Stand-Alone Biomimetic Supple Artificial Intervertebral Discs Composed of Cubic Triaxial Three-Dimensional Fabrics

Research Article

Austin J Orthopade & Rheumatol. 2019; 6(1): 1075.

Stand-Alone Biomimetic Supple Artificial Intervertebral Discs Composed of Cubic Triaxial Three-Dimensional Fabrics

Shikinami Y*

Shikinami Yasuo Institute LLC, Japan

*Corresponding author: Shikinami Yasuo, Shikinami Yasuo Institute LLC, Japan

Received: July 23, 2019; Accepted: August 29, 2019; Published: September 05, 2019

Abstract

Objective: Existing Artificial Discs (AD) to preserve original mobility of Biological Intervertebral Disc (BID) essentially consist of the superposition of solid plates and core materials, however they are unable to fully make up its movable faculty. This article is to provide a biomimetic supple Artificial Intervertebral Disc (AID) that fulfills the mobile function quite similar to BID, which is well supplied with long-term dynamic mechanical durability and stand-alone possibility along with less invasive insertion into the correct disc site required.

Study Design: The AID system was created on the basis of our original biomimetic concept, which is substantially composed of a cubic Three- Dimensional Fabric (3DF) with a triaxial (3A) X-, Y-, Z-axes fiber alignment, and then improved into the product comprising plural textural layers, which have an elemental usual flat textual intermediate layer and convex bioactive soft textual surface layers, on which bioactive hydroxyapatite particles were deposited. The tugging ropes penetrating through the AID body with the bioactive anchoring tappets at the both ends of filament were prepared to be well fixed for standingalone.

Results: It has been created that the biomimetic supple AID to exceed the mobile capability of existing AD, which can be effectively press-fitted after minimally invasive inserting and bond to the vertebral end plates, and stoodalone in the disc space with showing mobile behavior quite similar to BID.

Conclusion: The potential clinical availability of this AID system was substantiated as one particular fibrous cartilage, the AID for the next generation.

Keywords: Artificial intervertebral disc; Biomimetic; Stand-alone; Motion preservation; Minimally invasive

Introduction

This article compiles the total process to create the supple standalone biomimetic Artificial Intervertebral Disc (AID) woven by the Tri-Axial (3A), Three-Dimensional Fabric (3DF) [1-3] that should be clinically available in the next generation. Here, the AID is not the product with same concept as the AD (Artificial Disc), and the substitute for Biological Intervertebral Disc (BID) itself, nevertheless the both are construed as a synonymous term. Spinal surgeons by no means satisfy the existing ADs in the clinical outcomes especially in lumbar for the cause of solid material construction, biomechanical motion, stand-alone system and less invasive insertion, as well as simple revision surgery. The ADs generally form three separate layers consisted of the super-positional construction with a spherical (ball or oval) core and sockets or troughs engraved on two separated plates and slide two-dimensionally on the curvature surface while contacting to the core, but cannot deform compressively due to rigidity of solid metal and plastic components [4-6], which are markedly dissimilar to BID and the disadvantages were examined in the previous works [7-10].

The BID [11,12] have a monolithic fibrous structure that mainly comprises a collagenous slant ring fiber component with lower physical strength than constituents of Solid Artificial Discs (SADs). The biological vertebral segment has limitless numbers of central axes to various normal physiological motions, and passively deforms three dimensionally responding to simultaneous or independent external loadings, along with a limitless number of central axes for distortion of the annulus including the jelly nucleus. Namely the BID deforms three-dimensionally along with the multi-axes for distortion while receiving different loadings from various direction while following simultaneously to the plural complex loadings combined together vertical compression, lateral bending, torsional twisting, dorsally flexion, ventrally extension and so, on.

The physical endurance of supple BIDs with low strength materials is achieved through support from the surrounding ligaments and musculoskeletal regions as well as the shared loading by each consecutive BID. It might be impossible that ADs made of each component with excessively high physical strengths like those of existing SADs could provide the same efficient mobility as supple BIDs. When a BID is compressed, the height naturally reduces in proportion to the compressive loading and recovers to the normal state after unloading due to firmly bonding with the endplates sticking to the Vertebral Body (VB). In other word, another effect as the BID material is due to the damping behavior for adsorbing the external stress energy that is displayed by the downward convex ‘J’-shaped stress-strain (S-S) hysteresis-loss loop, but not the upward convex ‘S’ shaped S-S one like solid materials [3,13,14].

This article elucidates every solution for an optimal AID according to procedures as itemized below 1.

First, it must be composed of biologically safe materials with good biocompatibility, which causes no serious tissue reactions arise from the base components or secondary debris generated by usual movement during the lifespan. The AIDs should be constructed by known biomaterials that have been used for a long term in vivo for humans.

Second, biomimetic constructional materials and shape should be applied to replicate the biomechanical yielding behavior with ‘J’-shaped S-S curves of normal BIDs, and to allow translation and rotation in all three planes of independent or dependent complex motion along the x, y, and z axes. This will achieve 3D tunable deforming without specific fixed pivots as in BIDs, which naturally deform receiving complex and dependent external loadings, but not an independent loading only. Therefore, it is possible to response to complex and dependent translation and rotation, coincidental plural loadings with compression, flexion, extension, or lateral bending and axial rotation, and so on, and would bring to the less potential for low back pain than the existing ADs.

Third, it must display sufficient mechanical properties, biomimetic mobility, and superb endurance with little reducing fatigue resistance while restoring to the original height; mechanical testing over 100 million biomimetic repetitive motions to equate with a 40 or 50 year lifespan would be a typical design criterion.

Fourth, several designs with size variation and deformable shape by external various loadings need to be produced in order to allow accurate placement, the ‘sweet spot’ where the implant is positioned at the correct height and depth within the disc space. Therefore, it should be a soft material to be contoured by press–fitting to the disc body inner-surface geometry; even if it would not be the lordotic shape of AID, but the convex one; this will allow the AID to be applied in cases with disc heights, spaces, and geometries that vary according to differences in patients and indications.

Fifth, the reliable stand-alone system, which can adjust to the disc space with tight press-fitting and firm bone bonding via the end plate stuck to VB, is essential, and the AID has to show osteological bioactivity on the surface to bond to disc bone.

Sixth, the AID should be set easily into the disc space by minimally invasive inserting into disc space without over distracting to endow over compression to adjoining IDs and to fix firmly with VBs and be devised with no using fixation pins or plates that can suppress original motion of an AID and break into hard debris to bring about physical irritation. In other words, the practical AID should be designed into a supple monolithic device similar to BID.

Seventh, it is provable that natural bone deposit and produce the bridging between VBs to miss the movability of AID, especially in the lumbar. Therefore, bioinert biomaterials on which bone tissues never deposit should be used essentially.

Materials, Methods and Results

Weaving method [1]

Binding up thin multi-filaments into a thick monofilament is to bring about superior flexibility than a thick monofilament with same diameter as a multifilament bound up. The respective figure and photograph as shown in due order solved every indispensable criterion to really materialize the clinical available 3DF AIDs. The construction of a high strength bioinert filament to weave the 3DF AID and the weaving method were described in previous works [3, 13,14]. Safety of the fiber materials has been already guaranteed as a biomaterial previously used in orthopedic devices and the bioinert biocompatibility doesn’t constrain hardening of AID due to bone ingrowth (ossification) into space of 3DF textures. The mobility is consequently retained as it was.

Improving on the shape adaptable to the disc space

The 3DF AID with the flat surface was selected as the first prototype (Figure 1(1)-1(4)). Thereafter they were improved to endow more flexible concave surface layers. Thereby, they could coincide with the surface geometry of reduced VB after excising BID affected. The softer concave surface layer was woven by thin filaments than the normal core layer woven by thick ones in order to easily apply to the irregular surface geometry of reduced VB (Figure 1(5) - 1(6)).