China
Africa
Explore chapters and articles related to this topic
Encapsulation Technologies for Modifying Food Performance
Published in Munmaya K. Mishra, Applications of Encapsulation and Controlled Release, 2019
Maria Inês Ré, Maria Helena Andrade Santana, Marcos Akira d’Ávila
Physicochemical stability determines the shelf-life stability of liposomes. By optimizing the size distribution, pH, and ionic strength, as well as by the addition of antioxidants and chelant agents, the stability of liposomes can be preserved for years. They can be stored in frozen or dried form, but cryoprotectants have to be added to prevent fusion. Electrostatic and steric stabilization also reduce fusion and disintegration by freezing. Biological in vivo stabilization is obtained by reducing the interactions of liposomes with macromolecules, blood protein, and disintegrating enzymes as well as adverse pH conditions. Therefore, the in vivo stability of liposomes depends on the route of administration. Steric stabilization is generally provided by a protective coating made by grafting the liposome surface with inert hydrophilic polymers such as polyethylene glycol (Lasic, 1995) or hyaluronic acid (Eliaz and Szoka, 2001).
Cellular Therapeutics: A Novel Modality with Great Therapeutic Potential
Published in Sandeep Nema, John D. Ludwig, Parenteral Medications, 2019
An important part of preserving the longevity of cells is ensuring that they are stable prior to going through the freezing process for storage. They must possess high viability and be at a sufficient concentration to simplify preparation of the frozen product. Mammalian cells currently have to be stored frozen and if prepared properly, can be stored for decades at ultracold temperatures (≤−135°C). One of the most common materials used for cryopreservation is dimethyl sulfoxide (DMSO). The DMSO replaces the water molecules in the cell membrane so that when cells are frozen, ice crystals will not form (if they do, they would cause the cells to lyse during the freezing process). Concentrations of DMSO used in cell therapy applications range from 1% to 10% depending on the cells and the intended final use. It is important that once the cells come into contact with DMSO, the cells are frozen as soon as possible, as prolonged exposure of the cells to DMSO can be toxic (preference is 1–4 h depending on the concentration of DMSO and type of cells). During the initial freezing process, a controlled rate freeze is critical to helping preserve viability upon thaw and typically uses a drop of ~1°C/min. Conversely, if cells are not administered immediately after thaw, cells should either be washed or be processed to minimize the effects of DMSO. There have been other formulations examined using sucrose, dextrans, and polyampholytes like poly-l-lysine, but DMSO is still the most widely used cryoprotectant.
Bioprinting-enabled technologies for cryopreservation
Published in Ali Khademhosseini, Gulden Camci-Unal, 3D Bioprinting in Regenerative Engineering, 2018
Fariba Ghaderinezhad, Reza Amin, Savas Tasoglu
Since cryoinjury occurs at a low temperature due to ice formation, a cryoprotectant agent is used to protect the cells. In fact, CPAs play the role of osmotic buffers for preventing harmful critical electrolyte concentration gradients. Furthermore, they help the cell membranes stabilize and prevent macromolecules from changing from their native form. However, using a high concentration of CPA may be toxic, so finding the optimal concentration is crucial. CPAs should be as highly permeable and nontoxic as possible. Adding sugars (e.g., sucrose and trehalose), polymers (e.g., polyvinylpyrrolidone and polyvinyl alcohol), or other nonpermeable CPAs are possible options that decrease the toxicity of CPAs. Another way is to perform a stepwise loading of CPAs with lower concentrations to minimize the toxicity and osmotic shock. Dimethylsulphoxide (DMSO), 1,2-propanediol (PROH), ethylene glycol (EG), sucrose, trehalose, and mannitol are a number of the widely used CPAs (Dou et al. 2015, Zhang et al. 2011, Sheikhi et al. 2013, Selman 2005). CPAs used in cryopreservation studies coupled with the bioprinting method are presented in Table 14.1.
Synergistic combination of cryoprotectants for high freeze-dried survival rate and viable cell counts of Streptococcus thermophilus
Published in Drying Technology, 2023
Lijun Di, Wenlong Ma, Wenli Kang, Yujun Huang, Zhongkun Wu, Boxing Yin, Renqin Yang, Xuecong Liu, Lina Pan, Jiaqi Wang, Li Wei, Ruixia Gu
Vacuum freeze-drying is a common method to prepare the probiotic starter.[3] However, due to low temperature and water crystallization, cell membrane and proteins could be damaged during the freeze-drying process,[4,5] leading to a decrease in viable cell count. Cryoprotectants commonly used include carbohydrates, proteins, salts, amino acids, etc. Carbohydrates could avoid the integrity of the cell membrane and protein being damaged by forming hydrogen bonds with the phospholipid group of the cell membrane or polar group of cell protein during freeze-drying.[6] Proteins could form a protective film on the surface of bacteria during drying.[7] Salts buffered the damage caused by the dehydration of cells by regulating the osmotic pressure of the lyophilized system.[8] Several studies have shown that combinations of different cryoprotectants could synergistically improve the freeze-dried survival rate of probiotic powder. However, the guiding principle of synergistic cryoprotectants combination is not clear now.
Efficient eco-friendly approach towards bimetallic nanoparticles synthesis and characterization using Exiguobacterium aestuarii by statistical optimization
Published in Green Chemistry Letters and Reviews, 2019
M. V. S. Sandhya, Karthik Rajkumar, Sandeepta Burgula
The long-term stability of Np upon storage at 4°C, −20°C, and −80°C up to 6 months was studied (Supplementary Table 2). Tween-20, glycerol, dextrose, PEG – 4000, and PEG – 6000 were used as cryoprotectants. Among all the cryoprotectants, glycerol is proved to be good at all temperatures for suspended Np, when compared with pelleted or dried samples followed by Tween-20, which proved to be suitable for storage and handling of Np at 4°C and −20°C. Dextrose, PEG-4000, and PEG-6000 were found to be less useful for persevering both suspended and dried samples under all three conditions, as they result in aggregation. Therefore, the present preservation process is easier to handle compared with previous methods suggested by Abdelwahed et al. (21).
A comprehensive review on stability of therapeutic proteins treated by freeze-drying: induced stresses and stabilization mechanisms involved in processing
Published in Drying Technology, 2022
Zhe Wang, Linlin Li, Guangyue Ren, Xu Duan, Jingfang Guo, Wenchao Liu, Yuan Ang, Lewen Zhu, Xing Ren
In order to maintain the natural structure of proteins and prevent protein denaturation under the stress caused by freezing and drying, stabilizers (cryoprotectants and lyoprotectants, surfactants, etc.) are required to be included in the protein formulation. Cryoprotectants can inhibit ice nuclei, promote vitrification, and help stabilize the natural structure of proteins.[67] The main mechanisms for stabilizers to maintain protein stability during lyophilization include preferential interaction, vitrification, and water replacement theory.[68] In addition, some recent studies have introduced some supplements to these stabilization mechanisms.