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MID AMERICA Taping and Reeling, Inc.
www.us-
tech.com
630.629.6646
www.matr.com
Production
Treating Titanium and Polymer with Plasma Processing
By Jeff Elliott T Tape and Reel Service & Supplies Surface Mount Axial / Radial Custom Carrier
oday, the materials used to create artificial implants include surgical- grade stainless steel, titanium, titanium alloys, and cobalt-chromium. The materials are often subjected to high, variable loads based on body
position and movement. These metals have also been demonstrated to be highly biocompatible and corrosion resistant. There are drawbacks to metals and alloys, however, including the poten-
tial to interfere with diagnostic imaging, such as MRI and CT scans. The other concern is stress shielding, the reduction in bone density as a result of removal of normal stress from the bone by an implant. This occurs, in part, because the modulus of elasticity of metal is higher than bone, which can af- fect load distribution and lead to bone resorption. That has driven research into alternative solutions, namely resorbable
and non-resorbable polymer implants that have a similar modulus of elastic- ity to bone. The most used polymer in orthopedics is ultra-high molecular- weight polyethylene (UHMWP) or high-density polyethylene (HDP). Among the growing options is the organic polymer thermoplastic Poly-
etheretherketone (commonly known as PEEK), which is already used to cre- ate cages in the $1 billion spinal fusion market. “This is the dilemma: if you use a polymeric material you may be able to
match the modulus of elasticity of bone better, but the downside is it doesn’t in- tegrate into the host bone in the same way,” says Keyvan Behnam of Zimmer Biomet, a medical device company that specializes in orthopedic implants.
Trays Vacuum Sealers Programming 121 Exchange Blvd Glendale Heights, IL 60139
Approaches to Surface Modification A new technique in surface modification using a unique form of electron-
driven plasma treatment has been shown to improve performance of metal and alloys, but also to improve osseointegration of polymer implants. Behnam says his initial interest in examining potential solutions to the
issue was driven by a desire to modify the surface of titanium, PEEK, poly- mers, and other materials to improve cell growth and proliferation relative to the base material. One available technique is the use of plasma spray coatings, where the
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surface is modified by depositing materials such as titanium on a polymer or hy- droxyapatite on titanium. Hydroxyapatite is a calcium phosphate plasma sprayed onto the surface of titanium or some other kind of metal. Titanium plasma spray, on the other hand, is applied to a titanium or polymer surface to roughen it. The other traditional alternative is RF plasma treatment, which modifies
the surface of the implant. Plasma is a state of matter, like a solid, liquid or gas. When enough energy is added to a gas it becomes ionized into a plasma state. The collective properties of these active ingredients can be controlled to clean, ac- tivate, chemically graft, and deposit a wide range of chemistries. RF plasma is created by applying a radio frequency signal (typically
13.56 MHz) that causes the atoms or molecules of the gases introduced into the chamber to increase in temperature until they ionize into a plasma. A sep- arately controlled radio frequency signal under the item pulls the positive ions down to bombard the surface of the material. With Electron Enhanced Material Processing™ (EEMP), a new plasma
etching process developed by VelvETch in partnership with leading plasma equipment manufacturer, PVA TePla America, provides a different low-tem- perature approach for etching of sensitive polymers or metals. In EEMP, precisely controlled waves of electrons — not ions — are accel-
erated to the surface of the material at specific voltages designed to create chemical reactions that release the surface atomic bonds. This allows the ma- terial at the surface of the sample to be gently lifted away. Because electrons have little mass, there is no impact damage to the surface and only nominal heat is generated as a result of the chemical reaction, thus the sample re- mains at room temperature. Unlike RF plasma, which generates a specific re- sult no matter the type of material being processed, EEMP is extremely flex- ible and adaptable to a variety of applications and materials. The variables that can be manipulated and tuned to achieve specific unique results include the gases utilized in the chamber, the electron energy in the discharge (based on the material to be etched) and the temperature. “You can really tune what you are doing to attain the ideal surface you
are trying to create, based on the physical chemical properties,” says Samir Anz of VelvETch. “You may want a certain level of roughness or certain level of smoothness. You may want a surface that is hydrophobic or hydrophilic. The EEMP process essentially has the capacity to do that. Among the additional benefits of EEMP is the ability to achieve atomi-
cally smooth surfaces due to the nature of the process, which removes atoms layer-by-layer, beginning with any existing peaks to within one lattice con- stant of atomic smoothness — less than 0.25 nanometers. Today, plasma chambers are available for EEMP along with contract processing services through a partnership with PVA TePla, a company that
designs and manufactures plasma systems. Contact: PVA TePla America, Inc., 251 Corporate Terrace, Corona, CA
92879 % 951-371-2500 E-mail:
billm@pvateplaamerica.com Web:
www.pvateplaamerica.com r
December, 2020
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