Search results

The purpose of this study was to bring a new structural hybrid design approach to improve the mechanical and biological properties of the bone scaffolds fabricated by laser powder bed fusion, selective laser melting (SLM).

In designing the hybrid scaffolds, different unit cells were used such as dodecahedron (DCH), grid (G), octet-truss (OCT) with partially dense (PDsl) and fully dense (FDsl) surface layers. After fabrication of scaffolds on SLM machine, compression test and cell viability test were applied to observe the effect of hybrid design on mechanical and biological properties of the scaffolds.

It has been observed that designing the scaffold with partially dense or FDsl surfaces did not have a critical effect on the cell viability. On the contrary, the compression strength of scaffold increased from 56  to 100 MPa when the surface layer of the scaffold was designed as FDsl surface instead of partially dense surface. It has also been observed that the scaffold having the highest hybridity (PDsl+G+DCH+OCT) delivered the highest cell viability performance and had a compressive strength slightly higher than that of the scaffolds with single unit cell, PDsl+OCT.

This study brings a new approach to designing femur bone scaffold for fabricating with SLM. This hybrid design approach, including different unit cells in a single scaffold, covers many requirements of femur bone in terms of mechanical and biological properties.

With technology advances, metallic implants claim to improve the quality and durability of human life. In the recent decade, Ti-6Al-4V biomaterial has been additively manufactured via selective laser melting (SLM) for orthopedic applications. This paper aims to provide state-of-the-art on mechanobiology of these fabricated components.

A literature review has been done to explore the potential of SLM fabricated Ti-6Al-4V porous lattice structures (LS) as bone substitutes. The emphasize was on the effect of process parameters and porosity on mechanical and biological properties. The papers published since 2007 were considered here. The keywords used to search were porous Ti-6Al-4V, additive manufacturing, metal three-dimensional printing, osseointegration, porous LS, SLM, in vitro and in vivo.

The properties of SLM porous biomaterials were compared with different human bones, and bulk SLM fabricated Ti-6Al-4V structures. The comparison was also made between LS with different unit cells to find out whether there is any particular design that can mimic the human bone functionality and enhance osseointegration.

The implant porosity plays a crucial role in mechanical and biological characteristics that relies on the optimum controlled process variables and design attributes. It was also indicated that although the mechanical strength (compressive and fatigue) of porous LS is not mostly close to natural cortical bone, elastic modulus can be adjusted to match that of cortical or cancellous bone. Porous Ti-6Al-4V provide favorable bone formation. However, the effect of design variables on biological behavior cannot be fully conclusive as few studies have been dedicated to this.

Additive manufacturing (AM) or solid freeform fabrication (SFF) technique is extensively used to produce intrinsic 3D structures with high accuracy. Its significant contributions in the field of tissue engineering (TE) have significantly increased in the recent years. TE is used to regenerate or repair impaired tissues which are caused by trauma, disease and injury in human body. There are a number of novel materials such as polymers, ceramics and composites, which possess immense potential for production of scaffolds. However, the major challenge is in developing those bioactive and patient-specific scaffolds, which have a required controlled design like pore architecture with good interconnectivity, optimized porosity and microstructure. Such design not only supports cell proliferation but also promotes good adhesion and differentiation. However, the traditional techniques fail to fulfill all the required specific properties in tissue scaffold. The purpose of this study is to report the review on AM techniques for the fabrication of TE scaffolds.

The present review paper provides a detailed analysis of the widely used AM techniques to construct tissue scaffolds using stereolithography (SLA), selective laser sintering (SLS), fused deposition modeling (FDM), binder jetting (BJ) and advanced or hybrid additive manufacturing methods.

Subsequently, this study also focuses on understanding the concepts of TE scaffolds and their characteristics, working principle of scaffolds fabrication process. Besides this, mechanical properties, characteristics of microstructure, in vitro and in vivo analysis of the fabricated scaffolds have also been discussed in detail.

The review paper highlights the way forward in the area of additive manufacturing applications in TE field by following a systematic review methodology.

The main cause of aseptic inflammation after an in vivo implantation is that Poly(L-lactide) (PLLA) and Poly(D-lactide) have a slower degradation and absorption rate, while Poly(D, L-lactide) (PDLLA) has a much faster degradation rate than PLLA because of its amorphous structure. Also, the hydrolyzate of Hydroxyapatite (HA) is alkaline, which can neutralize local tissue peracid caused by hydrolysis of Polylactic acid.

In this study, the selective laser sintering (SLS) technique was chosen to prepare bone scaffolds using nano-HA/PDLLA composite microspheres, which were prepared by the solid-in-oil-in-water (S/O/W) method. First, the SLS parameters range of bulk was determined by the result of a single-layer experiment and the optimized parameters were then obtained by the orthogonal experiment. The tensile property, hydrophobicity, biocompatibility, biological toxicity and in vitro degradation of the samples with optimized SLS parameters were characterized.

As a result, the samples showed a lower tensile strength because of the many holes in their interior, which was conducive to better cell adhesion and nutrient transport. In addition, the samples retained their inherent properties after SLS and the hydrophobicity was improved after adding nano-HA because of the OH group. Furthermore, the samples showed good biocompatibility with the large number of cells adhering to the material through pseudopods and there was no significant difference between the pure PDLLA and 10% HA/PDLLA in terms of biological toxicity. Finally, the degradation rate of the composites could be tailored by the amount of nano-HA.

This study combined the S/O/W and SLS technique and provides a theoretical future basis for the preparation of drug-loaded microsphere scaffolds through SLS using HA/PDLLA composites.

Successes in scaffold guided tissue engineering require scaffolds to have specific macroscopic geometries and internal architectures to provide the needed biological and biophysical functions. Freeform fabrication provides an effective process tool to manufacture many advanced scaffolds with designed properties. This paper reports our recent study on using a novel precision extruding deposition (PED) process technique to directly fabricate cellular poly‐ε_rm;‐caprolactone (PCL) scaffolds. Scaffolds with a controlled pore size of 250 μm and designed structural orientations were fabricated.

The purpose of this paper is to fabricate the scaffolds with different pore architectures using additive manufacturing and analyze its mechanical and biological properties for bone tissue engineering applications.

The polylactic acid (PLA)/composite filament were fabricated through single screw extrusion and scaffolds were printed with four different pore architectures, i.e. circle, square, triangle and parallelogram with fused deposition modelling. Afterwards, scaffolds were coated with hydroxyapatite (HA) using dip coating technique. Various physical and thermo-mechanical tests have been conducted to confirm the feasibility. Furthermore, the biological tests were conducted with MG63 fibroblast cell lines to investigate the biocompatibility of the developed scaffolds.

The scaffolds were successfully printed with different pore architectures. The pore size of the scaffolds was found to be nearly 1,500 µm, and porosity varied between 53% and 63%. The fabricated circular pore architecture resulted in highest average compression strength of 13.7 MPa and modulus of 525 MPa. The characterizations showed the fidelity of the work. After seven days of cell culture, it was observed that the developed composites were non-toxic and supported cellular activities. The coating of HA made the scaffolds bioactive, showing higher wettability, degradation and high cellular responses.

The research attempts highlight the development of novel biodegradable and biocompatible polymer (PLA)/bioactive ceramic (Al₂O₃) composite for additive manufacturing with application in the tissue engineering field.

The purpose of this paper is to fabricate and characterize osteochondral beta‐tricalcium phosphate/collagen scaffold with bio‐inspired design by ceramic stereolithography (CSL) and gel casting.

Histological analysis was applied to explore the morphological characteristics of the transitional structure between the bone and the cartilage. The acquired data were used to design biomimetic biphasic scaffolds, which include the bone phase, cartilage phase, and their transitional structure. The engineered scaffolds were fabricated from β‐TCP‐collagen by CSL and gel casting. The cartilage phase was added to the ceramic phase by gel‐casting and freeze drying.

The resulting ceramic scaffolds were composed of a bone phase with the following properties: 700‐900 μm pore size, 200‐500 μm interconnected pores size, 50‐65 percent porosity, fully interconnected, ∼12 Mpa compressive strength. A suitable binding force between cartilage phase and ceramic phase was achieved by physical locking that was created by the biomimetic transitional structure. Cellular evaluation showed satisfactory results.

This study is the first try to apply CSL to fabricate biological implants with β‐TCP and type‐I collagen. There are still some defects in the composition of the slurry and the fabrication process.

This strategy of osteochondral scaffold fabrication can be implemented to construct an osteochondral complex that is similar to native tissue.

The CSL technique is highly accurate, as well as biologically secure, when fabricating ceramic tissue engineering scaffolds and may be a promising method to construct hard tissue with delicate structures. The present strategy enhances the versatility of scaffold fabrication by RP.

Heritability studies attempt to estimate the contribution of genes (vs. environments) to variation in phenotypes (or outcomes of interest) in a given population at a given time. This chapter scrutinizes heritability studies of adverse health phenotypes, emphasizing flaws that have become more glaring in light of recent advances in the life sciences and manifest most visibly in epigenetics.

Drawing on a diverse body of research and critical scholarship, this chapter examines the veracity of methodological and conceptual assumptions of heritability studies.

The chapter argues that heritability studies are futile for two reasons: (1) heritability studies suffer from serious methodological flaws with the overall effect of making estimates inaccurate and likely biased toward inflated heritability, and, more importantly (2) the conceptual (biological) model on which heritability studies depend – that of identifiably separate effects of genes versus the environment on phenotype variance – is unsound. As discussed, contemporary bioscientific work indicates that genes and environments are enmeshed in a complex (bidirectional, interactional), dynamic relationship that defies any attempt to demarcate separate contributions to phenotype variance. Thus, heritability studies attempt the biologically impossible. The emerging research on the importance of microbiota is also discussed, including how the commensal relationship between microbial and human cells further stymies heritability studies.

Understandably, few sociologists have the time or interest to be informed about the methodological and theoretical underpinnings of heritability studies or to keep pace with the incredible advances in genetics and epigenetics over the last several years. The present chapter aims to provide interested scholars with information about heritability and heritability estimates of adverse health outcomes in light of recent advances in the biosciences.

Aims to provide information on organism manufacturing engineering (OME), a newly proposed interdisciplinary research area.

A conceptual discussion and approach are taken.

OME is based on layer‐by‐layer RP principles and the integration of the new advancement of manufacturing science, biomaterials, cell molecular biology and developmental biology. OME aims to construct live tissues and organs through controlled assembly of 3D cell structure with the principles and methods of modern manufacturing science and life science.

Focuses on important processes for indirect and direct cell assembly using OME approaches.

The purpose of this study to investigate the organized porous network zinc (OPNZ) scaffolds. Their mechanical characteristics, surface roughness and fracture mechanism were assessed in relation to their structural properties. The prospects of fused deposition modeling (FDM) for printing metal scaffolds via rapid tooling have also been studied.

Zn scaffolds with different pore and strut sizes were manufactured via the rapid tooling method. This method is a multistep process that begins with the 3D printing of a polymer template. Later, a paraffin template was obtained from the prepared polymer template. Finally, this paraffin template was used to fabricate the Zn scaffold using microwave sintering. The characterization of prepared Zn samples involved structural characterization, microstructural study, surface roughness testing and compression testing. Moreover, based on the Gibson–Ashby model analysis, the model equations’ constant values were evaluated, which can help in predicting the mechanical properties of Zn scaffolds.

The scanning electron microscopy study confirmed that the fabricated sample pores were open and interconnected. The X-ray diffraction analysis revealed that the Zn scaffold contained hexagonal closed-packed Zn peaks related to the a-Zn phase, validating that scaffolds were free from contamination and impurity. The range for ultimate compressive strength, compressive modulus and plateau stresses for Zn samples were found to be 6.75–39 MPa, 0.14–3.51 GPa and 1.85–12.6 MPa by adjusting their porosity, which are comparable with the cancellous bones. The average roughness value for the Zn scaffolds was found to be 1.86 µm.

This research work can widen the scope for extrusion-based FDM printers for fabricating biocompatible and biodegradable metal Zn scaffolds. This study also revealed the effects of scaffold structural properties like porosity, pore and strut size effect on their mechanical characteristics in view of tissue engineering applications.