The availability, biocompatibility, non-toxicity, and ease of chemical modification make cellulose a promising natural polymer for the production of biomedical materials. Cryogelation is a relatively ...new and straightforward technique for producing porous light and super-macroporous cellulose materials. The production stages include dissolution of cellulose in an appropriate solvent, regeneration (coagulation) from the solution, removal of the excessive solvent, and then freezing. Subsequent freeze-drying preserves the micro- and nanostructures of the material formed during the regeneration and freezing steps. Various factors can affect the structure and properties of cellulose cryogels, including the cellulose origin, the dissolution parameters, the solvent type, and the temperature and rate of freezing, as well as the inclusion of different fillers. Adjustment of these parameters can change the morphology and properties of cellulose cryogels to impart the desired characteristics. This review discusses the structure of cellulose and its properties as a biomaterial, the strategies for cellulose dissolution, and the factors affecting the structure and properties of the formed cryogels. We focus on the advantages of the freeze-drying process, highlighting recent studies on the production and application of cellulose cryogels in biomedicine and the main cryogel quality characteristics. Finally, conclusions and prospects are presented regarding the application of cellulose cryogels in wound healing, in the regeneration of various tissues (e.g., damaged cartilage, bone tissue, and nerves), and in controlled-release drug delivery.
Processing hydrogels into solid foams or aerogels via freeze-drying broaden their applications. However, one challenge is its inherent processing instability, often leading to dimensional shrinkage ...and structural collapse of the resultant solid foams. To address this, our study investigated the role of hydrogel state in the solid foam formation. Specifically, polyvinyl alcohol (PVA) hydrogel, synthesized through repeated freeze-thaw (FT) cycles, was investigated. It was found that PVA concentration and FT cycles played a vital role; specifically, higher PVA concentration and more FT cycles negatively affected solid foam formation. These hydrogels exhibited an increase in hydrogel viscoelasticity and crystallizability of the most flexible chains, indicative of strong and denser network structure. We proposed that the final solid foam structure was determined by a balance between the volumetric expansion due to water-to-ice transition during freezing and the intense inter-polymeric chain attractions within the denser network during sublimation.
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•The effect of hydrogel state on the polyvinyl alcohol solid foam formation was studied.•Decrease the polymer concentration and freeze-thaw cycles promote foam formation.•The mechanism for solid foam formation from the perspective of hydrogel state was proposed.
Freeze drying, aka lyophilization, is a process by which a pharmaceutical product is dried via sublimation under vacuum. An alternative to the conventional process is microwave-assisted freeze ...drying, which relies on microwave irradiation for drying the product, offering a reduction in the drying time by 70%–80%. This article derives exact and approximate analytical solutions to a mechanistic model for conventional, microwave-assisted, and hybrid freeze drying. The exact solution serves as a reference solution for validating numerical or approximate results due to its highest accuracy up to machine precision. The approximate solution can be computed about 4-fold faster than the numerical solutions and 200-fold faster than the exact solution with the maximum error of less than 1%, which is highly computationally efficient and accurate. Applications of the analytical solutions are demonstrated in the context of parameter estimation, optimal control, and parameter space analysis.
•Analytical solutions are derived for microwave-assisted and hybrid freeze drying.•The analytical solutions are validated using numerical methods.•The exact analytical solution requires transcendental equations.•The approximate solution is 200-fold faster while having less than 1% error.•The analytical solutions are used for analysis, parameter estimation, and control.
Staphylococcus aureus phage ISP was lyophilized, using an Amsco-Finn Aqua GT4 freeze dryer, in the presence of six different stabilizers at different concentrations. Stability of the lyophilized ...phage at 4 °C was monitored up to 37 months and compared to stability in Luria Bertani broth and physiological saline at 4 °C. Sucrose and trehalose were shown to be the best stabilizing additives, causing a decrease of only 1 log immediately after the lyophilization procedure and showing high stability during a 27 month storage period.
Freeze-drying is a widely used method for obtaining polymer scaffolds for use in tissue engineering. The intensification of the vacuum freeze-drying will increase the productivity of the process and ...reduce its costs. The 1st part of the article describes the modernization of the vacuum freeze-dryer design to organizing a process with simultaneous infrared radiation and ultrasonic exposure. The algorithms to control the freeze-drying process will be discussed too. The 2nd part of the article will discuss how the drying modes effect on the freeze-drying kinetics of various polymer frameworks. In addition, the application of mathematical modeling to predict the drying kinetics of various polymer scaffolds and the selection of optimal freeze-drying modes will be considered.
•Spray–freeze-drying (SFD) technique used for microencapsulation of vanillin flavour.•β-Cyclodextrin, whey protein isolate (WPI) and their combinations effects as wall materials was ...evaluated.•Vanillin+WPI by SFD method exhibited better thermal stability than the spray drying and freeze-drying techniques.
Vanillin flavour is highly volatile in nature and due to that application in food incorporation is limited; hence microencapsulation of vanillin is an ideal technique to increase its stability and functionality. In this study, vanillin was microencapsulated for the first time by non-thermal spray–freeze-drying (SFD) technique and its stability was compared with other conventional techniques such as spray drying (SD) and freeze-drying (FD). Different wall materials like β-cyclodextrin (β-cyd), whey protein isolate (WPI) and combinations of these wall materials (β-cyd+WPI) were used to encapsulate vanillin. SFD microencapsulated vanillin with WPI showed spherical shape with numerous fine pores on the surface, which in turn exhibited good rehydration ability. On the other hand, SD powder depicted spherical shape without pores and FD encapsulated powder yielded larger particle sizes with flaky structure. FTIR analysis confirmed that there was no interaction between vanillin and wall materials. Moreover, spray–freeze-dried vanillin+WPI sample exhibited better thermal stability than spray dried and freeze-dried microencapsulated samples.
Freeze-drying (FD) is often used for therapeutic proteins and other biological drugs to extend their shelf life, but it usually reduces the activity and stability of the protein and has a longer ...drying cycle. A microwave-assisted freeze-drying (MFD) was proposed to produce immunoglobulin of yolk (IgY) preparations. The effects of FD and MFD on the immunological activity and structure of IgY with different amounts of trehalose were investigated. Results showed that lyophilization led to a partial loss of secondary structure in IgY, which resulted in the activity loss. As the trehalose content increased from 0% to 5%, the activity retention of MFD samples increased from 20.31% to 75.57%, which was comparable to FD samples (from 23.57% to 67.78%). However, MFD had a shorter drying cycle when compared with FD. MFD can be a potential alternative to FD as a common therapeutic protein drying method.
Aims
To determine the effect of three different freezing temperatures on post‐freeze‐drying survival rates of wine yeasts and lactic acid bacteria (LAB). To know if a similar freeze‐drying protocol ...can be used for both micro‐organisms.
Methods and Results
Cells from liquid culture media were recovered and concentrated in appropriate lyoprotectants. Aliquots of each strain were frozen at −20, −80 and −196°C before vacuum drying. Viable cell counts were done before freezing and after freeze‐drying. Survival rates were calculated. Freezing temperatures differently affected yeast and bacteria survival. The highest survival rates were obtained at −20 and −80°C for yeasts, but at −196°C for LAB. Major differences in survival rates were recorded among freeze‐dried yeasts, but were less drastic for LAB. Yeasts Pichia membranifaciens, Starmerella bacillaris and Metschnikowia pulcherrima, and LAB Lactobacillus paracasei, Pediococcus parvulus and Lactobacillus mali, were the most tolerant species to freeze‐drying, regardless of freezing temperature.
Conclusions
Yeast and LAB survival rates differed for each tested freezing temperature. For yeasts, −20°C ensured the highest post‐freeze‐drying viability and −196°C for LAB.
Significance and Impact of the Study
Freezing temperature to freeze‐dry cells is a crucial factor for ensuring good wine yeast and LAB survival. These results are important for appropriately preserving micro‐organisms and for improving starter production processes.
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