Supercritical drying of gels is considered as the most important step of aerogel production since it enables preservation of the three-dimensional pore structure which lead to unique material properties such as high porosity, low density, and large surface area. An understanding of the kinetics of supercritical drying is necessary to provide insight into material development, scale-up, and optimization of the aerogel manufacturing process. Thus, investigation of supercritical drying is gaining increased attention in recent years. This review paper covers the experimental considerations and techniques to study the kinetics of supercritical drying, fundamental mass transfer mechanisms during the drying process and modeling efforts to predict the drying kinetics for varying operating conditions and gel properties. Transport phenomena involving diffusion, convection, spillage by volume expansion, and axial dispersion are discussed by providing the fundamental equations and empirical correlations to predict transfer coefficients. A detailed review of literature covering experimental and theoretical studies on kinetics of supercritical drying is presented.

Hydrogels wound dressings have enormous advantages due to their ability to absorb high wound exudate, capacity to load drugs, and provide quick pain relief. The use of hydrogels as wound dressings in their original form is a considerable challenge, as these are difficult to apply on wounds without support. Therefore, the incorporation of polymeric hydrogels with a certain substrate is an emerging field of interest. The present study fabricated cellulose hydrogel using the sol–gel technique and reinforced it with nonwoven cotton for sustainable wound dressing application. The nonwoven cotton was immersed inside the prepared solution of cellulose and heated at 50 °C for 2 h to form cellulose hydrogel–nonwoven cotton composites and characterized for a range of properties. In addition, the prepared hydrogel composite was also loaded with titania particles to attain antibacterial properties. The Fourier transform infrared spectroscopy and scanning electron microscopy confirmed the formation of cellulose hydrogel layers inside the nonwoven cotton structure. The fabricated composite hydrogels showed good moisture management and air permeability, which are essential for comfortable wound healing. The wound exudate testing revealed that the fluid absorptive capacity of cellulose hydrogel nonwoven cotton composite was improved significantly in comparison to pure nonwoven cotton. The results reveal the successful hydrogel formation, having excellent absorbing, antimicrobial, and sustainable properties.

The increasing knowledge on skin physiology, formulation science and nanotechnology has led to continuous improvements in cosmetics, and introduction of dermocosmetics has been increasing particularly for the management of skin disorders such as acne, eczema, psoriasis, etc. Nowadays, research has been focused on the development of products which can efficiently administer active compounds to the target skin layers while minimizing side effects. The use of multifunctional lipid nanoparticles for cosmetic and dermocosmetic purposes is promising not only because biocompatible ingredients are used in their composition, but also because of their ability to show enhanced skin penetration. Although the introduction of liposomes has been a hallmark of lipid nanoparticles, development of novel systems capable of encapsulating active compounds with tunable release profiles, that show good stability, are easy to manufacture and handle remains a necessity. Solid lipid nanoparticles (SLN) were introduced as alternative formulations for emulsions, liposomes and polymeric nanoparticles, whereas nanostructured lipid carriers (NLC) were developed later as second-generation nanoparticles. However, both SLN and NLC show many inherited advantageous properties to be used for dermal applications including ability to provide occlusion and photoprotective effect and skin hydration, and various SLN and NLC based products are already in the market. This review provides an overview on the current state-of-art of SLN and NLC particularly for cosmetic and dermocosmetic purposes, discuss their formulation composition, structures and preparation techniques. Their use for the topical delivery of active compounds in different skin disorders is highlighted along with examples of commercialized products.

In this study, cotton-reinforced alginate hydrogel fibers were successfully synthesized using the wet spinning technique to improve hydrogel fibers’ mechanical strength and durability. Structural, chemical, and mechanical properties of the prepared fibers were characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray Diffraction, differential scanning calorimeter, and single fiber strength tester. Based on the results obtained from fourier transform infrared spectroscopy and x-ray Diffraction, cotton fibers have been successfully incorporated into the structure of the hydrogel fibers. It was seen from the differential scanning calorimeter results that the incorporation of fibers in the structure even enhanced the thermal stability of the fiber and is viable to be implanted in the human body. Cotton reinforcement in alginate hydrogel fibers increases the modulus up to 56.45 MPa providing significant stiffness and toughness for the hydrogel composite fiber. The tenacity of the fibers increased by increasing the concentration of alginate from 2.1 cN/Tex (1% w/v) to 8.16 cN/Tex (1.5% w/v). Fiber strength increased by 26.75% and water absorbance increased by 120% by incorporating (10% w/w) cotton fibers into the fibrous structure. It was concluded that these cotton-reinforced alginate hydrogel fibers have improved mechanical properties and liquid absorption properties suitable for use in various biomedical applications.

Textiles have been used for clothing purposes since ancient times. However, due to their functional properties, their importance—as well as their use in various fields such as filtration, protective clothing, and medical applications—increased over time. Properties of the textile fabrics depend mostly on the fiber type, fabrication technique, and structure. Moreover, fabric porosity is one of the properties that provide comfort, increased thermal insulation, and filtration capability to the end products. The porous structure of woven, knitted, and nonwoven fabrics has been used for many years to get the desired porosity. Usually, macroporous structures are achieved using these types of textiles. Electrospinning is used to produce nanoporous textile fibrous web, but its poor mechanical properties and low production rate limit its use. Aerogels are solid materials with ultrahigh porosity at the nanoscale with low density and good thermal insulation properties, due to which they are considered potential insulation materials today. On the other hand, pure aerogels are sometimes brittle and have poor mechanical properties. Thus, they cannot be directly used in various applications. Consequently, textile reinforced aerogel composites have been developed, which could provide flexibility and strength to aerogels and impart nanoporous structure to textiles. This review summarizes conventional techniques to produce the porous structure in textiles followed by the modern techniques to develop a nanoporous structure. Further, different mechanisms to synthesize textile reinforced aerogel composites are discussed to get a nanoporous structure for filtration and thermal insulation applications. The porosity, mechanical properties, and thermal insulation of textile reinforced aerogel composites are also highlighted. In the end, we give a conclusion that not only summarizes the literature, but also includes recommendations for the researchers.

Tragacanth, an anionic polysaccharide, is a natural material widely investigated for the synthesis of aerogels as drug delivery vehicles. Its biocompatibility, biodegradability, and affordability are all key features for its use in pharmaceutical applications. In this study, tragacanth and tragacanth alginate composite aerogels were prepared using the sol-gel technique followed by supercritical drying. Paracetamol was selected as a model drug for drug loading and release studies owing to its high solubility in ethanol and low solubility in supercritical carbon dioxide. The paracetamol loading into the aerogel pores was confirmed by infrared spectroscopy (IR) and x-ray diffraction (XRD) spectra of the resulting samples. Scanning electron microscopy (SEM) images showed that all aerogels were porous with a macroporous-mesoporous network. Due to the high porosity of the prepared aerogels, a loading of 99 wt% (mg drug/mg aerogel) for tragacanth and 114 wt% (mg drug/mg aerogel) for composite aerogels was achieved. Moreover, the release rate of the drug could be modified by manipulating the aerogel composition. Tragacanth aerogels had a faster release rate, while the addition of alginate prolonged the release rate of the model drug. Various empirical release models were investigated and the release rate was found to follow the Korsmeyer-Peppas (Power Law) model suggesting a diffusion-based release kinetics. Based on the results, the feasibility of utilizing tragacanth for the preparation of drug-loaded aerogels was shown. Graphical Abstract