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Ultra small nano-crystalline diamond coatings for biomedical applications

This article talks about using PVD technology for tailored metal doped Ultra-nanocrystalline Diamond Coatings in Next-Generation High-Tech and Medical Devices

The field of biomaterials has become a pioneer in materials science during the recent years. The term "biomaterials" represent a multidisciplinary field because of the many diverse technological applications.

Biomaterials are defined as “materials used for production of new generations of implantable medical devices. prostheses to replace natural bone-based human body parts, and human body engineered tissue and artificial organs”.

The funniest thing is "this definition is pillared by the reality that biomaterials are currently used in as many as more than 7800 medical devices".

Biomaterials are also being used in a variety of fields such as

  • development of stem cells

  • tissue engineering

  • gene therapy

  • micro- and nanoelectromechanical systems, which enables new generation of biosensors and

  • implantable power generation devices to galvanize electronics based medical devices.

A lot of technologies are using biomaterials and the range is very wide;

  • cardiovascular and gastrointestinal stents,

  • defibrillators

  • artificial hips and knees

  • dental implants and

  • pacemakers

(only few are mentioned here) all of which are happening in escalating numbers in the worldwide medical market.

The most crucial thing is the product, which save the lives of millions of people in the world every year, must be manufactured with acute precision while employing appropriate/functional biomaterials that are biologically safe, optimum, robust, long-life performance when implanted in the human body.

Carbon is the most biocompatible material as it is the major building blocks of human body.

Diamond is the most stable form of carbon.

Several researches have demonstrated the growth and physical properties of diamond films and reported valuable information for understanding the underlying physical, chemical and structural properties of the various kind of diamond films that are ranging from single crystalline diamond to microcrystalline diamond to nanocrystalline diamond films, which were synthesized by choosing appropriate processes parameters either by Physical Vapor Deposition (PVD) or Chemical Vapor Deposition (CVD) techniques.

Plasma-based physical vapor deposition (PVD) technologies have demonstrated its uniqueness by establishing itself in a widespread use in various industrial applications.

In plasma based PVD processes, the deposition species are either vaporized by supplying heat (thermal evaporation) or by sputtering the target using the plasma by ion bombardment of ideal gas, preferably argon.

Sputter deposition has been popular for many years owing to its flexible, reliable, and effective coating method. At initial days the dc diode sputtering discharge was used as a sputter source, while magnetron sputtering technique was later in the 1970s by including the magnets behing the sputtering target.

Magnetron sputtering has been the workhorse of plasma-based sputtering applications for the past forty-five years.

With the introduction of magnetron sputtering, the several disadvantages of diode sputtering, such as poor deposition rate, non-uniformity over the surface of coating substrates were overcome as the applied voltage can be reduced easily owing to its low-pressure stable operation.

With the further improvement, pulsed magnetron sputtering has been developed where the ionized species of deposits are very high. This helps to increase the energetic impact of deposits on the growing layers, and thus achieve densification and mechanical hardness of the overall coatings.

However, still cathodic arc technology, another PVD technology had been staying as a superior one owing to its ability to produce highly ionized flux of the depositing material.

Cathodic arc technology has their own limitations due to high roughness and bad adhesion of coated layers. Further coating of microtools and biosensors are almost impossible using the cathodic arc technology.

As an improvement in the different dimensions of magnetron sputtering, high power pulsed magnetron sputtering discharges either in unipolar mode or in bipolar mode, referred to as high power impulse magnetron sputtering (HiPIMS) has been proposed as one solution to stay below the power limit for target/magnetron damage, while at the same time achieving a highly ionized flux of the sputtered material.

Using such high-power pulses, carbon can be sputtered out of the target.

Martina Latteman demonstrated the deposition of hard carbon coatings using HiPIMS technology together with Prof. Marcela Bilek and Prof. David McKenzie.

Further deposition of ultrananocrystalline diamond (u-NCDs) through PVD becomes very popular as diamond can be formed in the high arc generations.

Deposition of u-NCD through HiPIMS has been very useful to fabricate lab-on-a-chip, a miniaturized device that integrates onto a single chip. Using that single chip, several analyses such as DNA sequencing or biochemical detection have been done in a laboratory; Research on lab-on-a-chip mainly focuses on human diagnostics and DNA analysis.

Miniaturization of biochemical operations handled in a laboratory has numerous advantages such as:

  • cost efficiency

  • parallelization of treatment

  • ergonomics

  • swift diagnostics

  • sensitivity

Si strips coated with a UNCD film PVD

Schematic of Si strips covered by a mask to inhibit growth of the UNCD film (a) and Si strips coated coated with a UNCD film (b) to perform electrical impedance measurements as described in the text. (c) Cross-section SEM image of an Si microchip encapsulated with a resistant UNCD coating exhibiting superior biocompatibility and corrosion resistance. Figure Curtesy: MRS Bull. vol. 39, p. 621, 2014

SEM top view of UNCD coating on Si microchip PVD

SEM top view of the UNCD coating on an Si microchip before implantation in a rabbit’s eye. (b) UNCD-coated Si microchip implanted in a rabbit’s eye for ~3 years. (c) SEM top view of a UNCD coating on an Si microchip after implantation in a rabbit’s eye for ~3 years. (d) XPS chemical analysis of the surface of the UNCD coating after implantation in a rabbit’s eyes for three years, showing no chemical corrosion.

Figure Curtesy: MRS Bull. vol. 39, p. 621, 2014


Beitrag: Blog2_Post
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