Mechanical and Biomechanical Characterization of a Polyurethane Nucleus Replacement Device Injected and Cured In Situ Within a Balloon

Abstract

BackgroundThe DASCOR device has recently been introduced as an innovative nucleus replacement alternative for the treatment of low-back pain caused by degenerative intervertebral disc disease. The purpose of this study was to characterize, through a series of preclinical mechanical bench and biomechanical tests, the effectiveness of this device.MethodsA number of samples were created using similar preparation methods in order to characterize the nucleus replacement device in multiple mechanical bench tests, using ASTM-guided protocols, where appropriate. Mechanical bench testing included static testing to characterize the device's compressive, shear properties, and fatigue testing to determine the device's compressive fatigue strength, wear, and durability. Biomechanical testing, using human cadaveric lumbar spines, was also conducted to determine the ability of the device to restore multidirectional segmental flexibility and to determine its resulting endplate contact stress.ResultsThe static compressive and shear moduli of the nucleus replacement device were determined to be between 4.2–5.6 MPa and 1.4–1.9 MPa, respectively. Similarly, the ultimate compressive and shear strength were 12,400 N and 6,993 N, respectively. The maximum axial compressive fatigue strength of the tested device that was able to withstand a runout without failure was determined to be approximately 3 MPa. The wear assessment determined that the device is durable and yielded minimal wear rates of 0.29mg/Mc. Finally, the biomechanical testing demonstrated that the device can restore the multidirectional segmental flexibility to a level seen in the intact condition while concurrently producing a uniform endplate contact stress.ConclusionsThe results of the present study provided a mechanical justification supporting the clinical use of the nucleus replacement device and also help explain and support the positive clinical results obtained from two European studies and one US pilot study.Clinical RelevanceNucleus replacement devices are rapidly emerging to address specific conditions of degenerative disc disease. Preclinical testing of such devices is paramount in order to potentially ensure successful clinical outcomes post implantation

Bionate Lumbar Disc Nucleus Prosthesis: Biomechanical Studies in Cadaveric Human Spines

“…After nucleotomy, compared to the intact nucleus, motion range recovery is not complete in our nucleus replacement, as reported with other nucleus implant devices. ,,,− The most significant improvement is in lateral bending, axial torsion, and flexion-extension, as in our nucleus replacement. Therefore, in this area, there is still room for improvement.…”

“…Nucleus replacement technology, available since the 90’ (PDN, Raymedica Inc., Minneapolis, USA), had good clinical results initially, followed by complications related to subsidence and extrusion. − As a result, many other implants have been created, ,,− only a few reaching the market, ,− and most are no longer in use. The reason is that although they achieve biomechanical restoration close to but not equal to an intact intervertebral disc, ,,,− extrusion and subsidence are not fully solved yet. ,,,, …”

“…In addition, some of these materials fracture or break under cycling loading . Some designs have an outside bag that prevents the spillage of implant debris, but the injected core-curing process poses another challenge. , …”

Glutathione-responsive biodegradable poly(urea-urethane)s containing L-cystine-based chain extender

“…Polyurethane, usually prepared through step polymerization of diisocyanate and polyols, possessed a microstructure of alternating soft and hard segments which fulfilled itself with excellent mechanical properties and favorable biocompatibility [2]. In a wide variety of applications as biomaterials, PU was especially utilized in implantable devices such as drug administration carriers [3,4], artificial blood vessels [5,6], heart valves [7][8][9], nucleus prosthesis [10,11], and other tissue engineering materials [12,13]. Some articles have reported biodegradable PU or poly(urea-urethane)s, mainly depending on the soft segment undergoing hydrolytic, enzymatic, and oxidative pathways [14][15][16][17][18], in which hydrolyzation of polyester and oxidation of polyether were the most common pattern [19][20][21].…”

An In Vitro Assessment of Wear Particulate Generated From NUBAC

“…However, regardless of design and material combination, these devices are expected to wear and produce particulate debris over the course of their expected lifetime. [1][2][3][4][5][6][7] Throughout its over 40-year history, the survivorship of total joint arthroplasty has been limited primarily by the generation of wear debris and its subsequent biologic sequela; aseptic loosening caused by a wear particle-mediated infl ammation and osteolytic cascade. 8,9 Therefore, given that the expected lifetime of a disc arthroplasty device can be 40 or more years, signifi cantly longer than that of a total hip or knee implant, wear and the accumulating wear particulate is of clinical concern, as this is considered a critical determinant of the devices' expected lifetime.…”