9 hydrogel films demonstrated a slow rate of degradation, losing <15 % of their weight. Moreover, all three types of hydrogel films exhibited high biocompatibility (higher than 95 % after three days), as confirmed by the MTT assay. The hemolysis rates of CSCP hydrogel films were <2 %, which could be deemed safe for contact with a blood environment. The presence of no costly and bio-based crosslinking agents and desired characteristics for tissue engineering applications suggest that CSCP hydrogel films may be promising candidates for use in artificial tendons.

Thymol@Natural Zeolite Nanohybrids for Chitosan/Polyvinyl-Alcohol-Based Hydrogels Applied as Active Pads

Currently, food saving, a circular economy, and zero environmental fingerprints are of major interest. Scientific efforts for enhanced food preservation using "green" methods have been intensified. Even though chemicals could achieve such targets effectively, the global trend against the "greenhouse effect" suggests the use of environmentally friendly biobased materials for this purpose. In this study, the promising biopolymer chitosan is incorporated with the promising biodegradable polymer polyvinyl alcohol to produce an improved biopolymeric matrix. This biodegradable biopolymer was further mixed homogeneously with 15% thymol/nano-zeolite nanohybrid material. The properties of the final developed film were improved compared to the relevant values of chitosan/polyvinyl alcohol film. The mechanical properties were enhanced significantly, i.e., there was a 34% increase in Young's modulus and a 4.5% increase in the ultimate tensile strength, while the antioxidant activity increased by 53.4%. The antibacterial activity increased by 134% for Escherichia coli, 87.5% for Staphylococcus aureus, 32% for Listeria monocytogenes, and 9% for Salmonella enterica. The water vapor diffusion coefficient and the oxygen permeability coefficient decreased to -51% and -74%, respectively, and thus, the water vapor and oxygen barrier increased significantly. The active pads were used in strawberries, and the antimicrobial activity evaluation against the mold of fungi was carried out. The visual evaluation shows that the active pads could extend the shelf life duration of strawberries.

Facile Synthesis of Cyclic Polyamidine with High Cationic Degree Using Environmentally Benign Approach

An environmentally benign approach was developed to fabricate cyclic polyamidine via polymerization in supercritical carbon dioxide (SCCO2) and subsequently amidinization in water. Synthetic parameters were evaluated using response surface methodology. In comparison with aqueous solution polymerization for the fabrication of PNVF-co-PAN, polymerization using SCCO2 is favorable to promote the yield and viscosity of PNVF-co-PAN and diminished reaction time on account of excellent solvation capacity and transport property of SCCO2. Replacing the traditional water solution with SCCO2 as a green solvent could heighten the purity of PNVF-co-PAN by virtue of the excellent extraction of SCCO2. The cationic degree (5.66 mmol/g) of polyamidine fabricated by environmentally benign approach was significantly higher than that in previous reported studies.

Recent advances of antibacterial starch-based materials

Starch has attracted a lot of attention because it is biodegradable, renewable, nontoxic and low cost. By adding antibacterial substances to starch, starch-based materials have antibacterial properties. The composite with other materials can improve the comprehensive performance of starch-based materials, thus broadening the application field of the material. In this paper, we focus on antibacterial starch-based materials and review their preparation and applications. It was found that antibacterial starch-based materials were most widely used in packaging, followed by medicine, and the research on smart starch-based materials was relatively less. This review may provide some reference value for subsequent studies of starch-based materials.

Application of the Integrated Supercritical Fluid Extraction–Impregnation Process (SFE-SSI) for Development of Materials with Antiviral Properties

The integrated supercritical fluid extraction–impregnation process (SFE-SSI) was performed to fabricate material with antiviral properties against the herpes simplex virus (HSV). Cotton gauze and starch/chitosan polymer films (SCF) were impregnated with components extracted from Melissa officinalis at 10 MPa and 40 °C using a green medium, supercritical carbon dioxide (scCO2). The influences of the processing mode regarding the flow of the supercritical fluid through the system, and the mass ratio of the plant material and the solid carrier, on the impregnation yield of M. officinalis extract were studied. The results revealed that the introduction of a fresh amount of CO2 into the system enabled the highest impregnation yield of 2.24% for cotton gauze and 8.71% for SCF. The presence of M. officinalis extract on the surface of both impregnated cotton gaze and SCF was confirmed by FTIR and GC analyses after the re-extraction of the impregnated samples. The M. officinalis impregnated materials showed a strong inhibitory effect against Bovine herpesvirus type 1 (BHV-1).

Supercritical Foaming and Impregnation of Polycaprolactone and Polycaprolactone-Hydroxyapatite Composites with Carvacrol

Polycaprolactone (PCL) and polycaprolactone-hydroxyapatite (PCL-HA) scaffolds were produced by foaming in supercritical carbon dioxide (scCO2) at 20 MPa, as well as in one-step foaming and impregnation process using carvacrol as an antibacterial agent with proven activity against Gram-positive and Gram-negative bacteria. The experimental design was developed to study the influence of temperature (40 °C and 50 °C), HA content (10 and 20 wt.%), and depressurization rate (one and two-step decompression) on the foams’ morphology, porosity, pore size distribution, and carvacrol impregnation yield. The characterization of the foams was carried out using scanning electron microscopy (SEM, SEM-FIB), Gay-Lussac density bottle measurements, and Fourier–transform infrared (FTIR) analyses. The obtained results demonstrate that processing PCL and PCL-HA scaffolds by means of scCO2 foaming enables preparing foams with porosity in the range of 65.55–74.39% and 61.98–67.13%, at 40 °C and 50 °C, respectively. The presence of carvacrol led to a lower porosity. At 40 °C and one-step decompression at a slow rate, the porosity of impregnated scaffolds was higher than at 50 °C and two- step fast decompression. However, a narrower pore size distribution was obtained at the last processing conditions. PCL scaffolds with HA resulted in higher carvacrol impregnation yields than neat PCL foams. The highest carvacrol loading (10.57%) was observed in the scaffold with 10 wt.% HA obtained at 50 °C.

Triggered and controlled release of active gaseous/volatile compounds for active packaging applications of agri-food products: A review

Gaseous and volatile active compounds are versatile to enhance safety and preserve quality of agri-food products during storage and distribution. However, the use of these compounds is limited by their high vapor pressure and/or chemical instability, especially in active packaging (AP) applications. Various approaches for stabilizing and controlling the release of active gaseous/volatile compounds have been developed, including encapsulation (e.g., into supramolecular matrices, polymer-based films, electrospun nonwovens) and triggered release systems involving precursor technology, thereby allowing their safe and effective use in AP applications. In this review, encapsulation technologies of gases (e.g., CO₂ , ClO₂ , SO₂ , ethylene, 1-methylcyclopropene) and volatiles (e.g., ethanol, ethyl formate, essential oils and their constituents) into different solid matrices, polymeric films, and electrospun nonwovens are reviewed, especially with regard to encapsulation mechanisms and controlled release properties. Recent developments on utilizing precursor compounds of bioactive gases/volatiles to enhance their storage stability and better control their release profiles are discussed. The potential applications of these controlled release systems in AP of agri-food products are presented as well.

Supercritical Carbon Dioxide-Based Processes in Photocatalytic Applications

Conventional methods generally used to synthesize heterogeneous photocatalysts have some drawbacks, mainly the difficult control/preservation of catalysts’ morphology, size or structure, which strongly affect the photocatalytic activity. Supercritical carbon dioxide (scCO₂)-assisted techniques have recently been shown to be a promising approach to overcome these limitations, which are still a challenge. In addition, compared to traditional methods, these innovative techniques permit the synthesis of high-performance photocatalysts by reducing the use of toxic and polluting solvents and, consequently, the environmental impact of long-term catalyst preparation. Specifically, the versatility of scCO₂ allows to prepare catalysts with different structures (e.g., nanoparticles or metal-loaded supports) by several supercritical processes for the photocatalytic degradation of various compounds. This is the first updated review on the use of scCO₂-assisted techniques for photocatalytic applications. We hope this review provides useful information on different approaches and future perspectives.

New Trends in the Use of Volatile Compounds in Food Packaging

In the last years, many of the research studies in the packaging industry have been focused on food active packaging in order to develop new materials capable of retaining the active agent in the polymeric matrix and controlling its release into food, which is not easy in many cases due to the high volatility of the chemical compounds, as well as their ease of diffusion within polymeric matrices. This review presents a complete revision of the studies that have been carried out on the incorporation of volatile compounds to food packaging applications. We provide an overview of the type of volatile compounds used in active food packaging and the most recent trends in the strategies used to incorporate them into different polymeric matrices. Moreover, a thorough discussion regarding the main factors affecting the retention capacity and controlled release of volatile compounds from active food packaging is presented.

Editorial for the “Green Chemistry” Section in the Journal Molecules: Focus on Solvents

It is a pleasure to write this editorial highlighting some of the recent papers discussing solvents in the Green Chemistry section of Molecules [...]