On the effect of design and fabrication parameters on mechanical performance of 3D printed PLA scaffolds

Improving physio-mechanical and biological properties of 3D-printed PLA scaffolds via in-situ argon cold plasma treatment

As a bone tissue engineering material, polylactic acid (PLA) has received significant attention and interest due to its ease of processing and biocompatibility. However, its insufficient mechanical properties and poor wettability are two major drawbacks that limit its extensive use. For this purpose, the present study uses in-situ cold argon plasma treatment coupled with a fused deposition modeling printer to enhance the physio-mechanical and biological behavior of 3D-printed PLA scaffolds. Following plasma treatment, field emission scanning electron microscopy images indicated that the surface of the modified scaffold became rough, and the interlayer bonding was enhanced. This resulted in an improvement in the tensile properties of samples printed in the X, Y, and Z directions, with the enhancement being more significant in the Z direction. Additionally, the root mean square value of PLA scaffolds increased (up to 70-fold) after plasma treatment. X-ray photoelectron spectroscopy analysis demonstrated that the plasma technique increased the intensity of oxygen-containing bonds, thereby reducing the water contact angle from 92.5° to 42.1°. The in-vitro degradation study also demonstrated that argon plasma treatment resulted in a 77% increase in PLA scaffold degradation rate. Furthermore, the modified scaffold improved the viability, attachment, and proliferation of human adipose-derived stem cells. These findings suggest that in-situ argon plasma treatment may be a facile and effective method for improving the properties of 3D-printed parts for bone tissue engineering and other applications.

Additive Manufacturing of Bioceramic Implants for Restoration Bone Engineering: Technologies, Advances, and Future Perspectives

Treating bone defects is highly challenging because they do not heal on their own inside the patients, so implants are needed to assist in the reconstruction of the bone. Bioceramic implants based on additive manufacturing (AM) are currently emerging as promising treatment options for restoration bone engineering. On the one hand, additively manufactured bioceramic implants have excellent mechanical properties and biocompatibility, which are suitable for bone regeneration. On the other hand, the designable structure and adjustable pores of additively manufactured bioceramic implants allow them to promote suitable cell growth and tissue climbing. Herein, this review unfolds to introduce several frequently employed AM technologies for bioceramic implants. After that, advances in commonly used additively manufactured bioceramic implants, including bioinert ceramic implants, bioactive ceramic implants, and bioceramic/organic composite implants, are categorized and summarized. Finally, the future perspectives of additively manufactured bioceramic implants, in terms of mechanical performance improvement, innovative structural design, biological property enhancement, and other functionalization approaches, are proposed and forecasted. This review is believed to provide some fundamental understanding and cutting-edge knowledge for the additive manufacturing of bioceramic implants for restoration bone engineering.

A Review of 3D Polymeric Scaffolds for Bone Tissue Engineering: Principles, Fabrication Techniques, Immunomodulatory Roles, and Challenges

Over the last few years, biopolymers have attracted great interest in tissue engineering and regenerative medicine due to the great diversity of their chemical, mechanical, and physical properties for the fabrication of 3D scaffolds. This review is devoted to recent advances in synthetic and natural polymeric 3D scaffolds for bone tissue engineering (BTE) and regenerative therapies. The review comprehensively discusses the implications of biological macromolecules, structure, and composition of polymeric scaffolds used in BTE. Various approaches to fabricating 3D BTE scaffolds are discussed, including solvent casting and particle leaching, freeze-drying, thermally induced phase separation, gas foaming, electrospinning, and sol-gel techniques. Rapid prototyping technologies such as stereolithography, fused deposition modeling, selective laser sintering, and 3D bioprinting are also covered. The immunomodulatory roles of polymeric scaffolds utilized for BTE applications are discussed. In addition, the features and challenges of 3D polymer scaffolds fabricated using advanced additive manufacturing technologies (rapid prototyping) are addressed and compared to conventional subtractive manufacturing techniques. Finally, the challenges of applying scaffold-based BTE treatments in practice are discussed in-depth.

Additive manufacturing of PLA-Mg composite scaffolds for hard tissue engineering applications

Polylactic acid (PLA) is considered as a great option to be employed as 3D porous scaffold in hard tissue engineering applications owing to its excellent biocompatibility and processability. However, relatively weak mechanical properties and inappropriate biodegradability limit its extensive usage. In order to overcome the mentioned challenges, micrometric magnesium particles were incorporated into the PLA matrix by the fused deposition modeling (FDM) technique. The effects of various Mg contents (i.e., 2, 4, 6, 8 and 10 wt%) on the structural, thermal, rheological, mechanical, wettability, degradability characteristics and cellular behavior of the 3D porous PLA-Mg composite scaffolds were examined. The developed PLA-Mg composites exhibit an interconnected porous structure with a mostly uniform distribution of Mg particles in the PLA matrix. It was found that incorporation of Mg particles into the PLA matrix enhances the mechanical, physical, chemical and biological characteristics of PLA. The cell studies demonstrate that the PLA-6Mg composite scaffold provides the best cellular response in terms of cell atachment and viability. The obtained results in this investigation greatly suggest that the 3D-printed PLA-Mg composite scaffold is a promising candidate for hard tissue engineering applications.

Personalized 3D printed bone scaffolds: A review

3D printed bone scaffolds have the potential to replace autografts and allografts because of advantages such as unlimited supply and the ability to tailor the scaffolds' biochemical, biological and biophysical properties. Significant progress has been made over the past decade in additive manufacturing techniques to 3D print bone grafts, but challenges remain in the lack of manufacturing techniques that can recapitulate both mechanical and biological functions of native bones. The purpose of this review is to outline the recent progress and challenges of engineering an ideal synthetic bone scaffold and to provide suggestions for overcoming these challenges through bioinspiration, high-resolution 3D printing, and advanced modeling techniques. The article provides a short overview of the progress in developing the 3D printed scaffolds for the repair and regeneration of critical size bone defects. STATEMENT OF SIGNIFICANCE: Treatment of critical size bone defects is still a tremendous clinical challenge. To address this challenge, diverse sets of advanced manufacturing approaches and materials have been developed for bone tissue scaffolds. 3D printing has sparked much interest because it provides a close control over the scaffold's internal architecture and in turn its mechanical and biological properties. This article provides a critical overview of the relationships between material compositions, printing techniques, and properties of the scaffolds and discusses the current technical challenges facing their successful translation to the clinic. Bioinspiration, high-resolution printing, and advanced modeling techniques are discussed as future directions to address the current challenges.

Biomimetic surface modification of Three-dimensional printed Polylactic acid scaffolds with custom mechanical properties for bone reconstruction

3D printing has recently emerged as an innovative fabrication method to construct critical-sized and patient-specific bone scaffolds. The ability to control the bulk geometry of scaffolds in both macro and micro-scales distinguishes this technology from other fabrication methods. In this study, bone tissue-specific scaffolds with different pore geometries were printed from polylactic acid (PLA) filaments at three given infill densities ranging from 20 to 30%. A hybrid hydrogel made of synthetic biphasic calcium phosphate (BCP) and collagen was applied to coat 3D printed well-structured triangular samples with 30% infill density. The coating process changed the surface texture, increased the average strand diameter and average pore size, and decreased the open porosity of samples, all of which increased the mechanical strength of biomimetic-coated scaffolds. According to matrix mineralization staining and osteo-related gene expression, the coating of scaffolds significantly facilitates metabolic activity and osteogenic differentiation of dental pulp-derived mesenchymal stem cells (DPSCs). Taken together, these results indicated that the biomimetic coating is a highly promising approach that could be taken into consideration in the design of a porous scaffold for bone tissue engineering.

Additive Manufacturing of Polymer/Mg-Based Composites for Porous Tissue Scaffolds

Due to their commercial availability, superior processability, and biocompatibility, polymers are frequently used to build three-dimensional (3D) porous scaffolds. The main issues limiting the widespread clinical use of monophasic polymer scaffolds in the bone healing process are their inadequate mechanical strength and inappropriate biodegradation. Due to their mechanical strength and biocompatibility, metal-based scaffolds have been used for various bone regenerative applications. However, due to the mismatch in mechanical properties and nondegradability, they lack integration with the host tissues, resulting in the production of fiber tissue and the release of toxic ions, posing a risk to the durability of scaffolds. Due to their natural degradability in the body, Mg and its alloys increasingly attract attention for orthopedic and cardiovascular applications. Incorporating Mg micro-nano-scale particles into biodegradable polymers dramatically improves scaffolds and implants' strength, biocompatibility, and biodegradability. Polymer biodegradable implants also improve the quality of life, particularly for an aging society, by eliminating the secondary surgery often needed to remove permanent implants and significantly reducing healthcare costs. This paper reviews the suitability of various biodegradable polymer/Mg composites for bone tissue scaffolds and then summarizes the current status and challenges of polymer/magnesium composite scaffolds. In addition, this paper reviews the potential use of 3D printing, which has a unique design capability for developing complex structures with fewer material waste at a faster rate, and with a personalized and on-site fabrication possibility.

Physicochemical Characterization and Finite Element Analysis-Assisted Mechanical Behavior of Polylactic Acid- Montmorillonite 3D Printed Nanocomposites

This work aims to improve the properties of poly(lactic acid) (PLA) for future biomedical applications by investigating the effect of montmorillonite (MMT) nanoclay on physicochemical and mechanical behavior. PLA nanocomposite filaments were fabricated using different amounts of MMT (1.0, 2.0, and 4.0 wt.%) and 2 wt.% Joncryl chain extenders. The 3D-printed specimens were manufactured using Fused Filament Fabrication (FFF). The composites were characterized by Gel Permeation Chromatography (GPC), Melt Flow Index (MFI), X-ray Diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). The thermal properties were studied by means of Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). Moreover, the hydrophilicity of the PLA/MMT nanocomposites was investigated by measuring the water contact angle. The mechanical behavior of the PLA/MMT nanocomposites was examined with nanoindentation, compression tests, and Dynamic Mechanical Analysis (DMA). The presence of Joncryl, as well as the pretreatment of MMT before filament fabrication, improved the MMT distribution in the nanocomposites. Furthermore, MMT enhanced the printability of PLA and improved the hydrophilicity of its surface. In addition, the results of nanoindentation testing coupled with Finite Element Analysis showed that as the MMT weight fraction increased, as well as an increased Young’s modulus. According to the results of the mechanical analysis, the best mechanical behavior was achieved for PLA nanocomposite with 4 wt.% MMT.

Multi-objective Shape Optimization of Bone Scaffolds: Enhancement of Mechanical Properties and Permeability

Porous scaffolds have recently attracted attention in bone tissue engineering. The implanted scaffolds are supposed to satisfy the mechanical and biological requirements. In this study, two porous structures named MFCC-1 (modified face centered cubic-1) and MFCC-2 (modified face centered cubic-2) are introduced. The proposed porous architectures are evaluated, optimized, and tested to enhance mechanical and biological properties. The geometric parameters of the scaffolds with porosities ranging from 70% to 90% are optimized to find a compromise between the effective Young's modulus and permeability, as well as satisfying the pore size and specific surface area requirements. To optimize the effective Young's modulus and permeability, we integrated a mathematical formulation, finite element analysis, and computational fluid dynamics simulations. For validation, the optimized scaffolds were 3D-printed, tested, and compared with two different orthogonal cylindrical struts (OCS) scaffold architectures. The MFCC designs are preferred to the generic OCS scaffolds from various perspectives: a) the MFCC architecture allows scaffold designs with porosities up to 96%; b) the very porous architecture of MFCC scaffolds allows achieving high permeabilities, which could potentially improve the cell diffusion; c) despite having a higher porosity compared to the OCS scaffolds, MFCC scaffolds improve mechanical performance regarding Young's modulus, stress concentration, and apparent yield strength; d) the proposed structures with different porosities are able to cover all the range of permeability for the human trabecular bones. The optimized MFCC designs have simple architectures and can be easily fabricated and used to improve the quality of load-bearing orthopedic scaffolds. STATEMENT OF SIGNIFICANCE: Porous scaffolds are increasingly being studied to repair large bone defects. A scaffold is supposed to withstand mechanical loads and provide an appropriate environment for bone cell growth after implantation. These mechanical and biological requirements are usually contradicting; improving the mechanical performance would require a reduction in porosity and a lower porosity is likely to reduce the biological performance of the scaffold. Various studies have shown that the mechanical and biological performance of bone scaffolds can be improved by internal architecture modification. In this study, we propose two scaffold architectures named MFCC-1 and MFCC-2 and provide an optimization framework to simultaneously optimize their stiffness and permeability to improve their mechanical and biological performances.

3D Printing of Polymeric Bioresorbable Stents: A Strategy to Improve Both Cellular Compatibility and Mechanical Properties

One of the leading causes of death is cardiovascular disease, and the most common cardiovascular disease is coronary artery disease. Percutaneous coronary intervention and vascular stents have emerged as a solution to treat coronary artery disease. Nowadays, several types of vascular stents share the same purpose: to reduce the percentage of restenosis, thrombosis, and neointimal hyperplasia and supply mechanical support to the blood vessels. Despite the numerous efforts to create an ideal stent, there is no coronary stent that simultaneously presents the appropriate cellular compatibility and mechanical properties to avoid stent collapse and failure. One of the emerging approaches to solve these problems is improving the mechanical performance of polymeric bioresorbable stents produced through additive manufacturing. Although there have been numerous studies in this field, normalized control parameters for 3D-printed polymeric vascular stents fabrication are absent. The present paper aims to present an overview of the current types of stents and the main polymeric materials used to fabricate the bioresorbable vascular stents. Furthermore, a detailed description of the printing parameters' influence on the mechanical performance and degradation profile of polymeric bioresorbable stents is presented.

Porosity and pore design influence on fatigue behavior of 3D printed scaffolds for trabecular bone replacement

Polymeric scaffolds provide several advantages when compared with other bone replacement and regenerating techniques. Namely, when compared with the current gold standard, bone autografts, there is no shortage of supply nor donor site morbidity. Contrarily to metallic implants, their mechanical properties are similar to those of cortical bone and they are biodegradable, therefore stress shielding is not expected to occur, and they will be gradually replaced by new bone tissue. Yet, there are still several challenges to overcome. After implantation scaffolds are subjected to dynamic loads, thus understanding polymeric scaffolds' fatigue behavior plays a major role on the design of better products. In this work PLA scaffolds were manufactured using 3D printing with optimized parameters. A total of six configurations were tested under static and dynamic load conditions. Static compression testing and numerical simulation showed good correlation. Numerical simulation provided a viable resource for scaffold design and innovation. Four different low-cycle fatigue loads were applied, during 3600 cycles with a frequency of 0.25 Hz. While under dynamic conditions, with a maximum stress of 24 MPa and R = 0.1, the apparent compressive modulus reached 973 MPa, due to pore collapse. Even after 3600 cycles no significant fatigue damage mechanisms were found on low porosity scaffolds, rendering them useful for trabecular bone replacement under dynamic conditions.