Basic SciencePlasma-sprayed titanium coating to polyetheretherketone improves the bone-implant interface
Introduction
The definition and understanding of biomaterials used in medical devices continues to be refined and clarified. Professor David Williams refined the biomaterial paradigm and redefined the word “biomaterial” that should be considered for all implantable materials; “a biomaterial is a substance that has been engineered to take a form which, alone or as part of a complex system, is used to direct, by control of interactions with components of living systems, the course of any therapeutic or diagnostic procedure, in human or veterinary medicine” [1]. It is within the context of the complex in vivo environment that one must consider any implantable material.
Interbody bony fusion is an established treatment for a variety of degenerative conditions of the spine. Biomechanically, the interbody spacer and graft material combine to provide anterior column support and means to bridge the levels with a biological fusion. The ability to assess fusion status with simple radiographic means as well as clinical issues of delayed union, loss of correction, and device subsidence remain a significant concern for surgeons. Design and development of biomaterials used for interbody fusion have undergone a rapid evolution [2], [3] since the days of autograft and allograft spacers [3], [4] in attempts to address the above concerns. Developments starting from stainless steel cages [5], [6] to carbon fiber implants [7], [8] and degradable polylactides [9], [10] have provided some improvements and increased understanding of the complexity of interbody fusion. Polyetheretherketone (PEEK) [2], [11], [12], [13] has clear benefits in terms of reduced modulus and radiolucency to assist in confirmation of fusion status, whereas the lack of direct bone apposition remains a potential concern.
Early stable fixation and ultimately a biological bridge (fusion) rely on the mechanical and the biological environment to work in concert. Perhaps the ideal interbody fusion device would be one that provides a mechanical environment that can stabilize not only axial loads but off-axis loading in all planes and assist in controlling local micromotion. Direct bone contact to the implant and a robust bone-implant interface appears to be required to achieve all this mechanical stabilization.
Rapid and stable fixation at the bone-implant interface would be regarded as one of the primary goals to achieve clinical efficacy regardless of the surgical site. This has been proven to be true in the traditional orthopedic realm in fixation of uncemented total joint replacements, where bony ongrowth or ingrowth to the implants provides a biological means to achieve implant fixation [14], [15] and dental implants [16], [17], [18]. The application of surface topography or coatings to metal substrates has been shown to improve biological implant fixation [18] through bony ongrowth or ingrowth in preclinical [15], [19], [20], [21], [22], [23], [24] and clinical studies [14], [15], [25]. Direct bone attachment and integration at the implant interface can play a vital role in stress transfer and micromotion as well as influence healing and mechanical performance of the implant.
Although many studies have demonstrated PEEK as biocompatible, [26], [27], [28], [29] preclinical studies and many human studies demonstrate that PEEK does not directly bond to the bone [12], [13], [30], [31], [32]. The present study examined the effects of plasma-spraying titanium on PEEK to present an implant interface to bone that would support early bone integration and long-term stability of the implant-bone interface using an established bone implantation model [21], [22], [23], [24], [33], [34], [35]. We hypothesized that the application of a plasma-sprayed titanium layer to PEEK would encourage early bony fixation and improve the mechanical properties at the bone-implant interface. Early bone fixation of the implant surface has the potential additional benefits of reducing implant complications, such as subsidence, expulsion, or nonunion.
Section snippets
Material and methods
Cylindrical dowels (6×20 mm) of either PEEK or PEEK with a plasma-sprayed coating of titanium (Ti-bond, Spinal Elements) were used in the study. The surface features of the PEEK and Ti-bond samples were qualitatively examined macroscopically using a stereozoom microscope (Olympus BH2; Olympus, Tokyo, Japan) and an environmental scanning electron microscope (eSEM) (Hitachi TM 1000, Hitachi High-Technologies Europe GmbH, Krefeld, Germany). Macroscopic assessment was performed up to ×4
Results
Macroscopic (Fig. 2) and eSEM assessments revealed the lack of surface features on the PEEK sample with a smooth interface, whereas the Ti-bond sample demonstrated the presence of the plasma-sprayed titanium layer (Fig. 3). The plasma-sprayed titanium layer was uniform along the length of the implant. Examining Ti-bond sample after sectioning confirmed a uniform plasma-sprayed titanium layer of approximately 200 microns. The mean surface roughness (Ra) of the Ti-bond and PEEK samples were 33.7
Discussion
Poly (aryl-ether-ether-ketone) commonly referred to as PEEK is perhaps one of the most versatile biomaterials ever implanted. The US patent office revealed the conception date of polyaromatic ketones to be October 27, 1959, with the filing of a US patent by W.H. Bonner and the patent granted to the E. I. du Pont de Nemours and Company commonly known as DuPont in 1962 [37]. A number of excellent reviews are available [11], [12], [26], [29], [31] highlighting the history and characteristics of
References (42)
On the nature of biomaterials
Biomaterials
(2009)- et al.
PEEK biomaterials in trauma, orthopedic, and spinal implants
Biomaterials
(2007) - et al.
Implant fixation by bone ingrowth
J Arthroplasty
(1999) - et al.
Surface treatments of titanium dental implants for rapid osseointegration
Dent Mater
(2007) - et al.
Influence of electron beam melting manufactured implants on ingrowth and shear strength in an ovine model
J Arthroplasty
(2012) - et al.
Polyetheretherketone as a biomaterial for spinal applications
Biomaterials
(2006) - et al.
The effect of substrate roughness and hydroxyapatite coating thickness on implant shear strength
J Arthroplasty
(2002) - et al.
Effect of surgical fit on integration of cancellous bone and implant cortical bone shear strength for a porous titanium
J Arthroplasty
(2011) - et al.
Osseointegration of multiphase anodic spark deposition treated porous titanium implants in an ovine model
J Arthroplasty
(2015) - et al.
Fixation and bone remodeling around a low-modulus stem: seven-year follow-up of a randomized study with use of radiostereometry and dual-energy x-ray absorptiometer
J Arthroplasty
(2012)
Polyetheretherketone—cytotoxicity and mutagenicity in vitro
Biomaterials
The electron beam deposition of titanium on polyetheretherketone (PEEK) and the resulting enhanced biological properties
Biomaterials
Polyetheretherketone (PEEK) cages in cervical applications: a systematic review
Spine J
Current concepts review-interbody fusion cages in reconstructive operations on the spine
J Bone Joint Surg Am
Anterior interbody lumbar spine fusion analysis of Mayo Clinic series
J Bone Joint Surg Am
Arthrodesis by the distraction-compression method using a stainless steel implant
Orthopedics
The Bagby and Kuslich method of lumbar interbody fusion: history, techniques, and 2-year follow-up results of a United States prospective, multicenter trial
Spine
Interbody lumbar fusion using a carbon fiber cage implant versus allograft bone: an investigational study in the Spanish goat
Spine
A carbon fiber implant to aid interbody lumbar fusion: two-year clinical results in the first 26 patients
Spine
Bioabsorbable poly-L-lactic acid cages for lumbar interbody fusion: three-year follow-up radiographic, histologic, and histomorphometric analysis in goats
Spine
The effect of cage stiffness on the rate of lumbar interbody fusion: an in vivo model using poly (l-lactic Acid) and titanium cages
Spine
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FDA device/drug status: Approved (Plasma Sprayed Titanium, Ti Bond-Spinal elements).
Author disclosures: WRW: Grant: Spinal Element (C, Paid directly to institution); Consultant: Medtronic (B), Microport (B); Scientific Advisory Board/Other Office: Teragenix (C). NB: Grant: Spinal Elements (Paid directly to institution). CC: Grant: Spinal Elements (C, Paid directly to institution). DS: Nothing to disclose. RJM: Royalties: Stryker Spine (E); Stock Ownership: Medtronic (F); Research Support (Investigator Salary, Staff/Materials): Cerapedics (C).
The disclosure key can be found on the Table of Contents and at www.TheSpineJournalOnline.com.