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Due to their capacity to conduct complex organic transformations, enzymes find extensive use in medical and industrial settings. Unfortunately, enzymes are limited by their poor stability when exposed to harsh non-native conditions. While a host of methods have been developed to stabilize enzymes in non-native conditions, recent research into the synthesis of polymer-enzyme biohybrids using reversible deactivation radical polymerization approaches has demonstrated the potential of increased enzymatic activity in both native and non-native environments. In this manuscript, we utilize the enzyme lipase, as a model system, to explore the impact that modulation of grafted polymer molecular weight has on enzyme activity in both aqueous and organic media. We studied the properties of these hybrids using both solution-phase enzyme activity methods and coarse-grain modeling to assess the impact of polymer grafting density and grafted polymer molecular weight on enzyme activity to gain a deeper insight into this understudied property of the biohybrid system.

Advancements in electrode technologies to both stimulate and record the central nervous system’s electrical activities are enabling significant improvements in both the understanding and treatment of different neurological diseases. However, the current neural recording and stimulating electrodes are metallic, requiring invasive and damaging methods to interface with neural tissue. These electrodes may also degrade, resulting in additional invasive procedures. Furthermore, metal electrodes may cause nerve damage due to their inherent rigidity. This paper demonstrates that novel electrically conductive organic fibers (ECFs) can be used for direct nerve stimulation. The ECFs were prepared using a standard polyester material as the structural base, with a carbon nanotube ink applied to the surface as the electrical conductor. We report on three experiments: the first one to characterize the conductive properties of the ECFs; the second one to investigate the fiber cytotoxic properties in vitro; and the third one to demonstrate the utility of the ECF for direct nerve stimulation in an in vivo rodent model.

Background: Expandable cages that allow for bidirectional expansion, in both height and width, may offer benefits over traditional expandable cages or static cages. Effective stiffness must also be considered, as implants with exceedingly high stiffness may increase subsidence risk and reduce graft loading. Methods: A retrospective case series of 7 patients were assessed with computed tomography (CT) scan at the final 1-year follow-up to evaluate the interbody fusion and configuration of the expandable cage related to the endplates within the intervertebral space. CT scans were reformatted using cage9s tantalum markers as fiducials for single-plane orientation for each intervertebral cage. Device height and width at maximum in situ expansion was measured at its anterior and posterior aspects to evaluate implant deformation. The new bone volume within each cage was measured from the same CT scan data sets and by the Bridwell classification of interbody fusion. Results: The average difference between medial and lateral height measurements was 1.82 mm (±1.08) at the device9s anterior aspect and 1.41 mm (±0.98) at the posterior aspect. The average difference between medial and lateral heights was 18.55% (±9.34) anteriorly and 15.49% (±9.24) posteriorly. There was a successful fusion in all 7 patients, as evidenced by measurable bone volume in the center of each interbody cage with an average of 586.42 mm3 (±237.06). Conclusion: The authors demonstrated the feasibility of successfully using bidirectionally expandable multimaterial cages to achieve interbody fusion. These composite open-architecture cages were found to conform to each patient9s endplate configuration. The authors9 observations support the concept of material selection impacting the effective construct stiffness. The design investigated by the authors provided sufficient anterior column support and successful fusion in all patients. Level of Evidence: 4.

Polyether ether ketone (PEEK, 1) is an important material for the fabrication of implants employed in spinal fusion surgery. Although its radiolucency and favorable elastic modulus have made PEEK an attractive choice for interbody fusion devices, its poor osseointegrative properties prevent the formation of a strong union between implant and surrounding bone structures and remain a major liability. Recent advancements in PEEK surface technology have resulted in improved osseointegration; however, the identification of an ideal implant material has proven challenging. In this manuscript, we describe our preliminary investigation into the realm of PEEK-based fusion devices that has culminated in the discovery of a mild, solution-based process for the preparation of covalently surface modified PEEK biomaterials that display enhanced osteoconductive properties. Surface modification occurred under mild reaction conditions via the acid-mediated addition of various commercially available hydrophilic oxyamine and...

Background Polyetheretherketone (PEEK), and more recently titanium-coated PEEK, have been given serious consideration as biomaterial design choices for spinal interbody implants. Shortcomings in these materials necessitate further innovation into materials research, for example, on polyetherketoneketone (PEKK). Common complications such as surface delamination (as with titanium coating) and lack of bone apposition (as with PEEK) indicate the need for a new material that inherently displays preferable bone growth characteristics without sacrificing structural integrity. Purpose To compare three biomaterials with respect to their osseointegrative capacity. Study Design Evaluate the in vivo material characteristics of three separate biomaterials in an ovine bone defect model: PEEK, titanium-coated PEEK (Ti-coated PEEK), and 3D printed PEKK. Biomechanical, histological and radiographic testing was the basis for evaluation and material characterization. Methods Eight ovine specimens were implanted with one of each of the three types of biomaterials tested in both left and right epicondyles using a femoral bone defect model, and were sacrificed at 8 and 16 weeks. Implants were then analyzed using a push-out method, histological staining, and various radiographic tests. Industry funding was provided for the completion of this research study, followed by an independent third party review of all relevant data for publication. Results PEKK implants demonstrated bone ingrowth, no radiographic interference, no fibrotic tissue membrane formation, significant increase in bony apposition over time, and significantly higher push-out strength compared to standard PEEK. The PEKK implant displayed bone growth characteristics comparable to Ti-coated PEEK with significant improvements in implant integrity and radiographic properties. Conclusion This study found that PEKK displayed preferable characteristics when compared to PEEK and Ti-coated PEEK, and is therefore a potential alternative to their use.

Boyle C Cheng,1 Sravanthi Koduri,1 Charles A Wing,2 Natalie Woolery,3 Daniel J Cook,1 Robert C Spiro2,3 1Neuroscience Institute, Allegheny Health Network, Pittsburgh, PA 15212, USA; 2Research and Development, Aesculap Implant Systems, LLC, Breinigsville, PA 18031, USA; 3Research and Development, Aesculap Biologics, LLC, Breinigsville, PA 18031, USA Purpose: Spinal interbody fusion cages are designed to provide immediate stabilization for adjoining vertebrae and ideally enable bony ingrowth to achieve successful integration. For such an implant, cells must be able to attach, move, grow, and differentiate on its surface. These cellular interactions are dependent on how the implant surface enables the coating and binding of blood and tissue fluid proteins that support cell adhesion. The purpose of this study was to evaluate the in vitro and in vivo osteoblast cell–implant surface interactions that result in osseointegration onto a surface composed of plasma-sprayed titanium on a polyetheretherketone (PEEK) substrate or titanium-coated PEEK (Ti-PEEK) (PlasmaporeXP®) as compared to uncoated PEEK implants.Materials and methods: The influence of the Ti-PEEK surface modification on the biochemical, biomechanical, and histological properties at the bone–implant interface is demonstrated both in vitro using simulated bone-forming cell culture experiments and in vivo using a 12- and 24-week ovine implant model.Results: Osteoblast-like cells attached to the Ti-PEEK surface upregulated early bone-forming activity as measured by an increase in transcription and translation of ALP and BMP-2 when compared to cells on PEEK. Similarly, a significant increase in new bone formation, bony apposition, and pullout strength was demonstrated on Ti-PEEK implants when compared to PEEK implants at 12 and 24 weeks in an ovine implant in vivo model.Conclusion: The study shows that the Ti-PEEK surface demonstrated enhanced osseointegrative properties compared to PEEK both in vitro and in vivo. Keywords: porous titanium, implant coating, osteoblast differentiation, osseointegration, pullout test, sheep

Noninvasive ventilator support using bi-level positive airway pressure/continuous positive airway pressure (BiPAP/CPAP) is commonly utilized for chronic medical conditions like sleep apnea and neuromuscular disorders like amyotrophic lateral sclerosis (ALS) that lead to weakness of respiratory muscles. Generic masks come in standard sizes and are often perceived by patients as being uncomfortable, ill-fitting, and leaky. A significant number of patients are unable to tolerate the masks and eventually stop using their devices. The goal of this project is to develop custom-fit masks to increase comfort, decrease air leakage, and thereby improve patient compliance. A single-patient case study of a patient with variant ALS was performed to evaluate the custom-fit masks. His high nose bridge and overbite of lower jaw caused poor fit with generic masks, and he was noncompliant with his machine. Using desktop Stereolithography three-dimensional (3D) printing and magnetic resonance imaging (MRI) data, a generic mask was extended with a rigid interface such that it was complementary to the patient's unique facial contours. Patient or clinicians interactively select a desired mask shape using a newly developed computer program. Subsequently, a compliant silicone layer was applied to the rigid interface. Ten different custom-fit mask designs were made using computer-aided design software. Patient evaluated the comfort, extent of leakage, and satisfaction of each mask via a questionnaire. All custom-fit masks were rated higher than the standard mask except for two. Our results suggest that modifying generic masks with a 3D-printed custom-fit interface is a promising strategy to improve compliance with BiPAP/CPAP machines.

The two most popular models used in anatomical training for residents, clinicians, or surgeons are cadavers and sawbones. The former is extremely costly and difficult to attain due to cost, ethical implications, and availability, while the latter is said to not have the same tactile fidelity or mechanical properties as human bone. This study examined the potential use of 3D-printed phantoms to emulate cadaveric, human vertebrae, in hopes of acting as a future use over cadavers. In so doing, we developed 3D-printed MedPhantom®, with the intended use to offer similar tactile feel, mechanical characteristics, and visual appearance as human bone. In order to quantify tactility, a mechanical test was developed where a 5-mm diameter diamond-coated bur spinning at 75,000 RPM swept across the specimens while continuously recording the resultant forces (N) and moments (N-cm), The bur sweep motion is common in orthopedic surgery and neurosurgery. Since most 3D-prints do not offer internal, trabecular structure similar to bone, an algorithm was written to create a stochastic framework of internal mesh to mimic cancellous bone within an STL (stereolithography) file. The ranges of mesh parameters were chosen after several visits with the neurosurgeons participating in the project. In order to quantify structural combinations of wall thickness, gap sizes, and varying cylindrical radii within a print, 1000 RPM compression test with a 5-mm diamond-coated bur was performed with resultant forces (N). Two sample t-test shows statistical significance that samples are not equal to the vertebrae (p

The history and rationale of posterior dynamic spinal fusion devices has been derived through the experiences with arthrodesis and devices that serve as adjuncts to such procedures. Dynamic fusion devices provide stabilization through immediate fixation while allowing load sharing. Historically, incorporating these two important concepts in surgical techniques along with the implanted devices facilitates the bone healing process. It stands to reason, spinal fusion techniques that provide immediate stabilization and simultaneously significant graft loading should have the same clinical success seen in other long bone and cervical spine arthrodesis techniques. The load-sharing capability is device-dependent and posterior dynamic constructs theoretically allow dynamic compression of the anterior column higher than that of traditional rigid rod fixation.

STUDY DESIGN Biomechanical human cadaveric cervical flexibility testing with direct load-sharing measurement. OBJECTIVE To determine if the flexibility and load-sharing characteristics of a functional spinal unit were affected by anterior treatments for cervical pathologies. SUMMARY OF BACKGROUND DATA With advancements in polymers, anterior cervical plates have used thermoplastics including recent designs from biodegradable polylactide acids. However, the difference in material properties between metal and polymer can be significant. METHODS Thirteen cervical spine specimens were subjected to 5 treatments at C4-C5. Each treatment for each specimen was subjected to multidirectional flexibility testing. The third cycle was used for treatment comparisons. RESULTS With the integrated load cell spacer, the mean range of motion for the functional spinal unit measured on average 104% + or - 40% normalized to the intact control. The mean biodegradable and titanium plate were 55% + or - 31% and 40% + or - 36%, respectively. Both plates exhibited statistically lower mean range of motions (P = 0.001 and P < 0.001) compared with spacers. The load transmitted through the interbody space was 54% + or - 20%, 43% + or - 20%, and 33% + or - 15% on average for the spacer, biodegradable, and titanium plate constructs, respectively. No statistically significant difference was detected between the biodegradable plate and spacer (P = 0.214). CONCLUSIONS From this research, a biodegradable plate offers immediate postoperative stability significantly different than spacer alone treatments but with graft load sharing that is statistically no different. Thus, the intrinsic lower native material modulus of elasticity of biodegradable polymers has biomechanical implications. However, clinical evidence, particularly for long-term outcomes, will be required in understanding the efficacy of biodegradable polymers.

Background Pure-moment loading is the test method of choice for spinal implant evaluation. However, the apparatuses and boundary conditions employed by laboratories in performing spine flexibility testing vary. The purpose of this study was to quantify the differences, if they exist, in intervertebral range of motion (ROM) resulting from different pure-moment loading apparatuses used in two laboratories. Methods Twenty-four (laboratory A) and forty-two (laboratory B) intact L1-S1 specimens were loaded using pure moments (±7.5 Nm) in flexion-extension (FE), lateral bending (LB) and axial torsion (AT). At laboratory A, pure moments were applied using a system of cables, pulleys and suspended weights in 1.5 Nm increments. At laboratory B, specimens were loaded in a pneumatic biaxial test frame mounted with counteracting stepper-motor-driven biaxial gimbals. ROM was obtained in both labs using identical optoelectronic systems and compared. Results In FE, total L1-L5 ROM was similar, on average, between the two laboratories (lab A: 37.4° ± 9.1°; lab B: 35.0° ± 8.9°, p=0.289). Larger apparent differences, on average, were noted between labs in AT (lab A: 19.4° ± 7.3°; lab B: 15.7° ± 7.1°, p=0.074), and this finding was significant for combined right and left LB (lab A: 45.5° ± 11.4°; lab B: 35.3° ± 8.5°, p Conclusions To our knowledge, this is the first study comparing ROM of multi-segment lumbar spines between laboratories utilizing different apparatuses. The results of this study show that intervertebral ROM in multi-segment lumbar spine constructs are markedly similar in FE loading. Differences in boundary conditions are likely the source of small and sometimes statistically significant differences between the two techniques in LB and AT ROM. The relative merits of each testing strategy with regard to the physiologic conditions that are to be simulated should be considered in the design of a study including LB and AT modes of loading. An understanding of these differences also serves as important information when comparing study results across different laboratories.

Background Lumbar interbody fusion is a common treatment for a variety of spinal pathologies. It has been hypothesized that insufficient mechanical loading of the interbody graft can prevent proper fusion of the joint. The purpose of this study was to evaluate the mechanical stability and anterior column loading sharing characteristics of a posterior dynamic system compared to titanium rods in an anterior lumbar interbody fusion (ALIF) model. Methods Range of motion, interpedicular kinematics and interbody graft loading were measured in human cadaveric lumbar segments tested under a pure moment flexibility testing protocol. Results Both systems provided significant fixation compared to the intact condition and to an interbody spacer alone in flexion extension and lateral bending. No significant differences in fixation were detected between the devices. A significant decrease in graft loading was detected in flexion for the titanium rod treatment compared to spacer alone. No significant differences in graft loading were detected between the spacer alone and posterior dynamic system or between the posterior dynamic system and the titanium rod. Conclusions The results of this study indicate that the posterior dynamic system provides similar fixation compared to that of a titanium rod, however, studies designed to evaluate the efficacy of fixation in a cadaver model may not be sufficiently powered to establish differences in load sharing using the techniques described here.

Introduction. Pedicle based posterior dynamic stabilization systems aim to stabilize the pathologic spine while also allowing sufficient motion to mitigate adjacent level effects. Two flexible constructs that have been proposed to act in such a manner, the Dynesys Dynamic Stabilization System and PEEK rod, have yet to be directly comparedin vitroto a rigid Titanium rod.Methods. Human lumbar specimens were tested in flexion extension, lateral bending, and axial torsion to evaluate the following conditions at L4-L5: Intact, Dynesys, PEEK rod, Titanium rod, and Destabilized. Intervertebral range of motion, interpedicular travel, and interpedicular displacement metrics were evaluated from 3rd-cycle data using an optoelectric tracking system.Results. Statistically significant decreases in ROM compared to Intact and Destabilized conditions were detected for the instrumented conditions during flexion extension and lateral bending. AT ROM was significantly less than Destabilized but not the Intact condition. Similar trends were found for interpedicular displacement in all modes of loading; however, interpedicular travel trends were less consistent. More importantly, no metrics under any mode of loading revealed significant differences between Dynesys, PEEK, and Titanium.Conclusion. The results of this study support previous findings that Dynesys and PEEK constructs behave similarly to a Titanium rodin vitro.

There is currently no universal model or fitting method to characterize the visco-elastic behavior of the lumbar spine observed in displacement versus load hysteresis loops. In this study, proposed methods for fitting these loops, along with the metrics obtained, were thoroughly analyzed. A spline fitting technique was shown to provide a consistent approximation of spinal kinetic behavior that can be differentiated and integrated. Using this tool, previously established metrics were analyzed using data from two separate studies evaluating different motion preservation technologies. Many of the metrics, however, provided no significant differences beyond range of motion analysis. Particular attention was paid to how different definitions of the neutral zone capture the high-flexibility region often seen in lumbar hysteresis loops. As a result, the maximum slope was introduced and shown to be well defined. This new parameter offers promise as a descriptive measurement of spinal instability in vitro and may have future implications in clinical diagnosis and treatment of spinal instability. In particular, it could help in assigning treatments to specific stabilizing effects in the lumbar spine.

Study Design: A comparative biomechanical human cadaveric spine study of a dynamic fusion rod and a traditional titanium rod. Objective: The purpose of this study was to measure and compare the biomechanical metrics associated with a dynamic fusion device, Isobar TTL Evolution, and a rigid rod. Summary of Background Data: Dynamic fusion rods may enhance arthrodesis compared with a rigid rod. Wolff’s law implies that bone remodeling and growth may be enhanced through anterior column loading (AL). This is important for dynamic fusion rods because their purpose is to increase AL. Methods: Six fresh-frozen lumbar cadaveric specimens were used. Each untreated specimen (Intact) underwent biomechanical testing. Next, each specimen had a unilateral transforaminal lumbar interbody fusion performed at L3–L4 using a cage with an integrated load cell. Pedicle screws were also placed at this time. Subsequently, the Isobar was implanted and tested, and finally, a rigid rod replaced the Isobar in the same pedicle screw arrangement. Results: In terms of range of motion, the Isobar performed comparably to the rigid rod and there was no statistical difference found between Isobar and rigid rod. There was a significant difference between the intact and rigid rod and also between intact and Isobar conditions in flexion extension. For interpedicular displacement, there was a significant increase in flexion extension (P=0.017) for the Isobar compared with the rigid rod. Isobar showed increased AL under axial compression compared with the rigid rod (P=0.024). Conclusions: Isobar provided comparable stabilization to a rigid rod when using range of motion as the metric, however, AL was increased because of the greater interpedicular displacement of dynamic rod compared with a rigid rod. By increasing interpedicular displacement and AL, it potentially brings clinical benefit to procedures relying on arthrodesis.

The subtle effects of motion preservation devices are comparatively more difficult to detect based wholly on the range of motion (RoM) parameter, despite the historical success in characterizing fixation devices. Additional approaches such as descriptive facet techniques, i.e., facet translations analysis, and newly defined metrics, i.e., interpedicular displacement (ID) must first be established, verified and standardized. Ideally, more complete biomechanical parameters would facilitate clinical understanding of specific new devices. The recent focus in our lab has been to measure the RoM in conjunction with other parameters, including ID, to more completely characterize a lumbar spine treated with a posterior dynamic systems (PDS). Furthermore, understanding the construct and which components dominate overall tissue response is important for PDS systems.Copyright © 2012 by ASME

Imaging modalities such as X-Ray, computerized tomography (CT), magnetic resonance imaging (MRI), and bone scan have all become essential to the evaluation of bone and soft tissue in patients with back pain. All techniques provide valuable static images of the spine, yet lack the capability of providing detailed information about spinal motion. Dynamic end-range x-rays, the standard in assessment of range of motion and vertebral translation, are taken at the patient’s maximum voluntary bending angle in flexion and extension (FE) and/or lateral bending (LB). The current standard of practice is to measure, with ruler and protractor, the relative change between adjacent vertebrae at each bending extreme. The resulting rotational or translational values are then expressed as the intervertebral angle (IVA) or as a percentage of vertebral body depth, respectively. This method, however, is subject to a high level of patient, imaging site, and observer related variability, in the form of uncontrolled bending angles, disparities in equipment and practices, and manual image analysis. An additional limitation of static imagery is the inability to assess motion in the spine as it traverses between end ranges. This information may expose motion abnormalities that occur mid-range that might otherwise be missed by clinicians. Lastly, motion of the spine may present differently in weighted and un-weighted positions. Effects of muscle activation and gravitational forces are not accounted for by current standards.Copyright © 2012 by ASME

Study Design. In vitro flexibility testing of the lumbar spine. Objective. The goal of this study was to evaluate a motion-preserving posterior dynamic stabilization (PDS) implant based on newly defined parameters describing interpedicular kinematics. Summary of Background Data. PDS implants have been designed as either motion-preserving or adjunct-to-fusion devices to treat various degenerative spinal pathologies. The ambiguity of design and evaluation goals and the inability of traditional biomechanical parameters to appropriately describe the behavior of PDS devices in vitro have served as the impetus to develop kinematic parameters more specific to this class of device. Methods. Flexibility testing of 6 fresh-frozen human lumbar spines was conducted before and after destabilization of the index level (L4–L5). Testing under the same protocol was repeated after treatment at the index level with a 1-level PDS device, extension of the device to the adjacent inferior level (L5–S1), and treatment with a hybrid construct consisting of the PDS implant at L4–L5 and rigid fixation at L5–S1. The kinematic response was recorded using an optoelectric tracking system and reported in terms of intervertebral range of motion (ROM) and newly developed parameters describing interpedicular motion. Results. Based on ROM and interpedicular kinematics, the devices implanted at L4–L5 provide significant but not differing stabilization in flexion-extension with implantation after a significant destabilization procedure. Interpedicular kinematic results indicate that the 2-level construct contributes to significantly more motion at L5–S1 compared with rigid fixation. This result was not detected when evaluated by the ROM metric. Conclusion. Those involved in the design and evaluation of PDS devices may benefit from evaluation of interpedicular kinematics. Evaluating intervertebral motion from the perspective of the pedicle screw allows for a direct and intuitive translation between in vitro test results and design parameters. Furthermore, these parameters may provide additional clinical insight into the biomechanics of the healthy and pathological spine. The study presented indicates that this approach may be more sensitive in detecting differences in implant motion between PDS devices.

Motion preservation technology for the spine has specific design goals that differ dramatically from fixation technology. In order to accurately characterize motion preservation devices, new methods of biomechanical testing along with new metrics for comparison are needed. Devices designed to serve as an adjunct to fusion, i.e., spinal fixation instrumentation, have traditionally relied on arthrodesis to off load the implant over time as the fusion mass gains structural integrity. However, motion preservation devices are expected to function continuously for extended periods of time.Copyright © 2009 by ASME

Motion preservation of the cervical spine has been attractive from several vantage points. Clinically, the ability to limit adjacent level disease has been an important consideration. In addition, the cervical loading conditions may not be as demanding compared to other spinal segments, e.g., the lumbar region. Thus, devices that are designed to preserve motion for the cervical spine are widely perceived as promising technologies and require new methods of evaluation in order to more accurately predict clinical performance.Copyright © 2008 by ASME

BACKGROUND CONTEXT: Nucleus replacement devices are intended to replace or augment the pathologic intervertebral disc, particularly in the early stages of the degenerative cascade. In order to evaluate the clinical viability of these devices, it is necessary to conduct tests simulating potential failure modes in the physiologic setting in addition to bench-top mechanical device testing and traditional in vitro flexibility evaluation. PURPOSE: To evaluate the compressive failure loads of lumbar functional spinal units (FSU) following augmentation with an injectiable in situ cured hydrogel. STUDY DESIGN/SETTING: In vitro biomechanical study. PATIENT SAMPLE: Twenty-three functional spinal units derived from 12 human lumbar segments. OUTCOME MEASURES: Compressive failure load. METHODS: After screening available specimens for advanced degeneration based on computed tomography scans, 23 lumbar FSU were prepared for testing from 12 full lumbar segments. Each FSU underwent injection with the nucleus augmentation gel and removal of all posterior elements by transection of the pedicles. Eleven FSU were randomly selected to the Annulectomy subgroup and subjected to a circumferential outer annulectomy. Each of the 23 FSU was then subjected to compressive load to failure at a rate of 0.1 mm/sec on a compression load frame (MTS 858 Bionix, Eden Prairie, MN). Specimens were loaded at this constant rate until an increase in load was no longer achieved in spite of further displacement or until axial displacement of 6 mm was reached. The maximum load achieved during testing was defined as the failure load. RESULTS: The average failure load for the specimens in the Annulectomy group was 3761 N (SD 1728, Range [1772, 8156]). The average failure load for the specimens without annulectomy was 4636 N (SD 2142, Range [1557, 9134]). A group-wise t-test was conducted between the two treatment groups, and a significant difference was not detected (p50.29). CONCLUSIONS: Surprisingly a difference in compressive failure load could not be detected between treatment groups in spite of the removal of the entire outer annulus in the Annulectomy group. The predominant mode of failure within the Annulectomy group was extrusion of the native nucleus and/or nucleus augmentation mass through the remaining annulus. Five of the 11 specimens failed in this manner. None of the specimens with a fully intact annulus failed in this mode, but rather, failed by visible fracture of the vertebral body or expulsion of the nuclear mass through the inferior or superior endplate. In order for potential failure modes of nucleus augmentation devices to be fully elucidated, further study investigating device migration and extrusion under various modes of loading must be evaluated. Additionally, further studies investigating the influence of bone density and other degenerative characteristics should be conducted. FDA DEVICE/DRUG STATUS: Hydrogel (Not approved for this indication).