# Use of Hydrogels to Regulate Orthodontic Tooth Movement in Animal Models: A Systematic Review
## 3 Results
### Study Characteristics Relevant to Hydrogel Administration and Characterization  
In the study of [PERSON] et al., they evaluated two hydrogels' formulations; the first with 4% chitosan (Sigma-Aldrich Chemie GmbH, Burlington, MA, USA) and acetic acid was prepared in a solution of double distilled water (1% \(v/v\)), the pH of which was adjusted to 6.8 with 1 N NaOH. Chitosan powder was gradually added to the solution. The pH at 7.4 led to gelation. Afterward, in the second with 10% gelatin (Sigma-Aldrich (FLUKA)), thermosensitive gelatin hydrogels were prepared to undergo gelation at physiological temperature, 1% \(w/v\) ready-made chitosan solution was added to increase mechanical properties, both loaded with 50% of their weight in curcumin (SBU Institute of Medical Drugs) [20]. Another study on rats by [PERSON] et at. used three different concentrations of sclerostin injection (R&D systems, Minneapolis, MN, USA), 0.8 \(\upmu\)g/kg, 4 \(\upmu\)g/kg, or 20 \(\upmu\)g/kg. The sclerosin was transported by a polyethylene glycol-polycaprolactone-polyethylene glycol (PECE) hydrogel [21]. In the study by [PERSON] et al., the authors fabricated hollow porous microspheres with PLGA (poly lactic acid-co-glycolic acid) by the standard double emulsion technique, and adsorbed rat soluble RANKL onto the sterilized microspheres at a ratio of \(\upmu\)g RANKL \(\times\) 1 mg microspheres, using a concentration of 100 \(\upmu\)g/mL RANKL in phosphate buffered saline (PBS) at room temperature for 30 min, which they lyophilized overnight to produce RANKL-PLGA microspheres. Then they embedded the RANKL-PLGA microspheres in a 10% hydroxymethyl cellulose (HEC) aqueous gel at a ratio of 1:3 (RANKL-PLGA: HEC, \(w/v\)) in PBS at room temperature to produce the RANKL-loaded hydrogel formulation [22]. [PERSON] et al. occupied a 2% (\(w/v\)) methylcellulose hydrogel with PTH obtained by adding 4 g of methylcellulose powder (Wako Purc Chemical Industry, Osaka, Japan) to 100 mL of saline solution at a temperature of 90 to 100 \({}^{\circ}\)C with constant agitation, followed by the addition of synthetic PTH (Peptide InstitLtC Inc., Mino, Japan) dissolved in 0.9% saline at 2 p.g/p.L [23]. [PERSON] et al. reported the use of an epigallocatechin gallate (EGCG-GL) hydrogel formulation, which was made with 100 mg of type A porcine skin gelatin (Sigma-Aldrich Co. LLC., St. Louis, MO, USA) dissolved in 5 mL of warm water at 50 \({}^{\circ}\)C. After cooling the solution to room temperature, 27.5 \(\upmu\)L of N-methylmorpholine (NMM) (Nacalai Tesque Inc., Kyoto, Japan), and 0.07 or 0.7 mg EGCG (BioVerde Inc, Kyoto, Japan) and 69.2 mg 4-(4.6-dimethoxy-1,3,5-triazin-2-yl)-4-morpholinium chloride (DMT-MM) (Tokyo Chemical Industry Co., Tokyo, Japan) and the solution was stirred for 24 h at room temperature [26]. [PERSON] at al. conducted their experiments on guinea pigs by topical administration of two hydrogels loaded with 400 mg Bis-CR250 and 400 mg Bis-CR500. Gelatin (G-2554P, 100286; Nitta Gelatin Inc., Osaka, Japan) was dissolved in distilled water (3% \(w/v\)) and homogenized for 3 h at 37 \({}^{\circ}\)C. Risedronate sodium (Cat No. 51428; Selleck Chemical, Scoresby, Australia) was added and stirred for 2 h. The mixture was cross-linked with 25% glutaraldehyde (Merck, Darmstadt, Germany) and rinsed with glycine (Merck) three times. These contained 1 mg and 1.92 mg of pure risedronate and was prepared in 5 mL of phosphate buffer solution [27]. [PERSON] et al. fabricated a hydrogel of carbonated hydroxyapatite (CHA) and platelet-rich fibrin by adding \(\upbeta\)-type gelatin from bovine bone (Nitta Co., Osaka, Japan) to Ca (OH)\({}_{2}\) in a sodium citrate solution. In addition, 10 mL of blood was collected by venipuncture from the rabbit ear marginal vein, the fibrin clot was pressed into an advanced platelet-rich fibrin (aPRF) processing box. Then 200 \(\upmu\)L of a PRF releaser (Osung Ltd., Houston, TX, USA) was loaded into 10 mg of CHA hydrogel to administer as an injection to the rabbits [24]  
Another study by [PERSON] et al.