A polyvinyl alcohol (PVA) hydrogel loaded with guava leaf extract (GLE) has potential applications as a wound dressing with good antibacterial activity.

Andrographolide (AG) is one of the compounds in Andrographis paniculata, which has a high antibacterial activity. This paper reports the freeze–thaw method’s use to synthesize polyvinyl alcohol (PVA) hydrogels loaded with AG and its characterization. From the morphological examination, the porosity of the PVA/AG hydrogel was found to increase with the increasing AG concentration. The swelling degree test revealed that the hydrogels’ maximum swelling degrees were generally greater than 100%. The composite hydrogel with the highest fraction of andrographolide (PAG-4) showed greater weight loss than the hydrogel without AG (PAG-0). The molecular interaction between PVA and AG resulted in the narrowing of the band attributed to the O–H and CO stretching bonds and the emergence of an amorphous domain in the composite hydrogels. The loading of AG disrupted the formation of hydroxyl groups in PVA and interrupted the cross-linking between PVA chains, which lead to the decrease of the compression strength and the crystallinity increased with increasing AG. The antibacterial activity of the composite hydrogel increased with increasing AG. The PAG-4 hydrogel had the highest antibacterial activity of 37.9 ± 4.6b %. Therefore, the PVA/AG hydrogel has the potential to be used as an antibacterial device.

Hydrogel is being broadly studied due to their tremendous properties, such as swelling ability and biocompatibility. Numerous review articles have discussed hydrogel polymer types, hydrogel synthesis methods, hydrogel properties, and hydrogel applications. Hydrogel can be synthesized by physical and chemical cross-linking methods. One type of the physical cross-linking method is freeze-thaw (F–T), which works based on the crystallization process of the precursor solution to form a physical cross-link. To date, there has been no review paper which discusses the F–T technique specifically and comprehensively. Most of the previous review articles that exposed the hydrogel synthesis method usually mentioned the F–T process as a small part of the physical cross-linking method. This review attempts to discuss the F–T hydrogel specifically and comprehensively. In more detail, this review covers the basic principles of hydrogel formation in an F–T way, the parameters that influence hydrogel formation, the properties of the hydrogel, and its application in the biomedical field.

Microwave wide-spread results in electromagnetic interference, environmental pollution, and hazards for health, thus microwave absorber is immediately needed. Mn4+doped barium natural ferrites were synthesized using the modified solid-state reaction method, which is a combination of the sol-gel method and the solid-state reaction. Commercial Ba(NO3)2, MnO2 and natural Fe3O4 were used as raw materials. Structural, magnetic properties and microwave absorption of the barium ferrites were characterized using XRD, VSM, and VNA, respectively. The results reveal that phase of BaFe2.37Mn9.63O19 dominates the diffraction peaks with the average size of crystallite 23.74 nm after adding Mn4+ ions in the barium ferrites. Ms value of the barium ferrite decreases with increasing concentrations of Mn4+ due to the surface effect of the nanoparticle. The MBF3 exhibited excellent performance that absorbs all given microwave frequencies with RL below -10 dB and bandwidth of 4 GHz compared to the other samples.

Hydrogels are three-dimensional (3D) polymer networks that are water-absorbent, insoluble, flexible, and biocompatible. The freeze-thaw technique is a physical cross-linking method for hydrogel synthesis, which can form a stable structure and non-toxic materials. Biopolymer hydrogel is a solution to environmental pollution due to synthetic polymers, which have been widely used as hydrogel base materials. This paper uses starch composite as precursor solutions for the preparation of hydrogels. The precursor solution ratios (potato starch/gelatin) of 20:0, 20:1, 20:2, 20:3, and 0:20 were labeled as SCG1, SCG2, SCG3, SCG4, and SCG5, respectively. Morphological results showed a cross-linking between polymer chains (solid area) and porosity (liquid area). During the freeze-thaw process, gelatin interfered with a cross-linking process of the hydroxyl group so that the solid phase decreased and the pore size was irregular and enlarged. The swelling degree increased with the gelatin composition, while the weight loss showed the opposite result. SCG1 showed the highest swelling degree value of around 319.39 ± 35.05a % and lower weight loss of about 19.26 ± 9.91a %, which showed a higher degradability. SCG1 has good mechanical properties with Young Modulus, onset strain, and onset stress of about 1.4 ± 0.33a KPa, 145.11 ± 47.28b %, and 1.62 ± 0.08c KPa, although the highest compressive strength was shown by SCG5 of 25.63 ± 2.75a KPa. In general, we found that the physical properties of starch hydrogels showed a potential to be used as a functional food matrix: higher swelling degree, modulus elasticity, and degradability. For gelatin hydrogels, it is necessary to modify the process to become a potential matrix as a media delivery.