WO2012176224A1

WO2012176224A1 - Bio-mimetic and biodegradable polymeric cement

Info

Publication number: WO2012176224A1
Application number: PCT/IT2012/000182
Authority: WO
Inventors: Gianluca Ciardelli; Piergiorgio Gentile; Chiara TONDA-TURRO; Valeria Chiono; Clara MATTU; Ana Marina FERREIRA-DUARTE
Original assignee: Politecnico Di Torino
Priority date: 2011-06-23
Filing date: 2012-06-18
Publication date: 2012-12-27
Also published as: ITTO20110549A1

Abstract

A biomimetic and biodegradable injectable polymeric cement is described, composed of a mixture comprising a first amount (Q₁) of at least one natural polymeric material containing at least one free amino group in the repeating unit; a second amount (Q₂) of at least one inorganic phase adapted to reinforce such natural polymeric material; and a third amount (Q₃) of at least one crosslinking agent able to react with such free amino groups in order to perform a cross-linking of such natural polymeric material.

Description

BIOMIMETIC AND BIODEGRADABLE POLYMERIC CEMENT

The present invention refers to a biomimetic and biodegradable polymeric cement.

According to the state of the art, materials that are able to replace bone tissue have always been a relevant problem for the orthopaedic sector, especially for spinal and vertebral surgery.. . In this context, the use of implants made of autologus material (for example taken from the iliac ridge) is associated with severe problems and limitations from the mechanical point of view, while the efficacy of allografts remains even today a strongly debated and controversial issue in literature, in spite of their long history as bone replacements. Bone growth factors (BMP), used for example to prepare collagen-based bone replacements, show, on the other hand, an enormous potential arising from encouraging experimentations and preliminary clinical trials.

In spite of these opportunities arising from tissue engineering approaches, surgical techniques involve the use of synthetic materials called "cements", with _. particular reference to vertebroplasty , in which bone cement is injected through a small hole in the skin (percutaneously) into a fractured vertebra with the goal of relieving the pain of vertebral compression fractures. Cements must possess an additional fundamental property: inj ectability . Moreover, as reported in the literature, an optimum bone substitute for vertebroplasty must be easily applied, must have easily workable and handled components, the mixing procedure of such components must be simple and quick and the material must be injected percutaneously through cannulas or needles directly in the vertebral body. All. the above- mentioned requirements imply that the cement has a low initial viscosity, that must however always be controlled so that the cement itself does not become too liquid to leak out of the implant site. Moreover, radio-opacity is required, in order to make the cement flow detectable, the "setting time" (required time for the cement hardening) must be approximately 10 minutes and viscosity during such period must remain approximately constant. Moreover, the temperature required to conduct the polymerisation (curing temperature) must be as low as possible, because temperatures exceeding 40°C can generate necrosis of tissues surrounding the implant zone.

Although the optimum mechanical properties required have not so far been accurately defined, the cement should guarantee an immediate reinforcement of the vertebral body and allow, after a short time, the patient to correctly walk. Hardness and stress-resistance of the cement should then be similar to those of a healthy bone, in order to avoid excessive stress differences between the treated vertebrae and the healthy ones; the vertebral reinforcement obtained must not decay with time. The cement must not generate allergic reactions in neighbouring tissues and should be convenient from the point of view of the costs- efficiency ratio in order to allow a widespread application .

Currently, polymethylmetacrylate (PMMA) is the cement material of election in percutaneous treatments of spinal intervention radiology, due to its well-known biocompatibility and to the long experience in its use in the orthopaedic field. As known, PMMA is an acrylic homopolymer with straight chain (given by the repetition of metacrylate monomers) showing a good stiffness and stability, It is a glassy material at room temperature. PM A, has other important advantages in its uses in the orthopaedic field as bone replacement, , such as:

- intrinsic bio-inertia;

- good biocompatibility on medium/long range follow-up;

- familiarity of surgeons and orthopaedics with its use;

- easy handling and application;

- good resistance and stability from the bio- mechanical point of view if subjected to cyclic loads;

- very good cost-efficiency ratio.

In spite of this, PMMA also several drawbacks, including :

- no potential for biological remodelling and integration into the surrounding bone tissue;

- higher risk of fracture of vertebrae, adjacent to the treated ones, due to the different mechanical stiffness of the material with respect to a healthy bone;

- intrinsic citotoxicity of the (residual) methilmetacrylate (MMA) monomer;

- excessive fragility;

- high polymerisation temperatures (over 40°C) ;

- no bone-conductivity, namely it does not spontaneously promote on its surface the formation of new bone tissue;

Moreover, PMMA, once injected in the vertebrae, it causes the formation of a fine layer of fibrous tissue with time.

The state of the art describes a series of cements with alternative compositions to simple PMMA .

WO20100228358 discloses an injectable bone cement for filling bone vacuums with mechanical properties that are comparable with the sponge tissue of vertebral bodies. It is composed of an acrylic polymer and a radio-opaque inorganic agent: however, . it does not propose the use of biocompatible and biodegradable polymeric materials, based on natural polymers, and has components of acrylic nature, with all the problems related to their use.

O2008117043 discloses a bone cement composed of magnesium oxide, magnesium chloride and a polymer such as poly- ( ) caprolactone and does not provide for any type of release of active agents.

WO2007064304 discloses a biocompatible bone cement, based on chitosan and its derivatives, PMMA powders, MMA monomers in liquid form and suitable initiators for the polymerisation process. The cement also provides for the ^■ presence of antibiotics, like gentamicine or tobramicine. Even if such cement provides for the use .of natural polymeric materials, they anyway remain mixed with PMMA.

WO20100136120 discloses optimum compositions for regenerating bone tissue and methodologies for filling bone vacuums, promoting the fast fusion of fractured bones and a quick reinforcement of osteoporotic bones. Though such compositions provide, among the various used materials, for the use of chitosan, they do not include the use of genipin as cross-linking agent (glutaraldeyde and carbodiimides are mentioned as cross-linkers) and the release of anti-inflammatory agents is not provided .

US20100183699 discloses matrices of polymeric fibres cross-linked with genipine, but does not provide for the realisation of injectable cements.

WO2009073068 discloses a porous composite scaffold based on polyamines and tricalcium phosphate with materials, cross-linking technique and type of end device that are different from those of the present invention, since it does not propose the preparation of an injectable gel.

Chun-Hsu Yao et al.: "Biocompatibility and biodegradation of a bone composite containing tricalcium phosphate and genipin crosslinked gelatin", JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, vol. 69A, no. 4, 1 January 2004, pages 709-717, discloses a porous composite scaffold based on gelatine and tricalcium phosphate, cross-linked with genipin, from which the present invention differs due to the choice of the natural polymeric material (a mix of natural polymers instead of gelatin alone) and the characteristics of the final product, namely an injectable gel instead of a porous scaffold.

A. B. A. Araujo et al.: "Rheological , microstructural , and in vitro characterization of hybrid chitosan-polylactic acid/hydroxyapatite composites", JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A, vol. 88A, no. 4, 15 March 2009, pages 916-922 discloses a porous composite scaffold based on chitosan, poly (lactic acid) and hydroxyapatite, crosslinked with genipin, from which the present invention differs due to the choice of the polymeric material (natural polymeric mixture instead of a polymeric mixture containing both natural and synthetic polymers) and the end device, namely an injectable gel instead of a porous scaffold. Moreover, the presence of the synthetic polymeric material such as poly (lactic acid) implies the use of toxic solvents, the use of which is avoided in the inventive cement.

Meng Li et al: "Creation of macroporous calcium phosphate cements as bone substitutes by using genipin-crosslinked gelatin microspheres", JOURNAL OF MATERIALS SCIENCE: MATERIALS IN MEDICINE, KLUWER ACADEMIC PUBLISHERS, BO, vol. 29, no. 4, 4 December 2008, pages 925-934 discloses porous scaffold based on gelatin micro-spheres and calcium phosphate powders crosslinked with genipin, from which the present invention differs in that it does not propose gelatin as micro-spheres, but in a mixture with another natural polymer, chitosan, and the end device, namely an injectable gel instead of a porous scaffold.

Therefore, object of the present invention is solving the above prior art problems by providing a biomimetic and biodegradable polymeric cement based on natural polymeric materials and free from components of acrylic nature (PMMA), thereby overcoming the limitations associated with the intrinsic citotoxicity of PMMA and the risk of necrosis of surrounding tissue caused by its polymerisation temperature.

Another object of the present invention is providing a biomimetic and biodegradable polymeric cement that is able to induce specific cellular responses by mimicking the interaction mechanisms of biologic systems (biomimicry) and promoting the biomineralisation process (bioactivity) .

Moreover, an object of the present invention is providing a biomimetic and biodegradable polymeric cement that is able to perfectly adapt to a bone cavity defect to be preferably used in orthopaedic surgery, neurological surgery, periodontology, maxillo-facial surgery and for the treatment . of injuries caused by vertebrae osteoporosis .

Another object of the present invention is providing a biomimetic and biodegradable polymeric cement that can be injected.

Moreover, an object of the present invention is providing a biomimetic and biodegradable polymeric cement comprising at least one crosslinking agent, such as genipin, that is able to guarantee hardening . of the cement itself at a temperature close to the body temperature (37 °C) in a period of time included between 15 and 22 minutes.

Another object of the present invention is providing a biomimetic and biodegradable polymeric cement comprising an inorganic phase, such as β- tricalcium phosphate (TCP), having the same composition as that of the bone tissue, that is able to guarantee high bone-conductivity properties.

Moreover, an object of the present invention is providing a biomimetic and biodegradable polymeric cement containing nanoparticles capable of releasing, in a controlled way, at least one anti-inflammatory drug previously encapsulated therein.

The above and other objects are advantages of the invention, as it will appear from the following description, are obtained with a biomimetic and biodegradable polymeric cement as claimed in claim 1. Preferred embodiments and non-trivial variations of the present invention are the subject matter of the dependent claims.

It is intended that the claims are an integral part of the present specification.

It will be immediately obvious that numerous variations and modifications (for example related to the different composition) can be made to what it is described, without departing from the scope of the invention as appears from the enclosed claims.

The present invention will be better described herein below by some preferred embodiments thereof, provided as a non-limiting example.

The present invention therefore refers to a cement, to be preferably used in orthopaedic surgery, neurological surgery, periodontology, maxilla-facial surgery and for the treatment of vertebras osteoporosis lesions, made of a mixture composed, at least, of biocompatible and bioreabsorbed materials based on natural polymers, of an inorganic phase adapted to reinforce the polymeric component and at least one crosslinking agent .

The biomimetic and biodegradable polymeric cement according to the present invention has therefore as a major feature the fact that is allows the preparation of. an injectable gel, composed of a composite phase based on a mixture of suitably crosslinked natural polymers, and an inorganic phase, in order to obtain a material for vertebroplasty able to become gel at 37 °C in 12-15 minutes.

. For such purpose, the inventive biomimetic polymeric cement finds application in the field of vertebroplasty and it is formed after a chemical- physical transition from liguid phase at room temperature to gel phase at physiologic temperature (37 °C) .

Such biomimetic and biodegradable polymeric cement is therefore composed of a mixture comprising:

- a first amount Qi of at least one natural polymeric material containing at least one free amino group;

- a second amount Q₂ of at least one inorganic phase adapted to reinforce such natural polymeric material ;

- a third amount Q₃ of at least one crosslinking agent adapted to react with such free amino groups to perform the crosslinking of the mixture composing the cement according to the present invention.

■Preferably:

the first amount Qi of natural polymeric material is included between 20% and 40% in weight; the second amount Q₂ of inorganic phase is included between 80% and 60% in weight;

the third amount Q₃ of crosslinking agent is included between 5% and 7.5% wt/wt in weight (with respect to the first amount Qi in weight of the polymeric material being present in the mixture) .

Preferably, the natural polymeric material is chosen between . natural proteins or natural polysaccharides, containing free amino groups suitable for being crosslinked by the crosslinking agent .

Still more preferably, the natural polymeric material is chosen between collagen, gelatin or chitosan. Alternatively, the natural polymeric material can be a mixture of different materials chosen between natural proteins or natural polysaccharides, for example a mixture of collagen and/or gelatin and/or chitosan.

The inorganic phase that can be used to reinforce the polymeric component has, preferably, the same composition of the bone tissue in order to obtain a biomimetic cement with suitable mechanical properties, in particular, for the treatment of vertebral osteoporosis lesions: therefore. the inorganic phase can be chosen, preferably, among all calcium phosphates or bioactive glass/ceramics or glasses. Still more preferably, the inorganic phase is composed of β-tricalcium phosphate.

Preferably, the crosslinking agent is of natural origin and still more preferably such natural crosslinking agent is genipin. The natural crosslinking agent is therefore used for the hardening phase of the cement according to the present invention and to simulate the polymerisation process that occurs in PMMA-based acrylic cements.

Moreover, the mixture of the biomimetic and biodegradable polymeric cement can comprise at least one fourth amount Q₄ of at least one radio- opaque substance, such radio-opaque substance being preferably bismuth salicilate that, from in-vitro cellular tests performed by the Applicant, has proven to be biocompatible. Preferably, the fourth amount Q₄ of the radio-opaque substance is included between 10% and 25% wt/wt in weight (with respect to the first amount Q: in weight of the polymeric material being present in the mixture) .

Moreover, the mixture of the biomimetic and biodegradable polymeric cement can comprise at least one, fifth amount Q₅ of an anti-inflammatory and/or pain killer agent, encapsulated inside nanoparticles , preferably made of biodegradable synthetic polymeric materials, such as polycaprolactone, poly(lactic acid), poly (glicolic acid), polyurethanes and their copolymers. Object of such nanoparticles is favouring a controlled release with time of pain-killer or antiinflammatory drugs contained therein. Still more preferably,_. such nanoparticles contain indomethacin, an anti-inflammatory drug.

Preferably, the fifth amount Q₅ of nanoparticles containing the anti-inflammatory and/or pain-killer agent is included between 5% and 20% wt/wt in weight (with respect to the first amount Qi in weight of the polymeric material being present in the mixture) . The nanoparticles are preferably made through a solvent displacement method or by oil-in- water emulsification methods.

As an example, from tests performed by the Applicant, the optimal composition of the mixture composing the cement according to the present invention included is described in the following Example 1.

EXAMPLE 1

The cement according to the present invention has been obtained by mutually mixing:

- 30% wt/wt of a polymeric mixture with 3% wt/vol of chitosan and collagen (weight ratio 2:1);

- 70% wt/wt (with respect to the amount in weight of the polymeric material being present in the mixture) of β-tricalcium phosphate;

- 7.5% wt/wt (with respect to the amount in weight of the polymeric material being present in the mixture) of genipin;

- 15% wt/wt (with respect to the amount in weight of the polymeric material being present in the mixture) of bismuth salicylate;

- 10% ' wt/wt (with respect to the amount in weight of. the polymeric material being present in the mixture) of nanoparticles of polycaprolactone charged with indomethacin .

Claims

1. Biomimetic and biodegradable natural-based polymeric cement suitable for being injected, to be applied in the field of vertebroplasty, characterised in that it .undergoes a chemical- physical transition from liquid phase- at room temperature to gel phase at physiologic temperature, namely 37 °C.

2. Cement according to claim 1, characterised in that it is composed of a mixture comprising:

- a first amount, Q of at least one natural polymeric material containing at least one free amino group in the repeating unit;

- a second amount, Q₂, of at least one inorganic phase adapted to reinforce the above stated natural polymeric material;

- a third amount, Q₃, of at least one cross- linking agent adapted to react with above mentioned free amino groups in ^' order to perform a crosslinking of said mixture.

3. Cement according to claim 1, characterised in that said first amount, Q_x, is included between 20% and 40% in weight, said second amount, Q₂, is included between 80% and 60% in weight and said third amount, Q₃, is included between 5% and 7.5% wt/wt with respect to said first amount, Q_lr in weight of said polymeric material being present in said mixture.

4. Cement according to claim 1, characterised in that said natural polymeric material is chosen between natural proteins or natural polysaccharides containing said free amino groups . adapted to be crosslinked by said crosslinking agent.

5. Cement according to claim 4, characterised in that said natural polymeric material is chosen among collagen, gelatin or chitosan.

6. Cement according to claim 4 or 5, characterised in that said natural polymeric material is a mixture of different materials chosen between natural proteins or natural polysaccharides, preferably a mixture of collagen and/or gelatin and/or chitosan.

7. Cement according to claim 1, characterised in that said inorganic phase has a similar composition of that of the bone tissue.

8. Cement according to claim 1, characterised in that said inorganic phase is chosen between calcium phosphates or bioactive glass/ceramics or glasses.

9. Cement according to claim 8, characterised in that said inorganic phase is β-tricalcium phosphate.

10. Cement according to claim 1, characterised in that said crosslinking agent is of natural origin.

11. Cement according to claim 1, characterised in that said cross-linking agent is genipin.

12. Cement according to claim 1, characterised in that it comprises at least one fourth amount, Q₄, of at least one radio-opaque substance.

13. Cement according to claim 12, characterised in that said fourth amount, Q₄, is included between

10% and 25% wt/wt with respect to said first amount, Q_lf in weight of said polymeric material being present in said mixture.

14. Cement according to claim 12, characterised in that said radio-opaque substance is bismuth salicilate .

15. Cement according to claim 1, characterised in that it comprises at least one fifth amount, Q₅, of nanoparticles containing an anti-inflammatory and/or pain-killer agent.

16. Cement according to claim 15, characterised in that said fifth amount, Q₅, is included between 5% and 20% wt/wt with respect to said first amount, Qi , in weight of said polymeric material being present in said mixture.

17. Cement according to claim 15, characterised in that said anti-inflammatory and/or pain-killer agent is charged into nanoparticles composed of biodegradable synthetic polymeric material suitable for the controlled release of pain-killer or antiinflammatory drugs contained therein.

18. Cement according to claim 17, characterised in that said biodegradable synthetic polymeric material is chosen among polycaprolactone, poly (lactic acid), poly ( glicolic acid), polyurethanes and their copolymers.

19. Cement according to claim 17, characterised in that said nanoparticles contain indomethacin .