Effect of Graphene Addition on Polycaprolactone Scaffolds Fabricated Using Melt-Electrowriting

Melt-electrowriting (MEW) is an emerging method that combines electrospinning and extrusion printing, allowing the fabrication of micron-scale structures suitable for tissue engineering. Compared to other additive fabrication methods, melt-electro written structures can offer more appropriate substrates for cell culture due to filament size and mechanical characteristics of the fabricated scaffolds. In this study, polycaprolactone (PCL)/graphene composites were investigated for fabrication of micron-size scaffolds through MEW. It was demonstrated that the addition of graphene can considerably improve the processability of PCL to fabricate micron-scale scaffolds with enhanced resolution. The tensile strength of the scaffold prepared from PCL/graphene composite (with only 0.5 wt.% graphene) was proved significantly (by more than 270%), better than that of the pristine PCL scaffold. Furthermore, graphene was demonstrated to be a suitable material for tailoring the degradation process to avoid undesirable bulk degradation, rapid mass loss and damage to the internal matrix of the polymer. The findings of this study offer a promising route for the fabrication of high-resolution scaffolds with micron-scale resolution for tissue engineering.

Silicate-Based Electro-Conductive Inks for Printing Soft Electronics and Tissue Engineering

Hydrogel-based bio-inks have been extensively used for developing three-dimensional (3D) printed biomaterials for biomedical applications. However, poor mechanical performance and the inability to conduct electricity limit their application as wearable sensors. In this work, we formulate a novel, 3D printable electro-conductive hydrogel consisting of silicate nanosheets (Laponite), graphene oxide, and alginate. The result generated a stretchable, soft, but durable electro-conductive material suitable for utilization as a novel electro-conductive bio-ink for the extrusion printing of different biomedical platforms, including flexible electronics, tissue engineering, and drug delivery. A series of tensile tests were performed on the material, indicating excellent stability under significant stretching and bending without any conductive or mechanical failures. Rheological characterization revealed that the addition of Laponite enhanced the hydrogel’s mechanical properties, including stiffness, shear-thinning, and stretchability. We also illustrate the reproducibility and flexibility of our fabrication process by extrusion printing various patterns with different fiber diameters. Developing an electro-conductive bio-ink with favorable mechanical and electrical properties offers a new platform for advanced tissue engineering.

Characterization of 3D Printed Yttria-Stabilized Zirconia Parts for Use in Prostheses

The main aim of the present paper is to study and analyze surface roughness, shrinkage, porosity, and mechanical strength of dense yttria-stabilized zirconia (YSZ) samples obtained by means of the extrusion printing technique. In the experiments, both print speed and layer height were varied, according to a 22 factorial design. Cuboid samples were defined, and three replicates were obtained for each experiment. After sintering, the shrinkage percentage was calculated in width and in height. Areal surface roughness, Sa, was measured on the lateral walls of the cuboids, and total porosity was determined by means of weight measurement. The compressive strength of the samples was determined. The lowest Sa value of 9.4 μm was obtained with low layer height and high print speed. Shrinkage percentage values ranged between 19% and 28%, and porosity values between 12% and 24%, depending on the printing conditions. Lowest porosity values correspond to low layer height and low print speed. The same conditions allow obtaining the highest average compressive strength value of 176 MPa, although high variability was observed. For this reason, further research will be carried out about mechanical strength of ceramic 3D printed samples. The results of this work will help choose appropriate printing conditions extrusion processes for ceramics.

Evaluation of Printing Parameters on 3D Extrusion Printing of Pluronic Hydrogels and Machine Learning Guided Parameter Recommendation

Bioprinting is an emerging technology for the construction of complex three-dimensional (3D) constructs used in various biomedical applications. One of the challenges in this field is the delicate manipulation of material properties and various disparate printing parameters to create structures with high fidelity. Understanding the effects of certain parameters and identifying optimal parameters for creating highly accurate structures are therefore a worthwhile subject to investigate. The objective of this study is to investigate high-impact print parameters on the printing printability and develop a preliminary machine learning model to optimize printing parameters. The results of this study will lead to an exploration of machine learning applications in bioprinting and to an improved understanding between 3D printing parameters and structural printability. Reported results include the effects of rheological property, nozzle gauge, nozzle temperature, path height, and ink composition on the printability of Pluronic F127. The developed Support Vector Machine model generated a process map to assist the selection of optimal printing parameters to yield high quality prints with high probability (>75%). Future work with more generalized machine learning models in bioprinting is also discussed in this article. The finding of this study provides a simple tool to improve printability of extrusion-based bioprinting with minimum experimentations.

Consideration of requirements for materials for different bioprinting methods

The object of research is the characteristics of the materials used in the bioprinting process. One of the biggest problems in the field of bioprinting is the materials used for printing organs, in particular, the lack of mechanical properties of these materials, such as strength, elasticity, ductility, wear resistance, and the like. They are essential to achieve the stabilization of printed structures. During the study, the requirements for materials used in the technology of three-dimensional bioprinting, including hydrogels, were discussed. Three main methods were considered (extrusion bioprinting, drip bioprinting, laser bioprinting), for each of which separate requirements for materials are put forward. Comparative assessment of these materials for different types of printing techniques are obtained. It is also determined that the extrusion printing technique is the most used for this direction of use, however, there remains the problem of the viability of living cells through the force of the bias stress, which occurs when the substance is squeezed out from the side of the nozzle walls. It is determined that the main requirements are the ability to gel, low surface tension, wettability and viscosity of the substance. Through understanding and structured information, it is possible to provide biological connections for better cellular interactions and improve the nutrient medium for the creation of physiologically relevant, functional tissues that can be engrafted by the human body after implantation. With such initial data, it is possible to develop new materials and improve existing ones that would meet all these requirements. By identifying the key problem, new ways of solving it can be developed. The above problems are some of the main reasons why researchers are still far from the bioprinting of clinically significant functional organs. Nonetheless, thanks to the new development, bioprinting will become a key technology for future tissue engineering, regenerative medicine and pharmaceuticals.

Fundamentals of 3D Bioprinting Technology

3D bioprinting consists in the printing of synthetic 3D structures used as biomaterials, along with cells, growth factors, and other components necessary to create a new functional organ. This technology can be applied to regenerative medicine and tissue engineering to treat diseases, test pharmaceuticals, and study the mechanisms underlying diseases. Currently, there are three basic types of 3D bioprinting technologies: laser, droplet, and extrusion. Laser-based bioprinters (LBP) use laser energy to induce the bioink transfer. Droplet-based bioprinters (DBP) expel the bioink dropwise throughout a nozzle. Inkjet-based bioprinters are the DBP commonly used for biological proposes, it is also a non-contact approach that releases controlled volumes of bioink drops in a continuous (CIJ) or under demand way (DOD). The extrusion-based bioprinters (EBB) also use pressure to force out the bioink, but consists of a syringe containing the material with a pneumatic or mechanical mechanism as dispensing system. Comparing to the other bioprinting technologies, extrusion printing is the most versatile and is indicated for bioprinting of scaffold prosthetic implants. The bioinks used in 3D bioprinting are composed of a solution with a biomaterial mixture, usually encapsulating cells. Biomaterials are essential components of 3D bioprinting technologies because they provide scaffolds as supporting physical structures for cells to attach, grow, differentiate, and develop into tissues. Numerous cell types have been used in 3D bioprinting to build cardiovascular, musculoskeletal, neural, hepatic, adipose and skin tissues. Bioprinting is an emerging technology that has the ability to revolutionize the way we address many health issues.

Correlating rheology and printing performance of fiber-reinforced bioinks to assess predictive modelling for biofabrication

A crucial property for the evaluation of bioinks, besides biocompatibility, is printability, which is determined by resolution and shape fidelity. Recently, fiber reinforcement was used to overcome rheological limitations and introduce biomimetic structuring. This study provides a systematic approach to evaluate the printability of fiber reinforced hydrogels. Alginate and Pluronic hydrogels were blended with cellulose nanofibers (CeNF) and polycaprolactone (PCL) microfibers. SEM imaging revealed fiber-induced structural changes. Oscillatory rheological experiments showed that the addition of fiber fragments significantly altered the complex viscosity. A customized setup was utilized to determine strut spreading behavior in a real extrusion printing process. Strikingly, the data displayed excellent correlation with viscoelastic model-based predictions. CeNF increased the shape fidelity of both hydrogels, while PCL microfibers increased the viscosity but resulted in a time dependent loss of structural integrity in Pluronic. The results emphasize the need to complement shear-rheological analysis of bioinks by print-related customized analytical tools. Graphic abstract