Biomaterial surface modifications: Difference between revisions

Revision as of 11:49, 16 June 2013

Revision as of 11:54, 16 June 2013

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Biomaterials exhibit various degrees of compatibility with the harsh environment within a living organism. They need to un-reactive chemically and physically with the body, as well as integrate when with tissue.<ref name=biomaterial>{{cite journal |doi=10.1007/BF00680113 |title=Biomaterials for abdominal wall hernia surgery and principles of their applications |year=1994 |last1=Amid |first1=P. K. |last2=Shulman |first2=A. G. |last3=Lichtenstein |first3=I. L. |last4=Hakakha |first4=M. |journal=Langenbecks Archiv f�rfür Chirurgie |volume=379 |issue=3 |pages=168168–71}}</ref> The extent of compatibility varies based on the application and material required. Often modifications to the surface of a biomaterial system are required to maximize performance. The surface can be modified in many ways, including plasma modification and applying coatings to the substrate. Surface modifications can be used to affect [[Surface energy|surface energy]], [[Adhesion|adhesion]], [[Biocompatibility|biocompatibility]], chemical inertness, lubricity, [[Sterilization (microbiology)|sterility]], [[Asepsis|asepsis]], [[Thrombosis|thrombogenicity]], susceptibility to [[corrosion|corrosion]], degradation, and [[hydrophile|hydrophilicity]].

== Background of Polymer Biomaterials ==

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The [[Surface_energy|surface energy]] is equal to the sum of disrupted molecular bonds that occur at the interface between two different phases. Surface energy can be estimated by [[Contact angle|contact angle]] measurements using a version of the [[Young–Laplace equation|Young–Laplace equation]]:

<math> \gamma_{SV} - \gamma_{SL}= \gamma_{LV} cos\theta </math> <ref name=CA>{{cite journalbook |doi=10.1021/ba-1964-0043.ch001 |chapter=Relation of the Equilibrium Contact Angle to Liquid and Solid Constitution |title=Contact Angle, Wettability, and Adhesion |series=Advances in Chemistry |year=1964 |last1=Zisman |first1=W. A. |isbn=0-8412-0044-0 |volume=43 |pages=11–51 |editor1-first=Frederick M. |editor1-last=Fowkes}}</ref>

Where <math>\gamma_{SV}</math> is the surface tension at the interface of solid and vapor, <math>\gamma_{SL}</math> is the surface tension at the interface of solid and liquid, and <math>\gamma_{LV}</math> is the surface tension at the interface of liquid and vapor. Plasma modification techniques alter the surface of the material, and subsequently the surface energy. Changes in surface energy then alter the surface properties of the material.

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===== Plasma Treatment to Reduce Thrombogenisis =====

Ammonia plasma treatment can be used to attach amine functional groups. These functional groups lock on to anticoagulants like Heparin decreasing thrombogenicity.<ref>{{cite journal |pmid=8408111 |year=1993 |last1=Yuan |first1=S |last2=Szakalas-Gratzl |first2=G |last3=Ziats |first3=NP |last4=Jacobsen |first4=DW |last5=Kottke-Marchant |first5=K |last6=Marchant |first6=RE |title=Immobilization of high-affinity heparin oligosaccharides to radiofrequency plasma-modified polyethylene |volume=27 |issue=6 |pages=811–9 |doi=10.1002/jbm.820270614 |journal=Journal of biomedical materials research}}</ref>

==== Covalent Immobilization by Gas Plasma RF Glow Discharge ====

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[[Polysaccharide|Polysaccharides]] have been used as [[thin film|thin film]] coatings for biomaterial surfaces. Polysaccharides are extremely hydrophilic and will have small [[Contact angle|contact angles]]. They can be used for a wide range of applications due to their wide range of compositions. They can be used to reduce the [[adsorption|adsorption]] of proteins to biomaterial surfaces. Additionally, they can be used as receptor sites, targeting specific biomolecules. This can be used to activate specific biological responses.

Covalent attachment to a substrate is necessary to immobilize polysaccharides, otherwise they will rapidly desorb in a biological environment. This can be a challenge due to the fact that the majority of biomaterials do not posses the surface properties to covalently attach polysaccharides. This can be achieved by the introduction of [[amine|amine groups]] by RF glow discharge plasma. Gases used to form amine groups, including ammonia or n-heptylamine vapor, can be used to deposit a thin film coating containing surface amines. Polysaccharides must also be activated by oxidation of anhydroglucopyranoside subunits. This can be completed with sodium metaperiodate (NaIO₄). This reaction converts anhydroglucopyranoside subunits to cyclic hemiacetal structures, which can be reacted with amine groups to form a Schiff base linkage (a carbon-nitrogen double bond). These linkages are unstable and will easily [[dissociation (chemistry)|dissociate]]. Sodium cyanoborohydride (NaBH₃CN) can be used as a stabilizer by reducing the linkages back to an amine.<ref name=immobilization>{{cite journal |doi=10.1002/(SICI)1096-9918(200001)29:1<46::AID-SIA692>3.0.CO;2-6 |title=Biomedical coatings by the covalent immobilization of polysaccharides onto gas-plasma-activated polymer surfaces |year=2000 |last1=Dai |first1=Liming |last2=Stjohn |first2=Heather A. W. |last3=Bi |first3=Jingjing |last4=Zientek |first4=Paul |last5=Chatelier |first5=Ronald C. |last6=Griesser |first6=Hans J. |journal=Surface and Interface Analysis |volume=29 |pages=4646–55}}</ref>

=== Surface Cleaning ===

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==== Hydrophilic Coatings ====

Hydrophilic coatings can reduce friction in the arteries by up to 83% when compared to bare wires due to their high surface energy.<ref name=friction>{{cite journal |pmid=8485751 |year=1993 |last1=Schröder |first1=J |title=The mechanical properties of guidewires. Part III: Sliding friction |volume=16 |issue=2 |pages=93–7 |journal=Cardiovascular and interventional radiology}}</ref> When the hydrophilic coatings come into contact with bodily fluids they form a waxy surface texture that allows the wire to slide easily through the arteries. Guide wires with hydrophilic coatings have increased trackability and are not very thrombogenic; however the low coefficient of friction increases the risk of the wire slipping and perforating the artery. <ref name=techniques>{{cite journal |first1=Andrejs |last1=Erglis |first2=Inga |last2=Narbute |first3=Dace |last3=Sondore |first4=Alona |last4=Grave |first5=Sanda |last5=Jegere |title=Tools & Techniques: coronary guidewires |journal=EuroIntervention |url=http://www.pcronline.com/eurointervention/tools-and-techniques/coronary-guidewires/download_pdf.php |pmid=20542813 |year=2010 |volume=6 |issue=1 |pages=168–9 |doi=10.4244/ |doi_brokendate=June 16, 2013}}</ref>

==== Hydrophobic Coatings ====

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| Teflon || 24 <ref name=teflonse>{{cite web |url=http://www.vtcoatings.com/plastics.htm|title= Coating Plastics - Some Important Concepts from a Formulators Perspective |last1= Van Iseghem |first1= Lawrence |website= Van Technologies Inc |accessdate=2 June 2013}}</ref>

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| Silicone || 22 <ref name=Siliconese>{{cite journal | author = Shilpa K. Thanawala, Manoj K. Chaudhury | journal = Langmuir| year = 2000 | volume = 16 | pages = 1256–1260 | doi = 10.1021/la9906626 | title = Surface Modification of Silicone Elastomer Using Perfluorinated Ether | issue = 3}}[http://www.lehigh.edu/~mkc4/our%20papers/shilpa_modification%20of%20pdms%20with%20PFE.pdf Link text.] </ref>

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| PEEK || 42.1 <ref name=PEEKse>{{cite web |url=http://www.surface-tension.de/solid-surface-energy.htm|title= Solid surface energy data (SFE) for common polymers |date= November 20, 2007 |accessdate=2 June 2013}}</ref>