WO2011161292A1

WO2011161292A1 - Polymer and magnesium particle material for biomedical applications

Info

Publication number: WO2011161292A1
Application number: PCT/ES2011/070440
Authority: WO
Inventors: José Luis GONZÁLEZ CARRASCO; Marta MULTIGNER DOMÍNGUEZ; Marcela LIEBLICH RODRÍGUEZ; Marta MUÑOZ HERNÁNDEZ; Emilio Frutos Torres; Laura SALDAÑA QUERO; Nuria VILABOA DÍAZ
Original assignee: Consejo Superior De Investigaciones Científicas (Csic); Ciber-Bbn; Fundación De La Investigación Biomédica Del Hospital Universitario De La Paz; Fundación Universidad Alfonso X El Sabio
Priority date: 2010-06-21
Filing date: 2011-06-20
Publication date: 2011-12-29
Also published as: ES2372341B8; ES2372341A1; ES2372341B1

Abstract

The present invention relates to a polymeric matrix and magnesium particle material that is biocompatible and absorbable and has medical applications, specifically as a material for osteosynthesis and in tissue engineering for regenerating dry tissue.

Description

COMPOSITE MATERIAL OF POLYMER AND MAGNESIUM PARTICLES FOR BIOMEDICAL APPLICATIONS

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

STATE OF THE PREVIOUS TECHNIQUE The search for new strategies and materials for the repair and regeneration of damaged bone tissue is 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. 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. 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. However, its weakness is related to the potential risk of disease transmission and Difficulties handling 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 appears 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 / cm ³ ). Additionally, its fracture toughness is higher than 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 Melé, Mal Res. 10 (2007) 5-10] Unfortunately this is being achieved from the introduction of alloy elements that, once the implant has been degraded, They could pose biocompatibility problems.

Tissue Engineering pursues the use of porous scaffolds, decorated or not with bioactive molecules, on which to grow cells to generate implantable constructs that promote tissue regeneration in the patient. The vast majority of scaffolds developed are based on polymeric materials.

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. It is considered that for proper colonization and vascularization the pore size should be in the range of 200 to 500 μιτι. 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, with metallic materials being the only ones that offer a combination of stiffness and porosity close to those of the 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 relates 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 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.

The biodegradable polymers of the present invention may be natural or synthetic and, optionally, may include one or more bioactive agents. In a preferred embodiment the biodegradable polymer may be, but not only, polycaprolactone (PCL), polyfumarates, polylactic acid (PLA), polyglycolic acid (PGA) or any combination thereof. Preferably, 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 comprising at least polylactic acid. And in a more preferred embodiment the weight ratio of polylactic acid to the other component of the copolymer is between 100: 0 to 60:40.

The magnesium present in the material of this invention may be present with or without alloy elements, it being preferable that it does not contain alloy elements.

Preferably the magnesium particles have a size between 50 and 500 μιτι if their use in tissue engineering (bone regeneration) is considered. More preferably, the magnesium particles have a size between 50 and 250 μιτι. On the other hand, the magnesium particles preferably have a size of less than 50 μιτι if their use as osteosynthesis material (bone repair) is considered.

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-polylactic acid, also known as L-PLA, PLLA or L-PLLA), when greater mechanical performance (or long degradation periods), or amorphous forms ( DL-PLA) since it is built by two isomeric forms of PLA, if lower mechanical loads (or shorter resorption times) are required. 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 of the matrix forming polymer and magnesium particles, and

b. processing of the product obtained in step (a).

In a preferred embodiment the mixing of step (a) is carried out by a technique that can be, but not exclusively, gel casting, dissolution and casting with particle release, membrane lamination, phase separation, lyophilization, fiber bonding, extrusion, etc. Preferably, 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, fiber bonding and extrusion.

Preferably step (a) comprises the addition of an organic solvent. More preferably, the solvent employed is chloroform. While any organic solvent that facilitates the dispersion of magnesium particles in the polymer matrix can be used.

In another preferred embodiment, the process comprises an additional stage of evaporation of the solvent used in step (a) and subsequent processing of the product obtained in this additional stage. Preferably, evaporation is performed by orbital agitation. After evaporation, a laminar product can be obtained, which can be prepared by cutting before processing. Any polymer forming method known to any person skilled in the art is processed.

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

In a fourth aspect, the present invention relates to a biomedical implant or device manufactured from the material of the present invention.

Preferably the implant is to allow bone repair, as an osteosynthesis material, more preferably when the magnesium particles are smaller than 50 μιτι. According to another preferred embodiment, the implant is for the regeneration of bone tissue in bone tissue engineering, more preferably the magnesium particles have a size between 50 and 500 μιτι, it being preferable that the magnesium particles have a size between 50 and 250 μιτι. Being a dense material, the possibility that the polymer / Mg set collapse and modify 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 regeneration and vascularization of the bone tissue 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 FIGURES

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 the load as a function of the depth for the L-PLLA and the L-PLLA / Mg.

Fig. 3. Voltage-displacement curve for the L-PLLA with and without magnesium.

Fig. 4. Viability of human mesenchymal stem cells cultured on L-PLLA / Mg samples. The results are expressed as a percentage of the cell viability measured after 1 day, to which an arbitrary value of 100 was assigned.

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 of obtaining for the manufacture of a bone regeneration biomaterial. Material Synthesis

A polylactic acid composite material in its L-isomeric form (L-PLLA) and a nominal volume fraction of 30% Mg has 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 cut and then extruded by extrusion at a temperature of 160 ° C. Microstructural analysis shows a homogeneous distribution of 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. The mechanical characterization has been carried out through instrumented indentation techniques, which allow the hardness and elastic modulus of the composite material to be measured simultaneously. The measurements have been made using a Nanotest 600 ultra-microindentator with a Berkovich type diamond tip. Its Young's modulus (Ei) and Poisson's coefficients (v¡) are 1,141 GPa and 0,07, respectively. Indentation tests have been carried out on different samples of L-PLLA and L-PLLA / Mg using loads of 500 mN, deformation rates in the loading and unloading curves of 12.5 nms ^"1 and 15 s of pressure with the maximum value reached in the load curve (500 mN) As can be seen in Figure 2, the loading and unloading curves have substantial differences, on the one hand, the greater penetration in the case of the L-PLLA puts it 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 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 reduced Young's modulus (E _R ), and the Young's modulus (E) for the polymer with and without magnesium, v represents the value of the Poisson coefficient used for the calculation of the module.

Table 1: Hardness and module values determined from ultra-microindentation measurements.

The elastic modulus of the L-PLLA 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 you can see as during the compression test the polymer without magnesium does not undergo any deformation, thus presenting a fragile rupture, however the polymer reinforced with magnesium shows plastic deformation similar to that of the metals. In none of the compression tests carried out on the L-PLLA / Mg samples, breakage was achieved, showing deformation in the skipjack.

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

Table 2: Average values of elastic limit (σο) and maximum load (a _max ) recorded in the compression test Comparing the values of Young's modulus and the tension corresponding to the elastic limit, obtained for the magnesium reinforced polymer with the corresponding to the trabecular bone, it can be seen how magnesium reinforcement allows to obtain polymer / metal composite materials with mechanical properties similar to those of human bone, thus allowing a better load transfer between this artificial material and bone tissue.

Biocompatibility assays The 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 L- samples PLLA Mg, 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 AlamarBIue ™. Figure 4 shows that cell viability increases with the culture time on polymer / metal composites.

Claims

Material comprising the mixture of:

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

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

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

Material according to any one of claims 1 to 4, wherein the volume percentage of the magnesium particles with respect to the total material is less than or equal to 70%.

Material according to any one of claims 1 to 5, wherein the magnesium particles have a size between 50 and 500 μιτι.

Material according to claim 6, wherein the magnesium particles have a size between 50 and 250 μιτι.

8. Material according to any one of claims 1 to 5, wherein the magnesium particles have a size of less than 50 μιτι.

9. Procedure for obtaining the material as defined in any one of claims 1 to 8, comprising the steps:

to. mixing of the matrix forming polymer and magnesium particles, and

b. processing of the product obtained in step (a).

10. Method according to claim 9, wherein 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, fiber bonding and extrusion.

eleven . Process according to any one of claims 9 or 10, wherein the process comprises the addition of an organic solvent in step (a).

12. A process according to claim 1, wherein the solvent used in step (a) is chloroform.

13. Process according to any one of claims 1 or 12, wherein the process comprises an additional stage of evaporation of the solvent added in step (a), and subsequently the product obtained in this additional stage is processed.

14. Method according to claim 13, wherein evaporation of the solvent in the additional step is carried out by orbital stirring.

15. Method according to any one of claims 9 to 14, the processing of step (b) is a thermomechanical processing of compaction and molding.

16. The method according to claim 15, wherein the thermomechanical processing of step (b) is carried out at a temperature range between 100 ° C and 200 ° C. 17. Method according to claim 16, wherein the thermomechanical processing of step (b) is performed at a temperature range between 130 ° C and 170 ° C.

18. - Use of the material as defined in any one of claims 1 to 8 to manufacture a biomedical implant or device.

19. - Implant or biomedical device manufactured from a material as defined in any one of claims 1 to 8. 20.- Implant manufactured from a material as defined in any one of claims 1 to 5 for use in bone tissue repair as osteosynthesis material.

twenty-one . - Implant according to claim 20, wherein the magnesium particles have a size of less than 50 μιτι

22. - Implant manufactured from a material as defined in any one of claims 1 to 5, for use in the regeneration of bone tissue in bone tissue engineering.

23. - Implant according to claim 22, wherein the magnesium particles have a size between 50 and 500 μιτι.

24. Implant according to claim 23, wherein the magnesium particles have a size between 50 and 250 μιτι.