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Bioresorbable Implant Materials

PIXE analysis with 2.25 MeV protons at bone sections, 4 weeks after implantation; image size 750 x 750 µm; alloy LAE442 (90 % Mg, 4 % Li, 4 % Al, 2 % SEE)

Many different materials are avaiable for application as supporting implant materials, among them steel, Ti alloys and Ti, Co-Cr alloys, ceramics and polymers. Investigation of the interaction of biomolecules and biological liquids with the surfaces of such implants is necessary, because under unfavorable conditions these interactions may result in failure of the implant, its degradation or unwanted body reactions. Since several years biodegradable implant materials and coatings are in the focus of scientific work. These materials should degrade in a predestined way and time, whereas implant materials have to guarantee proper functioning for a certain period of time and degradable coatings may have protecting function but more often are used to release pharmaceutically active substances.

Materials used in the musculoskeletal system provide supporting function as long as the newly grown bone is not or only partly loadable. After the degradation the implant does not need to be explanted in a second surgery. Good candidates for this field of application are Mg alloys because of a Youngs modulus close to the bone material and high biocompatibility. Alloying allows to tune the degradation processes and therewith the degradation time. During the degradation of the material these alloying components, e.g. Li, Zn or RE elements, could be transported and deposited in the organism or excreted. To test the biocompatibility of newly developed Mg alloys and to investigate the degradation mechanism the following topics have been elaborated:

  1. Investigation of surface properties and elemental distribution within the alloys prior to implantation
  2. Determination of concentration of all alloying elements in the tissue, all important organs and in blood and urine prior to implantation (determination of background values)
  3. Determination of all alloying elements in all important organs, tissues and body liquids after different prevailing times of the implants in the organism
  4. Further investigations to elucidate the degradation mechanism and to explain the observed growth of new bone material.

The application of coatings is mostly performed to support the healing process after the surgery. A targeted release of pharmaceutically active substances from these layers should help to ensure the long-lasting functioning of the implant. This could be supported by anti-inflammatory or anti-proliferating agents, as well as by growth hormons applied for optimal interaction of implant surface and surrounding tissue. The release of the agents may be guided by the chemical composition or the structural design of the coating, nevertheless the coatings and the release of the agents have to be tested prior to clinical applications. In studies performed at our lab the following topics have been addressed:

1. Degradation of polylactic acid coatings in animal models in dependence on time after implantation

2. Determination of restenosis after application of different anti-proliferating agents.

Quantification with matrix-matched standards made from synthetic bone material after measurement of concentrations along a traverse across implant, corrosion layer and surrounding bone material. Left column: quantification of Rare Earth elements by LA-ICP-MS, right column: Quantification of Ca, Al and Phosphorous by PIXE measurement.

Applied analytical methods

Analytical task

Applied method

Determination of composition and homogeneity of implant materials prior and after implantation

SEM-EDX, µ-XRF, ICP-OES, ICP-MS, PIXE, SY-XRF, IR, Raman

Concentration of elements from implant materials in bone, liver, blood, urine, …, prior and after implantation

ICP-MS, LA-ICP-MS, GF-AAS, PIXE, IC, ISE

Interaction of proteins with the alloy surface (bone implant)

SY-IR

Degradation mechanism

µ-RFA, PIXE, SY-RFA

Determination of restenosis in dependence on kind of pharmaceutically active substance in the coating

µ-RFA, PIXE, µ-Raman

Publications

  • S. Gruhl, Quantifizierung von Konzentrationsgradienten im µm-Bereich mittels Laserablation-ICP-MS, Dissertation, 2006, Leibniz Universität Hannover
  • S. Gruhl, F. Witte, J. Vogt, C. Vogt, Determination of concentration gradients in bone tissue generated by the degradation of a biologically degradable magnesium implant, JAAS 2009, 24(2)
  • F. Witte, N. Hort, C.Vogt, S. Cohen, K. U. Kainer, R. Willumeit, F. Feyerabend, Degradable biomaterials based on magnesium corrosion, Current Opinion in Solid State & Materials Science 12 (2008) 63-72
  • N. Hort, Y. Huang, D. Fechner, C. Blawert, F. Witte, C. Vogt, H. Drücker, R. Willumeit, K.U. Kainer, F. Feyerabend, Magnesium Alloys as Implant Materials – Principles of Property Design for Mg-RE Alloys, Acta Biomaterialica 6 (2010) 1714-1725
  • F. Witte, J. Fischer, C. Vogt, J. Vogt, T. Donath, F. Beckmann, In vivo corrosion and corrosion protection of magnesium alloy LAE442, Acta Biomaterialia 6 (2010) 1792-1799
  • C. Vogt, K. Bechstein, S. Gruhl, M. Lange, H. Drücker, F. Witte, J. Vogt, Investigation of the degradation of biodegradable Mg implant alloys in vitro and in vivo by analytical methods, In „Magnesium“, ed. K.U. Kainer, 2009, Wiley-VCH, p.1162-1174
  • F. Witte, K. Bobe, E. Willbold, I. Morgenthal, O. Anderson, T. Stuknitzky, J. Nellesen, W. Tillmann, k. Vano, C. Vogt, In vitro and in vivo evaluation of biodegradable, open-porous scaffolds made of sintered magnesium W4 short fibres, Acta Biomaterialia 9(10) (2013) 8611-8623
  • K. Vano-Hererra, A. Misiun, C. Vogt, Preparation and characterization of Poly(DL-lactic acid)/poly(methyl methacrylate) blend tablets for application in quantitative analysis by micro Raman spectroscopy, J Raman Spectrosc. 46 (2) (2015) 273–279, DOI: 10.1002/jrs.4603
  • N. Angrisani, F. Zimmermann, K. Vano-Herrera, R. Eifler, A. Meyer-Lindenberg,  J. Reifenrath, C. Vogt, Biocompatibility and degradation analysis of LAE442-based magnesium alloys after implantation of up to 3.5 years in a rabbit model, Acta Biomaterialia 44 (2016) 355-65; doi: 10.1016/j.actbio.2016.08.002
  • K. Vano-Herrera, C. Vogt, Degradation of poly(L-lactic acid) coating on permanent cardiovascular metal stents investigated ex vivo by micro Raman spectroscopy, J Raman Spectrosc. (in press), DOI: 10.1002/jrs.5111

Cooperation partners

  • Prof. F. Witte, Charité Berlin
  • Prof. P. Meier, Hochschule Rostock
  • Prof. R. Willumeit , Dr. N. Hort, Dr. F. Feyerabend, Helmholtz Zentrum Geesthacht
  • Dr. J. Reifenrath, Medizinische Hochschule Hannover
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