WO2007071242A1 - Procede de construction d'un produit expose a une charge, notamment un implant d'articulation biomedical contenant des materiaux nanocomposites - Google Patents

Procede de construction d'un produit expose a une charge, notamment un implant d'articulation biomedical contenant des materiaux nanocomposites Download PDF

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WO2007071242A1
WO2007071242A1 PCT/DK2006/000617 DK2006000617W WO2007071242A1 WO 2007071242 A1 WO2007071242 A1 WO 2007071242A1 DK 2006000617 W DK2006000617 W DK 2006000617W WO 2007071242 A1 WO2007071242 A1 WO 2007071242A1
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implant
product
hdpe
polymer
stress
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PCT/DK2006/000617
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Jesper Declaville Christiansen
Aleksey Dmitrievich Drozdov
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Aalborg Universitet
Ben Gurion University Of The Negev
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
    • A61L27/00—Materials for grafts or prostheses or for coating grafts or prostheses
    • A61L27/40—Composite materials, i.e. containing one material dispersed in a matrix of the same or different material
    • A61L27/44—Composite materials, i.e. containing one material dispersed in a matrix of the same or different material having a macromolecular matrix
    • A61L27/446—Composite materials, i.e. containing one material dispersed in a matrix of the same or different material having a macromolecular matrix with other specific inorganic fillers other than those covered by A61L27/443 or A61L27/46
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J3/00—Processes of treating or compounding macromolecular substances
    • C08J3/20—Compounding polymers with additives, e.g. colouring
    • C08J3/22—Compounding polymers with additives, e.g. colouring using masterbatch techniques
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J3/00—Processes of treating or compounding macromolecular substances
    • C08J3/20—Compounding polymers with additives, e.g. colouring
    • C08J3/22—Compounding polymers with additives, e.g. colouring using masterbatch techniques
    • C08J3/226—Compounding polymers with additives, e.g. colouring using masterbatch techniques using a polymer as a carrier
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
    • C08J5/005—Reinforced macromolecular compounds with nanosized materials, e.g. nanoparticles, nanofibres, nanotubes, nanowires, nanorods or nanolayered materials
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2423/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
    • C08J2423/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
    • C08J2423/10—Homopolymers or copolymers of propene
    • C08J2423/12—Polypropene

Definitions

  • the present invention relates to nanocomposites, especially the use of nanocomposites in biomedical joint implants.
  • Ultra High Molecular Weight PolyEthylene has been utilized as the syn- thetic replacement for articular cartilage in total joint replacements for nearly four decades. This is described in more detail by Krzypow D. J. and Rimnac CM in "Cyclic steady state stress-strain behavior of UHMWPE” published in Biomaterials 21 (2000) 2081-2087; and by Bergstrom J.S., Rimnac CM. and Kurtz S.M. in "An augmented hybrid constitutive model for simulation of unloading and cyclic loading be- haviour of conventional and highly cross linked UHMWPE” published in Biomaterials 25 (2004) 2171-2178; and by Meyer R. W. and Pruitt, L.A. in "The effect of cyclic true strain on the morphology, structure and relaxation behaviour of ultra high molecular weight polyethylene.” published in Polymer 43 (2001) 5293-5306.
  • UHMWPE has superior biomechanical properties including high toughness, low friction, and good biocompatibility.
  • the reasons for the use of UHMWPE as compared to other polyethylene groups are probably higher Young's modulus, tensile strength, impact toughness, mechanical stability at higher temperatures and abrasion resistance.
  • the only difference between UHMWPE and High Density Polyethylene (HDPE) is the size of the molecules.
  • HDPE High Density Polyethylene
  • UHMWPE is really a subgroup of HDPE (Plastics; Materials and processing, A. Brent Strong, Pearson, Prentice Hall 3 rd ed. Pp 231, 2006).
  • Low Density Polyethylene and Linear Low Density Polyethylene are chemically similar to HDPE but contain more branches per chain length.
  • a product for a biomedical joint implant or bone implant comprising nanocomposite material containing polymer and nano-material for resistance against stress softening, creep or for resistance against total plastic deformation due to cyclic loads, wherein the nano-material is in the form of nano- platelets with a ratio between an average height of the platelets and an average width of the platelets of at least 1 :20.
  • nanocomposite material containing polymer and nano-platelets such as in nanoclay
  • has a high resistance against deformation due to cyclic load It shows a significant reduction in the total plastic deformation after several load cycles compared to the unfilled polymer. Creep properties are improved, especially at high loads and the total plastic deformation is significantly reduced.
  • the deformation resistance has not yet been investigated in detail for such kind of nanocomposites, and polymer with nanoclay has not yet been proposed for the reason of withstanding cyclic stress on the long term basis.
  • a ratio between the average thickness and width of the platelets has been defined above to be at least 1 :20 to be useful for the invention, preferably, the ratio is at least 1:200, or even better at least 1:1000.
  • good results have been achieved with ratios in the order of 1 :2000, as it may be the case for nanoclay, for example Montmorillonite.
  • an example of the dimensions of large nanoclay platelets is one nanometer in thickness and of the order of one or two micrometer in diameter.
  • Rg is the average of the possible end-to-end distances for the polymer chains in the polymer product.
  • Rg is typically between 2 ran and 10 nm in average, whereas the polymer chain length itself is in the order of micrometer.
  • the platelet width of the nano-platelets should be much larger than Rg in order to have a substantial effect. In experiments, an effect is observed for nano-platelets with a diameter of 20 nm, the effect increasing with increasing diameter.
  • the platelets need not to be single platelets, but may as well be aggregations of platelets as it typically is seen in not completely exfoliated clay.
  • Creep Gradual alteration (deformation) in length of a part subjected to a load causing stresses to arise in the part.
  • the total deformation and speed of deformation is a func- tion of variables like time, stress and temperature.
  • the total deformation consist of an elastic (recoverable) part, and a viscoelastic part, where some part of this deformation might be recovered over time and another part be permanent (irrecoverable).
  • Total plastic deformation Subjecting a part to a high load can cause it to respond not only elastic (recoverable) but also give a permanent plastic deformation (irrecoverable). If the timescales are short, one will usually not use the word creep about the processes involved in a loading-unloading experiment.
  • the total plastic deformation is used to describe the alteration in length occurring after loading-unloading experiments. In a uniaxial tensile test experiment, stress can be plotted on one axis and de- formation on the other axis. After loading-unloading into the plastic region of the material, it can be observed that at unloading the curve does not return to zero deformation, but a certain degree of plastic deformation has taken place.
  • the degree of plastic deformation can again change and the sum of these plastic deformations is called the total plastic deformation.
  • the patient will be active, and this way subjects the implant to various stresses where plastic deformation might take place.
  • the sum of these plastic deformations is in scientific literature believed to play a major role for the life time of an implant.
  • the implant when used as an implant, it has to be determined whether the implant comprises the nanocomposite material as part or whole of its surface and whether it comprises the nanocomposite material as part or whole of its bulk material.
  • the practical embodiment of the nanocomposite may depend on the specific applica- tion. As mentioned above, nanocomposites reveal a high degree of resistance against long term deformation due to cyclic load, such that the nanocomposite material may, for example, be employed in those parts of the product, where the cyclic stress is high. In some instances, a surface coating may suffice, in other instances the bulk material or part of it is advantageously made of the nanocomposite.
  • HDPE High Density Polyethylene
  • UHMWPE Ultra High Molecular Weight Polyethylene
  • the clay may be smectite type clay, for example Montmorillonite. However, other clays may be used.
  • the product may comprise a ceramic filler material in order to adjust the physical properties of the product.
  • Useful applications of the invention may be any place where polyethylene is used for implants, and the implant has to resist a mechanical deformation over time. Examples are for instance hip joints, knee joints, acetabular sockets, finger joints, facial implants and any other kind of bone joint or part of bones.
  • the implant can be a total implant or a partial implant used in combination with e.g. metals or ceramics.
  • the above purpose of the invention is also achieved by a polyolefin material, for example HDPE, which has been subjected to annealing at a temperature higher than HO 0 C, for example between 110°C and 130°C.
  • a polyolefin material for example HDPE
  • annealing time 2 hours is appropriate, however, the time may vary, for ex- ample between 30 minutes and 4 hours, preferably between 1 and 3 hours.
  • the invention also comprises a method for minimising stress softening, creep or plastic deformation due to cyclic loads in a product for a biomedical joint implant or bone implant, the method comprising the steps of - providing a thermoplastic polymer
  • nano-mixing nano-material in the form of nano-platelets into the polymer the nano platelets having a ratio between the average height of the platelets and the average width of the platelets of at least 1:20.
  • the ratio is at least 1:200, for example at least 1:1000 or even 1:2000, as it may be the case for a nanoclay, for example Montmorillonite.
  • the method also implies constructing a product for a biomedical joint implant or bone implant with a high degree of resistance against stress softening, creep or of resistance against plastic deformation due to cyclic loads.
  • the method may comprise annealing the moulded product.
  • a typical moulding of a thermoplastic polymer product leads to a large degree of crystallisation in the middle of the product due to the slower cooling than at the outer parts of the product. If the crystallisation is increased by a factor of 30%-50%, it has been found that the Young's modulus increases by a factor of between 2 and 3.
  • the annealing may be performed at a temperature of more than 110°C for a predetermined time, for example more than one hour.
  • the annealing temperature is dependent on the product.
  • the temperature should be high enough to promote crystallisation but not so high that severe thermal disintegration occurs in the polymer.
  • the temperature should be more than 120°C, typically for a certain time in the order of hours.
  • the method in a further embodiment implies constructing a product, preferably a biomedical joint implant, with a high degree of resistance against stress softening, creep or of resistance against plastic deformation due to cyclic loads, the method comprising the steps of
  • the determined part or parts of the product may comprise the surface of the product, and in some instance be limited to the surface of the product.
  • the product may have a different bulk material coated with the nanocomposite.
  • the determined part or parts of the product include the bulk material of the product.
  • the surface may be a nanocomposite as well but could also comprise a different material.
  • the preferred polymers are from the group of polyolefins, for example High Density Polyethylene (HDPE) or Ultra High Molecular Weight Polyethylene (UHMWPE).
  • the preferred clay is smectite type clay, for example Montmorillonite. However, other clays may be used.
  • the method primarily is intended for products being bio- medical implant, especially biomedical implants or parts of a biomedical implants, for example biomedical joint implants.
  • biomedical joint implant or bone implant the described method and product are especially suited to achieve resistance against stress softening, creep or for resistance against total plastic deformation due to cyclic loads.
  • the method may be used more general and may as well apply to the design of other types of products that are exposed to cyclic load and where a long term deformation of the products is to be minimised.
  • An UHMWPE or HDPE or LDPE or LLDPE or PP nanocomposite could also be useful for other products that are exposed to cyclic loads or long term loads, for example earth crake resistant pipes.
  • the method according to the invention may as well be used for other applications with static or cyclic loads including pressurized pipes, for example used for transport of water, gas or chemicals and furthermore, bottles, loudspeaker membranes geomembranes, insti- tutional and container can liners, grocery sacks and merchandise bags, large blow moulded industrial containers.
  • nanoclay filled poly- olefmes can be enhanced by adding other nanoflllers, like nanoparticles or nanofibres thus obtaining a nanohybrid composite.
  • a polyolefm for example HDPE, annealed at a certain temperature below the temperature for thermal disintegration of the polymer, but preferably above 100 0 C or rather above HO 0 C, may successfully be used for a moulded product, for example for a biomedical joint implant or bone implant, to achieve a high resistance against stress softening, creep or resistance against total plastic deformation due to cyclic loads.
  • Annealing times are in the order of a larger fraction of an hour and some hours, for example between half an hour and 3 hours.
  • FIG. 1 shows measurements of the engineering stress ⁇ versus the tensile strain ⁇ during the first two cycles of tensile deformation of neat polymer with a cross head speed of lOmm/min.
  • the minimum stress ⁇ min 0.0 MPa
  • FIG. 2 shows measurements of the engineering stress ⁇ versus the tensile strain ⁇ during the first two cycles of tensile deformation of a hybrid nanocomposite with a cross head speed of lOmm/min.
  • FIG. 3 shows measurements of the dimensionless stress ⁇ / ⁇ max versus time t in tensile relaxation tests at various strains ⁇ for neat polymer
  • FIG. 4 shows measurements of the dimensionless stress ⁇ / ⁇ max versus time t in tensile relaxation tests at various strains ⁇ for hybrid nanocomposite
  • FIG. 7 shows measurements of the engineering stress ⁇ versus the tensile strain ⁇ during 10 cycles of tensile deformation of a neat polymer with a cross head speed of 2 mm/min.
  • FIG. 8 shows measurements of the engineering stress ⁇ versus the tensile strain ⁇ during 10 cycles of tensile deformation of a hybrid nanocomposite with a cross head speed of 2 mm/min.
  • FIG. 9 shows measurements of the engineering stress ⁇ versus strain ⁇ for neat poly- mer at tensile deformations with various cross-head speeds. Symbols are experimental data. Solid lines are results of numerical simulation;
  • FIG. 10 shows measurements of the engineering stress ⁇ versus strain ⁇ for nanocomposite at tensile deformations with various cross-head speeds. Symbols are experimental data. Solid lines are results of numerical simulation; FIG. 11 shows measurements of the engineering strain ⁇ versus time t in tensile creep tests with various engineering stresses ⁇ (MPa). Symbols: experimental data on non-annealed HDPE; FIG. 12 shows measurements of the engineering strain ⁇ versus time t in tensile creep tests with various engineering stresses ⁇ (MPa). Symbols: experimental data on non-annealed HDPE + MMT nanocomposite;
  • HDPE+MMT annealed T I lO 0 C for 2 h, c) HDPE+MMT annealed at
  • FIG. 19 The adjustable parameters Ic 4 . and k. versus increment of elastic strain
  • FIG. 20 The adjustable parameters Ic + and k. versus increment of elastic strain
  • FIG. 21 The Young's modulus of neat HDPE (left) and HDPE/MMT nanocomposite
  • FIG. 22 The adjustable parameter ⁇ for neat HDPE (left) and HDPE/MMT nanocomposite (right) annealed for 2 h at various temperatures,
  • FIG. 23 The adjustable parameter ⁇ for neat HDPE (left) and HDPE/MMT nanocomposite (right) annealed for 2 h at various temperatures,
  • FIG. 24 The adjustable parameter a° + for neat HDPE (left) and HDPE/MMT nano- composite (right) annealed for 2 h at various temperatures,
  • FIG. 25 The adjustable parameter b° + for neat HDPE (left) and HDPE/MMT nanocomposite (right) annealed for 2 h at various temperatures,
  • FIG. 26 The adjustable parameter a 0 , for neat HDPE (left) and HDPE/MMT nanocomposite (right) annealed for 2 h at various temperatures
  • FIG. 27 The adjustable parameter b°_ for neat HDPE (left) and HDPE/MMT nanocomposite (right) annealed for 2 h at various temperatures
  • FIG. 28 The adjustable parameter K . for neat HDPE (left) and HDPE/MMT nanocomposite (right) annealed for 2 h at various temperatures
  • FIG. 29 The adjustable parameter K for neat HDPE (left) and HDPE/MMT nanocom- posite (right) annealed for 2 h at various temperatures.
  • Clay is known as filler in polymers in order to improve the stability of polymers.
  • Clay consists of a stack of platelets. This stack has a surface area more or less corresponding to the surface of the stack. If the plates in the clay can be separated some distance from each other, which is known as exfoliation, a polymer will start interacting with the individual platelets, and hence the effective surface area of the clay dramatically changes.
  • the surface of the clays normally does not tend to bind to the polymers. Therefore, in the preparation of clay, different steps are followed to chemically modify the surface in order to make it compatible with a given polymer, and to achieve the desired exfoliation.
  • Fig. 1 illustrates the complications that have been reported in the above mentioned articles by Krzypow D. J. and Rimnac CM in "Cyclic steady state stress-strain behaviour of UHMWPE” published in Biomaterials 21 (2000) 2081-2087; and by Bergstr ⁇ m J.S., Rimnac CM. and Kurtz S.M. in "An augmented hybrid constitutive model for simulation of unloading and cyclic loading behaviour of conventional and highly cross linked UHMWPE” published in Biomaterials 25 (2004) 2171-2178; and by Meyer R.W. and Pruitt, L. A.
  • Fig. 1 shows measurements of the engineering stress ⁇ versus the tensile strain ⁇ during the first two cycles of tensile deformation of neat polymer - where neat polymer means polymer without fill material and without previous load - with a cross head speed of lOmm/min.
  • the minimum stress ⁇ min 0.0 MPa
  • polypropylene differs from polyethylene in the composing units of propylene instead of ethylene.
  • the chemical nature is very similar, despite the fact that the introduction of a more bulky side group provides a steric effect.
  • Polyethylene and polypropylene are often given a joint name to indicate this similarity in nature: They are called polyolefmes. They only consist of carbon and hydrogen and are aliphatic (nonaromatic) groups. It is therefore fair to assume that results from the measurements on polypropelene are similar in nature to results that can be obtained from UHMWPE. With the standard measurements of FIG. 1 through FIG.
  • FIG. 7 corresponds to the unfilled PP
  • figure 8 corresponds to the nanoclay filled PP.
  • the stress loadings are not exactly the same in the two plots, the figures clearly demonstrate that stress softening has been significantly improved by the addition of nanoclay.
  • an improvement has been achieved concerning the lifetime to fracture, because the permanent deformation after 10 cycles of load has been significantly reduced when adding the nanoclay.
  • FIG. 9 The engineering stress ⁇ versus strain ⁇ at tensile deformations with various cross- head speeds is illustrated in FIG. 9 for neat polymer and in FIG. 10 for nanocomposite polymer. Symbols indicate experimental data and solid lines are results of numerical simulation.
  • UHMWPE total implants such as but not limited to joint replacements and bone implants, where at least a number of references attribute the failure with the cyclic loading and softening.
  • the idea is to make such kind of implant of a polyolefin, for example HDPE or a UHMWPE, with a percentage of chemically prepared nanoclay.
  • an amount of clay in the order of 1-8%. In certain cases 10% clay may be useful. However, often it is not necessary with such high amounts, especially not, if the exfoliation is efficient.
  • An UHMWPE or HDPE or LDPE or LLDPE or PP nanocomposite could also be useful for other products that are exposed to cyclic loads or long term loads, for example earth crake resistant pipes.
  • Other applications with static or cyclic loads involve pressurized pipes, for example used for transport of water, gas or chemical and further, bottles, loudspeaker membranes geomembranes, institutional and container can liners, grocery sacks and merchandise bags, large blow moulded industrial containers.
  • NanoblendTM concentrates are high-performance materials based on nanocomposite technology. Nanoclays make up approximately 40% (weight) of the NanoblendTM concentrates and mixed the NanoblendTM concentrate with a commercial grade of polypropylene in an injection moulding machine.
  • the same nanoclay master batch can be mixed with e.g. UHMWPE or HDPE.
  • injection moulding as the forming process, other industrial processes can be used like compression moulding, extrusion, foaming, blow moulding, fibre spinning and more.
  • nanoclay mastebatch one could use other types of commercially available clays, for example Closite 2OA from Southern Clay Inc. mixed with the polymer and around 1% of a maleate polypropylene.
  • the improved properties of nanocom- posites depend on the high surface area of the individual platelets of the clay, for example montmorillonite (MMT). Both the compatibility of the clay chemical treatment with the resin matrix and the melt blending conditions determine the degree of de- lamination and dispersion.
  • MMT montmorillonite
  • the natural cation is replaced by a Na+ exchange.
  • Such prepared clay is commercially available from e.g. Southern Clay Inc. When water is added, the clay exfoliates and a surfactant can be added.
  • a surfactant is molecules with affinity to the clay surface by certain group(s) and affinity to the polymer system by another group.
  • the polymer can then be added after drying or dissolved or in situ polymerized — there are many ways of bringing polymer and clay together:
  • Melt intercalation is a method where clay is treated such that a surfactant compatible with the polymer is inserted between the clay platelets. Intercalation implies that the distance between clay platelets is increased slightly, but not more than that they still have an attraction keeping the clay platelets sticking together. Adding the clay to a compatible polymer and applying heat mechanical deformation by mixing for a certain time causes the system to exfoliate, and nanoclay is obtained.
  • Exfoliation and adsorption occurs when the clay is exfoliated in a solvent, and the polymer also exists dissolved in the same system such that it can be attracted to the surface of the clay.
  • solvent is removed, for example by evaporation, an exfoliated nanoclay loaded polymer is obtained.
  • In-situ polymerization is a variant where the polymer is not dissolved but where the solvent itself is the monomers of the polymer. In this process, the growth of polymer chains can push clay platelets apart if they are only intercalated.
  • Nanoclay could also be made by use of template synthesis, so that the polymer solution contains silicates that will grow to obtain a mixture of silicate crystals and polymer.
  • the surfactant 0 can be formulated in a large number of different ways.
  • the bonding to the clay can be weak secondary forces, ion bonds or covalent bonds.
  • ammonium surfactants employed at the intercalation stage are replaced by polyethylene oxide (PEO) or polymer chains also involving polypropylene oxides (PPO) such that PEO-PPO-PEO copolymers and 5 polysaccharides.
  • PEO polyethylene oxide
  • PPO polypropylene oxides
  • nanoclay should be used which has a biocompatible and non-toxic effect when mixed with a polyolefrn, such as PE. It should be prepared in a way so the exfoliated polymer nanoclay is readily formed. In addition, the use of a biocompatible surfactant is advantageous.
  • High-density polyethylene Eraclene MM 95 (density 0.953 g/cm 3 , melt flow index 11 g/10 min) was supplied by Polimeri Europa SpA (Italy).
  • Dumbbell specimens (ASTM standard D638) with length 148 mm, width 9.8 mm and thickness 3.8 mm were prepared by using the injection-molding machine Ferromatic Kl 10/S60-2K.
  • Masterbatch MB 1001 E was purchased from PolyOne Inc. (nanocomposite with poly- propylene matrix filled with 40 wt.-% of Nanoblend concentrate, chemically modifed MMT nanoclay). Pellets of polyethylene and masterbatch were carefully mixed in proportion 80:20 by weight, which corresponded to approximately 8 wt.-% of the modifed nanoclay in the nanocomposite. Nanocomposite samples for testing were prepared in the same way as specimens of neat HDPE.
  • the concentration of nanoclay in the hybrid nanocomposite was chosen for two reasons:
  • FIG. 11 experimental data on HDPE (high density polyethylene) are shown, illustrating the engineering strain ⁇ versus time t in tensile creep tests with various engineering stresses ⁇ (MPa) as indicated in the upper left corner of the figure.
  • ⁇ engineering stresses
  • FIG. 16 illustrates the corresponding shows measurements for HDPE with 8 wt.-% of the modifed nanoclay in the nanocomposite.
  • the yield stress of HDPE and HDPE/MMT specimens strongly increases with temperature of annealing.
  • the yield stress of nanocomposite exceeds that of neat polymer for each temperature of annealing.
  • a semicrystalline polymer is treated as a two-phase composite consisting of amorphous and crystalline domains. It is convenient to consider the crystalline phase as a skeleton composed of mutually connected spherulites. Each spherulite consists of a number of crystalline lamellae organized in a rather complicated manner. The amorphous phase is thought of as a polymer network in the rubbery state. This network is located between crystallites and between lamellae in spherulites.
  • strain energy (per unit volume) of an incompressible medium is given by
  • the Clau- sius-Duhem inequality reads dW dp dt dt where Q stands for energy dissipation per unit time and unit volume, ⁇ is the stress tensor, and prime denotes the deviatoric component of a tensor.
  • Equations (1.2) and (1.5) are satisfied for an arbitrary deformation program ⁇ t) .
  • ⁇ (t) that characterizes the viscoplastic response of a solid polymer.
  • Eq. (1.6) involves only two material constants, a and ⁇ , to be found by fitting observations.
  • Equation (1.7) is chosen for the following rea- sons:
  • Equations (1.9) and (1.10) mean that the coefficients a and b in Eq. (1.8) are affected in the same way by deformation history.
  • Equations (1.9) and (1.10) mean that the coefficients a and b in Eq. (1.8) are affected in the same way by deformation history.
  • J e the current intensity of elastic strain when the strain rate changes its sign
  • J° the intensity of elastic strain at the instant when the first retraction (reloading) starts.
  • constitutive equations (1.2), (1.5), (1.6), (1.8), (1.9), (1.10), (1.12) and (1.14) involve 9 adjustable parameters ⁇ , a , ⁇ , al, bl, a_ o , b_°, K , ⁇ .
  • This number is substantially lower than the number of material constants in other models for cyclic viscoplasticity of polymers.
  • ⁇ (i) stands for longitudinal engineering strain
  • ® denotes tensor product.
  • E , a and ⁇ in Eqs. (1.17)-(1.19) are found by matching the stress- strain curves depicted in Figures 17 and 18 with the help of the following algorithm.
  • the pre-factor E in Eq. (1.18) is found by the least-squares method from the condition of minimum of the functional
  • the exponent ⁇ is weakly affected by reinforcement and annealing. For all samples (except for those annealed at the highest temperature), the exponent ⁇ of HDPE/MMT nanocomposite slightly exceeds that of neat HDPE.
  • the adjustable parameter strongly increases with temperature of anneal- ing both for neat HDPE and HDPE/MMT nanocomposite.
  • the growth is monotonic for HDPE, whereas for the nanocomposite, annealing at 110 and 12O 0 C results in practically the same values of this parameter.
  • the coefficient ⁇ ° of nanocomposite exceeds that of HDPE.
  • the adjustable parameter b ⁇ grows with temperature of annealing both for neat HDPE and HDPE/MMT nanocomposite. The increase is stronger for HDPE and appears to be less pronounced for the nanocomposite.
  • the parameter of the nanocomposite substantially (by several times) exceeds that of neat HDPE. Second cycle of deformation
  • the adjustable parameter ⁇ ° strongly increases with temperature of annealing for neat HDPE.
  • the influence of temperature of annealing on a° for HDPE/MMT nanocomposite appears to be non-monotonic.
  • the coefficient ⁇ ° of nanocomposite exceeds that of HDPE.
  • the adjustable parameter ⁇ >° grows with temperature of annealing both for neat HDPE and HDPE/MMT nanocomposite.
  • the coefficient b°_ of nanocomposite exceeds that of HDPE.
  • the parameters K and K monotonically increase with temperature of an- nealing both for neat HDPE and HDPE/MMT nanocomposite.
  • This decrease in plastic creep may be associated with changes in crystalline morphology of HDPE driven by annealing.
  • a constitutive model is developed that allows experimental data in cyclic tensile tests to be adequately described.
  • An algorithm is proposed that al- lows adjustable parameters in the stress-strain relations to be found with the help of a relatively simple procedure by fitting observations in uniaxial cyclic tensile tests.
  • the constitutive equations may be applied for the analysis of cyclic deformations of nanocomposite structures with complicated geometry.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Health & Medical Sciences (AREA)
  • Materials Engineering (AREA)
  • Medicinal Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Nanotechnology (AREA)
  • Organic Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Composite Materials (AREA)
  • Dermatology (AREA)
  • Transplantation (AREA)
  • Animal Behavior & Ethology (AREA)
  • General Health & Medical Sciences (AREA)
  • Public Health (AREA)
  • Veterinary Medicine (AREA)
  • Epidemiology (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Oral & Maxillofacial Surgery (AREA)
  • Inorganic Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Materials For Medical Uses (AREA)

Abstract

L'invention concerne un procédé destiné à construire un produit à degré élevé de résistance à la déformation à long terme contre une charge cyclique, de préférence un implant d'articulation biomédical, le produit comprenant un matériau nanocomposite qui contient du polymère et de la nanoargile.
PCT/DK2006/000617 2005-12-23 2006-11-09 Procede de construction d'un produit expose a une charge, notamment un implant d'articulation biomedical contenant des materiaux nanocomposites WO2007071242A1 (fr)

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DKPA200601293 2006-10-05

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3043837A4 (fr) * 2013-09-12 2017-05-17 Ronen Shavit Revêtements pour implants chirurgicaux articulaires présentant une résistance à l'usure améliorée

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000034378A1 (fr) * 1998-12-07 2000-06-15 Eastman Chemical Company Nanocomposite a base de polymere/d'argile et procede de preparation correspondant
WO2002079318A2 (fr) * 2001-04-02 2002-10-10 Pachmas Metal Plastic & Fibre Industries Nanocomposites, leur procede de production et produits obtenus a partir de ceux-ci
WO2003065996A2 (fr) * 2002-02-05 2003-08-14 Cambridge Scientific, Inc. Compositions osteoconductrices bioresorbables destinees a la regeneration osseuse
WO2004098574A1 (fr) * 2003-05-06 2004-11-18 The Queen's University Of Belfast Composition nanocomposite pour administration de medicament
US20040260000A1 (en) * 2003-06-23 2004-12-23 Chaiko David J. Polyolefin nanocomposites
WO2005044904A2 (fr) * 2003-07-18 2005-05-19 The Penn State Research Foundation Nanocomposites de polyolefine/argile exfolies utilisant une polyolefine fonctionnalisee en fin de chaine comme tensioactif polymere
US20050181015A1 (en) * 2004-02-12 2005-08-18 Sheng-Ping (Samuel) Zhong Layered silicate nanoparticles for controlled delivery of therapeutic agents from medical articles

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000034378A1 (fr) * 1998-12-07 2000-06-15 Eastman Chemical Company Nanocomposite a base de polymere/d'argile et procede de preparation correspondant
WO2002079318A2 (fr) * 2001-04-02 2002-10-10 Pachmas Metal Plastic & Fibre Industries Nanocomposites, leur procede de production et produits obtenus a partir de ceux-ci
WO2003065996A2 (fr) * 2002-02-05 2003-08-14 Cambridge Scientific, Inc. Compositions osteoconductrices bioresorbables destinees a la regeneration osseuse
WO2004098574A1 (fr) * 2003-05-06 2004-11-18 The Queen's University Of Belfast Composition nanocomposite pour administration de medicament
US20040260000A1 (en) * 2003-06-23 2004-12-23 Chaiko David J. Polyolefin nanocomposites
WO2005044904A2 (fr) * 2003-07-18 2005-05-19 The Penn State Research Foundation Nanocomposites de polyolefine/argile exfolies utilisant une polyolefine fonctionnalisee en fin de chaine comme tensioactif polymere
US20050181015A1 (en) * 2004-02-12 2005-08-18 Sheng-Ping (Samuel) Zhong Layered silicate nanoparticles for controlled delivery of therapeutic agents from medical articles

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3043837A4 (fr) * 2013-09-12 2017-05-17 Ronen Shavit Revêtements pour implants chirurgicaux articulaires présentant une résistance à l'usure améliorée

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