Method to prepare a filler with hyaluronic acid base comprising a neutralization step

A method to prepare a filler with a hyaluronic acid base comprising the following steps:

• A) a crosslinking step comprising crosslinking hyaluronic acid by mixing the following components in a reaction chamber to form a reaction mixture:
• water, hyaluronic acid (HA), a solution of alkali metal hydroxide, a crosslinking agent chosen from polyethylene glycol diglycidyl ether (PEG DE), polypropylene glycol diglycidyl ether (PPG DE), or polytetramethylene glycol diglycidyl ether, for a mixing time of 10 minutes to 40 minutes, to obtain a gel of crosslinked HA;
• and,
• B) a neutralization step comprising contacting the gel of crosslinked HA obtained from the crosslinking step A) with a single neutralization solution comprising the following components:
• water, hydrochloric acid (HCI), a buffer agent, and lidocaine or derivatives of lidocaine as an anesthetic agent to obtain a filler with a hyaluronic acid base, wherein in said step B) a percentage in weight (w/w) of the individual components with respect to a total weight of the neutralization solution is as follows:
• from 78% to 98% water;
• from 4% to 25% hydrochloric acid;
• from 0.1% to 1.5% buffer agent;
• and,
• up to 1.5% in weight of lidocaine or derivatives of lidocaine.