Bionate biocompatibility: in vivo study in rabbits

Response to foreign materials includes local tissue reaction, osteolysis, implant loosening, and migration to lymph nodes and organs. Bionate 80A human explants show minor wear and slight local tissue reaction, but we do not know the response at the spinal cord, nerve roots, lymph nodes, or distant organs. This study aims to figure out reactions against Bionate 80A when implanted at the spinal epidural space of 24 20-week-old New Zealand white rabbits. In one group of 12 rabbits, we implanted Bionate 80A on the spinal epidural space, and another group of 12 rabbits was used as the control group. We studied tissues, organs, and tissue damage markers on blood biochemistry, urine tests, and necropsy. The animals' clinical parameters and weight showed no statistically significant differences. At 3 months, the basophils increased slightly in the implant group, platelets decreased in all, and at 6 months, implanted animals showed slight eosinophilia, but none of these changes was statistically significant. External, organ, and spinal tissue examination showed neither toxic reaction, inflammatory changes, or noticeable differences between groups or survival periods. Under microscopic examination, the Bionate 80A particles induced a chronic granulomatous response always outside the dura mater, with giant multinucleated cells holding phagocytized particles and no particle migration to lymph nodes or organs. Thus, it was concluded that Bionate particles, when implanted in the rabbit lumbar epidural space, do not generate a significant reaction limited to the surrounding soft tissues with giant multinucleated cells. In addition, the particles did not cross the dura mater or migrate to lymph nodes or organs

Finite Element Analysis of a Bionate Ring-Shaped Customized Lumbar Disc Nucleus Prosthesis

[EN] Study design: Biomechanical study of a nucleus replacement with a finite element model. Objective: To validate a Bionate 80A ring-shaped nucleus replacement. Methods: The ANSYS lumbar spine model made from lumbar spine X-rays and magnetic resonance images obtained from cadaveric spine specimens were used. All materials were assumed homogeneous, isotropic, and linearly elastic. We studied three options: intact spine, nucleotomy, and nucleus implant. Two loading conditions were evaluated at L-3-L-4, L-4-L-5, and L-5-S-1 discs: a 1000 N axial compression load and this load after the addition of 8 Nm flexion moment in the sagittal plane plus 8 Nm axial rotation torque. Results: Maximum nucleus implant axial compression stresses in the range of 16-34 MPa and tensile stress in the range of 5-16 MPa, below Bionate 80A resistance were obtained. Therefore, there is little risk of permanent implant deformation or severe damage under normal loading conditions. Nucleotomy increased segment mobility, zygapophyseal joint and end plate pressures, and annulus stresses and strains. All these parameters were restored satisfactorily by nucleus replacement but never reached the intact status. In addition, annulus stresses and strains were lower with the nucleus implant than in the intact spine under axial compression and higher under complex loading conditions. Conclusions: Under normal loading conditions, there is a negligible risk of nucleus replacement, permanent deformation or severe damage. Nucleotomy increased segmental mobility, zygapophyseal joint pressures, and annulus stresses and strains. Nucleus replacement restored segmental mobility and zygapophyseal joint pressures close to the intact spine. End plate pressures were similar for the intact and nucleus implant conditions under both loading modes. Manufacturing customized nucleus implants is considered feasible, as satisfactory biomechanical performance is confirmed.This project received funding from the European Union's 6th Framework Programme under project number IP 026599-s.Vanaclocha-Saiz, A.; Vanaclocha, V.; Atienza Vicente, CM.; Clavel, P.; Jorda-Gomez, P.; Barrios, C.; Vanaclocha, L. (2022). Finite Element Analysis of a Bionate Ring-Shaped Customized Lumbar Disc Nucleus Prosthesis. ACS Applied Bio Materials. 5(1):172-182. https://doi.org/10.1021/acsabm.1c01027S1721825

ICR in human cadaveric specimens: An essential parameter to consider in a new lumbar disc prosthesis design

[EN] Study design Biomechanical study in cadaveric specimens. Background The commercially available lumbar disc prostheses do not reproduce the intact disc's Instantaneous centre of Rotation (ICR), thus inducing an overload on adjacent anatomical structures, promoting secondary degeneration. Aim To examine biomechanical testing of cadaveric lumbar spine specimens in order to evaluate and define the ICR of intact lumbar discs. Material and Methods Twelve cold preserved fresh human cadaveric lumbosacral spine specimens were subjected to computerized tomography (CT), magnetic resonance imaging (MRI) and biomechanical testing. Kinematic studies were performed to analyse range of movements in order to determine ICR. Results Flexoextension and lateral bending tests showed a positive linear correlation between the angle rotated and the displacement of the ICR in different axes. Discussion ICR has not been taken into account in any of the available literature regarding lumbar disc prosthesis. Considering our results, neither the actual ball-and-socket nor the withdrawn elastomeric nucleus models fit the biomechanics of the lumbar spine, which could at least in part explain the failure rates of the implants in terms of postoperative failed back syndrome (low back pain). It is reasonable to consider then that an implant should also adapt the equations of the movement of the intact ICR of the joint to the post-surgical ICR. Conclusions This is the first cadaveric study on the ICR of the human lumbar spine. We have shown that it is feasible to calculate and consider this parameter in order to design future prosthesis with improved clinical and biomechanical characteristics.Vanaclocha-Saiz, A.; Atienza Vicente, CM.; Vanaclocha, V.; Belloch, V.; Santabarbara, JM.; Jordá-Gómez, P.; Vanaclocha, L. (2020). ICR in human cadaveric specimens: An essential parameter to consider in a new lumbar disc prosthesis design. North American Spine Society Journal. 2:1-8. https://doi.org/10.1016/j.xnsj.2020.100016S18

Barbed Dental Ti6Al4V Alloy Screw : Design and Bench Testing

Background context. Dental implants are designed to replace a missing tooth. Implant stability is vital to achieving osseointegration and successful implantation. Although there are many implants available on the market, there is room for improvement. Purpose. We describe a new dental implant with improved primary stability features. Study design. Lab bench test studies. Methods. We evaluated the new implant using static and flexion-compression fatigue tests with compression loads, 35 Ncm tightening torque, displacement control, 0.01 mm/s actuator movement speed, and 9-10 Hz load application frequency, obtaining a cyclic load diagram. We applied variable cyclic loadings of predetermined amplitude and recorded the number of cycles until failure. The test ended with implant failure (breakage or permanent deformation) or reaching five million cycles for each load. Results. Mean stiffness was 1151.13 ± 133.62 SD N/mm, mean elastic limit force 463.94 ± 75.03 SD N, and displacement 0.52 ± 0.04 SD mm, at failure force 663.21 ± 54.23 SD N and displacement 1.56 ± 0.18 SD mm, fatigue load limit 132.6 ± 10.4 N, and maximum bending moment 729.3 ± 69.43 mm/N. Conclusions. The implant fatigue limit is satisfactory for incisor and canine teeth and between the values for premolars and molars for healthy patients. The system exceeds five million cycles when subjected to a 132.60 N load, ensuring long-lasting life against loads below the fatigue limit

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

Design: cadaveric spine nucleus replacement study. Objective: determining Bionate 80A nucleus replacement biomechanics in cadaveric spines. Methods: in cold preserved spines, with ligaments and discs intact, and no muscles, L3-L4, L4-L5, and L5-S1 nucleus implantation was done. Differences between customized and overdimensioned implants were compared. Flexion, extension, lateral bending, and torsion were measured in the intact spine, nucleotomy, and nucleus implantation specimens. Increasing load or bending moment was applied four times at 2, 4, 6, and 8 Nm, twice in increasing mode and twice in decreasing mode. Spine motion was recorded using stereophotogrammetry. Expulsion tests: cyclic compression of 50-550 N for 50,000 cycles, increasing the load until there was extreme flexion, implant extrusion, or anatomical structure collapse. Subsidence tests were done by increasing the compression to 6000 N load. Results: nucleotomy increased the disc mobility, which remained unchanged for the adjacent upper level but increased for the lower adjacent one, particularly in lateral bending and torsion. Nucleus implantation, compared to nucleotomy, reduced disc mobility except in flexion-extension and torsion, but intact mobility was no longer recovered, with no effect on upper or lower adjacent segments. The overdimensioned implant, compared to the customized implant, provided equal or sometimes higher mobility. Lamina, facet joint, and annulus removal during nucleotomy caused more damaged than that restored by nucleus implantation. No implant extrusion was observed under compression loads of 925-1068 N as anatomical structures collapsed before. No subsidence or vertebral body fractures were observed under compression loads of 6697.8-6812.3 N. Conclusions: nucleotomized disc and L1-S1 mobility increased moderately after cadaveric spine nucleus implantation compared to the intact status, partly due to operative anatomical damage. Our implant had shallow expulsion and subsidence risks

Nucleus disc replacement : designs and material selection FEA analysis

Study design. Material selection, implant design and Finite Element Analysis (FEA) studies. Background. Nucleus disc replacements, implanted since 1960, have undergone continuous evolution in materials and designs, but subsidence, extrusion, and in vivo degradation limit widespread use. Aim: To create a new nucleus disc replacement that avoids the abovementioned drawbacks. Material and Methods. We created eighteen designs with varied materials and analyzed them with FEA in compression and shear tests in a lumbar spine model programmed in Ansys Parametric Design Language. Results. Bionate® 80A had the closest mechanical characteristics to the intact disc nucleus. Monobloc designs bore the physiological stresses correctly but suffered significant deformations with permanent damage during surgical insertion through the annulus opening. In addition, sandwich designs were too rigid and had an unreliable curing process. Therefore, we chose an oval doughnut-like 5 mm wall monobloc Bionate® 80A nucleus replacement. It minimized implant stress in loading, distributed the loads uniformly, and tolerated the lateral compression during implantation. Conclusions. Out of the eighteen designs we analyzed with FEA, we found that the monobloc oval doughnut-like Bionate 80A nucleus replacement reproduced best the biomechanics of the natural disc nucleus and had the lowest subsidence risk as it transmits the load to the ring apophysis. Furthermore, due to its elasticity implanting it through the average annulotomy required to perform a lumbar microdiscectomy should be possible

ADDISC lumbar disc prosthesis : Analytical and FEA testing of novel implants

The intact intervertebral disc is a six-freedom degree elastic deformation structure with shock absorption. 'Ball-and-socket' TDR do not reproduce these properties inducing zygapophyseal joint overload. Elastomeric TDRs reproduce better normal disc kinematics, but repeated core deformation causes its degeneration. We aimed to create a new TDR (ADDISC) reproducing healthy disc features. We designed TDR, analyzed (Finite Element Analysis), and measured every 500,000 cycles for 10 million cycles of the flexion-extension, lateral bending, and axial rotation cyclic compression bench-testing. In the inlay case, we weighted it and measured its deformation. ADDISC has two semi-spherical articular surfaces, one rotation centre for flexion, another for extension, the third for lateral bending, and a polycarbonate urethane inlay providing shock absorption. The first contact is between PCU and metal surfaces. There is no metal-metal contact up to 2000 N, and CoCr28Mo6 absorbs the load. After 10 million cycles at 1.2-2.0 kN loads, wear 140.96 mg (35.50 mm3), but no implant failures. Our TDR has a physiological motion range due to its articular surfaces' shape and the PCU inlay bumpers, minimizing the facet joint overload. ADDISC mimics healthy disc biomechanics and Instantaneous Rotation Center, absorbs shock, reduces wear, and has excellent long-term endurance

Cadaveric biomechanical studies of ADDISC total lumbar disc prosthesis

Pablo Jorda-Gomez: Methodology, Formal analysis, Data curation. Vicente Vanaclocha: Writing – review & editing, Writing – original draft, Validation, Formal analysis, Data curation, Conceptualization. Amparo Vanaclocha: Writing – review & editing, Writing – original draft, Software, Methodology, Investigation, Data curation. Carlos M. Atienza: Validation, Supervision, Resources, Project administration, Methodology, Investigation, Funding acquisition, Conceptualization. Vicente Belloch: Writing – review & editing, Writing – original draft, Validation, Formal analysis, Data curation, Conceptualization. Juan- Manuel Santabarbara: Validation, Supervision, Project administration, Methodology, Investigation. Carlos Barrios: Writing – review & editing, Validation, Supervision, Methodology, Investigation. Nieves Saiz- Sapena: Writing – review & editing, Visualization, Validation, Super- vision, Project administration. Enrique Medina-Ripoll: Writing – re- view & editing, Writing – original draft, Validation, Formal analysis, Data curation, Conceptualization. Leyre Vanaclocha: Writing – review & editing, Writing – original draft, Methodology, Formal analysis, Data curation.Most total disc replacements provide excessive mobility and not reproduce spinal kinematics, inducing zygapophyseal joint arthritic changes and chronic back pain. In cadaveric lumbosacral spines, we studied if a new lumbar disc prosthesis kinematics mimics the intact intervertebral disc.Medicin