Biomaterial surface modifications: Difference between revisions

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Biomaterials exhibit various degrees of compatibility with the harsh environment within a living organism. They need to be nonreactive chemically and physically with the body, as well as integrate when deposited into tissue.<ref name=biomaterial>{{cite journal |doi=10.1007/BF00680113 |pmid=8052058 |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 für Chirurgie |volume=379 |issue=3 |pages=168–71|s2cid=22297566 }}</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]], [[adhesion]], [[biocompatibility]], chemical inertness, lubricity, [[Sterilization (microbiology)|sterility]], [[asepsis]], [[Thrombosis|thrombogenicity]], susceptibility to [[corrosion]], degradation, and [[hydrophile|hydrophilicity]].

== Background of Polymer Biomaterials ==

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=== Polytetrafluoroethylene (Teflon) ===

[[polytetrafluoroethylene|Teflon]] is a hydrophobic polymer composed of a carbon chain saturated with fluorine atoms. The fluorine-carbon bond is largely ionic, producing a strong dipole. The dipole prevents Teflon from being susceptible to [[Van der Waals force|Van der Waals forces]]s, so other materials will not stick to the surface.<ref name=teflon>{{cite web |url=http://www.sigmaaldrich.com/technical-documents/articles/material-matters/fluorinated-hyperbranched.html |title= Fluorinated Hyperbranched Polymers |last1= Mueller |first1= Anja |year= 2006 |work= Sigma Aldrich |accessdate=19 May 2013}}</ref> Teflon is commonly used to reduce friction in biomaterial applications such as in arterial grafts, catheters, and guide wire coatings.

=== Polyetheretherketone (PEEK) ===

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== Plasma modification of biomaterials ==

Plasma modification is one way to alter the surface of biomaterials to enhance their properties. During plasma modification techniques, the surface is subjected to high levels of excited gases that alter the surface of the material. Plasma's are generally generated with a [[Radio frequency|radio frequency (RF)]] field. Additional methods include applying a large (~1KV) DC voltage across electrodes engulfed in a gas. The plasma is then used to expose the biomaterial surface, which can break or form chemical bonds. This is the result of physical collisions or chemical reactions of the excited gas molecules with the surface. This changes the surface chemistry and therefore surface energy of the material which affects the adhesion, biocompatibility, chemical inertness, lubricity, and sterilization of the material. The table below shows several biomaterial applications of plasma treatments.<ref>{{cite webjournal |last=Loh |first=Ih-Houng |workjournal=AST Technical Journal |title=Plasma Surface Modification In Biomedical Applications |year=1999 |volume=10 |issue=1 |pages=24–30 |pmid=10344871 |url=http://www.astp.com/PDFs/PSBiomed.pdf |url-status=dead |archiveurl=https://web.archive.org/web/20080514091530/http://www.astp.com/PDFs/PSBiomed.pdf |archivedate=2008-05-14 }}</ref>

{| class="wikitable"

|-

! Applications of Plasma Treatments!! Devices !! Materials !! Purposes

|-

| Biosensor || Sensor Membranes, Diagnostic biosensors || PC, Cellulose,[[Cuprophane]], PP, PS || Immobilization of biomolecules, non-fouling surfaces

|-

| Cardiovascular || Vascular grafts, Catheters || PET,PTFE,PE,SiR || Improved biocompatibility, Wettability tailoring, lubricious coatings, Reduced friction, Antimicrobial coatings

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[[Surface modification]] techniques have been extensively researched for the application of adsorbing biological molecules. Surface functionalization can be performed by exposing surfaces to RF plasma. Many gases can be excited and used to functionalize surfaces for a wide variety of applications. Common techniques include using air plasma, oxygen plasma, and ammonia plasma as well as other exotic gases. Each gas can have varying effects on a substrate. These effects decay with time as reactions with molecules in air and contamination occur.

[[File:Argon plasma used for polymer surface functionalization prior to bonding.Argon plasma used for polymer surface functionalization prior to bonding.png|125 × 240 pixels.0px|thumb|right|Argon plasma used for polymer surface functionalization prior to bonding.]]

==== Plasma Treatment to Reduce Thrombogenesis ====

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==== Corrosion Protection ====

Organic coatings are a common way to protect a metallic substrate from [[corrosion]]. Up until ~1950 it was thought that coatings act as a physical barrier which disallows moisture and oxygen to contact the metallic substrate and form a corrosion cell. This cannot be the case because the [[Permeation|permeability]] of paint films is very high. It has since been discovered that corrosion protection of steel depends greatly upon the adhesion of a noncorrosive coating when in the presence of water. With low adhesion, osmotic cells form underneath the coating with high enough pressures to form blisters, which expose more unprotected steel. Additional non-osmotic mechanisms have also been proposed. In either case, sufficient adhesion to resist displacement forces is required for corrosion protection.<ref name=CoatingsBook>{{cite book|author1=Z.W. Wicks |author2=Frank N. Jones |author3=S. Peter Pappas |author4=Douglas A. Wicks | title = Organic Coatings Science and Technology | edition = 2nd expanded | ___location = New Jersey | publisher = [[John Wiley & Sons, Inc.]] }}{{page needed|date=June 2013}}</ref>

=== Guide Wires ===

Guide wires are an example of an application for biomedical coatings. Guide wires are used in [[percutaneous coronary intervention|coronary angioplasty]] to correct the effects of [[coronary artery disease]], a disease that allows plaque build up on the walls of the arteries. The guide wire is threaded up through the femoral artery to the obstruction. The guide wire guides the balloon catheter to the obstruction where the catheter is inflated to press the plaque against the arterial walls.<ref name=angioplasty>{{cite web |url=https://www.nlm.nihmedlineplus.gov/medlineplus/ency/anatomyvideos/000096.htm |title= Percutaneous transluminal coronary angioplasty (PTCA) |last1= Gandelman |first1= Glenn |date= March 22, 2013 |work= Medline Plus |accessdateaccess-date=19 May 2013}}</ref> Guide wires are commonly made from stainless steel or [[Nickel Titanium|Nitinol]] and require polymer coatings as a surface modification to reduce friction in the arteries. The coating of the guide wire can affect the trackability, or the ability of the wire to move through the artery without kinking, the tactile feel, or the ability of the doctor to feel the guide wire's movements, and the thrombogenicity of the wire.

==== 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=CardiovascularCardioVascular and Interventional Radiology |doi=10.1007/BF02602986|s2cid=7941986 }}</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/eijv6i1a24 |url-access=subscription }}</ref>

==== Hydrophobic Coatings ====

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{{Reflist}}

[[Category:BiologyBiomaterials]]