Biomaterial surface modifications

Last updated June 13, 2024

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.^[1] 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, sterility, asepsis, thrombogenicity, susceptibility to corrosion, degradation, and hydrophilicity.

Background of Polymer Biomaterials

Polytetrafluoroethylene (Teflon)

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 forces, so other materials will not stick to the surface.^[2] Teflon is commonly used to reduce friction in biomaterial applications such as in arterial grafts, catheters, and guide wire coatings.

Polyetheretherketone (PEEK)

PEEK is a semicrystalline polymer composed of benzene, ketone, and ether groups. PEEK is known for having good physical properties including high wear resistance and low moisture absorption ^[3] and has been used for biomedical implants due to its relative inertness inside of the human body.

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 (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.^[4]

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
Dental	Dental Implants	Ti alloys	Enhanced Cell growth
Orthopedic	Joints,Ligaments	UHMWPE,PET	Enhance bone adhesion, Enhanced tissue in-growth
Others	General uses	Example	Sterilization, Surface cleaning, Etching, Adhesion promotion, Lubricity tailoring

Abbreviations used in table: PC: polycarbonate, PS: polystyrene, PP: polypropylene, PET: poly (ethylene terephthalate), PTFE: polytetrafluoroethylene, UHMWPE: ultra high molecular weight PE, SiR: silicone rubber

Surface Energy

The 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 measurements using a version of the Young–Laplace equation:

$\gamma _{SV}-\gamma _{SL}=\gamma _{LV}cos\theta$ ^[5]

Where $\gamma _{SV}$ is the surface tension at the interface of solid and vapor, $\gamma _{SL}$ is the surface tension at the interface of solid and liquid, and $\gamma _{LV}$ 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.

Surface Functionalization

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.

Plasma Treatment to Reduce Thrombogenesis

Ammonia plasma treatment can be used to attach amine functional groups. These functional groups lock on to anticoagulants like Heparin decreasing thrombogenicity.^[6]

Covalent Immobilization by Gas Plasma RF Glow Discharge

Polysaccharides have been used as thin film coatings for biomaterial surfaces. Polysaccharides are extremely hydrophilic and will have small 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 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 possess the surface properties to covalently attach polysaccharides. This can be achieved by the introduction of 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 dissociate. Sodium cyanoborohydride (NaBH₃CN) can be used as a stabilizer by reducing the linkages back to an amine.^[7]

Surface Cleaning

There are many examples of contamination of biomaterials that are specific to the preparation or manufacturing process. Additionally, nearly all surfaces are prone to contamination of organic impurities in the air. Contamination layers are usually limited to a monolayer or less of atoms and are thus only detectable by surface analysis techniques, such as XPS. It is unknown whether this sort of contamination is harmful, yet it is still regarded as contamination and will most certainly affect surface properties.

Glow discharge plasma treatment is a technique that is used for cleaning contamination from biomaterial surfaces. Plasma treatment has been used for various biological evaluation studies to increase the surface energy of biomaterial surfaces, as well as cleaning.^[8] Plasma treatment has also been proposed for sterilization of biomaterials for potential implants.^[9]

Schematic of cleaning of a polymer surface using glow plasma discharge. Note the removal of adsorbed molecules and presence of dangling bonds. Glow Plasma Discharge Schematic Polymer Chemistry.png — Schematic of cleaning of a polymer surface using glow plasma discharge. Note the removal of adsorbed molecules and presence of dangling bonds.

Modification of Biomaterials with Polymer Coatings

Another method of altering surface properties of biomaterials is to coat the surface. Coatings are used in many applications to improve biocompatibility and alter properties such as adsorption, lubricity, thrombogenicity, degradation, and corrosion.

Adhesion of Coatings

In general, the lower the surface tension of a liquid coating, the easier it will be to form a satisfactory wet film from it. The difference between the surface tension of a coating and the surface energy of a solid substrate to which a coating is applied affects how the liquid coating flows out over the substrate. It also affects the strength of the adhesive bond between the substrate and the dry film. If for instance, the surface tension of the coating is higher than the surface tension of the substrate, then the coating will not spread out and form a film. As the surface tension of the substrate is increased, it will reach a point to where the coating will successfully wet the substrate but have poor adhesion. Continuous increase in the coating surface tension will result in better wetting in film formation and better dry film adhesion.^[10]

More specifically whether a liquid coating will spread across a solid substrate can be determined from the surface energies of the involved materials by using the following equation:

$S=\gamma _{SA}+(\gamma _{CA}-\gamma _{SC})$ ^[11]

Where S is the coefficient of spreading, $\gamma _{SA}$ is the surface energy of the substrate in air, $\gamma _{CA}$ is the surface energy of the liquid coating in air and $\gamma _{SC}$ is the interfacial energy between the coating and the substrate. If S is positive the liquid will cover the surface and the coating will adhere well. If S is negative the coating will not completely cover the surface, producing poor adhesion.

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 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.^[12]

Guide Wires

Guide wires are an example of an application for biomedical coatings. Guide wires are used in 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.^[13] Guide wires are commonly made from stainless steel or 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.^[14] 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.^[15]

Hydrophobic Coatings

Teflon and Silicone are commonly used hydrophobic coatings for coronary guide wires. Hydrophobic coatings have a lower surface energy and reduce friction in the arteries by up to 48%.^[14] Hydrophobic coatings do not need to be in contact with fluids to form a slippery texture. Hydrophobic coatings maintain tactile sensation in the artery, giving doctors full control of the wire at all times and reducing the risk of perforation; though, the coatings are more thrombogenic than hydrophilic coatings.^[15] The thrombogenicity is due to the proteins in the blood adapting to the hydrophobic environment when they adhere to the coating. This causes an irreversible change for the protein, and the protein remains stuck to the coating allowing for a blood clot to form.^[16]

Magnetic Resonance Compatible Guide Wires

Using an MRI to image the guide wire during use would have an advantage over using x-rays because the surrounding tissue can be examined while the guide wire is advanced. Because most guide wires' core materials are stainless steel they are not capable of being imaged with an MRI. Nitinol wires are not magnetic and could potentially be imaged, but in practice the conductive nitinol heats up under the magnetic radiation which would damage surrounding tissues. An alternative that is being examined is to replace contemporary guide wires with PEEK cores, coated with iron particle embedded synthetic polymers.^[17]

Material	Surface Energy (mN/m)
Teflon	24 ^[11]
Silicone	22 ^[18]
PEEK	42.1 ^[19]
Stainless Steel	44.5 ^[20]
Nitinol	49 ^[21]

Related Research Articles

In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water. In contrast, hydrophiles are attracted to water.

In surface science, surface energy quantifies the disruption of intermolecular bonds that occurs when a surface is created. In solid-state physics, surfaces must be intrinsically less energetically favorable than the bulk of the material, otherwise there would be a driving force for surfaces to be created, removing the bulk of the material by sublimation. The surface energy may therefore be defined as the excess energy at the surface of a material compared to the bulk, or it is the work required to build an area of a particular surface. Another way to view the surface energy is to relate it to the work required to cut a bulk sample, creating two surfaces. There is "excess energy" as a result of the now-incomplete, unrealized bonding between the two created surfaces.

In fluid mechanics, dewetting is one of the processes that can occur at a solid–liquid, solid–solid or liquid–liquid interface. Generally, dewetting describes the process of retraction of a fluid from a non-wettable surface it was forced to cover. The opposite process—spreading of a liquid on a substrate—is called wetting. The factor determining the spontaneous spreading and dewetting for a drop of liquid placed on a solid substrate with ambient gas, is the so-called spreading coefficient $S$ :

<span class="mw-page-title-main">Langmuir–Blodgett trough</span> Laboratory equipment

A Langmuir–Blodgett trough is an item of laboratory apparatus that is used to compress monolayers of molecules on the surface of a given subphase and to measure surface phenomena due to this compression. It can also be used to deposit single or multiple monolayers on a solid substrate.

The contact angle is the angle between a liquid surface and a solid surface where they meet. More specifically, it is the angle between the surface tangent on the liquid–vapor interface and the tangent on the solid–liquid interface at their intersection. It quantifies the wettability of a solid surface by a liquid via the Young equation.

A Langmuir–Blodgett (LB) film is a nanostructured system formed when Langmuir films—or Langmuir monolayers (LM)—are transferred from the liquid-gas interface to solid supports during the vertical passage of the support through the monolayers. LB films can contain one or more monolayers of an organic material, deposited from the surface of a liquid onto a solid by immersing the solid substrate into the liquid. A monolayer is adsorbed homogeneously with each immersion or emersion step, thus films with very accurate thickness can be formed. This thickness is accurate because the thickness of each monolayer is known and can therefore be added to find the total thickness of a Langmuir–Blodgett film.

Plasma cleaning is the removal of impurities and contaminants from surfaces through the use of an energetic plasma or dielectric barrier discharge (DBD) plasma created from gaseous species. Gases such as argon and oxygen, as well as mixtures such as air and hydrogen/nitrogen are used. The plasma is created by using high frequency voltages to ionise the low pressure gas, although atmospheric pressure plasmas are now also common.

Thermal spraying techniques are coating processes in which melted materials are sprayed onto a surface. The "feedstock" is heated by electrical or chemical means.

<span class="mw-page-title-main">Chemical force microscopy</span> Method of microscopy which measures chemical bonding between the probe and surface

In materials science, chemical force microscopy (CFM) is a variation of atomic force microscopy (AFM) which has become a versatile tool for characterization of materials surfaces. With AFM, structural morphology is probed using simple tapping or contact modes that utilize van der Waals interactions between tip and sample to maintain a constant probe deflection amplitude or maintain height while measuring tip deflection. CFM, on the other hand, uses chemical interactions between functionalized probe tip and sample. Choice chemistry is typically gold-coated tip and surface with R−SH thiols attached, R being the functional groups of interest. CFM enables the ability to determine the chemical nature of surfaces, irrespective of their specific morphology, and facilitates studies of basic chemical bonding enthalpy and surface energy. Typically, CFM is limited by thermal vibrations within the cantilever holding the probe. This limits force measurement resolution to ~1 pN, which is still very suitable considering weak COOH/CH₃ interactions are ~20 pN per pair. Hydrophobicity is used as the primary example throughout this consideration of CFM, but certainly any type of bonding can be probed with this method.

Biofilm formation occurs when free floating microorganisms attach themselves to a surface. Although there are some beneficial uses of biofilms, they are generally considered undesirable, and means of biofilm prevention have been developed. Biofilms secrete extracellular polymeric substance that provides a structural matrix and facilitates adhesion for the microorganisms; the means of prevention have thus concentrated largely on two areas: killing the microbes that form the film, or preventing the adhesion of the microbes to a surface. Because biofilms protect the bacteria, they are often more resistant to traditional antimicrobial treatments, making them a serious health risk. For example, there are more than one million cases of catheter-associated urinary tract infections (CAUTI) reported each year, many of which can be attributed to bacterial biofilms. There is much research into the prevention of biofilms.

Adsorption is the accumulation and adhesion of molecules, atoms, ions, or larger particles to a surface, but without surface penetration occurring. The adsorption of larger biomolecules such as proteins is of high physiological relevance, and as such they adsorb with different mechanisms than their molecular or atomic analogs. Some of the major driving forces behind protein adsorption include: surface energy, intermolecular forces, hydrophobicity, and ionic or electrostatic interaction. By knowing how these factors affect protein adsorption, they can then be manipulated by machining, alloying, and other engineering techniques to select for the most optimal performance in biomedical or physiological applications.

Adsorption is the adhesion of ions or molecules onto the surface of another phase. Adsorption may occur via physisorption and chemisorption. Ions and molecules can adsorb to many types of surfaces including polymer surfaces. A polymer is a large molecule composed of repeating subunits bound together by covalent bonds. In dilute solution, polymers form globule structures. When a polymer adsorbs to a surface that it interacts favorably with, the globule is essentially squashed, and the polymer has a pancake structure.

Biomaterials are materials that are used in contact with biological systems. Biocompatibility and applicability of surface modification with current uses of metallic, polymeric and ceramic biomaterials allow alteration of properties to enhance performance in a biological environment while retaining bulk properties of the desired device.

Polymeric materials have widespread application due to their versatile characteristics, cost-effectiveness, and highly tailored production. The science of polymer synthesis allows for excellent control over the properties of a bulk polymer sample. However, surface interactions of polymer substrates are an essential area of study in biotechnology, nanotechnology, and in all forms of coating applications. In these cases, the surface characteristics of the polymer and material, and the resulting forces between them largely determine its utility and reliability. In biomedical applications for example, the bodily response to foreign material, and thus biocompatibility, is governed by surface interactions. In addition, surface science is integral part of the formulation, manufacturing, and application of coatings.

Photolithography is a process in removing select portions of thin films used in microfabrication. Microfabrication is the production of parts on the micro- and nano- scale, typically on the surface of silicon wafers, for the production of integrated circuits, microelectromechanical systems (MEMS), solar cells, and other devices. Photolithography makes this process possible through the combined use of hexamethyldisilazane (HMDS), photoresist, spin coating, photomask, an exposure system and other various chemicals. By carefully manipulating these factors it is possible to create nearly any geometry microstructure on the surface of a silicon wafer. The chemical interaction between all the different components and the surface of the silicon wafer makes photolithography an interesting chemistry problem. Current engineering has been able to create features on the surface of silicon wafers between 1 and 100 μm.

Bovine submaxillary mucin (BSM) coatings are a surface treatment provided to biomaterials intended to reduce the growth of disadvantageous bacteria and fungi such as S. epidermidis, E. coli, and Candida albicans. BSM is a substance extracted from the fresh salivary glands of cows. It exhibits unique physical properties, such as high molecular weight and amphiphilicity, that allow it to be used for many biomedical applications.

The surface chemistry of paper is responsible for many important paper properties, such as gloss, waterproofing, and printability. Many components are used in the paper-making process that affect the surface.

Ultra-low fouling is a rating of a surface's ability to shed potential contamination. Surfaces are prone to contamination, which is a phenomenon known as fouling. Unwanted adsorbates caused by fouling change the properties of a surface, which is often counter-productive to the function of that surface. Consequently, a necessity for anti-fouling surfaces has arisen in many fields: blocked pipes inhibit factory productivity, biofouling increases fuel consumption on ships, medical devices must be kept sanitary, etc. Although chemical fouling inhibitors, metallic coatings, and cleaning processes can be used to reduce fouling, non-toxic surfaces with anti-fouling properties are ideal for fouling prevention. To be considered effective, an ultra-low fouling surface must be able to repel and withstand the accumulation of detrimental aggregates down to less than 5 ng/cm². A recent surge of research has been conducted to create these surfaces in order to benefit the biological, nautical, mechanical, and medical fields.

<span class="mw-page-title-main">Self-healing hydrogels</span> Type of hydrogel

Self-healing hydrogels are a specialized type of polymer hydrogel. A hydrogel is a macromolecular polymer gel constructed of a network of crosslinked polymer chains. Hydrogels are synthesized from hydrophilic monomers by either chain or step growth, along with a functional crosslinker to promote network formation. A net-like structure along with void imperfections enhance the hydrogel's ability to absorb large amounts of water via hydrogen bonding. As a result, hydrogels, self-healing alike, develop characteristic firm yet elastic mechanical properties. Self-healing refers to the spontaneous formation of new bonds when old bonds are broken within a material. The structure of the hydrogel along with electrostatic attraction forces drive new bond formation through reconstructive covalent dangling side chain or non-covalent hydrogen bonding. These flesh-like properties have motivated the research and development of self-healing hydrogels in fields such as reconstructive tissue engineering as scaffolding, as well as use in passive and preventive applications.

Self-cleaning surfaces are a class of materials with the inherent ability to remove any debris or bacteria from their surfaces in a variety of ways. The self-cleaning functionality of these surfaces are commonly inspired by natural phenomena observed in lotus leaves, gecko feet, and water striders to name a few. The majority of self-cleaning surfaces can be placed into three categories:

superhydrophobic
superhydrophilic
photocatalytic.

References

↑ Amid, P. K.; Shulman, A. G.; Lichtenstein, I. L.; Hakakha, M. (1994). "Biomaterials for abdominal wall hernia surgery and principles of their applications". Langenbecks Archiv für Chirurgie. 379 (3): 168–71. doi:10.1007/BF00680113. PMID 8052058. S2CID 22297566.
↑ Mueller, Anja (2006). "Fluorinated Hyperbranched Polymers". Sigma Aldrich. Retrieved 19 May 2013.
↑ "PEEK (PolyEtherEtherKetone) Specifications". Boedeker Plastics. 2013. Retrieved 20 May 2013.
↑ Loh, Ih-Houng (1999). "Plasma Surface Modification In Biomedical Applications" (PDF). AST Technical Journal. 10 (1): 24–30. PMID 10344871. Archived from the original (PDF) on 2008-05-14.
↑ Zisman, W. A. (1964). "Relation of the Equilibrium Contact Angle to Liquid and Solid Constitution". In Fowkes, Frederick M. (ed.). Contact Angle, Wettability, and Adhesion. Advances in Chemistry. Vol. 43. pp. 1–51. doi:10.1021/ba-1964-0043.ch001. ISBN 978-0-8412-0044-9.
↑ Yuan, Shengmei; Szakalas-Gratzl, Gyongyi; Ziats, Nicholas P.; Jacobsen, Donald W.; Kottke-Marchant, Kandice; Marchant, Roger E. (1993). "Immobilization of high-affinity heparin oligosaccharides to radiofrequency plasma-modified polyethylene". Journal of Biomedical Materials Research. 27 (6): 811–9. doi:10.1002/jbm.820270614. PMID 8408111.
↑ Dai, Liming; Stjohn, Heather A. W.; Bi, Jingjing; Zientek, Paul; Chatelier, Ronald C.; Griesser, Hans J. (2000). "Biomedical coatings by the covalent immobilization of polysaccharides onto gas-plasma-activated polymer surfaces". Surface and Interface Analysis. 29: 46–55. doi:10.1002/(SICI)1096-9918(200001)29:1<46::AID-SIA692>3.0.CO;2-6.
↑ den Braber, E.T.; de Ruijter, J.E.; Smits, H.T.J; Ginsel, L.A.; von Recum, A.F.; Jamsen, J.A. (1995). "Effect of parallel surface microgrooves and surface energy on cell growth". Journal of Biomedical Materials Research. 29 (1): 511–518. doi:10.1002/jbm.820290411. hdl: 2066/21896 . PMID 7622536.
↑ Aronsson, B.-O.; Lausmaa, J.; Kasemo, B. (1997). "Glow discharge plasma treatment for surface cleaning and modification of metallic biomaterials". Journal of Biomedical Materials Research. 35 (1): 49–73. doi:10.1002/(SICI)1097-4636(199704)35:1<49::AID-JBM6>3.0.CO;2-M. PMID 9104698.
↑ "Surface Tension, Surface Energy, Contact Angle and Adhesion". Paint Research Association. 2013. Archived from the original on 9 January 2013. Retrieved 22 May 2013.
1 2 Van Iseghem, Lawrence. "Coating Plastics - Some Important Concepts from a Formulators Perspective". Van Technologies Inc. Retrieved 2 June 2013.
↑ Z.W. Wicks; Frank N. Jones; S. Peter Pappas; Douglas A. Wicks. Organic Coatings Science and Technology (2nd expanded ed.). New Jersey: John Wiley & Sons, Inc. ^{[ page needed ]}
↑ Gandelman, Glenn (March 22, 2013). "Percutaneous transluminal coronary angioplasty (PTCA)". Medline Plus. Retrieved 19 May 2013.
1 2 Schröder, J (1993). "The mechanical properties of guidewires. Part III: Sliding friction". CardioVascular and Interventional Radiology. 16 (2): 93–7. doi:10.1007/BF02602986. PMID 8485751. S2CID 7941986.
1 2 Erglis, Andrejs; Narbute, Inga; Sondore, Dace; Grave, Alona; Jegere, Sanda (2010). "Tools & Techniques: coronary guidewires". EuroIntervention. 6 (1): 168–9. doi:10.4244/eijv6i1a24. PMID 20542813.
↑ Labarre, Denis (2001). "Improving blood compatibility of polymeric surfaces". Trends in Biomaterials & Artificial Organs. 15 (1): 1–3. Archived from the original on 2016-03-04. Retrieved 2013-06-16.
↑ Mekle, Ralf; Hofmann, Eugen; Scheffler, Klaus; Bilecen, Deniz (2006). "A polymer-based MR-compatible guidewire: A study to explore new prospects for interventional peripheral magnetic resonance angiography (ipMRA)". Journal of Magnetic Resonance Imaging. 23 (2): 145–55. doi: 10.1002/jmri.20486 . PMID 16374877.
↑ Thanawala, Shilpa K.; Chaudhury, Manoj K. (2000). "Surface Modification of Silicone Elastomer Using Perfluorinated Ether". Langmuir. 16 (3): 1256–60. doi:10.1021/la9906626.
↑ "Solid surface energy data (SFE) for common polymers". November 20, 2007. Retrieved 2 June 2013.
↑ "Selected literature values for surface free energy of solids". Archived from the original on 29 May 2013. Retrieved 5 June 2013.
↑ Michiardi, Alexandra; Aparicio, Conrado; Ratner, Buddy D.; Planell, Josep A.; Gil, Javier (2007). "The influence of surface energy on competitive protein adsorption on oxidized NiTi surfaces". Biomaterials. 28 (4): 586–94. doi:10.1016/j.biomaterials.2006.09.040. PMID 17046057.

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[biomaterial-1] Amid, P. K.; Shulman, A. G.; Lichtenstein, I. L.; Hakakha, M. (1994). "Biomaterials for abdominal wall hernia surgery and principles of their applications". Langenbecks Archiv für Chirurgie. 379 (3): 168–71. doi:10.1007/BF00680113. PMID 8052058. S2CID 22297566.

[teflon-2] Mueller, Anja (2006). "Fluorinated Hyperbranched Polymers". Sigma Aldrich. Retrieved 19 May 2013.

[teflon2-3] "PEEK (PolyEtherEtherKetone) Specifications". Boedeker Plastics. 2013. Retrieved 20 May 2013.

[4] Loh, Ih-Houng (1999). "Plasma Surface Modification In Biomedical Applications" (PDF). AST Technical Journal. 10 (1): 24–30. PMID 10344871. Archived from the original (PDF) on 2008-05-14.

[CA-5] Zisman, W. A. (1964). "Relation of the Equilibrium Contact Angle to Liquid and Solid Constitution". In Fowkes, Frederick M. (ed.). Contact Angle, Wettability, and Adhesion. Advances in Chemistry. Vol. 43. pp. 1–51. doi:10.1021/ba-1964-0043.ch001. ISBN 978-0-8412-0044-9.

[6] Yuan, Shengmei; Szakalas-Gratzl, Gyongyi; Ziats, Nicholas P.; Jacobsen, Donald W.; Kottke-Marchant, Kandice; Marchant, Roger E. (1993). "Immobilization of high-affinity heparin oligosaccharides to radiofrequency plasma-modified polyethylene". Journal of Biomedical Materials Research. 27 (6): 811–9. doi:10.1002/jbm.820270614. PMID 8408111.

[immobilization-7] Dai, Liming; Stjohn, Heather A. W.; Bi, Jingjing; Zientek, Paul; Chatelier, Ronald C.; Griesser, Hans J. (2000). "Biomedical coatings by the covalent immobilization of polysaccharides onto gas-plasma-activated polymer surfaces". Surface and Interface Analysis. 29: 46–55. doi:10.1002/(SICI)1096-9918(200001)29:1<46::AID-SIA692>3.0.CO;2-6.

[RFGD-8] Braber, E.T.; de Ruijter, J.E.; Smits, H.T.J; Ginsel, L.A.; von Recum, A.F.; Jamsen, J.A. (1995). "Effect of parallel surface microgrooves and surface energy on cell growth". Journal of Biomedical Materials Research. 29 (1): 511–518. doi:10.1002/jbm.820290411. hdl: 2066/21896 . PMID 7622536.

[glow-9] Aronsson, B.-O.; Lausmaa, J.; Kasemo, B. (1997). "Glow discharge plasma treatment for surface cleaning and modification of metallic biomaterials". Journal of Biomedical Materials Research. 35 (1): 49–73. doi:10.1002/(SICI)1097-4636(199704)35:1<49::AID-JBM6>3.0.CO;2-M. PMID 9104698.

[SurfaceTension-10] "Surface Tension, Surface Energy, Contact Angle and Adhesion". Paint Research Association. 2013. Archived from the original on 9 January 2013. Retrieved 22 May 2013.

[teflonse-11] 1 2 Van Iseghem, Lawrence. "Coating Plastics - Some Important Concepts from a Formulators Perspective". Van Technologies Inc. Retrieved 2 June 2013.

[CoatingsBook-12] Z.W. Wicks; Frank N. Jones; S. Peter Pappas; Douglas A. Wicks. Organic Coatings Science and Technology (2nd expanded ed.). New Jersey: John Wiley & Sons, Inc. ^{[ page needed ]}

[angioplasty-13] Gandelman, Glenn (March 22, 2013). "Percutaneous transluminal coronary angioplasty (PTCA)". Medline Plus. Retrieved 19 May 2013.

[friction-14] 1 2 Schröder, J (1993). "The mechanical properties of guidewires. Part III: Sliding friction". CardioVascular and Interventional Radiology. 16 (2): 93–7. doi:10.1007/BF02602986. PMID 8485751. S2CID 7941986.

[techniques-15] 1 2 Erglis, Andrejs; Narbute, Inga; Sondore, Dace; Grave, Alona; Jegere, Sanda (2010). "Tools & Techniques: coronary guidewires". EuroIntervention. 6 (1): 168–9. doi:10.4244/eijv6i1a24. PMID 20542813.

[thrombo-16] Labarre, Denis (2001). "Improving blood compatibility of polymeric surfaces". Trends in Biomaterials & Artificial Organs. 15 (1): 1–3. Archived from the original on 2016-03-04. Retrieved 2013-06-16.

[MRI-17] Mekle, Ralf; Hofmann, Eugen; Scheffler, Klaus; Bilecen, Deniz (2006). "A polymer-based MR-compatible guidewire: A study to explore new prospects for interventional peripheral magnetic resonance angiography (ipMRA)". Journal of Magnetic Resonance Imaging. 23 (2): 145–55. doi: 10.1002/jmri.20486 . PMID 16374877.

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