ES2372341B1 - COMPOSITE MATERIAL OF POLYMER AND MAGNESIUM PARTICLES FOR BIOMEDICAL APPLICATIONS. - Google Patents

Abstract

Composite material of polymer and magnesium particles for biomedical applications. # The present invention relates to a polymer matrix material and magnesium particles, biocompatible and reabsorbable with medical applications in particular for application as osteosynthesis material and bone tissue engineering for Bone tissue regeneration.

Description

Composite material of polymer and magnesium particles for biomedical applications.

The present invention relates to a polymeric matrix material and biocompatible magnesium particles and reabsorbable with medical applications, in particular as osteosynthesis material and in bone tissue engineering.

Prior art

Bone is a tissue that is renewed continuously throughout the life of the individual through the process of bone remodeling. This continuous remodeling allows the bone to regenerate after being damaged by creating a tissue identical to the original. Usually, bone dynamics is sufficient to repair fractures and reconstruct common defects. However, after the destruction of large volumes of bone mass, as in the case of severe trauma, tumors, infections and developmental disorders, the damaged tissue is not able to regenerate on its own. In these cases, a bone graft or a synthetic substitute is required to help or complete the repair of skeletal deficiency. The best bone substitute is the bone itself, either from the patient himself or from a donor. However, there are problems associated with the use of bone grafts, such as the insufficient amount of tissue available when dealing with the same patient or the risk of disease transmission in the case of donations. As an alternative, Tissue Engineering proposes the development of synthetic materials of different nature (polymers, ceramics or metals) on which to grow cells to be implanted later in the patient. The search for new strategies and materials for the repair and regeneration of damaged bone tissue is also a priority motivated by the socio-economic challenge that derives from the increase in bone pathologies associated with the aging of the population in advanced societies.

In the 50s bioinert materials were sought, with minimal interaction with the biological environment. The second generation of biomaterials, in the eighties, led to the development of bioactive materials that pursued a controlled reaction with the environment. Since 2000, the objective has been to develop third generation biomaterials that allow tissue regeneration instead of replacement. In the case of bone tissue repairs, the materials should preferably be osteoconductive, allowing bone growth into the material, biocompatible, that is, that they are tolerated by the surrounding tissue and do not promote an adverse response, and as far as Possible should incorporate osteoinductive molecules, capable of promoting bone formation. Many of the materials developed are bioactive ceramics, bioactive glasses, synthetic or biological polymers, and their compounds.

Bioactive inorganic materials of clinical interest have a composition similar to the mineral phase of bone. Bioactive glasses, for example, when immersed in biological fluids quickly produce a layer of bioactive apatite that can bind to biological tissue. In addition, they can be formulated to release Si ions in a controlled manner, capable of increasing cell differentiation and osteogenesis. The reabsorption rate of bioactive and bioceramic glasses can be adjusted with crystalline hydroxyapatite for long periods of time, while there are other calcium phosphates that have a greater capacity to reabsorb but little resistance to withstand loads.

Biological polymers such as collagen and hyaluronic acid are materials in use for tissue reconstruction in clinical applications. However, its weakness is related to the potential risk of disease transmission and the difficulties in handling it. On the other hand, synthetic polymers such as polycaprolactone (PCL), polyfumarates, polylactic acid (PLA), polyglycolic acid (PGA) and their copolymers (PLGA), are currently used for the manufacture of sutures, nails, screws and plates , constituting a very versatile alternative. Although its degradation products are metabolized and eliminated by the body, when they are in very high concentrations they can cause a local decrease in pH, compromising the viability of the tissues.

In general, the fragile nature of bioactive ceramic materials and the low mechanical properties of biodegradable polymers discourage their use in applications where high loads are required, as in most orthopedic applications.

Composite materials of organic-inorganic origin tend to mimic the nature of the bone by combining the toughness of a polymer with the compressive strength of a ceramic, which results in materials with better mechanical properties and degradation profiles. As reinforcement materials, both hydroxyapatite and biovidrios have been used (ME Navarro, Development and Characterization of Biodegradable Materials for Bone Regeneration, Doctoral Thesis, UPC, 2005). The use of composite materials loaded with metals has been little investigated in this field. However, it seems to be an effective way to control metal degradation, as observed during the degradation of Cu nanocomposites with low density polyethylenes (S Cai, Xia X, Xie C, Biomaterials 26 (2005) 2671-2676 ).

Note the development of degradable metal materials for components subjected to loads. Mg alloys, widely investigated today, were introduced in the first half of the last century. Its main advantage in relation to other metal biomaterials is its low density (1.7-2.0 g / cm3). Additionally, its fracture toughness is superior to that of ceramic materials, with an elastic modulus value (41-45 GPa) very close to that of natural bone (<20 GPa). One of the problems associated with its use was related to its rapid rate of corrosion in vivo (D. Williams, Med. Device Technol. 17 (2006), 9, p8-10), which produced a significant accumulation of hydrogen (1 liter per gram of Mg). Due to this problem, its use became obsolete with the development of stainless steels. At present there are numerous efforts being made to decrease its degradation rate and increase its mechanical properties (MP Staiger, AM Pietak, J Huadmai, G Dias, Biomaterials 27 (2006) 1728-1734 and in WD Müller, ML Nascimento , M Sedéis, M. Corsico, LM Gassa, MAF Lorenzo de Mele, Mat. Res. 10 (2007) 5-10] Unfortunately this is being achieved from the introduction of alloy elements that, once the implant is degraded , could pose biocompatibility problems.

Tissue Engineering pursues the use of scaffolds or material structures, decorated or not with bioactive molecules, on which to grow cells to generate implantable constructs that promote tissue regeneration in the patient. This approach, which is part of what is known as Regenerative Medicine, seeks a substrate that could ideally be biodegradable, so that the tissue regeneration was as complete as possible, at least in most applications, and in the case of bone tissue regeneration, which is necessarily porous to ensure osteoconduction and vascularization of the new tissue. The vast majority of scaffolds developed for applications in Tissue Engineering, are based on polymeric materials. There are several processing techniques to generate three-dimensional structures with varying degrees of porosity and surface characteristics.

An essential aspect to guarantee osteoconduction in scaffolding is that its porosity is interconnected (Hing et al. J. Mater. Sci .: Mater. Med. 16, (2005) 469-475), to allow not only cell colonization , but also adequate vascularization. This consideration requires that the pores have a size greater than 100 microns in diameter so that the precursor cells of the bone-forming cells colonic deep areas of the material and regenerate a three-dimensional structure as close as possible to that of the trabecular bone. Thus, the osteoconduction process will be favored by a high porosity of the polymer matrix. It is considered that for proper colonization and vascularization the pore size should be in the range of 200 to 500 μm. However, this requirement is limited by the need for the scaffold to have an adequate mechanical resistance to compression and an elastic modulus value equal to or slightly greater than that of the bone to prevent it from collapsing once subjected to in vivo loads. The effect of porosity on the elastic modulus is different for different types of materials, the only metallic materials offering a combination of stiffness and porosity close to those of bone (40-80%). Consequently, there have been numerous recent studies with porous materials of a metallic nature (Ti, Mg, NiTi). Among them, only Mg can be considered biodegradable. Its use in aqueous environments is discouraged by the rapid degradation rate, as previously mentioned.

Description of the invention

The present invention provides biodegradable material for the manufacture of useful devices such as osteosynthesis material or for bone regeneration, and its method of production.

A first aspect of the present invention refers to a material (from now on material of the invention) comprising the mixture of:

to.

a polymeric matrix comprising a biodegradable polymer, and

b.

magnesium particles

This invention focuses on the development of hybrid materials based on biocompatible and biodegradable commercial polymers loaded with Mg particles, with a degradation profile modulated by the volume and size fraction of the Mg particles. It is expected that, in this way, the rate of hydrogen release during the degradation process will be tolerated by human tissues, allowing the repair and / or regeneration of bone tissue as its reabsorption occurs. Among the advantages of using Mg, its biocompatibility and osteoconductive properties stand out. In addition, the ions released during the degradation process are soluble in physiological media and are easily excreted in the urine.

In a preferred embodiment the biodegradable polymer is selected from polycaprolactone (PCL), polyfumarates, polylactic acid (PLA), polyglycolic acid (PGA) and any combination thereof.

In a more preferred embodiment the biodegradable polymer is a copolymer formed by at least polylactic acid. And in a more preferred embodiment the weight ratio of polylactic acid to copolymer is between 100: 0 to

60:40

Preferably the magnesium particles have a size between 50 and 250 μm if their use in tissue engineering (bone regeneration) is considered, and preferably the magnesium particles have a size less than 50 μm if their use as osteosynthesis material is considered (bone repair).

In another preferred embodiment the volume percentage of the magnesium particles with respect to the total material is less than or equal to 70%.

The polymer / Mg assembly has mechanical characteristics (strength, modulus) superior to that of dense or porous resorbable polymers. The selection of the polymer will depend on its application, using semi-crystalline forms (L-PLA), when greater mechanical performance (or long degradation periods), or amorphous forms (DL-PLA) are required since it is constructed by the two isomeric forms of the PLA, if lower mechanical loads are required (or shorter resorption times). Copolymers could also be used to modulate both mechanical properties and degradation rates. For example, the L-PLA has an elastic modulus of 3 GPa, while combining the DL-PLA with polycaprolactone (PCL) in a 60PLA / 40PCL ratio, a manually moldable material is obtained.

A second aspect of the present invention relates to a process for obtaining the material of the invention, which comprises the steps:

to.

mixing the matrix forming polymer and the magnesium particles with an organic solvent.

b.

evaporation of the organic solvent from the product obtained in step (a), and

C.

processing of the product obtained in step (b).

In a preferred embodiment the mixing of step (a) is performed by a technique that is selected from: gel casting, dissolution and casting with particle release, membrane lamination, phase separation, lyophilization

or union of fi bers.

Preferably the solvent used in step (a) is chloroform. While any organic solvent that facilitates the dispersion of magnesium particles in the polymer matrix can be used.

Preferably evaporation of the solvent in step (b) is performed by orbital agitation. After evaporation a laminar product can be obtained which can be prepared by chopping prior to processing, this method being any polymer forming method known to any person skilled in the art.

In another preferred embodiment the processing of step (c) is a thermomechanical processing of compaction and molding. In a more preferred embodiment the thermomechanical processing of step (c) is performed at a temperature range of between 100 and 200 ° C. And in an even more preferred embodiment the thermomechanical processing of the stage

(c) is performed at a temperature range between 130 and 170 ° C.

In a third aspect, the present invention relates to the use of the material of the invention, for the manufacture of a biomedical implant or device.

Preferably the implant is to allow bone repair, as an osteosynthesis material, more preferably when the magnesium particles are less than 50 μm in size, or preferably the implant is for bone tissue regeneration in bone tissue engineering, more preferably Magnesium particles have a size between 50 and 250 μm.

Being a dense material, the possibility of the polymer / Mg set collapsing and modifying its architecture due to the effect of mechanical loads in vivo would be lower, which would facilitate it to play its role as scaffold while tissue regeneration and vascularization occurs bone on the surface. The use of a completely biodegradable material offers important advantages in relation to the use of conventional metal alloys such as elimination of the effect of load protection (“stress shielding”) and the possibility of post-operative diagnosis using electromagnetic fields. Throughout the description and the claims the word "comprises" and its variants are not intended to exclude other technical characteristics, additives, components or steps. For those skilled in the art, other objects, advantages and features of the invention will be derived partly from the description and partly from the practice of the invention. The following examples and drawings are provided by way of illustration, and are not intended to be limiting of the present invention.

Description of the fi gures

Fig. 1. Optical microscopy images corresponding to: A) appearance of the Mg-loaded polymer specimens; and B) cross section thereof; Image C corresponds to an electronic scanning image showing a detail of the polymer / Mg interface.

Fig. 2. Variation of load as a function of depth for PLA and PLA / Mg.

Fig. 3. Voltage-displacement curve for PLA with and without magnesium.

Fig. 4. Viability of human mesenchymal stem cells cultured on PLA / Mg samples. The results are expressed as a percentage of the cell viability measured after 1 day, to which an arbitrary value of

100

Examples

The invention will now be illustrated by tests carried out by the inventors, which show the specificity and effectiveness of the material of the invention and its method for obtaining a bone regeneration biomaterial.

Material Synthesis

A composite material of polylactic acid (PLA) and a nominal volume fraction of 30% have been prepared. The mixture has been produced after dissolving the polymer in chloroform. Once dissolved it has been mixed with the Mg powder, with an average size of about 250 microns, and then evaporation of the solvent. The images in Figure 1 show the appearance of the material after mixing (A), and the cross sections examined in the optical (B) and electron microscope (C).

Once dried, it has been chopped and then extruded at a temperature of 160 ° C. The microstructural analysis shows a homogeneous distribution of the Mg powder.

Measurement of material properties

The mechanical properties of polymers are generally insufficient for use as a biomaterial, whether for application as scaffolding, as filler material, etc. Therefore, the combination of polymer / metal mechanical properties is necessary to increase the mechanical performance that the polymer alone is unable to offer, and resemble those of the bone.

Mechanical characterization has been carried out through instrumented indentation techniques, using a Nanotest 600 ultramicroindentifier. The use of this equipment allows the hardness and elastic modulus of the composite material to be measured simultaneously using the Oliver & Pharr model, using The following equations.

In equation (1) the parameters Pmax and Ac represent the maximum load and the projected contact area between the indenter and the sample, respectively. In equation (2), ν and νi, and E and Ei, denote Poisson's relationship and Young's modulus of the sample and the indenter's head, respectively. Er refers to the value of the reduced Young's modulus corresponding to the sample. The measurements have been made with a Berkovich type diamond tip. Its Young's modulus (Ei) and Poisson's coefficients (νi) are 1141 GPa and 0.07, respectively.

Indentation tests have been carried out on different samples of PLA and PLA / Mg using in both cases loads of 500 mN, deformation speeds in the loading and unloading curves of 12.5 nms − 1 and 15 s of pressure with the value maximum reached in the load curve (500 mN). Figure 2 shows the loading / unloading curves for the polymer with and without magnesium. As you can see in the image, the loading and unloading curves have substantial differences. On the one hand, the greater penetration in the case of the PLA shows its lower hardness. On the other hand, the slope corresponding to the discharge curve for the composite material is greater than in the case of the polymer, which indicates that the Young's modulus corresponding to the composite material is greater than that of the polymer.

Table 1 shows the values of the hardness (H), the Young's reduced module (ER), and the Young's module

(E) calculated from equation 2 for the polymer with and without magnesium. ν represents the value of the Poisson coefficient used to calculate the module.

TABLE 1

Hardness and module values determined from ultra-microindentation measurements

The elastic modulus of the PLA depends on the degree of polymerization of the monomer chains. It should be noted that with a volume fraction of 30% Mg, the value of the elastic modulus almost triples, approaching the value corresponding to the cortical bone.

Compression tests show a clear increase in the maximum tension reached during the test. In Figure 3 it can be seen how during the compression test the polymer without magnesium does not undergo any deformation, thus presenting a fragile rupture, however the magnesium reinforced polymer manifests this plastic deformation similar to that presented by the metals. In none of the compression tests carried out on the PLA / Mg samples, breakage was achieved, showing deformation in the skipjack.

Table 2 shows the values of elastic limits (σ0) and maximum load (σmax) recorded in the compression test.

TABLE 2

Average values of elastic limit (σ0) and maximum load (σmax) recorded in the compression test

By comparing the values of the Young's modulus and the tension corresponding to the elastic limit, obtained for the polymer reinforced with magnesium with those corresponding to the trabecular bone, it can be verified how the reinforcement with magnesium allows obtaining polymer / metal composite materials with mechanical properties similar to those of the human bone, thus allowing a better load transfer between this arti fi cial material and the bone tissue.

Biocompatibility tests

In vitro biocompatibility of the magnesium reinforced polymer has been tested using human mesenchymal stem cells from bone marrow. The cells were grown for up to 15 days on the PLA / Mg samples, previously incubated in culture medium for at least 1 h. After these incubation times the metabolic activity was quantified, as a parameter associated with cell viability, using the commercial reagent AlamarBlueTM. Figure 4 shows that cell viability increases with the culture time on polymer / metal composites.

Claims (20)

1. Material comprising the mixture of:

to.

a polymeric matrix comprising a biodegradable polymer, and

b.

magnesium particles

2.

Material according to claim 1, wherein the biodegradable polymer is selected from polycaprolactone, polyfumarates, polylactic acid, polyglycolic acid and any combination thereof.

3.

Material according to any one of claims 1 or 2, wherein the biodegradable polymer is a copolymer formed by at least polylactic acid.

Four.

Material according to claim 3, wherein the weight ratio of polylactic acid to copolymer is between 100: 0 to 60:40.

5.

Material according to any one of claims 1 to 4, wherein the magnesium particles have a size between 50 and 250 μm.

6.

Material according to any of claims 1-4, wherein the magnesium particles have a size less than 50 μm.

7.

Material according to any one of claims 1 to 6, wherein the volume percentage of the magnesium particles with respect to the total material is less than or equal to 70%.

8.

Method of obtaining the material according to any of claims 1 to 7, comprising the steps:

to.

mixing the matrix forming polymer and the magnesium particles with an organic solvent.

b.

evaporation of the organic solvent from the product obtained in step (a), and

C.

processing of the product obtained in step (b).

9.

Method according to claim 8, wherein the mixing of step (a) is carried out by a technique that is selected from: gel casting, dissolution and casting with particle release, membrane lamination, phase separation, lyophilization or bonding of fibers. .

10.

Process according to any of claims 8 or 9, wherein the solvent used in step (a) is chloroform.

11. Process according to any of claims 8 to 10, wherein evaporation of the solvent in the step (b) is performed by orbital agitation.

12.

Method according to any of claims 8 to 11, the processing of step (c) is a thermomechanical processing of compaction and molding.

13.

Process according to claim 12, wherein the thermomechanical processing of step (c) is carried out at a temperature range between 100 ° C and 200 ° C.

14.

Method according to claim 13, wherein the thermomechanical processing of step (c) is carried out at a temperature range between 130 ° C and 170 ° C.

fifteen.

Use of the material according to any of claims 1-7, for the manufacture of a biomedical implant or device.

16.

Use of the material according to claim 15, wherein the implant is for bone tissue repair as osteosynthesis material.

17.

Use of the material according to claim 16, wherein the magnesium particles are less than 50 μm in size.

18.

Use of the material according to claim 15, wherein the implant is for the regeneration of bone tissue in bone tissue engineering.

19.

Use of the material according to claim 18, wherein the magnesium particles are between 50 and 250 μm in size.

SPANISH OFFICE OF THE PATENTS AND BRAND Application no .: 201030950 SPAIN Date of submission of the application: 06.21.2010 Priority Date: REPORT ON THE STATE OF THE TECHNIQUE 51 Int. Cl.: A61L27 / 44 (2006.01) A61F2 / 28 (2006.01) RELEVANT DOCUMENTS

Category

Documents cited Claims Affected

X

US 2002127265 A1 (BOWMAN et al.) 12.09.2002, 1-3,15,16,18

paragraphs [0010], [0028] - [0033], [0037] - [0039], claims 9,12.

X

US 2008249638 A1 (ASGARI) 09.10.2008, 1,2,5,6,15-19

paragraphs [0002], [0037], [0054] - [0059], [0067], [0077].

TO

US 2006024377 A1 (YING et al.) 02.02.2006, 1-19

claims 1,4,5,20,72-76.

TO

US 2007191963 A1 (WINTERBOTTOM et al.) 16.08.2007, 1-19

paragraphs [0008] - [0011].

Category of the documents cited X: of particular relevance Y: of particular relevance combined with other / s of the same category A: reflects the state of the art O: refers to unwritten disclosure P: published between the priority date and the date of priority submission of the application E: previous document, but published after the date of submission of the application

This report has been prepared • for all claims • for claims no:

Date of completion of the report 13.10.2011

Examiner N. Vera Gutiérrez Page 1/4

REPORT OF THE STATE OF THE TECHNIQUE Application number: 201030950 Minimum documentation sought (classification system followed by classification symbols) A61L, A61F Electronic databases consulted during the search (name of the database and, if possible, terms of search used) INVENES, EPODOC, WPI, CAS, EMBASE, BIOSIS, MEDLINE, NPL State of the Art Report Page 2/4  WRITTEN OPINION Application number: 201030950 Date of Completion of Written Opinion: 13.10.2011 Statement

Novelty (Art. 6.1 LP 11/1986)

Claims Claims 4, 7-14 1-3, 5, 6, 15-19 IF NOT

Inventive activity (Art. 8.1 LP11 / 1986)

Claims Claims 4, 7-14 1-3, 5, 6, 15-19 IF NOT

The application is considered to comply with the industrial application requirement. This requirement was evaluated during the formal and technical examination phase of the application (Article 31.2 Law 11/1986).  Opinion Base.- This opinion has been made on the basis of the patent application as published. State of the Art Report Page 3/4  WRITTEN OPINION Application number: 201030950 1. Documents considered.- The documents belonging to the state of the art taken into consideration for the realization of this opinion are listed below.

Document

Publication or Identification Number publication date

D01

US 2002127265 A1 12.09.2002

D02

US 2008249638 A1 09.10.2008

2. Statement motivated according to articles 29.6 and 29.7 of the Regulations for the execution of Law 11/1986, of March 20, on Patents on novelty and inventive activity; quotes and explanations in support of this statement The invention relates to a material comprising the mixture of: a) a polymeric matrix comprising a biodegradable polymer and b) magnesium particles, as well as its method of obtaining and its use for the manufacture of a biomedical implant or device. Document D01 discloses biocompatible porous implants for use in tissue repair. The implants comprise a bioabsorbable polymer foam, with a porous open-cell structure, and a reinforcing material. In the examples, devices based on polycaprolactone / polylactic acid foams are prepared. As a reinforcing material, solid particles such as magnesium can be added (paragraphs [0038], [0039]. Document D02 refers to a biodegradable implant for the repair of bone or cartilaginous tissue, comprising a porous matrix with an open pore structure with a multitude of interconnected spaces, whose channels are filled with particles of metallic material (paragraph [0002]) . These particles are selected from biodegradable metals or alloys, for example, magnesium (paragraphs [0054] - [0059]) and have a particle size between 0.5 nm and 5000 microns, preferably between 30 nm and 250 microns (paragraph [ 0067]). The polymeric material constituting the porous matrix can be selected from derivatives of polylactic acid, polyglycolic acid or polycaprolactone (paragraph [0077]). Therefore, as disclosed in D01 and D02, it is considered that the invention as defined in claims 1-3, 5, 6, 15-19 does not meet the requirements of novelty and inventive activity (Articles 6.1 and 8.1 LP) . No documents have been found that disclose a process for preparing the material of the application as defined in claim 8, nor materials with the compositional characteristics detailed in claims 4 and 7. Therefore, it is considered that claims 4, 7-14 are new and involve inventive activity (Articles 6.1 and 8.1 LP). State of the Art Report Page 4/4