Computational analysis of electrical stimulation to promote tissue healing for hernia repair at varying mesh placement planes.

Development of a tear in the abdominal wall allowing for protrusion of intra-abdominal contents is known as a hernia. This can cause pain, discomfort, and may need surgical repair. Hernias can affect people of any age or demographic. In the USA, over 1 million hernia repair procedures are performed each year. During these surgeries, it is common for a mesh to be utilized to strengthen the repair. Different techniques allow for the mesh to be placed in different anatomical planes depending on hernia location and approach. The locations are onlay, inlay, and sublay, with sublay being split into retromuscular or preperitoneal with sublay being the most commonly used. The use of an electrically active hernia repair mesh is of interest to model as electrical stimulation has been shown to improve soft tissue healing which could reduce recurrence rates. Theoretical 3D COMSOL models were built to evaluate the varying electric fields of an electrically active hernia repair mesh at each of the different anatomical planes. Three voltages were chosen (10, 20, and 30 mV) for the study to simulate a low-level electrical signal and the electric field from a piezoelectric material at the tissue layers surrounding the mesh construct. Based on the model outputs, the optimal mesh placement location was the sublay-retromuscular as this location had the highest electric field values in the connective tissues and rectus abdominis muscle, which are the primary tissues of concern for the healing process and a successful repair.

A preliminary In Vitro viability study of an electrically active hernia mesh on mouse fibroblasts.

Hernias occur when part of an organ, typically the intestines, protrudes through a disruption of the fascia in the abdominal wall, leading to patient pain, discomfort, and surgical intervention. Over one million hernia repair surgeries occur annually in the USA, but globally, hernia surgeries can exceed 20 million. Standard practice includes hernia repair mesh to help hold the compromised tissue together, depending on where the fascial disruption is located and the patient's condition. However, the recurrence rate for hernias after using the most common type of hernia mesh, synthetic, is currently high. Physiological-level electrical stimulation (ES) has shown beneficial effects in improving healing in soft tissue regeneration. Piezoelectric materials can produce low-level electrical signals from mechanical loading to help speed healing. Combining the novelty of piezo elements to create an electrically active hernia repair mesh for faster healing prospects is explored in this study through simulated transcutaneous mechanical loading of the piezo element with therapeutic ultrasound. A tissue phantom was developed using Gelatin #0 and Metamucil® to better simulate a clinical application of the therapeutic ultrasound loading modality. The cellular viability of varying ultrasound intensities and temporal effects was analyzed. Overall, minimal cytotoxicity was observed across all experimental groups during the ultrasound intensity and temporal viability studies.

Design considerations for piezoelectrically powered electrical stimulation: The balance between power generation and fatigue resistance.

Quality and timing of bone healing from orthopedic surgeries, especially lumbar spinal fusion procedures, is problematic for many patients. To address this issue, clinicians often use electrical stimulation to improve surgery success rates and decrease healing time in patients with increased risk of pseudarthrosis, including smokers and diabetics. Current invasive electrical stimulation devices require an implantable battery and a second surgery for removal. Piezoelectric composites within an interbody implant generate sufficient power under physiologic loads to deliver pulsed electrical stimulation without a battery and have demonstrated promising preclinical bone growth and fusion success. The objective of the current study was to assess the power generation and fatigue resistance of three commercially manufactured piezocomposite configurations in a modified implant design to demonstrate efficacy as a robust biomaterial within osteogenic implants. The three configurations were electromechanically assessed under physiological lumbar loading conditions, and all configurations produced sufficient power to promote bone healing. Additionally, electrical and mechanical fatigue performance was assessed under high load, low cycle conditions. All configurations demonstrated runout with no gross mechanical failure and two configurations demonstrated electrical fatigue resistance. Future piezoelectric implant design decisions should be based on power generation needs to stimulate bone growth, as mechanical fatigue efficacy was proven for all piezocomposite configurations tested.

Integration of clinical perspective into biomimetic bioreactor design for orthopedics.

The challenges to accommodate multiple tissue formation metrics in conventional bioreactors have resulted in an increased interest to explore novel bioreactor designs. Bioreactors allow researchers to isolate variables in controlled environments to quantify cell response. While current bioreactor designs can effectively provide either mechanical, electrical, or chemical stimuli to the controlled environment, these systems lack the ability to combine all these stimuli simultaneously to better recapitulate the physiological environment. Introducing a dynamic and systematic combination of biomimetic stimuli bioreactor systems could tremendously enhance its clinical relevance in research. Thus, cues from different tissue responses should be studied collectively and included in the design of a biomimetic bioreactor platform. This review begins by providing a summary on the progression of bioreactors from simple to complex designs, focusing on the major advances in bioreactor technology and the approaches employed to better simulate in vivo conditions. The current state of bioreactors in terms of their clinical relevance is also analyzed. Finally, this review provides a comprehensive overview of individual biophysical stimuli and their role in establishing a biomimetic microenvironment for tissue engineering. To date, the most advanced bioreactor designs only incorporate one or two stimuli. Thus, the cell response measured is likely unrelated to the actual clinical performance. Integrating clinically relevant stimuli in bioreactor designs to study cell response can further advance the understanding of physical phenomenon naturally occurring in the body. In the future, the clinically informed biomimetic bioreactor could yield more efficiently translatable results for improved patient care.

Management of single-level thoracic disc herniation through a modified transfacet approach: A review of 86 patients.

BACKGROUND: Symptomatic thoracic disc herniation (TDH) is rare and does not typically resolve with conservative management. Traditional surgical management is the transthoracic approach; however, this approach can carry significant risk. Posterolateral approaches are less invasive, but no single approach has proven to be more effective than the other results are often dependent on surgeon experience with a particular approach, as well as the location and characteristics of the disc herniation. METHODS: This was retrospective review of a prospectively collected database. Eighty-six patients with TDH treated surgically through the modified transfacet approach were reviewed and evaluated for pain improvement, Nurick grade, and neurological symptoms. Patients were followed for 12 months postoperatively; estimated blood loss, length of hospital stay, hospital course, and postoperative complications were also assessed. RESULTS: All attempts at disc resection were successful. Most patients reported improvement in pain, sensory involvement, and strength. Seventy-nine patients had complete resolution of their symptoms while four patients had unchanged symptoms. Three patients experienced mild neurologic worsening postoperatively, but this resolved back to baseline. One patient experienced myelopathy during the postoperative period that resolved with steroid administration. The procedure was well tolerated with minimal complications. CONCLUSION: TDH can be managed surgically through a variety of approaches. The selection of approach is dependent on surgeon experience with an approach, the patient's health, and the location and type of disc. The transfacet approach is safe and efficacious.

Moment-rotation behavior of intervertebral joints in flexion-extension, lateral bending, and axial rotation at all levels of the human spine: A structured review and meta-regression analysis.

Spinal intervertebral joints are complex structures allowing motion in multiple directions, and many experimental studies have reported moment-rotation response. However, experimental methods, reporting of results, and levels of the spine tested vary widely, and a comprehensive assessment of moment-rotation response across all levels of the spine is lacking. This review aims to characterize moment-rotation response in a consistent manner for all levels of the human spine. A literature search was conducted in PubMed for moment versus rotation data from mechanical testing of intact human cadaveric intervertebral joint specimens in flexion-extension, lateral bending, and axial rotation. A total of 45 studies were included, providing data from testing of an estimated 1,648 intervertebral joints from 518 human cadavers. We used mixed-effects regression analysis to create 75 regression models of moment-rotation response (25 intervertebral joints × 3 directions). We found that a cubic polynomial model provides a good representation of the moment-rotation behavior of most intervertebral joints, and that compressive loading increases rotational stiffness throughout the spine in all directions. The results allow for the direct evaluation of intervertebral ranges of motion across the whole of the spine for given loading conditions. The random-effects outcomes, representing standard deviations of the model coefficients across the dataset, can aid understanding of normal variations in moment-rotation responses. Overall these results fill a large gap, providing the first realistic and comprehensive representations of moment-rotation behavior at all levels of the spine, with broad implications for surgical planning, medical device design, computational modeling, and understanding of spine biomechanics.

Analysis of how compliant layers and encapsulation affect power generated from piezoelectric stacked composites for bone healing medical devices.

Use of piezoelectric materials to harvest energy from human motion is commonly investigated. Traditional piezoelectric materials are inefficient at low frequencies but composite structures can increase efficiency at these frequencies. Compliant layer adaptive composite stack (CLACS) is a new piezoelectric PZT (lead zirconate titanate) structure designed for orthopedic implants to use loads generated during walking to provide electrical stimulation for bone healing. The CLACS structure increases power efficiency and structural properties as compared to PZT alone. The purpose of this study was to investigate the effects of compliant layer and encapsulation thicknesses on strain-related parameters for CLACS predicted by finite element models. Percent changes in strain as compliant layer thickness increased were compared to percent changes in power experimentally produced by CLACS given similar geometries and loading conditions. Percent changes in PZT z-strain matched the trends for increases in experimental power, but was not directly proportional. PZT z-strain and radial strain increased as compliant layer and top and bottom encapsulation thickness increased. PZT z-strain and radial strain decreased as side encapsulation thickness increased for a normalized distributed force on the PZT. The overall goal of this study was to inform future design decisions regarding CLACS structures specifically for use in orthopedic implants.

Stacked PZT Discs Generate Necessary Power for Bone Healing through Electrical Stimulation in a Composite Spinal Fusion Implant.

Electrical stimulation devices can be used as adjunct therapy to lumbar spinal fusion to promote bone healing, but their adoption has been hindered by the large battery packs necessary to provide power. Piezoelectric composite materials within a spinal interbody cage to produce power in response to physiological lumbar loads have recently been investigated. A piezoelectric macro-fiber composite spinal interbody generated sufficient power to stimulate bone growth in a pilot ovine study, despite fabrication challenges. The objective of the present study was to electromechanically evaluate three new piezoelectric disc composites, 15-disc insert, seven-disc insert, and seven-disc Compliant Layer Adaptive Composite Stack (CLACS) insert, within a spinal interbody, and validate their use for electrical stimulation and promoting bone growth. All implants were electromechanically assessed under cyclic loads of 1000 N at 2 Hz, representing physiological lumbar loading. All three configurations produced at least as much power as the piezoelectric macro-fiber composites, validating the use of piezoelectric discs for this application. Future work is needed to characterize the electromechanical performance of commercially manufactured piezoelectric stacks under physiological lumbar loads, and mechanically assess the composite implants according to FDA guidelines for lumbar interbody fusion devices.

The rib cage stiffens the thoracic spine in a cadaveric model with body weight load under dynamic moments.

The thoracic spine presents a challenge for biomechanical testing. With more segments than the lumbar and cervical regions and the integration with the rib cage, experimental approaches to evaluate the mechanical behavior of cadaveric thoracic spines have varied widely. Some researchers are now including the rib cage intact during testing, and some are incorporating follower load techniques in the thoracic spine. Both of these approaches aim to more closely model physiological conditions. To date, no studies have examined the impact of the rib cage on thoracic spine motion and stiffness in conjunction with follower loads. The purpose of this research was to quantify the mechanical effect of the rib cage on cadaveric thoracic spine motion and stiffness with a follower load under dynamic moments. It was hypothesized that the rib cage would increase stiffness and decrease motion of the thoracic spine with a follower load. Eight fresh-frozen human cadaveric thoracic spines with rib cages (T1-T12) were loaded with a 400 N compressive follower load. Dynamic moments of ±â€¯5 N m were applied in lateral bending, flexion/extension, and axial rotation, and the motion and stiffness of the specimens with the rib cage intact have been previously reported. This study evaluated the motion and stiffness of the specimens after rib cage removal, and compared the data to the rib cage intact condition. Range-of-motion and stiffness were calculated for the upper, middle, and lower segments of the thoracic spine. Range-of-motion significantly increased with the removal of the rib cage in lateral bending, flexion/extension, and axial rotation by 63.5%, 63.0%, and 58.8%, respectively (p < 0.05). Neutral and elastic zones increased in flexion/extension and axial rotation, and neutral zone stiffness decreased in axial rotation with rib cage removal. Overall, the removal of the rib cage increases the range-of-motion and decreases the stiffness of cadaveric thoracic spines under compressive follower loads in vitro. This study suggests that the rib cage should be included when testing a cadaveric thoracic spine with a follower load to optimize clinical relevance.

The rib cage reduces intervertebral disc pressures in cadaveric thoracic spines by sharing loading under applied dynamic moments.

The effects of the rib cage on thoracic spine loading are not well studied, but the rib cage may provide stability or share loads with the spine. Intervertebral disc pressure provides insight into spinal loading, but such measurements are lacking in the thoracic spine. Thus, our objective was to examine thoracic intradiscal pressures under applied pure moments, and to determine the effect of the rib cage on these pressures. Human cadaveric thoracic spine specimens were positioned upright in a testing machine, and Dynamic pure moments (0 to ±5 N·m) with a compressive follower load of 400 N were applied in axial rotation, flexion - extension, and lateral bending. Disc pressures were measured at T4-T5 and T8-T9 using needle-mounted pressure transducers, first with the rib cage intact, and again after the rib cage was removed. Changes in pressure vs. moment slopes with rib cage removal were examined. Pressure generally increased with applied moments, and pressure-moment slope increased with rib cage removal at T4-T5 for axial rotation, extension, and lateral bending, and at T8-T9 for axial rotation. The results suggest the intact rib cage carried about 62% and 56% of axial rotation moments about T4-T5 and T8-T9, respectively, as well as 42% of extension moment and 36-43% of lateral bending moment about T4-T5 only. The rib cage likely plays a larger role in supporting moments than compressive loads, and may also play a larger role in the upper thorax than the lower thorax.

Influence of Sequential Ponte Osteotomies on the Human Thoracic Spine With a Rib Cage.

STUDY DESIGN: Biomechanical cadaveric study. OBJECTIVES: The purpose of this study was to determine the change in range of motion (ROM) of the human thoracic spine and rib cage due to sequential Ponte osteotomies (POs). SUMMARY OF BACKGROUND DATA: POs are often performed in deformity correction surgeries to provide flexibility in the sagittal plane at an estimated correction potential of 5° per PO, but no studies have evaluated the biomechanical impact of the procedure on a cadaveric model with an intact rib cage. METHODS: Seven human thoracic cadavers with intact rib cages were loaded with pure moments in flexion, extension, axial rotation, and lateral bending for five conditions: intact, PO at T9-T10, PO at T8-T9, PO at T7-T8, and PO at T6-T7. Motion of T1, T6, and T10 were measured, and overall (T1-T12) and regional (T6-T10) ROMs were reported for each mode of bending at each condition. RESULTS: POs increased ROM in flexion both overall (T1-T12) and regionally (T6-T10), although the magnitude of the increase was marginal (<1°/PO). No significant differences were found in axial rotation or lateral bending. CONCLUSIONS: POs may increase sagittal correction potential before fusion in patients with hyperkyphosis, though more work should be done to determine the magnitude of the changes. LEVEL OF EVIDENCE: Level V.

Evaluation of apparent fracture toughness of articular cartilage and hydrogels.

Recently, biomaterials-based tissue-engineering strategies, including the use of hydrogels, have offered great promise for repairing articular cartilage. Mechanical failure testing in outcome analyses is of crucial clinical importance to the success of engineered constructs. Interpenetrating networks (IPNs) are gaining more attention, due to their superior mechanical integrity. This study provided a combination testing method of apparent fracture toughness, which was applied to both articular cartilage and hydrogels. The apparent fracture toughnesses of two groups, hydrogels and articular cartilage, were evaluated based on the modified single-edge notch test and ASTM standards on the single-edge notch test and compact tension test. The results demonstrated that the toughness for articular cartilage (348 ± 43 MPa/mm½ ) was much higher than that for hydrogels. With a toughness value of 10.8 ± 1.4 MPa/mm½ , IPNs of agarose and poly(ethylene glycol) diacrylate (PEG-DA) looked promising. The IPNs were 1.4 times tougher than PEG-DA alone, although still over an order of magnitude less tough than cartilage. A new method was developed to evaluate hydrogels and cartilage in a manner that enabled a more relevant direct comparison for fracture testing of hydrogels for cartilage tissue engineering. Moreover, a target toughness value for cartilage of using this direct comparison method has been identified (348 ± 43 MPa/mm½ ), and the toughness discrepancy to be overcome between hydrogels and cartilage has been quantified. Copyright © 2014 John Wiley & Sons, Ltd.

Effect of follower load on motion and stiffness of the human thoracic spine with intact rib cage.

Researchers have reported on the importance of the rib cage in maintaining mechanical stability in the thoracic spine and on the validity of a compressive follower preload. However, dynamic mechanical testing using both the rib cage and follower load has never been studied. An in vitro biomechanical study of human cadaveric thoracic specimens with rib cage intact in lateral bending, flexion/extension, and axial rotation under varying compressive follower preloads was performed. The objective was to characterize the motion and stiffness of the thoracic spine with intact rib cage and follower preload. The hypotheses tested for all modes of bending were (i) range of motion, elastic zone, and neutral zone will be reduced with a follower load, and (ii) neutral and elastic zone stiffness will be increased with a follower load. Eight human cadaveric thoracic spine specimen (T1-T12) with intact rib cage were subjected to 5Nm pure moments in lateral bending, flexion/extension, and axial rotation under follower loads of 0-400N. Range of motion, elastic and neutral zones, and elastic and neutral zone stiffness values were calculated for functional spinal units and segments within the entire thoracic section. Combined segmental range of motion decreased by an average of 34% with follower load for every mode. Application of a follower load with intact rib cage impacts the motion and stiffness of the human cadaveric thoracic spine. Researchers should consider including both aspects to better represent the physiologic implications of human motion and improve clinically relevant biomechanical thoracic spine testing.

Effects of follower load and rib cage on intervertebral disc pressure and sagittal plane curvature in static tests of cadaveric thoracic spines.

The clinical relevance of mechanical testing studies of cadaveric human thoracic spines could be enhanced by using follower preload techniques, by including the intact rib cage, and by measuring thoracic intervertebral disc pressures, but studies to date have not incorporated all of these components simultaneously. Thus, this study aimed to implement a follower preload in the thoracic spine with intact rib cage, and examine the effects of follower load, rib cage stiffening and rib cage removal on intervertebral disc pressures and sagittal plane curvatures in unconstrained static conditions. Intervertebral disc pressures increased linearly with follower load magnitude. The effect of the rib cage on disc pressures in static conditions remains unclear because testing order likely confounded the results. Disc pressures compared well with previous reports in vitro, and comparison with in vivo values suggests the use of a follower load of about 400N to approximate loading in upright standing. Follower load had no effect on sagittal plane spine curvature overall, suggesting successful application of the technique, although increased flexion in the upper spine and reduced flexion in the lower spine suggest that the follower load path was not optimized. Rib cage stiffening and removal both increased overall spine flexion slightly, although with differing effects at specific spinal locations. Overall, the approaches demonstrated here will support the use of follower preloads, intact rib cage, and disc pressure measurements to enhance the clinical relevance of future studies of the thoracic spine.

Composite piezoelectric spinal fusion implant: Effects of stacked generators.

Spinal fusion surgeries have a high failure rate for difficult-to-fuse patients. A piezoelectric spinal fusion implant was developed to overcome the issues with other adjunct therapies. Stacked generators were used to improve power generation at low electrical load resistances. The effects of the number of layers on average maximum power and the optimal electrical load resistance were characterized. The effects of mechanical preload, load frequency, and amplitude on maximum power and optimal electrical load resistance were also characterized. Increasing the number of layers from one to nine was found to lower the optimal electrical load resistance from 1.00 GΩ to 16.78 MΩ while maintaining maximum power generation. Mechanical preload did not have a significant effect on power output or optimal electrical load resistance. Increases in mechanical loading frequency increased average maximum power, while decreasing the optimal electrical load resistance. Increases in mechanical loading amplitude increased average maximum power output without affecting the optimal electrical load resistance.

Grade 1 spondylolisthesis and interspinous device placement: removal in six patients and analysis of current data.

BACKGROUND: In the treatment of patients with Grade 1 spondylolisthesis, the use of interspinous devices has been controversial for nearly a decade. Several authors have suggested that Grade 1 spondylolisthesis be considered a contraindication for interspinous device placement. METHODS: We removed interspinous devices in six symptomatic Grade 1 spondylolisthesis patients and analyzed pertinent literature. RESULTS: All six patients reported an improvement in symptoms following device removal and subsequent instrumented fusion. One patient who had not been able to walk due to pain regained the ability to walk. Several articles were identified related to spondylolisthesis and interspinous devices. CONCLUSIONS: Regarding patients receiving interspinous devices for symptomatic lumbar spinal stenosis, several high-quality studies have failed to demonstrate a statistical difference in outcomes between patients with or without Grade 1 spondylolisthesis. Nevertheless, surgeons should have a high degree of suspicion when considering use of interspinous devices in this patient population.

Mechanical analysis of the human cadaveric thoracic spine with intact rib cage.

The goal of this study was to characterize the overall in-plane and basic coupled motion of a cadaveric human thoracic spine with intact true ribs. Researchers are becoming increasingly interested in the thoracic spine due to both the high prevalence of injury and pain in the region and also innovative surgical techniques that utilize the rib cage. Computational models can be useful tools to predict loading patterns and understand effects of surgical procedures or medical devices, but they are often limited by insufficient cadaveric input data. In this study, pure moments to ±5 Nm were applied in flexion-extension, lateral bending, and axial rotation to seven human cadaveric thoracic spine specimens (T1-T12) with intact true ribs to determine symmetry of in-plane motion, differences in neutral and elastic zone motion and stiffness, and significance of out-of-plane rotations and translations. Results showed that lateral bending and axial rotation exhibited symmetric motion, neutral and elastic zone motion and stiffness values were significantly different for all modes of bending (p<0.05), and out-of-plane rotations and translations were greater than zero for most rotations and translations. Overall in-plane rotations were 7.7±3.4° in flexion, 9.6±3.7° in extension, 23.3±8.4° in lateral bending, and 26.3±12.2° in axial rotation. Results of this study could provide inputs or validation comparisons for computational models. Future studies should characterize coupled motion patterns and local and regional level biomechanics of cadaveric human thoracic spines with intact true ribs.

Mechanical Contribution of the Rib Cage in the Human Cadaveric Thoracic Spine.

STUDY DESIGN: An in vitro biomechanical human cadaveric study of T1-T12 thoracic specimens was performed with 4 conditions (with and without rib cage, instrumented and uninstrumented) in flexion-extension, lateral bending, and axial rotation. OBJECTIVE: The objective was to understand the influence of the rib cage on motion and stiffness parameters of the human cadaveric thoracic spine. Hypotheses tested for overall motion in all modes of bending for both uninstrumented and instrumented specimens were (i) in-plane range of motion and neutral and elastic zones will be greater without the rib cage, (ii) neutral and elastic zone stiffness values will be different for specimens without the rib cage, and (iii) out-of-plane rotations will be different for specimens without the rib cage. SUMMARY OF BACKGROUND DATA: The rib cage is presumed to provide significant stability to the thoracic spine, but no studies have been conducted to determine the influence of the rib cage in both uninstrumented and instrumented conditions in the full thoracic human cadaveric specimens. METHODS: Seven human cadaveric spine specimens (T1-T12) with 4 conditions (with and without rib cage, instrumented and uninstrumented) were subjected to 5 N·m pure moments in flexion-extension, lateral bending, and axial rotation. Range of motion, neutral and elastic zones, neutral and elastic zone stiffness values, and out-of-plane rotations were calculated for the overall specimen. RESULTS: In-plane range of motion was significantly higher without a rib cage for most modes of bending. Out-of-plane motions were also influenced by the rib cage. Neutral zone stiffness was significantly higher with a rib cage present. CONCLUSION: Testing without a rib cage yields different motion and stiffness measures, directly impacting the translation of research results to clinical interpretation. Researchers should consider these differences when evaluating the mechanical impact of surgical procedures or instrumentation in cadaveric or computational models. LEVEL OF EVIDENCE: 5.

Theoretical model of a piezoelectric composite spinal fusion interbody implant.

Failure rates of spinal fusion are high in smokers and diabetics. The authors are investigating the development of a piezoelectric composite biomaterial and interbody device design that could generate clinically relevant levels of electrical stimulation to help improve the rate of fusion for these patients. A lumped parameter model of the piezoelectric composite implant was developed based on a model that has been utilized to successfully predict power generation for piezoceramics. Seven variables (fiber material, matrix material, fiber volume fraction, fiber aspect ratio, implant cross-sectional area, implant thickness, and electrical load resistance) were parametrically analyzed to determine their effects on power generation within reasonable implant constraints. Influences of implant geometry and fiber aspect ratio were independent of material parameters. For a cyclic force of constant magnitude, implant thickness was directly and cross-sectional area inversely proportional to power generation potential. Fiber aspect ratios above 30 yielded maximum power generation potential while volume fractions above 15% showed superior performance. This investigation demonstrates the feasibility of using composite piezoelectric biomaterials in medical implants to generate therapeutic levels of direct current electrical stimulation. The piezoelectric spinal fusion interbody implant shows promise for helping increase success rates of spinal fusion.