3D-printed β-TCP/Ti6Al4V composite scaffolds for bone regeneration: Process parameter optimization and evaluation

Purpose The aim of this study is to improve printability by studying the effects of ink’s viscosity, pattern width and length and the process parameters of direct ink write (DIW) technique on the printed carbon patterns for applications in functional sensors and devices. The primary focus is to understand the effects of all the possible parameters, including rheological and geometrical characteristics associated with direct ink writing of conductive carbon and their effects on the performance of the printed pattern, followed by their optimization for desired applications. Moreover, the research work seeks to draw a relationship accounting for the influencing parameters to improve printability and performance. Design/methodology/approach The research performed a comprehensive analysis of ink’s rheological characteristics, geometrical attributes and process parameters on the performance of DIW printed carbon. The rheological characteristics involve the viscosity and shear thinning effects on the process parameters and their fine-tuning. Moreover, the viscosity reduction was carried out to study the effects on printing parameters. Response surface modeling technique was adopted to statistically determine the significant parameters and their effects on the printed patterns. Furthermore, a lab-developed setup was used to realize samples, followed by a detailed study of the effects of each parameter on the pattern width and resistance. The experiments were performed for both pristine and reduced viscosity carbon paste, and the results were compared. Furthermore, the length of the pattern was varied, and the effects were recorded to conclude the study. Findings The research findings concluded establishing a relationship between the ink’s rheological characteristics, geometrical attributes and process parameters of the DIW technique to improve printability and electrical performance of printed functional devices of carbon ink. The statistical analysis carried through highlights extrusion pressure and print speed as the most significant process parameters for a given viscosity, and their optimization is dependent on the required output performance. The viscosity reduction significantly reduced the required extrusion pressure and enhanced print speed without altering the electrical characteristics. It was found experimentally that pattern width is influenced by printing parameters, which are associated with electrical characteristics. Furthermore, the results showed that the printed patterns obey Ohm’s law in terms of increased length at a fixed increment. Originality/value The study provides the very first comprehensive and systematic analysis of the critical impacts of rheological characteristics, geometrical attributes and process parameters of DIW of conductive carbon for applications in functional sensors and devices. The combination of statistical and experimental aspects of the study establishes a definitive, optimized printing window, moving ahead of qualitative aspects, thus providing a quantitative framework for the fabrication of stable, high-performance carbon-based devices via DIW. The printing window will ensure reproducibility and enhancement in the performance of carbon-based sensors fabricated through DIW, thus enabling robustness and cost-effectiveness.

Hierarchical porous materials are ubiquitous in nature and have inspired the fabrication of cellular structures for a multitude of applications. As an extrusion-based 3D printing technique, direct ink writing (DIW) allows for customizable design and accurate control of printed structures. Recently, its combination with colloidal processing methods used for bulk porous ceramics, such as emulsion templating, has further extended its capability of fabricating porous ceramics across multiple length scales. In light of the recent development, the ink formulation for emulsion-based DIW can be further explored, and there is still a need for a better understanding of the structure-property relationship. Herein, we introduce two types of gelling additives, i.e., poly(ethylenimine) (PEI) and Pluronic F-127, respectively, into particle-stabilized emulsions and fabricate hierarchical porous alumina lattices by DIW. We discover that the two gelling additives can lead to distinctive microstructures due to their different gelling mechanisms. Moreover, the 3D printed hierarchical porous ceramic lattices are found to exhibit a potential energy absorption property. The effects of ink formulations, including gelling additives and solid loading, on ink rheology, microstructure, and mechanical properties are investigated. The 3D printed hierarchical porous ceramic lattices exhibit a high average porosity of 73.7%-79.3% with an average compressive strength of 1.53-9.61 MPa and a specific energy absorption of 0.33-2.67 J/g. Featuring two distinctive microstructures with tunable structural features and mechanical properties, the 3D printed hierarchical porous ceramics in this study have potential in many applications, including lightweight structures, tissue engineering scaffolds, filtration, etc.

The application of solid-state electrolytes is one of the effective approaches to address the safety issues of lithium-ion batteries. From a manufacturing perspective, 3D printing based on direct ink writing (DIW) has attracted unprecedented interest due to its high design freedom and convenient fine-scale control. In this study, Li[Formula: see text]Al[Formula: see text]Ti[Formula: see text](PO4)3 (LATP) electrolyte nanoparticles were dispersed in polyethylene oxide (PEO) polymer to form a printable electrolyte ink, and a composite solid-state electrolyte was subsequently fabricated via DIW. The results show that the composite electrolyte ink containing 2 wt.% LATP exhibits the optimal rheological properties at room temperature. The addition of LATP nanofillers effectively enhances the structural stability, thermal stability, and electrochemical performance of the polymer electrolyte. The ionic conductivity of the printed composite solid-state electrolyte membrane is increased to 5.62 × 10[Formula: see text] S ⋅ cm[Formula: see text]. The NCA/graphite solid-state lithium-ion battery assembled with this electrolyte displays a specific discharge capacity of 236 mAh g[Formula: see text] at a 0.1 C rate, and exhibits excellent electrochemical reversibility and cycle stability. This multi-shaped, printable ink technology opens up new pathways for the manufacturing of scalable energy storage devices.

Three-dimensional printing (3DP) of functional materials is increasingly important for advanced applications requiring objects with complex or custom geometries or prints with gradients or zones with different properties. A common 3DP technique is direct ink writing (DIW), in which printable inks are comprised of a fluid matrix filled with solid particles, the latter of which can serve a dual purpose of rheology modifiers to enable extrusion and functional fillers for performance-related properties. Although the relationship between filler loading and viscosity has been described for many polymeric systems, a thorough description of the rheological properties of three-dimensional (3D) printable composites is needed to expedite the creation of new materials. In this manuscript, the relationship between filler loading and printability is studied using model paraffin/photopolymer composite inks containing between 0 and 73 vol. % paraffin microbeads. The liquid photopolymer resin is a Newtonian fluid, and incorporating paraffin microbeads increases the ink viscosity and imparts shear-thinning behavior, viscoelasticity, and thixotropy, as established by parallel plate rheometry experiments. Using Einstein and Batchelor's work on colloidal suspension rheology, models were developed to describe the thixotropic behavior of inks, having good agreement with experimental results. Each of these properties contributes to the printability of highly filled (≥43 vol. % paraffin) paraffin/photopolymer composite inks. Through this work, the ability to quantify the ideal rheological properties of a DIW ink and to selectively control and predict its rheological performance will facilitate the development of 3D printed materials with tunable functionalities, thus, advancing 3DP technology beyond current capabilities.

3D-printed hydroxyapatite/gelatin bone scaffolds reinforced with graphene oxide: Optimized fabrication and mechanical characterization

Polycaprolactone (PCL) is widely utilized in bone tissue engineering due to its excellent biocompatibility and processability; however, its inherent bioinertness and hydrophobicity significantly restrict its clinical osteogenic efficacy. To overcome these limitations, we incorporated sol–gel synthesized silicate-based bioactive glass (BG) into a PCL matrix and fabricated a series of composite scaffolds with varying BG contents via direct ink writing (DIW) 3D printing. Rheological characterization confirmed that all ink formulations exhibited shear-thinning behavior, with viscosity increasing monotonically with BG content. DSC analysis revealed that BG incorporation progressively reduced the crystallinity of PCL from 51.47% to 36.23%. We systematically evaluated the physicochemical properties, mechanical resilience, and in vitro degradation behavior of these scaffolds. The results indicated that BG incorporation significantly improved the surface hydrophilicity, with the contact angle decreasing from 104.8 ± 2.81° to 69.8 ± 2.91°. Furthermore, as the BG content increased, the porosity and mechanical strength exhibited an initial increase followed by a subsequent decrease, yet all values remained within the range of human cancellous bone. Notably, cellular assays revealed that the introduction of 58SBG enhanced cell–matrix interactions; the PCL/BG scaffolds promoted superior cell attachment and more extensive morphological spreading compared to pure PCL. Among all groups, the PCL/30BG composite scaffold demonstrated the most optimal balance of mechanical integrity and biological response. Consequently, the PCL/30BG scaffold developed in this study exhibits immense potential as a bone graft substitute, providing a promising approach for clinical bone defect repair strategies.

In the present study, we have fabricated a ternary composite nanofibrous scaffold from PCL/gelatin/chitosan, by electrospinning technique, using a solvent system—chloroform/methanol for polycaprolactone (PCL) and acetic acid for gelatin and chitosan, for tissue engineering applications. Field emission scanning electron microscopy (FE-SEM) was used to investigate the fiber morphology of the scaffold and it was found that the fiber morphology was influenced by the concentrations of PCL, gelatin, and chitosan in polymer solution during electrospinning. X-ray diffraction, Fourier transform infrared, and thermogravimetric (TG) analysis results showed some interactions among the molecules of PCL, gelatin, and chitosan within the scaffold. In-vitro cell culture studies were done by seeding L929 mouse fibroblasts on fabricated composite scaffold, which confirmed the cell viability, high cell proliferation rate, and cell adhesion on composite scaffold as indicated by MTT assay, DNA quantification, and FE-SEM analysis of cell-scaffold construct. Thus, the ternary composite scaffold made from the combination of PCL (synthetic polymer), gelatin, and chitosan (natural polymer) may find potential application in tissue engineering.

In this study, a tubular scaffold composed of polylactide fibers (outside layer) and silk fibroin-gelatin fibers (inner layer) was fabricated successfully by electrospinning. Morphological, biomechanical, and dissolvable properties of the composite scaffolds were examined, in particular, biocompatibility of the scaffolds were evaluated in vitro and in vivo by means of cell culture and subcutaneous implantation test. The PLA/SF-gelatin tubular scaffolds, with porosity of approximately 82 +/- 2%, possessed appropriate breaking strength (2.21 +/- 0.18 MPa), pliability (60.58 +/- 1.23%), and suture retention strength (4.58 +/- 0.62 N). The burst pressure strength of the composite scaffolds reached 1596 +/- 20 mmHg, which is much greater than that of the native vessels. The composite scaffolds could hardly dissolve in the water; the water-dissolved rate was only 0.3 +/- 0.1%. MTT assay and SEM observation indicated that both 3T3 mouse fibroblasts and human umbilical vein endothelial cells could adhere, spread, and proliferate well on the composite tubular scaffolds after culturing for 14 and 21 days, respectively. The subcutaneous implantation results showed that macrophages and lymphocytes were not observed, which indicated that the composite scaffolds could induce minor inflammatory reactions in vivo. The PLA/SF-gelatin tubular scaffolds are biocompatible, possess appropriate biomechanical properties, and provide a favorable environment that supports the growth of cells, which shows that the composite tube can be considered as an ideal candidate for tissue engineering blood vessel.

In this paper, for the first time, the role of manufacturing parameters of fused deposition modeling (FDM) on the shape memory effect (SME) is investigated by design of experiments. PLA-TPU blend with a weight composition of 30:70% is processed by melt mixing and then extruded into 1.75 mm filaments for 3D printing via FDM. SEM images reveal that TPU droplets are distributed in the PLA matrix, and the immiscible matrix-droplet morphology is evident. Box-Behnken design (BBD), as an experimental design of the response surface method (RSM), is implemented to fit the model between variables and responses. The shell, infill density, and nozzle temperature are selected as variables, and their effects on loading stress, recovery stress, shape fixity, and shape recovery ratio are studied in detail. An analysis of variance (ANOVA) is applied to estimate the importance of each printing parameter on the output response and assess the fitness of the presented model. The ANOVA results reveal the high accuracy of the model and the importance of the parameters. Infill density and nozzle temperature had the greatest and least roles on shape memory properties, respectively. Also, the values of shape fixity and shape recovery were obtained in the ranges of 58–100% and 53–91%, respectively. Despite many researches on 4D printing of PLA, low ductility at room temperature and high stress relaxation rate are its weakness, which are covered by adding TPU in this research. Due to the lack of similar outcomes in the specialized literature, this paper is likely to fill the gap in the state-of-the-art problem and supply pertinent data that are instrumental for FDM 3D printing of functional shape memory polymers with less material consumption.

Surface modification of nanofibrous polycaprolactone/gelatin composite scaffold by collagen type I grafting for skin tissue engineering

Additive manufacturing (AM) methods such as fused filament fabrication (FFF) and direct ink writing (DIW) enable the free-form design and printing of complex architectures using a range of materials. Compared with traditional manufacturing technologies, AM methods are highly automated to reduce waste, assembly costs, and processing errors. By combining different AM deposition methods, we can fabricate composite materials with desired spatial arrangements and anisotropies to meet unique design requirements and to produce integrated multi-material components that are not easily manufactured by traditional strategies. To address a wide variety of mechanical performance requirements, developing hybrid AM technologies into a low-cost, fully-automated manufacturing process can realize a number of new types of elastomer composite architectures. In this work, FFF and DIW methods have been combined to fabricate thermoplastic polyurethane (TPU) reinforced silicone composite materials. Several specimens with different silicone and TPU infill patterns have been designed to characterize the mechanical compression responses of these structures. With 40–80% infill percentages of silicone and 20–60% infill percentages of TPU, composites specimens can be designed to get any specified compression response between 600 N and 9000 N. This TPU-reinforced silicone printing technique can be applied for silicone composite architecture design in a wide range of applications that require tunable elastic responses.

The porous medium combustion (PMC) is an emerging area in liquid fuel combustion, which has the ability to reduce emission and increase the fuel economy. Various operational parameters will affect the performance of liquid fuel-fired Porous Medium Burner (PMB). So, this present work focuses on finding the effect of operational parameters on the performance of PMB and to optimize it. This study was conducted in a double-layered porous burner with self-aspirated pressurized stove. Three input factors were selected, namely, fuel pressure (bar), throttle angle (°), and type of burner (Conventional burner (CB), PMB). The three output responses selected are thermal efficiency (ηth), CO (ppm), and NOX (ppm) emissions. The inscribed central composite design (ICCD) was used to design the experimental run. The response surface methodology (RSM) with desirability approach was used to optimize the multi-objective responses. The statistical analysis with ANOVA confirmed the significance of all the three input variables on the output responses. The regression model was developed with quadratic fit and it well predicts the burner performance and emission with R2 value close to 1. The multi-objective optimum input settings are found by desirability approach, i.e. fuel pressure = 1.60 bar, throttle angle = 161.3°, and burner type = PMB. The corresponding optimized responses are found as ηth = 58.39%, CO = 201. 49 ppm, and NOX = 6.43 ppm. The above optimum settings and responses are confirmed with experimental confirmation test, which is in the satisfactory level.

This paper presents an antenna-based bidirectional stretch sensor for real-time wireless sensing applications. The proposed design utilizes an antenna structure with two orthogonal dipole elements operating at different frequency bands to independently sense strain in two perpendicular directions. One pair of elements is configured to operate at 2.4 GHz, while the other operate at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{5 GHz}$</tex>. The antenna is fabricated using direct ink writing (DIW) with stretchable silver ink on a flexible thermoplastic polyurethane (TPU) substrate, enabling the mechanical flexibility required for stretch sensing. Under applied stress, the antenna's physical dimensions change, leading to a shift in its resonant frequency. This frequency shift is observed to be linearly correlated with the applied strain along either axis (x-axis or <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$y$</tex>-axis). Experimental results show that for stretch levels ranging from 0 % to 10 % of the original dimensions, the resonant frequency shifts by approximately 6 % in the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{x}$</tex>-axis direction and 7 % in the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$y$</tex>-axis direction, respectively. The proposed design demonstrates potential for applications requiring simultaneous stretch sensing and wireless communication using the same antenna structure.

The objective of this study is to report the effect of Pluronic F-127 on osteoblast viability and phenotype maintenance in vitro. MG-63 cells are suspended in Pluronic F-127, and MTT assay, alkaline phosphatase activity, prostaglandin E(2) production, collagen-I, and cyclo-oxygenase-2 expression are assessed up to 6 days. Pluronic F-127 leads to a significant decrease in osteoblast viability throughout the 6-day experiment, without altering osteoblast phenotype. The addition of platelet-rich plasma to the polymer/cell construct leads to increased cell survival. When supplemented with bioactive factors, Pluronic F-127 could potentially be used as a cell carrier in bone tissue engineering.

Photopolymers are one of the fastest growing 3D printing material classes, despite the lack of diversity in performance or composition. A simple addition of graphite nanopowder is explored for tailoring aliphatic polycarbonate performance and enhancing advanced material properties, targeting the mechanical performance of the norbornene‐containing poly(norbornene trimethyl carbonate) using poly(trimethyl propane allyl ether carbonate) for thermoset formation using thiol‐ene photochemistry. A 30 wt% graphite‐composite photopolymer ink displays shear thinning behavior suitable for pneumatic direct ink write (DIW) printing, along with enhanced elastic modulus (15–542 MPa) and an increase in ultimate strength (2–22 MPa for the composite ink) without significant variation in the glass transition temperature. The composites are further demonstrated as 4D materials including shape memory, conductivity, and recyclability, with this work serving as a guide for designing DIW inks from photopolymer resins.