Biomaterials Introduction PDF

Elite Program “Advanced Materials and Processes” Biomaterial Surfaces Aldo R. Boccaccini Department of Materials Science Institute for Biomaterials (WW-VII) University of Erlangen-Nuremberg 91058 Erlangen Germany Biomaterial Interfaces: Set- up, Structural Analysis and Functional Aspects ...

Elite Program “Advanced Materials and Processes” Biomaterial Surfaces Aldo R. Boccaccini Department of Materials Science Institute for Biomaterials (WW-VII) University of Erlangen-Nuremberg 91058 Erlangen Germany Biomaterial Interfaces: Set- up, Structural Analysis and Functional Aspects  Biocompatibility Host (living organism) System - Species (in animal models) - Operating technique - Tissue type and –location - Connection implant – tissue - Age - Infektions - Sex - Systemic reactions - Health - …. - Local reactions - Involved molecules (proteins etc.) -… Biocompatibility Material - Bulk chemistry - Surface chemistry - Surface roughness Device - Surface charge - Size - Chemical stability - Form - Degradation products - Elastic properties - Physical stability -…  1. Introduction What is an interface? The interface separates two distinct contiguous phases. The interface of a material is interacts with the surrounding environment on a chemical and biological level Relevant surface properties that influence the interfacial interaction on a micro- and nanometer scale are in particular: - Chemical composition/contamination - Electric surface charge - Biologically recognisable functional groups - Surface energy/wettability (hydrophilic/hydrophob) - Topography/roughness - Morphology/crystallinity - Porosity BIOMATERIAL „BIOLOGICAL“ SIDE SIDE Chemische Wechselwirkungen auf Nanoebene: Tribologie und Biokompatibilität, M. Textor, N.D. Spencer ETH Zürich) INTERFACE ! Chemical properties ! Mechanical properties ! Topography/structure  1. Introduction Definition of an interface Other Definitions… Each of the two adjacent solid or liquid phases in contact with each other has atoms or molecules on its surface that are in energetic terms different to the bulk material due to the location on the surface but the two phases also influence each other. The contact area between the two phases is defined as the interface. At the interface a number of two-dimensional processes can take place, such as: Interfacial- or surface energy, specific adsorption, mass transfer, heterogenic catalysis, Marangoni-Effect, electric double layer formation etc. (Source: Fraunhofer IGB Webseite) The upper atom layers of a substance has considerable influence on its appearance, its reactivity and its end use. On the surface and other interfaces, where phases are in direct contact with each other, a number of important physical and chemical processes occur including: Phases changes such as growth, melting, dissolution, vaporisation, mechanical and chemical attack such as wear, corrosion, passivatio, and chemical conversion, eg. catalysis. The reason for this is that an atom or a molecule which is present at an interface has a different atomic surrounding to one that is within the bulk of a solid substance. (Source: Kleine Enzyklopädie Physik, Verlag Harri Deutsch)  2. Relevance of Interfaces Adhesion of Chemical & mechanical proteins compatibility Toxicity Bioactive vs RELEVANCE OF (tissue reaction) Bioinert material INTEFACES properties Corrosion of implant Adhesion of Cell-Implant- bacteria interaction (Biofilm formation) Interfacial properties are influenced by the surface of the biomaterial, e.g. by macroscopic, microscopic and nanoscale features.  2. Relevance of interfaces Interfacial reactions – General aspects All reactions between biomaterial and biological environmental take place at the interface Reaction and its magnitude dependent on physicochemical properties of interface (surface topography, surface chemistry, elasticity, roughness, hydrophilicity, charge, etc.) Challenge: Tailoring of surface chemistry and physics while maintaining the desired bulk properties of the biomaterial Surface functionalisation  Example Interface Bone-Implant Macroscopic aspects Examples of failure of orthopaedic temporary and permanent implants Fatigue failure Chronic inflammation -> In most cases, the implant failure is originated at the biomaterial- implant-interface " Lack of bonding between implant and bone at the interface  Biomaterial-Tissue-Interface Effect of interfaces on the tissue compatibility of the implant # Structure- and surface compatibility are important in relation to the tissue compatibility of an implant. # The surface compatibility is a deciding factor for the first reaction between foreign body and organism, i.e. Protein adsorption. # IMPORTANT: The composition of the first protein layer decides whether tissue cells, inflammatory cells or bacteria appear at the interface. The biomaterial-tissue-interaction can be described by a series of chronological and spatial processes.  3. Hierarchy of the Biomaterial-Tissue-Interaction The biomaterial-tissue- interaction can be described by a series of chronological and Surrounding BIOMATERIAL Cells spatial processes tissue Adsorbed layer (Water, ions, biomolecules) Formation of the interface Nach H. P. Jennissen, Essen  3. Hierarchy of the Biomaterial-Tissue-Interaction # First biological reaction: Adsorption of proteins (within seconds) # Here a first decision on the biocompatibility of the biomaterial takes place # The adsorptive surface bonding of proteins can be (a) with low affinity “reversible” or (b) with high affinity “irreversible”. # The bonding reaction can either be unspecific or specific # Normally, protein adsorption is unspecific and with high affinity, so that proteins lose their native structure and function through high surface forces, and their specific mode of action # Additionally, each biomaterial surface can adsorb a number of proteins, as a result of the unspecific binding sites available  3. Hierarchy of the Biomaterial-Tissue-Interaction After the adsorbed protein layer is in place the cells populations follow* The adsorbed proteins either become cues on the surfaces itself (through changes in conformation), or protein fragments are released on the surface (for example through proteolyse). If an unspecifically acting protein layer is present, it is possible that an inflammatory reaction can occur * A number of cells such as macrophages, granulocytes, immunocytes and finally tissue cells (fibroblasts, osteoblasts etc.) are relevant here, which can for example adhere to the material surface by means of integrins on the adsorbed proteins Nach H. P. Jennissen, Essen  3. Biomaterial-tissue interaction In the next step, the release of morphogenetic proteins and growth factors can occur, which attract tissue cell precursors. An essential condition for the integration of the implant is the adhesion of the cells of target tissue (e.g. bone) on the surface of the implant. If the material is biocompatible, then the desired integration occurs in the whole body (top of the pyramide) and thus a permanent implant occurs. Nach H. P. Jennissen, Essen  Hierarchy of biomaterial-tissue-interaction # Each implant leads to injury of the surrounding tissue, so that proteins are released, which can be adsorbed on the surface of the implant # It is hence improbable that the adsorbed protein layer is identical for all tissues and biomaterials and that the same type of inflammatory tissue reaction occurs. # However, the success of implantology shows that the right “unspecific protein layer” on the implant surface, even if it occurs by accident, can lead to long-term osseointegration, i.e. integration of a foreign body.  4. Biomaterial interfaces: Development of specific surfaces “Design” of the surface chemistry The problem of unspecific protein adsorption is the great number of different proteins adsorbed on the surface. " the desired single protein cannot act effectively In order to obtain a rapid and complete integration of the implant avoiding infections, a uniform layer should be built from the more or less unspecific protein layer, which should show now exhibit specific activity. Goal: " to create a functional surface on which only one protein (or a few desired proteins) with specific activity is adsorbed " this enables tissue reactions to be modulated (specific and selected reactions)  4. Biomaterial interfaces: Development of specific surfaces How it is possible to deposit a specific protein layer on the biomaterial surface? The following basic aspects must be taken into account: 1. The surface should exhibit the following characteristics: " the unspecific protein adsorption must be minimised or, " a specific protein for the desired (target) tissue should be fixed on the surface (this fixation could be non-covalent or covalent) Only few methods enable a specific adsorption of proteins on biomaterial surfaces " preferred method is the covalent coupling of proteins 2. The synthesis of a tissue specific implant surface comprises two steps: " Development of a surface with minimal unspecific protein adsorption, and " Surface coating with one or more tissue specific proteins (if possible in the native conformation)  4. Biomaterial interfaces: Development of specific surfaces Goal the surface functionalisation of biomaterials " Acting on the complex mechanisms of cell growth and differentiation has the following effects: (a) Accelerating the wound healing process and (b) Integration (permanent) of the “external body” (implant) Concept: by fixing tissue specific signalling molecules on the implant surface should lead to rapid and complete integration of the implant.  4. Biomaterial interfaces: Development of specific surfaces Surface funtionalization 1) Coating of implants with bioactive materials 2) Direct fixation of signalling molecules (e.g. growth factors*) 3) Combination of 1) und 2) Surface Coating of the material with a film of desired Chemical and/or chemical composition physical (and topography) modification of the existing surface *usually can be produced by gene technology  4. Biomaterial interfaces: Development of specific surfaces Functionalisation of biomaterial surfaces Thickness of the layer ? As thick as needed – as thin as possible E.g.: 3 Angstrom thick Silan monolayer Silan can change for example completely surface hydrophilicity However: PEG monolayer should be at least 1 nm thick, In order to achieve rapid and complete protein adsoption "But a film which is too thick can affect the bulk "properties of the material ! (e.g. typical thicknesses: a few Angstrom to few tens of Nanometers) Stability ? Surface coating/films must remain stable (in terms of morphology and chemical composition) for the desired period of time under harsh conditions -No delamination - No microcracking, etc.  5. Coating with bioactive materials Implementation of biological activity  5. Coating with bioactive materials Example: Hip replacement Beschichtung mit bioaktivem Glas, Kalziumphosphat (oder Zementierung mit PMMA- Knochenzement)  5. Coating with bioactive materials Biological activity of biomaterials Biactive surfaces, e.g. Coated with hydroxyapatite or Bioglass®  Types of Implant – Tissue Response If the material is toxic, the surrounding tissue dies If the material is nontoxic and biologically inactive (almost inert), a fibrous tissue of variable thickness forms If the material is nontoxic and biologically active (bioactive), an interfacial bond forms If the material is nontoxic and dissolves, the surrounding tissue replaces it Bioceramics – Traditional definititions " (Almost) Bioinert (e.g. Al2O3, ZrO2, Carbon, TiO2,...) " Bioactive (e.g. bioactive glasses, hydroxyapatite, apatite- wollastonite, etc.) " Resorbable (e.g. tricalcium phosphate, phosphate glasses) Bioactivity … ‘A bioactive material is a material that elicits a specific response at the interface of the material which results in the formation of a bond between the living tissues and the material’ Bioactive glasses e.g. Bioglass® Bioactive composites e.g. polyethylene-Hydroxyapatite Bioactive coatings e.g. Hydroxyapatite on porous titanium alloy All bioactive materials form a layer of hydroxy- carbonate apatite (HCA) when implanted  Hydroxy-Carbonate-Apatite (HCA) Layer Formation Migration of Ca2+ and PO4 3- to the surface through the SiO2 layer to form CaO-P2O5 film on top of SiO2 layer. Incorporation of soluble calcium and phosphates from solution to form amorphous CaO-P2O5 Crystallisation of amorphous CaO-P2O5 by incorporation of OH- and CO32- HCA LAYER Tissue bonding, growth of new tissue Sequence of interfacial reactions involved in forming a bond between bone and a bioactive glass (Hench, 1998)  5. Beschichtung mit bioaktiven Materialien Wichtige Definitionen - Bioaktive Materialien Ein bioaktives Material ist ein Stoff, der eine spezifische biologische Reaktion an der Grenzfläche zwischen Material und Gewebe hervorruft, sodass einer Bindung zwischen Gewebe und Material gebildet wird. Bildung von Knochengewebe (Osteogenese) wird angeregt und es ergibt sich starke Bindung an der Grenzfläche Man unterscheidet: Osteokonduktion = Implantat ruft durch chemische und/oder physikalische Faktoren gerichtetes Wachstum von Knochenzellen hervor; Knochenneubildung nur entlang der Oberfläche des Implantats Osteoinduktion = durch eine vom Implantat freigesetzte Substanz wird Knochenbildung nicht nur direkt an der Oberfläche des Implantats d.h. insgesamt höhere Knochenbildungskapazität  5. Beschichtung mit bioaktiven Materialien Arten von Grenzflächen zwischen Biokeramik und Knochen Anhaftung Beispiel Typ I: Dichte, nicht poröse und „inerte“ Al2O3 (Monokristallin und Polykristallin) Materialien – Knochenwachstum in Irregularitäten an Oberfläche, oder durch einzementieren des Bauteils („morphological fixation“) Typ II: Poröse, inerte Materialien – Knochen Al2O3 (Polykristallin), Hydroxylapatit wächst in poröse Struktur ein („biological beschichtete poröse Implantate fixation“) Typ III: Dichte, nicht poröse Bioaktives Glas („Bioglass®“), Hydroxylapatit oberflächenreaktive Materialien – chemische Bindung zwischen Knochen und Material („bioactive fixation“) Typ IV: Resorbierbare Materialien – Kalziumsulfat, Trikalziumphosphat Langsamer Ersatz des Materials durch Knochen  5. Coating with bioactive materials Bioactive inorganic material – Bioglass® „BIOGLASS®“ " strong bonding to bone tissue " typical chemical composition („45S5“) wt%: 45% SiO2, 24.5% Na2O, 24.5% CaO, 6% P2O5  J. BIOMED. MATER. RES. SYMPOSIUM NO. 2 (Part 1) PP. 117/141 Bonding Mechanisms at the Interface of Ceramic Prosthetic Materials L. L. HENCH, R. J. SPLINTER, and W. C. ALLEN College of Engineering. University of Florida, Gainesville, Florida 32601 and T. K. GREENLEE Veterans Administration Hospital, Gainesville, Florida 32601 Summary The development of a bone-bonding calcia-phosposilicate glass-ceramic is discussed. A theoretical model to explain the interfacial bonding is based upon in-vitro studies of glass-ceramic solubility in interfacial hydroxyapatite crystallization mechanisms, compared with in-vivo rat femur implant histology and ultrastructure results. Prof. Larry L. Hench INTRODUCTION Interfacial reactions between foreign materials and the body are critical in a wide variety of bioengineering problems including: thrombosis in artificial cardio-vascular systems, electrode stability in visual prosthesis, and the fixation of orthopaedic devices. Although this communication is primarily directed towards the more specific problem of orthopaedic fixation via ceramic to bone bonding, the general approach that is discussed should be applicable to other materials problem areas such as those mentioned above. The Interface Between Presently Used Materials and Bone Historically, many materials and different metals have been used to aid in either prosthetic replacement of bones or in osteosynthesis. Today, the most widely used implants in orthopedics are made from metals because of their relative tissue inertness and strength characteristics. In 1937, Venable, Stuck, and Beach published a paper on "The Effects on Bone of the Presence of Metals; Based Upon Electrolysis." In this paper they concluded that dissimilar metals will produce an electrolytic reaction within the tissues and that the alloy of least reaction was one called Vitallium. In 1955, Bowden, Williamson, and Laing published a paper on "The Significance of Metallic Transfer in Orthopaedic Surgery" in which they concluded the ! physiologic dangers of electrochemical dissolution were such that only metals having a very high corrosion resistance should be buried in the human body and also 117 © 1971 by John Wiley & Sons, Inc.  5. Coating with bioactive materials Bioglass®-surface reactions Surface reactivity attracts proteins and cells " strong interaction of proteins / cells with the inorganic surface (HA formation) The inorganic matrix encapsulates organic molecules (e.g. collagen) " Formation of an hybrid matrix MOREOVER … Bioglass® enhances bone formation through a direct control over genes that regulate cell cycle induction and progression “Gene-expression profiling of human osteoblasts following treatment with the ionic products of Bioglass 45S5 dissolution”, Xynos,…Hench, et al. JBMR 55 (2001) 151-157. Hench et al, 2006 Intracellular effects: Enhanced differentiation and proliferation of bone stem cells via gene activation Extracellular effects: Adsorption and desorption of growth factors without loss of conformation and biological activity --> the result is rapid regeneration of bone  5. Coating with bioactive materials Other bioactive materials for implant coatings Calcium phosphates CaHPO4, CaHPO4*2H2O, Ca(PO4)6(OH)2 - Hydroxyapatite " Degradation depends on Ca:P ratio and crystallinity " Application depends on biodegradability and extent of bioactivity "Si-doted hydroxyapatite (Bonfield et al, Cambridge, UK) " Glas-HA-composite coatings (e.g. graded coatings)  5. Coating with bioactive materials Bioglass®-Hydroxyapatite-composite-coatings with graded structure " Optimisation of the bonding between biactive surface and metallic implant " Minimisation of thermal stresses as consquence of different thermal expansion coefficients Bioglass(R)-Hydroxyapatit-composites with graded structure as coating for Ti and Ti alloys Bioglass(R)-Hydroxyapatit-composite with Graded structure (Ban et al. 1999)  5. Coating with bioactive materials Macroscopic aspects: implant-bone interface Stiffeness variation through Surface structuring enhances bond to the interface bone: effect of surface roughness  Examples of hip endoprostheses „Computer-hip stem“; cementless; high-strength titanium based alloy (Aldinger-stem): The shaft of the prothesis is adapted using computer tomography to fit the femur of the recipient patient. Setup of the Laser structuring On silicium  5. Coating with bioactive materials Functionalisation of Bioglass® surfaces OH Et Bioglass OH O O O OH + Et - O - Si NH2 + H H O OH Et OH Silanisation Glutaraldehyd (GA) Substrate Sol-Gel Precursor: Protein/Growth factor APTS Protein coupling agent (3-Aminopropyl-triethoxysilan) Covalent coupling # Specific binding of proteins / growth factors # Control release of proteins / growth factors [Heule M., Rezwan K., Cavalli L. , et al., Advanced Materials, 2003. 15(14): p. 1191-1194.] SBF Bioactivity" formation of HA crystals in SBF 28 days Bretcanu et al, 2007 6. Modification of surfaces  6. Modifizierung der bestehenden Oberflächenchemie Nicht-kovalente („physikalische“) Modifizierung von Oberflächen # Physisorption von Molekülen an Oberflächen aus Lösung # Langmuir-Blodgett-Kuhn Methode zur Übertragung von dünnen organischen Filmen auf Festkörpersubstrate # Gasphasenabscheidung von Metallen und organischen Materialien # Polymermultilagen  6. Modifizierung der bestehenden Oberflächenchemie Physisorption von Molekülen an Oberflächen Bsp.: Adsorption von Polymeren an Festkörperoberflächen # Vielzahl an Techniken –Aufschleudern, Aufrakeln, Aufsprühen, Tauchprozesse,... # Einfache Durchführung # Aber: Geringe Stabilität (Umorientierungen, Delaminierungen, Ausbluten etc.)  6. Modifizierung der bestehenden Oberflächenchemie „Kovalente“ Modifizierung von Oberflächen # Pfropfreaktionen an Oberflächen (durch energetische Strahlung) # Photoreaktionen an Oberflächen # Plasmamodifikationen # Gasphasenabscheidung # Selbstorganisierte Monolagen # Silanisierung  6. Modifizierung der bestehenden Oberflächenchemie Anbindung von Proteinen # Einschluss von biologisch aktiven Proteinen, z.B. Polymermatrizen (verschiedene Herstellungsverfahren) # Maschenweite bestimmt, ob Proteine die Matrix wieder verlassen können # Höhere “Beladung” möglich im Vergleich zu physikalischer Adsorption Structural surface hydrophilic hydrophobic Areas where proteins can attach easily are often also attractive to cells Very hydrophobic surfaces and some very strongly swollen (“soft”) surfaces are not attractive to cells and proteins Surface charge can also affect the attachment  Surface treatment using biological moieties Deposition of hydroxy apatite on collagen networks on Titanium surfaces Polished surface Sand blasted surface /Scharnweber et al./ What can be immobilised in/on synthetic polymers? Proteins, peptides Agent -Enzymes -Cancer therapeutics -Antibodies -Antibiotics -Antigens -Contraceptives -Cell adhesion marker -Peptides, proteins Saccharide Nucleic acids, nucleatides -Oligosaccharide (cell adhesion -Single strand DNA,RNA marker) -Double strands -Polysaccharide (Anti-fouling surface) Lipids Others -Fatty acids - Conjugates/mixtures of above -Phospholipids materials -Glycolipids General concepts and parameters of protein adsorption Hydrophobicity Charged surfaces – of the surface Influence of electrostatics General concepts and Texturing of parameter of protein adsorption protein films Thermodynamics Surface chemistry (e.g. self- (Bonded) polymer films on assembled monolayers the surface able to swell in (SAM’s) of lipid-oligo- water ethylenoxides Patterning of proteins – microstructuring Structure Soft-lithography Proteins Apply cells - Cells are oriented along the “chemical signals” (proteins)  7. Cell adhesion of biomaterial surfaces Surface for cell adhesion ? What determines cell adhesion ? Surface topography Chemical signals (receptor- ligand interactions Stiffness of the surface  7. Cell adhesion at the interface Chemical Signaling Induction of chemical signals on synthetic surfaces Passive Active Adsorption of proteins, Attachment of bioactive which impart cell adhesion ligands or proteins at interface  7. Cell adhesion at the interface Chemical Signaling Passive induction of chemical signals on synthetic surfaces: # Culture medium contains proteins, which are able to attach strongly to specially coated surfaces and convey adhesion # Additionally, cells also produce proteins, which impart adhesion Influence of interfacial properties on biocompatibility and biofunctionality #Reaction from biological systems on synthetic materials #Proteins on the surface #Acute, chronic infection and foreign body reaction #Blood-material contact, haemolysis, infection  7. Cell adhesion at the interface In a separate lecture series on cell biology we will also study: Cell adhesion #How are cells anchored (adhered) to the surface? #What kind of attachment takes place? # What influences the kinetics of cell adhesion on the surface? #Which parameters influences cell adhesion?  8. Interface properties and -characterisation Relevant interface properties # Structure (Gefügestruktur) and crystallinity # Local ion concentration # Local pH # Adsorption of proteins, bacteria etc. # Wettability # Surface morphology (smooth, rough, …) # Mechanical properties # Coating thickness # „Bioactivity“  8. Interface properties and -characterisation Spectroscopic methods # SIMS (Secondary Ion Mass Spectrometry) # XPS (X-Ray Photo Electron Spectroscopy) # ISS (Ion Scattering Spectroscopy) # NMR Nuclear Magnetic Resonance Spectroscopy # Vibration Spectroscopy (Infrared and Raman) # UV Ultraviolet Spectroscopy # EXAFS Extended X-Ray Absorption Fine Structure Spectroscopy Electron microscopic Analysis # SEM/EDS (Scanning Electron Microscope/Energy Dispersive X-Ray Micro Analysis) # ESEM (Environmental Scanning Electron Microscope) # TEM (Transmission Electron Microscope) Other methods (topography, wettability analysis) # Contact angle measurement # AFM Atomic force microscopy # White Light Interferometry Surface Analysis http://www.eag.com/ Surface Analysis http://www.eag. com/  9. Recommended reading Andrade, J. D. (1985): Principles of Protein Adsorption, in: Surface and Interfacial Aspects of Biomedical Polymers, Vol. 2, Protein Adsorption , (Andrade J. D., ed.) pp. 1–80 Jennissen, H. P. (1988): General Aspects of Protein Adsorption. Makromol Chem, Macromol Symp 17, 111–134 Kasemo, B., Lausmaa, J. (1991), in: The Bone – Biomaterial Interface. The Biomaterial-Tissue Interface and its Analogues in Surface Science and Technology (Davies J. E., ed.) University of Toronto Press, Toronto, Buffalo, London, pp. 19–32 Hench,L. L., Bioceramics, J. Am. Ceram. Soc. 81 (1998) 1705- 1728.