Three dimensional printing of bone tissue engineering scaffold: Design, structure, and mechanical properties / Mitra Asadi-Eydivand

Techniques to restore and replace bones in large fractures are still a major clinical need in the field of orthopedic surgery. Thus, tissue engineering is one of the most hopeful approaches for developing engineered alternatives for damaged bones. Scaffolds are important part of bone tissue engineering (BTE). They are three-dimensional (3D) porous structures that are expected to, at least, partially imitate the extracellular matrix (ECM) of natural bone. Due to the natural properties of bone that are similar to calcium-based ceramics, the fabrication of scaffolds with the same properties as patient’s bone and adaptability to fracture defect are still a matter of concern and have remained a challenging area in the BTE field. Since the microarchitecture of a scaffold, like its pore size, and interconnectivity cannot be fully controlled by conventional techniques, recently, the additive manufacturing (AM) techniques have drawn the attention among tissue engineering experts. Other than that, solid freeform fabrication (SFF) is a wellestablished AM technique that can be employed to produce prototypes from complex 3D data sets. Moreover, the ability of inkjet-based 3D printing (3DP) to fabricate biocompatible ceramics has made it one of the most favorable techniques to build BTE scaffolds. Furthermore, calcium sulfates, which exhibit various beneficial characteristics, can be used as a promising biomaterial in BTE and it is a low-cost material for 3DP. Hence, this project had designed and developed the optimal processing parameters based on the design of the experimental approach and evolutionary algorithms to evaluate the ability of commercial 3D printers for making calcium sulfate-based or in other words, commercial-materials-based scaffold prototypes. Besides the simple design to fulfill the BTE requirements and to study the printing parameters, a library of triply periodic minimal surfaces (TPMS) based unit cells was subjected to finite element analysis and computational fluid dynamic (CFD) simulations. Elastic modulus, compressive strength, as well as permeability, were characterized for different volume fractions of TPMS structures to develop structure-property correlations with emphasis on describing the architectural features of optimum models. The major printing parameters examined in this study for the simple design were layer thickness, delayed time of spreading the next layer, and build orientation of the specimens. However, low mechanical performance caused by the brittle character of ceramic materials had been the main weakness of the 3DP calcium sulfate scaffolds. Moreover, the presence of certain organic matters in the starting commercial powder and binder solution caused the products to have high toxicity levels. So, after fabrication, post-processing treatments were employed upon optimal specimens to further improve the physical, the chemical, and the biological behaviors of the printed samples. The first post-processing technique was heat treatment, while the second one was phosphate treatment of 3D-printed specimens to convert the calcium sulfate-based prototypes to calcium phosphate ones solely to improve their properties

Mechanical behavior of calcium sulfate scaffold prototypes built by solid free-form fabrication

Purpose: This paper aims to investigate the mechanical behavior of three-dimensional (3D) calcium sulfate porous structures created by a powder-based 3D printer. The effects of the binder-jetting and powder-spreading orientations on the microstructure of the specimens are studied. A micromechanical finite element model is also examined to predict the properties of the porous structures under the load. Design/methodology/approach: The authors printed cylindrical porous and solid samples based on a predefined designed model to study the mechanical behavior of the prototypes. They investigated the effect of three main build bed orientations (x, y and z) on the mechanical behavior of solid and porous specimens fabricated in each direction then evaluated the micromechanical finite-element model for each direction. The strut fractures were analyzed by scanning electron microscopy, micro-computed tomography and the von Mises stress distribution. Findings: Results showed that the orientation of powder spreading and binder jetting substantially influenced the mechanical behavior of the 3D-printed prototypes. The samples that were fabricated parallel to the applied load had higher compressive strength compared with those printed perpendicular to the load. The results of the finite element analysis agreed with the results of the experimental mechanical testing. Research limitations/implications: The mechanical behavior was studied for the material and the 3D-printing machine used in this research. If one were to use another material formulation or machine, the printing parameters would have to be set accordingly. Practical implications: This work aimed to re-tune the control factors of an existing rapid prototyping process for the given machine. The authors achieved these goals without major changes in the already developed hardware and software architecture. Originality/value: The results can be used as guidelines to set the printing parameters and a model to predict the mechanical properties of 3D-printed objects for the development of patient- and site-specific scaffolds

Modélisation des voies de la commande saccadique

A model of the saccadic pathways is proposed

3D Printing of Customized Drug Delivery Systems with Controlled Architecture via Reversible Addition‐Fragmentation Chain Transfer Polymerization

3D printing via reversible addition-fragmentation chain transfer (RAFT) polymerization has been recently developed to expand the scope of 3D printing technologies. A potentially high-impact but relatively unexplored opportunity that can be provided by RAFT-mediated 3D printing is a pathway toward personalized medicine through manufacturing bespoke drug delivery systems (DDSs). Herein, 3D printing of drug-eluting systems with precise geometry, size, drug dosage, and release duration/profiles is reported. This is achieved through engineering a range of 3D models with precise interconnected channel-pore structure and geometric proportions in architectural patterns. Notably, the application of the RAFT process is crucial in manufacturing materials with highly resolved macroscale features by confining curing to exposure precincts. This approach also allows spatiotemporal control of the drug loading and compositions within different layers of the scaffolds. The ratio between the polyethylene glycol units and the acrylate units in the crosslinkers is found to be a critical factor, with a higher ratio increasing swelling capacity, and thus enhancing the drug release profile, from the drug-eluting systems. This proof-of-concept research demonstrates that RAFT-mediated 3D printing enables the production of personalized drug delivery materials, providing a pathway to replace the “one-size-fits-all” approach in traditional health care

Cerebellum-inspired neural network solution of the inverse kinematics problem

The demand today for more complex robots that have manipulators with higher degrees of freedom is increasing because of technological advances. Obtaining the precise movement for a desired trajectory or a sequence of arm and positions requires the computation of the inverse kinematic (IK) function, which is a major problem in robotics. The solution of the IK problem leads robots to the precise position and orientation of their end-effector. We developed a bioinspired solution comparable with the cerebellar anatomy and function to solve the said problem. The proposed model is stable under all conditions merely by parameter determination, in contrast to recursive model-based solutions, which remain stable only under certain conditions. We modified the proposed model for the simple two-segmented arm to prove the feasibility of the model under a basic condition. A fuzzy neural network through its learning method was used to compute the parameters of the system. Simulation results show the practical feasibility and efficiency of the proposed model in robotics. The main advantage of the proposed model is its generalizability and potential use in any robot

SEM image of pores and struts on peripheral wall of samples printed in X direction.

<p>SEM image of pores and struts on peripheral wall of samples printed in X direction.</p

Fabrication condition of samples.

<p>Fabrication condition of samples.</p