FIELD OF THE INVENTION

Embodiments described here concern a method to prepare a filler with a hyaluronic acid base, which has better properties of chemical and physical stability over time and optimal viscoelasticity to be injected cutaneously.

In particular, the method according to the embodiments described here concerns a method to prepare a filler with a hyaluronic acid base (HA), which comprises a first step in which the hyaluronic acid is crosslinked and a subsequent step to neutralize and hydrate the crosslinked hyaluronic acid.

BACKGROUND OF THE INVENTION

It is known that hyaluronic acid is one of the fundamental components of the connective tissues of man and other mammals. It is a substance widely present in the human body in the epidermal, epithelial and neural tissues.

Hyaluronic acid gives the skin its peculiar properties of resistance and shape retention. A lack of hyaluronic acid causes a weakening of the skin, promoting the formation of wrinkles and imperfections.

The concentration of hyaluronic acid in the tissues of the human body tends to decrease with advancing age, so that its function of tissue repair is weakened. With progressive aging and after repeated exposure to ultra-violet sunrays, the epidermal cells decrease their production of hyaluronic acid and their speed of degradation increases. At the same time, the skin loses collagen, which is another natural substance necessary for maintaining the skin in a young and resilient form. With the passage of time, the loss of hyaluronic acid and collagen in the epidermal tissues causes the formation of folds and wrinkles.

From the chemical point of view, hyaluronic acid (HA) is a polymer compound, definable as a glycosaminoglycan with an un-branched polysaccharide chain, produced by the condensation of thousands of disaccharide units, which are in turn formed by residues of glucuronic acid and M-acetylglucosamine.

Thanks to its high solubility in water, the molecule of the salt corresponding to hyaluronic acid, that is, hyaluronate, is able to complex with many molecules of water reaching a high degree of hydration.

Moreover, by using specific crosslinking agents and suitable operating process conditions (temperature, pH, etc.), the extreme length of the hyaluronic acid molecule and its high degree of hydration allow the molecules to organize themselves to form a structure of the lattice type (crosslinked hyaluronic acid), so as to create a molecular scaffold to maintain the shape and tone of the epidermal tissue.

In recent years, various formulations based on hyaluronic acid have been developed for use in esthetic applications in order to fill wrinkles, folds and scars and, in general, to improve the appearance of the face, or to fill the lips.

These formulations are therefore in continuous development from the point of view of industrial research, and are very attractive from the commercial point of view. Hyaluronic acid, being naturally contained in the human body, is a filler that is well tolerated by the epidermal tissue. For this reason, the formulations based on HA are still today considered the best epidermal fillers on the market, because they do not carry the risk of allergic reactions by the skin.

Originally, the first formulations based on hyaluronic acid were prepared in the form of particles or microspheres suspended in a gel. However, these fillers based on gelled microspheres had the disadvantage of poor stability over time, with a tendency to chemical degradation a few months after being injected into the skin. Therefore, frequent re-injections of the filler were required over time, in order to maintain the repair and epidermal growth constant.

In more recent times the advantage has been discovered of subjecting the hyaluronic acid to a suitable crosslinking step by using specific crosslinking agents, and thus fillers based on crosslinked hyaluronic acid are used in esthetic treatments of the face. In this case, the polymer chains of hyaluronic acid are connected to each other to constitute a lattice.

As examples of the most commonly used crosslinking agents, we can cite 1,4-butanediol diglycidyl ether (BDDE), 1,2-ethanediol diglycidyl ether (EDDE), diepoxyoctane and divinyl sulfone. The crosslinking step allows to obtain a hydrogel polymer lattice, which is less soluble in water and more resistant to degradation, so as to require less frequent cutaneous injections than in the case of formulations based on non-crosslinked hyaluronic acid.

However, the use of said crosslinking agents leads to the formation of hydrogels of crosslinked HA which have an excessive level of swelling of the lattice, in the step where the hyaluronic acid is contacted with a chemical neutralizing solution.

Furthermore, an important disadvantage deriving from the crosslinking operating conditions adopted in the state of the art is the formation of fillers based on crosslinked HA with a poor homogeneity of distribution of the chemical-physical parameters (temperature, viscosity, density, etc.) inside the polymer lattice, in the sense that the homogeneity of the structure is interrupted by the unwanted presence of both air microbubbles and lumps of material, that is, narrow zones of thickened material.

This lack of homogeneity of the chemical-physical parameters inside the HA lattice has a negative effect on the chemical-physical stability of the filler prepared, so that its effectiveness over time is unsatisfactory and it is necessary to perform cutaneous re-injections of fillers fairly frequently.

As a consequence of these disadvantages, there is a need to make available in the field of esthetic medicine an innovative method to prepare a filler with a hyaluronic acid base, a method able to increase its chemical-physical stability and duration over time of its repairing action.

There is therefore a need to perfect a method to prepare a filler with a hyaluronic acid base which can overcome the disadvantages of the prior art.

In particular, it is a primary purpose of the present invention to provide a formulation based on hyaluronic acid having better properties of homogeneity/uniformity of the different chemical-physical parameters, so as to increase its stability over time, after it has been used as an esthetic filler.

A second purpose of the method according to the invention is to obtain a filler with a crosslinked HA base having adjustable viscoelasticity in a desired range, by controlling the parameters that define the crosslinking of hyaluronic acid and the subsequent hydration step.

Another purpose of the invention is to improve the efficiency of penetration of a neutralizing solution in the chemical neutralization step that follows the crosslinking of the hyaluronic acid, by means of a selection of innovative operating conditions during the neutralization step.

The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the present invention or variants to the main inventive idea.

Embodiments described here concern a method to prepare a filler with a hyaluronic acid (HA) base, which comprises a step in which the hyaluronic acid is crosslinked, and a subsequent step for the neutralization and hydration of the crosslinked hyaluronic acid.

The main advantage of the method claimed, which will be described in detail hereafter, is that the operating conditions used allow to obtain formulations with a hyaluronic acid base with innovative and improving characteristics with regard to the homogeneity and uniformity of the different chemical-physical parameters inside it (composition, temperature, viscosity, etc.). Consequently, its chemical-physical stability over time, after cutaneous injection, is considerably increased.

A first aspect of the invention concerns a method to prepare a filler with a hyaluronic acid base comprising the crosslinking of the hyaluronic acid by means of the following steps:A1) mixing the following components in a reaction chamber equipped with a mixer: water, hyaluronic acid (HA), a crosslinking agent selected from the class of polyethylene glycols (PEG), a solution of alkali metal hydroxide;A2) dividing the mixture thus obtained into a number n of partial portions and transferring said partial portions to a sequence of n containers to subject them to an ultrasound treatment, the number n of partial portions and containers being comprised between 4 and 32, preferably between 8 and 20;A3) disposing the n containers comprising these partial portions of mixture in an incubator for a period of time comprised between 4 and 8 hours in order to terminate the crosslinking of hyaluronic acid and promote the formation of a gel of crosslinked hyaluronic acid.

The particular operating conditions adopted during the steps A1), A2), A3) described above, in particular the use of a crosslinking agent selected from the polyethylene glycols and the division of the reaction mixture into n partial portions (step A2), lead to the formation of a lattice of hyaluronic acid HA in a gel form with innovative characteristics with respect to the state of the art techniques. Indeed, this lattice of hyaluronic acid will have a much lower level of swelling during the subsequent neutralization and hydration step.

Embodiments of the present invention also concern defining optimal operating conditions during the chemical neutralization of the hyaluronic acid gel deriving from the crosslinking step described above.

A method to prepare a filler with a hyaluronic acid base is therefore a second aspect of the present invention, and comprises the following steps:A) crosslinking the hyaluronic acid by mixing the following components in a reaction chamber: water, hyaluronic acid (HA), a crosslinking agent selected from the class of polyethylene glycols (PEG), a solution of alkali metal hydroxide, the mixing time being comprised between 10 and 40 minutesB) a chemical neutralization step of the crosslinked HA gel obtained in step A) comprising:B1) preparing a neutralizing solution by mixing the following components: water, hydrochloric acid HCl, a buffer agent, optionally lidocaine or its derivatives;B2) dividing the neutralizing solution thus obtained into a number n of partial portions and transferring these partial portions inside the n containers comprising the crosslinked HA gel obtained from step A), where n is a whole number comprised between 4 and 32, preferably between 8 and 20;B3) subjecting the n containers to mixing by means of a rotary device, making them rotate around the axis of the rotary device, so as to promote a penetration of the neutralizing solution inside the hyaluronic acid gel, and obtain a filler of crosslinked hyaluronic acid in the form of a hydrogel.

The particular operating conditions adopted during the neutralizing step B), in particular the division (step B2) of the neutralizing solution into a number n of partial portions, and the subsequent gentle rotation to which the n containers are subjected during step B3), allow to improve the penetration efficiency of the neutralizing solution inside the crosslinked HA gel. Consequently, an improved homogeneity and uniformity of chemical-physical parameters inside the filler obtained is obtained.

A third aspect of the present invention also concerns a specific embodiment of the method to prepare a filler with a hyaluronic acid base, which method comprises:

A) a crosslinking step of the hyaluronic acid comprising the following steps:A1) mixing the following components (w/w) in a reaction chamber for a time comprised between 10 and 40 minutes:from 25 to 60% in weight of water;from 6 to 18% in weight of hyaluronic acid;from 25 to 60% in weight of a solution of alkali metal hydroxide;from 0.5 to 4% in weight of a crosslinking agent selected from the class of polyethylene glycols;A2) dividing the mixture thus obtained into a number n of partial portions and transferring these partial portions to a sequence of n containers to subject them to an ultrasound treatment, the number n of partial portions and containers being comprised between 4 and 32;A3) disposing the n containers comprising these partial portions of mixture into an incubator for a time comprised between 4 and 8 hours;

B) a chemical neutralization step of the crosslinked HA gel obtained in step A) that comprises the following steps:B1) preparing a neutralizing solution by mixing the following components (w/w):from 78 to 98% in weight of water;from 4 to 25% in weight of hydrochloric acid;from 0.1 to 1.5% in weight of a buffer agent;up to 1.5% in weight of lidocaine or its derivatives;B2) dividing the neutralizing solution thus obtained into a number n of partial portions and transferring these partial portions inside the n containers comprising the crosslinked HA gel obtained from step A), where n is a whole number comprised between 4 and 32;B3) subjecting the n containers to mixing by means of a rotating device, making them rotate around the axis of the rotating device, so as to promote a penetration of the neutralizing solution inside the hyaluronic acid gel, and obtain a filler of crosslinked hyaluronic acid in the form of a hydrogel.

As well as the advantages correlated to the degree of homogeneity/uniformity of the different chemical-physical parameters (composition, viscosity, etc.) inside it and the consequent temporal increase of its chemical-physical stability, the method according to the embodiments described here allows to suitably adjust the final viscoelasticity of the filler prepared.

Indeed, the control of the crosslinking parameters and the subsequent hydration step of the gel, makes the product stable from the thermodynamic point of view, so that the rheology of the product is also adjusted and maintained under control. The adjustment of the final viscoelasticity of the hyaluronic acid filler allows, in the case of very viscous fillers, to be able to select the type of syringe most suitable for viscous fluids, so that the cutaneous injection can be performed without particular disadvantages linked to high viscosity.

Embodiments of the present invention also concern the use of lidocaine or its derivatives as an anesthetic agent during the chemical neutralization step of the hyaluronic acid gel.

A method to prepare a filler with a hyaluronic acid base is thus another aspect of the invention, which comprises the following steps:A) crosslinking the hyaluronic acid by mixing the following components in a reaction chamber: water, hyaluronic acid (HA), a solution of alkali metal hydroxide, a crosslinking agent selected from polyethylene glycol diglycidyl ether (PEG DE), polypropylene glycol diglycidyl ether (PPG DE) and polytetramethylene glycol diglycidyl ether, the mixing time being comprised between 10 and 40 minutes;B) a neutralization step in which the crosslinked HA gel obtained from the crosslinked step A) is contacted with a neutralizing solution comprising the flowing components: water, hydrochloric acid HCl, a buffer agent, lidocaine or its derivatives functioning as an anesthetic agent.

These and other aspects, characteristics and advantages of the present disclosure will be better understood with reference to the following description, drawings and attached claims.

The various aspects and characteristics described in the present description can be applied individually where possible. These individual aspects, for example aspects and characteristics described in the attached dependent claims, can be the object of divisional applications.

It is understood that any aspect or characteristic that is discovered, during the patenting process, to be already known, shall not be claimed and shall be the object of a disclaimer.

