INJECTABLE MONOPHASE HYDROGELS

Abstract

An injectable monophase hydrogel is provided that is made of a reaction mixture of hyaluronic acids having different molecular weights.

Claims

1. An injectable polymeric composition comprising a homogenized crosslinked mixture, wherein the mixture comprises a first hyaluronic acid salt having an intrinsic viscosity of 600 ml/g crosslinked with a second hyaluronic acid salt having an intrinsic viscosity of 2800 ml/g.

2. The composition of claim 1, wherein hyaluronic acid is present at a concentration of between 10 and 40 mg/g.

3. The composition of claim 1, wherein hyaluronic acid is present at a concentration of between 20 and 30 mg/g.

4. The composition of claim 1, wherein hyaluronic acid is present at a concentration of 26 mg/g.

5. The composition of claim 1, wherein the composition has an injection force of 14 N through a 27 G ½ needle/100 N dynamometer.

6. The composition of claim 1, prepared by a process comprising the steps of: mixing the first hyaluronic acid salt and the second hyaluronic acid salt; cross-linking the mixture; and homogenizing the crosslinked mixture to obtain the injectable composition.

7. The composition of claim 6, wherein the weight ratio of the first hyaluronic acid salt to the second hyaluronic acid salt is 90:10.

8. The composition of claim 6, wherein the cross-linking is performed in an aqueous solvent.

9. The composition of claim 6, wherein the cross-linking is performed in the presence of an effective and non-excessive amount of at least one cross-linking agent.

10. The composition of claim 9, wherein the cross-linking agent is 1,4-butanediol diglycidyl ether (BDDE).

11. The composition of claim 6, wherein the weight ratio of the first hyaluronic acid salt to the second hyaluronic acid is 90:10, and wherein the cross-linking is performed in an aqueous solvent in the presence of an effective and non-excessive amount of at least one cross-linking agent.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In the drawing:

[0059] The FIGURE shows the curve tan.Math.delta=f (stressing frequency) for each of the four hydrogels prepared according to Examples 1 to 4.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

[0060] It is now proposed to illustrate the invention in its various features by means of the Examples below. More precisely: [0061] Example 1 illustrates the prior art (crosslinking of a polymer of high molecular weight); [0062] Example 2 illustrates the remarks made in the introduction of the present text (crosslinking of the same polymer of low molecular weight); and [0063] Examples 3 and 4 illustrate the invention (crosslinking of the same polymer of low and high molecular weight, used in different relative amounts).

[0064] These are preceded by a description of a few methods of measurement used to characterize the products in question.

Measurement of the Intrinsic Viscosity

[0065] The intrinsic viscosity of sodium hyaluronate (NaHA) (in ml/g) is determined according to the European Pharmacopeia for NaHA (2.2.9) using a capillary viscometer of the Ubbelohde type.

Measurement of the Ejection Force

No Specific Standard for this Test

[0066] The injectability of the gel based on NaHA is determined by measuring the force (in Newtons, N) required to eject the gel contained in a standard syringe, through a needle of 27 G½, at a rate of 12.5 mm/min. The tests were performed on a Verstatet® tensile device marketed by Mecmesin.

Measurement of the Remanence

[0067] The consistency of the gel is characterized at 25° C. by rheological measurement of the moduli of elasticity (G′) and viscosity (G″) as a function of the frequency (from 0.05 to 10 Hz), in the constant deformation domains, using a controlled stress rheometer (Carrimed CSL 500 from TA Instruments) and a cone-and-plate geometry of 4 cm 2°. This rheometer is checked and calibrated regularly. Degradation of the crosslinked gel results in a change in its consistency, which is measured by the increase in the parameter tangent delta (tan.delta=G″/G′) as a function of time, at a frequency of 1 Hz. The gels are degraded by being heated to a temperature of 93° C. The time after which tan.delta reaches a value of 0.65 (corresponding to a degraded gel state) is measured at this temperature. A remanence index of 1 (corresponding to said time) was arbitrarily set for the gel of Example 1. The remanence index values indicated for the other gels are relative values.

Appearance of the Hydrogel

Monophase

[0068] Microscopic appearance: no apparent liquid phase—fine fragmentation of the gel into facets

[0069] Macroscopic appearance: soft and free-flowing

Biphase

[0070] Microscopic appearance: gel fragments bathed in a low-viscosity liquid medium

[0071] Macroscopic appearance: “purée” that fragments very easily—no cohesion of the gel and no free-flowing appearance

Example 1: High-Molecular Weight Fibers

[0072] 3.5 g of sodium hyaluronate (NaHA) fibers of intrinsic viscosity 2800 ml/g and moisture content 8.7% are weighed out and 25.6 g of 0.25 N NaOH are added. Hydration of the fibers takes 2 h with regular manual homogenization using a spatula. 0.96 g of a solution of 1,4-butanediol diglycidyl ether (BDDE) diluted to ⅕ in 0.25 N sodium hydroxide solution is added to the reaction medium, this being followed by mechanical homogenization for 15 min before immersion in a thermostatically controlled bath at 50° C.±1° C.

[0073] R=[BDDE].sub.0/[NaHA].sub.0=6%; [NaHA].sub.i=105 mg/g

[0074] The reaction takes 2 h. The crosslinked product is neutralized to pH 7.2 in a phosphate buffer solution and then dialyzed. The concentration of the resulting hydrogel is then adjusted ([NaHA].sub.f=26 mg/g) and the hydrogel is mechanically homogenized before being packed into syringes and sterilized in an autoclave by means of moist heat.

[0075] Injection force after sterilization: 25 N

[0076] Remanence index of the hydrogel: 1.0

[0077] Monophase Hydrogel

Example 2: Low-Molecular Weight Fibers

[0078] 1.56 g of sodium hyaluronate (NaHA) fibers of intrinsic viscosity 600 ml/g and moisture content 5.5% are weighed out and 7.15 g of 0.25 N NaOH are added. Hydration of the fibers takes 2 h with regular manual homogenization using a spatula. 0.31 g of a solution of 1,4-butanediol diglycidyl ether (BDDE) diluted to 1/5 in 0.25 N sodium hydroxide solution is added to the reaction medium, this being followed by mechanical homogenization for 15 min before immersion in a thermostatically controlled bath at 50° C.±1° C.

[0079] R=[BDDE].sub.0/[NaHA].sub.0=6.8%; [NaHA].sub.i=174 mg/g

[0080] The reaction takes 2 h. The crosslinked product is neutralized to pH 7.2 in a phosphate solution and then dialyzed. The concentration of the resulting hydrogel is then adjusted ([NaHA].sub.f=26 mg/g) and the hydrogel is mechanically homogenized before being packed into syringes and sterilized in an autoclave.

[0081] Injection force after sterilization: 24 N

[0082] Remanence index of the hydrogel: 6.0

[0083] Biphase Hydrogel

Example 3: Mixture of Fibers

[0084] 0.763 g of sodium hyaluronate (NaHA) fibers of intrinsic viscosity 600 ml/g and moisture content 5.5% and 0.237 g of sodium hyaluronate fibers of intrinsic viscosity 2800 ml/g and moisture content 9.3% are weighed out. Proportions by weight in the mixture: 600/2800:77/23 (w/w).

[0085] The procedure remains identical to that of Example 2.

[0086] R=[BDDE].sub.0/[NaHA].sub.0=7%; [NaHA].sub.i=140 mg/g; [NaHA].sub.f=26 mg/g

[0087] Injection force after sterilization: 15 N

[0088] Remanence index of the hydrogel: 3.6

[0089] Monophase Hydrogel

Example 4: Mixture of Fibers

[0090] The experiment of Example 3 is repeated, modifying the proportions by weight. Proportions by weight in the mixture: 600/2800:90/10 (w/w).

[0091] The procedure is identical to that of Example 2.

[0092] R=[BDDE].sub.0/[NaHA].sub.0=6.5%; [NaHA].sub.i=140 mg/g; [NaHA].sub.f=26 mg/g

[0093] Injection force after sterilization: 14 N

[0094] Remanence index of the hydrogel: 7.7

[0095] Monophase Hydrogel

[0096] Said Examples are summarized in the Table below.

TABLE-US-00001 TABLE [NaHA].sub.0 = concentration of NaHA in the reaction medium at t.sub.0 [NaHA].sub.f = concentration of NaHA in the final hydrogel after reaction and dilution with a sufficient amount of phosphate buffer G′: modulus of elasticity of the final hydrogel (Pa .Math. s) G″: modulus of viscosity of the final hydrogel (Pa .Math. s) Carrimed CSL 500 rheometer Tan.delta = G ″/G′ n.sub.int.: intrinsic viscosity of the NaHA fiber/Ubbelohde viscometer F: ejection force of the gel in N through a 27 G½ needle/100 N dynamometer [NaHA ].sub.f n.sub.int. (ml/g) in final G′, G″, % = proportion by R = [NaHA].sub.0 gel Appearance tan.delta F .sub.ap ster Remanence n ° weight in mixture m.sub.BDDE/m.sub.NaHA mg/g mg/g * (1 Hz) 27 G½ index 1 (100%)2800 6% 105 26 M  143/65/0.40 25 1 2 (100%)600 6.8% 174 26 B 1300/100/0.08 24 6 3  (77%)600 + (23%) 2800 7 140 26 M  262/27/0.10 15 3.6 4  (90%)600 + (10%) 2800 6.5 140 26 M  571/41/0.07 14 7.7 * M = monophase B = biphase

[0097] The attached FIGURE shows the following curve:

[0098] Tan.Math.delta=f (stressing frequency) for each of the four hydrogels prepared according to Examples 1 to 4.

[0099] The rheological behavior of the hydrogels of the invention (Examples 3 and 4) is different from that of the hydrogel of the prior art (Example 1).

[0100] Furthermore, the hydrogels of the invention are monophase and thus very different from the hydrogel of Example 2 (biphase).