Effect of DLC coating of growth-guidance system implants on changes in mechanical and kinematic properties of the spine
1Department of Mechanics, Materials and Biomedical Engineering, Faculty of Mechanical Engineering, Wrocław University of Science and Technology, Poland; 2Department of Internal Diseases With Clinic for Horses, Dogs and Cats, Faculty of Veterinary Medicine, Wrocław University of Environmental and Life Sciences, Poland; 3Department of Pediatric Surgery and Urology, Wroclaw Medical University, Poland; 4St. Hedwig of Silesia Hospital, Poland
Early onset scoliosis (EOS) is a three-dimensional curvature of the spine and trunk that occurs in children nine years of age or younger. The EOS tend to develop progressively, requiring early surgical intervention with spine stabilization. Currently stepwise treatment method involving the displacement of the stabilizer by operating methods is being used. It is necessary to develop a solution that would allow scoliosis to be corrected as soon as possible while reducing the number of operations and the risk of complications.
The research aimed to develop a modification of the internal spine stabilizer for the treating scoliosis in children by increasing its abrasion resistance and thus reducing the risk of tissue degradation and disorders in the kinematics of the spine column.The study used the scoliosis stabilisation system offered by Novaspine, which has kinetic pairs in its design to allow relative displacement of stabiliser components without external intervention.
In order to increase the abrasion resistance of the mating surfaces and increase the mobility of the stabilizer-spine system, a DLC (Diamond Like Carbon) coating was applied to the implant components. Then, tests were carried out to assess the mechanical and kinematic properties of the spine-stabilizer (SI) system for selected modifications. At this study stage, a more than 8% decrease in SI stiffness was demonstrated for DLC-coated implants compared to implants without DLC. Then, in vivo study was carried out on domestic pigs, assessing the effect of the applied modification on the reduction of the mass of titanium alloy particles infiltrating into the tissues surrounding the implant and determining the effect of modified stabilizing systems on changes in the vertebra bone structure. As a consequence, the increased mobility of the stabilizer follower node led to excessive movement between the transpedicular screw and the bone tissue, leading to their loosening and inflammation.
Finite element analysis of titanium-based hip implant modified surfaces
1Faculty of Engineering, University of Kragujevac, Serbia; 2Bioengineering Research and Development Center, Serbia; 3Graz University of Technology, Institute of Materials Science, Joining and Forming, Austria
As we age, we are faced with a variety of health challenges. Some of those challenges require surgeries to improve the quality of life. One of the most common surgeries is hip replacement surgery which provides mobility improvement and pain relief. During this procedure, a damaged part of the hip joint is replaced with an artificial one. Titanium and its alloys, especially Ti-6Al-4V, are most commonly used for hip implants due to their mechanical properties, excellent biocompatibility, and corrosion resistance. Cementless hip implants are considered to be more durable than cemented hip implants and they are recommended for the younger population. In order to ensure the proper function of the cementless hip implant, the connection between the femoral bone and the inserted implant has to be as strong as possible. If the connection is not strong, the implant starts to loosen and revision surgery is necessary. According to the experimental studies, implants with a rough surface reduce micro-movements between femoral bone and implant, which helps to form a stronger connection with a femoral bone. The goal of the present study was to employ the Finite Element Method, in order to analyze how ten different surface topographies of Ti-6Al-4V hip implant affect the shear stress values and distribution. The criteria that shear stress values at the implant-bone interface should be minimized to promote bone ingrowth was used to decide on the optimal surface topography of the presented models.
From 2D ultrasound images to 3D patient-specific models of atherosclerotic carotid bifurcation
1Institute for Information Technologies, University of Kragujevac, Serbia; 2Bioengineering Research and Development Center, BioIRC, Serbia; 3Faculty of Engineering, University of Kragujevac, Serbia; 4Faculty of Science, University of Kragujevac, Serbia; 5Clinic for Vascular and Endovascular Surgery, Serbian Clinical Centre, Serbia
Carotid artery atherosclerotic disease is an important risk factor for ischemic cerebrovascular events (stroke and transient ischemic attack). In order to prevent such events and life-threatening consequences, different imaging techniques are used for timely diagnosis and estimation of the carotid artery stenosis (CAS) condition. The use of ultrasound (US) images for assessment of atherosclerosis in the carotid artery is widely adopted due to ease of use, low costs and wide availability. The US examination can identify the severity of CAS in order to pre-estimate the risk of cardiovascular disease and ensure appropriate medical treatment. On the other hand, there are technical limitations in detection and characterization of the complex 3D carotid bifurcations and plaque components, which make diagnose inconsistent, even for an expert clinician. In order to contribute to a more reliable CAS examination, this study proposes the 3D reconstruction of patient-specific carotid bifurcation from US images, combining deep learning and meshing techniques. Deep learning is used for the segmentation of the carotid lumen and wall (including atherosclerotic plaque), while meshing is applied to create the 3D finite element (FE) model that is adapted to the specific patient, using data obtained from the segmented areas. The presented approach and methodology which combines the U-Net Convolutional Neural Networks (CNNs) and 3D reconstruction of carotid artery enables efficient segmentation, extraction of the morphological parameters and creation of 3D meshed volume models, ready for the further computational examinations. Improved 3D visualization and characterization of the carotid artery and plaque components, as well as possibility for further numerical simulations (atherosclerosis progression, stenting, blood flow, etc.) represent the step forward in risk assessment of the atherosclerosis disease.
Acknowledgement: This paper is supported by the TAXINOMISIS project that has received funding from the EU’s Horizon 2020 RIA programme (grant agreement No 755320).
Methods of evaluating mechanical parameters and the stability of the cervical interbody fusion cage
Wroclaw University of Science and Technology, Poland
In the case of interbody fusion cages, it is required to achieve optimal conditions between the geometry and the mechanical parameters to achieve a stable connection at the border with the bone tissue. In our work, we present the research results of the cervical interbody fusion cage based on assessing mechanical properties and the conditions related to osseointegration resulting from the adopted geometry. The cage was designed as a titanium alloy Ti6Al4V implant strengthened with mesh lattice structures to obtain larger osseointegration between the implant and bone tissue. Based on the indentation test, the stiffness and the maximum force values of the modification of the geometrical dimensions of the mesh lattice structures were determined. Also, was performed adhesion test for Balb/3T3 fibroblasts and NHOst osteoblasts. The research showed that an essential geometric parameter influencing the mesh strength is the height of the connection point between the arms of the mesh cells. There was no significant influence of the mesh geometry on the number and survival of Balb/3T3 and NHOst cells. Fibroblast cells more readily formed colonies in the area where cells of the mesh meet, unlike osteoblasts, which were more numerous at their tips. The mechanical parameters and quality of the construction cervical interbody fusion cage were determined in: a uniaxial compression test to the failure of the implant (with ASTM F2077 standard), CT scan and microscopic analysis. With a non-destructive load in the force range up to 500N, the implant stiffness was from 14 to 17KN/mm. On the other hand, the value of the ultimate forces does not exceed 40kN and the stiffness 22kN/mm. The CT scan showed that the structure of the implant is continuous and that there are no closed pores in the implants printed. The average porosity calculated from CT scans of control volume was 0.15÷0.3%.
The effect of the addition of bioglass, Zn and graphene on the resorption rate of PCL scaffolds after 18 months of incubation in PBS solution
1Wroclaw University of Science and Technology, Poland; 2University of Bielsko-Biala, Poland
One of the main directions of research is still the assessment of the rate of bioresorption and the release of the active phase that stimulates the processes of hydroxyapatite growth, resulting in faster tissue reconstruction. One of such solutions is the introduction of HAp additives or bioglass into polymers, making them a more bioactive material.
The aim of the research is to assess the rate of bioresorption of scaffolds prepared with the FDM 3D printing method made of PCL doped with bioglass, Zn and graphene. The research material consists of 20 samples divided into 4 groups: I – pure PCL with a molecular weight of 80kDa, II - PCL doped with bioglass (A2); III - PCL doped with zinc-modified bioglass (A2Zn5), IV - PCL with graphene flake (GNP). Currently, the tests cover an 18-month period of degradation in PBS solution at 37C. Each month, both the incubation fluid for which we determine the pH and conductivity values, as well as changes in the structure of the scaffold, are tested. The mass is measured for each sample, the surface of the material is also assessed using the Olympus Discovery v20 microscope, and the recording with a microCT (SkyScan 1172, Bruker). Using DataViewer®, Bruker software, it is possible to analyze changes in the geometry, which enables the analysis of changes in the structure of the samples. In our research, after 18 months of degradation we observe a decrease in weight of 2%. Although the changes are not yet visible in the microscopic image, thanks to the use of microtomography, they can already be observed. When analyzing the results of degradation, the corners of the tested scaffold underwent changes the most, and it is also possible to observe slower changes in its conformation due to twisting of the samples immersed in the PBS fluid.
The potential of mulberry and non-mulberry silk fibroin bioinks for meniscus regeneration by 3D-bioprinting
University for Continuing Education Krems, Austria
The meniscus is a vital structure for biomechanical and anatomical purposes and is frequently injured. Among the diverse biomaterials used for 3D-bioprinting in meniscus regeneration research, silk fibroin (SF) derived from mulberry Bombyx mori (BM) silkworm and from non-mulberry types like Antheraea mylitta (AM), with the inherent RGD motif, are being explored. Thus, we investigated the potential of mulberry and non-mulberry SF blends to obtain a printable hydrogel for meniscus regeneration.
Materials and methods
BM and AM SF were mixed with ruthenium photoinitiator for rheology and ATR-FTIR measurements and without any crosslinker to determine their gelation kinetics. The absorbance at 540 nm was monitored for 3 h at 37°C. For printing, SF blends were mixed with/without crosslinker. After gelation in syringes at 37°C, the gels were extruded into the shape of a meniscus on an Allevi bioprinter. To evaluate cell viability, human chondrocytes and infrapatellar fat pad-derived mesenchymal stem cells (IFP-MSCs) were seeded into SF blends with decellularized extracellular matrix (dECM) powder before gelation. After incubation of the chondrocyte gels in growth medium and the IFP-MSC gels in differentiation medium, the gels were stained with LIVE/DEAD® Viability/Cytotoxicity Kit and the gene expression of chondrogenic markers was analyzed in cast and printed gels.
The elastomeric properties of the crosslinked SF blend resembled a solid and the addition of more AM SF than BM SF has proven to be advantageous for a shorter gelation time. Printing 10% (w/v) SF blend with crosslinking during printing led to the most stable condition for printing a meniscus. The addition of dECM to the hydrogels increased the number of live cells in comparison to the SF blend and the BM SF alone. The chondrocytes expressed all tested chondrogenic markers except COL2A1 and the IFP-MSCs all markers except COL2A1 and MMP13.
Use of plasma electrolytic oxidation on electron beam structured surface of titanium alloy
1Departamento de Ingeniería Química y de Materiales, Universidad Complutense de Madrid, Spain; 2CIDETEC, Basque Research and Technology Alliance (BRTA), Spain; 3Institute of Materials Science, Joining and Forming, Graz University of Technology, Austria; 4Christian Doppler Laboratory for Design of High-Performance Alloys by Thermomechanical Processing, Austria
The development of surface modification strategies to enhance the osteoconductivity of metallic implants is a field of major interest. The use of multiscale topography and surface functionalization are two effective strategies to promote the generation of new bone on the implant surface. This work aims to combine electron beam surface structuring and plasma electrolytic oxidation in titanium alloys to develop surface with antibacterial properties, corrosion resistance and biomechanical interlocking. Ca and P containing coatings were produced via 45 s PEO treatments over multi-scale EB surface topographies. In general, the PEO process, morphology, composition, and growth rate of the coatings were almost identical independently of the topography treated. PEO coatings provided to the structuring an additional micrometre porosity and sub-micrometre scale surface roughness. All the PEO-coated substrates presented essentially the same corrosion resistance. Electrochemical tests revealed localised crevice corrosion susceptibility of all the bare EB topographies which was successfully prevented after the PEO treatment.