Mechanistic understanding of compression-compression fatigue behavior of functionally graded Ti–6Al–4V mesh structure fabricated by electron beam melting

Process-structure-biofunctional paradigm in cellular structured implants: an overview and perspective on the synergy between additive manufacturing, bio-mechanical behaviour and biological functions

The overview describes the synergy between biological sciences and cellular structures processed by additive manufacturing to elucidate the significance of cellular structured implants in eliminating stress shielding and in meeting the bio-mechanical property requirements of elastic modulus, impact resistance, and fatigue strength in conjunction with the biological functionality. The convergence of additive manufacturing, computer-aided design, and structure-property relationships is envisaged to provide the solution to the current day challenges in the biomedical arena. The traditional methods of fabrication of biomedical devices including casting and mechanical forming have limitations because of the mismatch in micro/microstructure, mechanical, and physical properties with the host site. Additive manufacturing of cellular structured alloys via electron beam melting and laser powder bed fusion has benefits of fabricating patient-specific design that is obtained from the computed tomography scan of the defect site. The discussion in the overview consists of two aspects - the first one describes the underlying reason that motivated 3D printing of implants from the perspective of minimising stress shielding together with the mechanical property requirements, where the mechanical properties of cellular structured implants depend on the cellular architecture and percentage cellular porosity. The second aspect focuses on the biological response of cellular structured devices.

Mechanical properties and osteointegration of the mesh structure of a lumbar fusion cage made by 3D printing

The currently popular 3D printing makes it possible to produce spatial scaffolds, the main purpose of which is to obtain implants that have favourable mechanical properties to promote cell adhesion. This study aims to prove the influence of changes in selected geometrical parameters of scaffolds, used in intervertebral cages, on the mechanical properties obtained and thus on the osteointegration of the studied constructs with osteoblasts and fibroblasts. The stiffness values and maximum failure force of four modifications to geometric dimensions of the meshes were determined from the intendation test. Adhesion assays were conducted (including gentle pendulum motion) for Balb/3T3 fibroblasts and NHOst osteoblasts. The study revealed that an important geometrical parameter affecting the strength of the mesh is the height (h) of the connection point between arms of successive mesh cells. There was no significant effect of the mesh geometry on the abundance and survival of Balb/3T3 and NHOst cells. At the same time, fibroblasts were more likely to form colonies in the area where there is fusion of mesh cells, as opposed to osteoblasts that were more numerous at vertices of the mesh.

Tribo-corrosive behavior of additive manufactured parts for orthopaedic applications

Background

Additive manufacturing (AM) being an integral component of the production offers a wide variety of applications in the production of different components. The medical industry after the introduction of Additive Manufacturing has resulted in several advancements. The production of intricate patient-specific implants is one of such advancements which greatly assist a surgeon during a surgery. Orthopedic implants apart from possessing good mechanical strength are also expected to exhibit good tribological and corrosion behavior. As a result, the development of various orthopaedic implants and tools has become simple with the use of additive manufacturing.

Objectives and Rationale

In the current paper an effort has been made to discuss actual scientific knowledge on the tribo-corrosive behavior of additive manufactured parts for orthopedic applications. Different studies dealing with the mechanisms of lubrication and friction in synovial joints have also been considered. A special focus has also been laid down to study the corrosive effect of implants on the human body. A section dedicated to texturing of orthopedic implants has also been provided. The paper further elaborates the different research challenges and issues related to the use of additive manufacturing for the production of optimized orthopedic implants.

Conclusion

The study revealed that additive manufacturing has greatly aided in the manufacture of different orthopaedic implants with enhanced properties. However, a detailed study of the effect of processes like friction, wear, lubrication and corrosion in these implants needs to be done. The performance of these implants in the presence of various synovial fluids also needs to be addressed. However, the lack of more biocompatible materials, scalability and cost issues hinder the widespread use of AM in the different orthopaedic applications.

Design and properties of biomimetic irregular scaffolds for bone tissue engineering

The treatment of sizeable segmental bone defects remains a challenge encountered by surgeons. In addition to bone transplantation, porous scaffolds have become a common option. Although the mechanical and biological properties of porous scaffold have recently been the subject of intense research, pore irregularity as a critical characteristic has been poorly explored. Therefore, this study aimed to design an irregular biomimetic scaffold for use in bone tissue engineering applications. The irregular scaffold was based on the Voronoi tessellation method for similarity with the primary histomorphological indexes of bone (porosity, trabecular thickness, cortical bone thickness, and surface to volume ratio). Moreover, a new gradient method was adopted, in which porosity was maintained constant, and the strut diameter was changed to generate a gradient in the irregular scaffold. The permeability and stress concentration characteristics of the irregular scaffold were compared against three conventional scaffolds (the octet, body-centered cubic, pillar body-centered cubic). The results illustrated that the microstructure of the irregular scaffold could be controlled similarly to that of the cortical/cancellous bone unit. Simultaneously, a broad range of permeability was identified for the irregular scaffold, and gradient irregular scaffolds performed better in terms of both permeability and stress distribution than regular scaffolds. This study describes a novel method for the design of irregular scaffolds, which have good controllability and excellent permeability.

Effect of unit configurations and parameters on the properties of Ti-6Al-4V unit-stacked scaffolds: A trade-off between mechanical and permeable performance

Scaffolds in tissue engineering can be created or printed nowadays with various structures that consist of a number of three-dimensional (3D) units stacked together periodically. The performance or properties of such scaffolds can be affected by the unit configurations and parameters, which, however, has not been well investigated and elucidated. This paper presents our study on the influence of unit configuration and parameters on the scaffolds performance by taking triply periodic minimal surfaces (TPMS) as the basic unit. The normalized values of elastic modulus, shear modulus and permeability were used to characterize the scaffold performance and analyzed by means of finite element analysis and CFD simulation, with focus on identifying the influence of unit configurations and parameters on the scaffold mechanical and permeable properties. Furthermore, by selective laser melting (SLM) printing technique, the cubic Primitive and IWP scaffolds with an oversize of 12 mm (2 × 2 × 2 units) were created and subjected to compressive tests. Both simulation and experiment results are in agreement to illustrate that unit configuration and parameters have significant influence on the mechanical and permeable properties of TPMS units. The methods and findings in the present work would serve as the base or rationales to regulate the unit configurations and parameters with trade-off solutions for given tissue engineering application.