The Woodruff School

SUMMARY

Orthopaedic injuries and disorders affect millions of people each year and often require surgical intervention using medical devices. Spinal fusion ranks as the third most common orthopaedic procedure with approximately 500,000 performed each year. Despite the high number and cost of these procedures, it is estimated that 5 – 20% of fusions experience surgical complication or must undergo revision. Many complications can be traced back to inadequate osseointegration of an implanted device. Interbody fusion devices (IBDs) are often used to maintain vertebral spacing and stabilize the spinal segment during fusion, but poor osseointegration and fixation can lead to fibrous encapsulation and migration of the device, causing pain and inhibiting fusion. Therefore, development of new materials-based strategies to enhance osseointegration and device fixation is a promising approach to improve spinal fusion outcomes. The primary goal of this work was to improve the osseointegration of a commonly used IBD material, polyether-ether-ketone (PEEK), by modifying its surface to be porous. Conventional PEEK devices exhibit limited osseointegration, which is often attributed to PEEK’s hydrophobic and chemically inert surface chemistry. However, the smooth surface of conventional PEEK surfaces also prevents osseointegration and fixation by limiting mechanical interlock with apposing bone. Indeed, rough and porous surfaces on non-PEEK devices, such as titanium, demonstrate greatly enhanced osseointegration compared to their smooth counterparts. Although this dependence on surface topography has been described for decades, the development of porous structures from PEEK that maintain sufficient mechanical properties for load-bearing applications has been limited. This thesis introduced a new porous PEEK material for load-bearing orthopaedic applications and investigated how surface topography and surface chemistry influenced its osseointegration. Herein, we demonstrate that porous PEEK enhanced osseointegration relative to smooth and rough surfaces made from PEEK or titanium. Systematic investigation into the relative influence of surface topography and surface chemistry using nano-scale titanium coatings demonstrated that osseointegration was greatest for porous surfaces regardless of whether they possessed a PEEK or titanium surface chemistry. However, surface chemistry was shown to influence osseointegration of smooth and rough surfaces. These results could provide valuable insight for the development of more effective devices for spinal fusions and other orthopaedic applications.

SUBJECT:	Ph.D. Dissertation Defense

BY:	Frederick Torstrick

TIME:	Friday, November 10, 2017, 1:00 p.m.

PLACE:	IBB Building, 1128

TITLE:	EFFECTS OF SURFACE CHEMISTRY AND SURFACE TOPOGRAPHY ON POLYETHER-ETHER-KETONE OSSEOINTEGRATION

COMMITTEE:	Robert E. Guldberg, PhD, Co-Chair (ME) Ken Gall, PhD, Co-Chair (Duke University) Scott D. Boden, MD (ME) Andrés J. García, PhD (University of Wisconsin) William L. Murphy, PhD (Emory University)

SUMMARY Orthopaedic injuries and disorders affect millions of people each year and often require surgical intervention using medical devices. Spinal fusion ranks as the third most common orthopaedic procedure with approximately 500,000 performed each year. Despite the high number and cost of these procedures, it is estimated that 5 – 20% of fusions experience surgical complication or must undergo revision. Many complications can be traced back to inadequate osseointegration of an implanted device. Interbody fusion devices (IBDs) are often used to maintain vertebral spacing and stabilize the spinal segment during fusion, but poor osseointegration and fixation can lead to fibrous encapsulation and migration of the device, causing pain and inhibiting fusion. Therefore, development of new materials-based strategies to enhance osseointegration and device fixation is a promising approach to improve spinal fusion outcomes. The primary goal of this work was to improve the osseointegration of a commonly used IBD material, polyether-ether-ketone (PEEK), by modifying its surface to be porous. Conventional PEEK devices exhibit limited osseointegration, which is often attributed to PEEK’s hydrophobic and chemically inert surface chemistry. However, the smooth surface of conventional PEEK surfaces also prevents osseointegration and fixation by limiting mechanical interlock with apposing bone. Indeed, rough and porous surfaces on non-PEEK devices, such as titanium, demonstrate greatly enhanced osseointegration compared to their smooth counterparts. Although this dependence on surface topography has been described for decades, the development of porous structures from PEEK that maintain sufficient mechanical properties for load-bearing applications has been limited. This thesis introduced a new porous PEEK material for load-bearing orthopaedic applications and investigated how surface topography and surface chemistry influenced its osseointegration. Herein, we demonstrate that porous PEEK enhanced osseointegration relative to smooth and rough surfaces made from PEEK or titanium. Systematic investigation into the relative influence of surface topography and surface chemistry using nano-scale titanium coatings demonstrated that osseointegration was greatest for porous surfaces regardless of whether they possessed a PEEK or titanium surface chemistry. However, surface chemistry was shown to influence osseointegration of smooth and rough surfaces. These results could provide valuable insight for the development of more effective devices for spinal fusions and other orthopaedic applications.