Table 4:

Surfactants, Lyoprotectants, and Cryoprotectants used for bioconjugates and nanomaterials

Surfactants, lyoprotectants and Cryoprotectants	Mechanism/purpose	Outcomes
Polyacids (polyacrylic acid, citric acid)	Coacervate precipitation due to hydrogen bonding between oxygen in surface peg group and hydroxyl ion in carboxylic part of polyacid. This method is of interest due to possibility of using heterobifunctional peg in for binding with biomolecules of interest.	Since bonding is reversible, the hypothesis was that neutralizing ph would resuspend the nanoparticles after lyophilization on plga-peg nanoparticles. Sucrose was used as a control to check redispersion in its presence or absence. In presence of high amount of sucrose, the nanoparticles resuspended, while for nanoparticles without sucrose, 15 minutes sonication was required. [67]
High molecular weight polyethylene glycol	PEG between 0.4–20 kDa was used as cryoprotectant at different freezing rates. The rate of aggregation depended on change in particle size. Higher particle size compared to initial size represents higher order of aggregation.	Aggregation was highest in low molecular weight peg in comparison to suspension with high molecular weight peg. Freezing rate did not affect the rate of aggregation. [81]
Surface stabilization with quaternary ammonium groups	As a second cryoprotectant lactose, microcrystalline cellulose or calcium phosphate was used. Four model polymeric nanoparticle were investigated. The surface stabilization through ammonium group caused low contact angles.	Higher wettability of polymer surface and high minimum film formation were attributed for better redispersion of polymeric nanoparticles released from granular, pelleted or tablet formulations. [68]
Polyvinyl alcohol (pva)	Freeze drying of polycaprolactone nano-capsules in presence of pva Comparing observations against sugars (glucose, mannitol, trehalose) used for cryoprotection	Using 5% w/v pva resulted in almost complete resuspension of nanoparticles (ratio of final to initial size was 1.008), and the trend remains similar for freezing in liquid nitrogen, in pre-chilled freezer, as well as freeze dryer shelf. Moreover, combining sugars can bring the ratio close to 1. Hence, a combination of cryoprotectants can offer better redispersion of nanosuspensions. [69]
Pluronics	Role of poloxamer 188 was investigated Surfactants such as these are supposed to be adsorbed in surface of polymer nanoparticles	Enhanced cake formation and combining with sugar lead to easily dispersible formulations. 5% poloxamer solution used lead to ratio of final and initial radiuses close to 1.1, while combining glucose resulted in ratio close to 1. [62]
Trehalose	Using trehalose to modify solvation layer around biomolecules due to larger hydrated volume. Designed polymers were formed from diazide-trehalose comonomer and dialkyne comonomer Flocculation levels were studied in media containing serum proteins	Presence of trehalose in the lyophilized nanomaterials resulted in lower flocculation and higher efficacy for delivering biomolecules (pdna into hela cell lines in mentioned study) [82]
Lactose and sucrose	Formation of glassy layer around particles to prevent aggregation. Studying change in physical properties of lyophilized cake with variation in amount of sugar cryoprotectants for cationic nanoparticles	In absence of cryoprotectants, higher freezing temperature can lead to higher flocculation. As amount of cryoprotectant increases, the effect of freezing temperature on size of nanomaterials started decreasing However, redipersion at 5% w/v of sugar used resulted in size closest to initial particle size, and as amount of sugar was increased, particle size went up as well. [65]
Dextran	Formation of stabilizing layer on particles, resulting in an interface between water and the latex particle	As amount of dextran increases, layer thickness on particles increase, and size when re-dispersed after freeze drying becomes closer to initial size. As molecular weight of dextran increases, lesser amount of dextran (w/w) is required for better resuspension of latex particles. [83]