Purpose This paper aims to discuss the successful fabrication of customized tubular scaffolds for tracheal tissue engineering with a novel route using solvent-based extrusion 3D printing. Design/methodology/approach The manufacturing approach involved extrusion of polymeric ink over a rotating predefined pattern to construct customized tubular structure of polycaprolactone (PCL) and polyurethane (PU). Dimensional deviation in thickness of scaffolds were calculated for various layer thicknesses of 3D printing. Physical and chemical properties of scaffolds were investigated by scanning electron microscope (SEM), contact angle measurement, Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD). Mechanical characterizations were performed, and the results were compared to the reported properties of human native trachea from previous reports. Additionally, in vitro cytotoxicity of the fabricated scaffolds was studied in terms of cell proliferation, cell adhesion and hemagglutination assay. Findings The developed fabrication route was flexible and accurate by printing customized tubular scaffolds of various scales. Physiochemical results showed good miscibility of PCL/PU blend, and decrease in crystalline nature of blend with the addition of PU. Preliminary mechanical assessments illustrated comparable mechanical properties with the native human trachea. Longitudinal compression test reported outstanding strength and flexibility to maintain an unobstructed lumen, necessary for the patency. Furthermore, the scaffolds were found to be biocompatible to promote cell adhesion and proliferation from the in vitro cytotoxicity results. Practical implications The attempt can potentially meet the demand for flexible tubular scaffolds that ease the concerns such as availability of suitable organ donors. Originality/value 3D printing over accurate predefined templates to fabricate customized grafts gives novelty to the present method. Various customized scaffolds were compared with conventional cylindrical scaffold in terms of flexibility.

The machining of Titanium alloy, Ti-6Al-4V has got an extensive attention from industries like aerospace, medical, and biomedical plants due its unique properties like high strength at elevated temperature and better strength to weight ratio. Still, properties like reduced thermal conductivity, affinity to react with the tool and work hardening make difficult to cut it by conventional turning process. Ultrasonic vibration-assisted turning (UVAT) is one of the advanced turning method in which tool is allowed to vibrate with ultrasonic frequency (~ 20 kHz) with small amplitude and hence converting the continuous cutting to an intermittent cutting process. In the present work a horn (acts as an amplifier as well as a tool holder) with inserted tool tip is designed and FEM analysis has been done for its suitability for the process. The dynamic analysis has also been performed to find out the stress distribution in both parts under cyclic loading conditions. It enables to locate the highly stressed nodal regions. Experimental investigation has been carried out for both conventional turning (CT) and UVAT processes to demonstrate effects of various inputs on the output responses like cutting forces, surface roughness, tool wear and temperature rise in UVAT. Additionally, a 3D finite element model for UVAT and CT has been prepared. The simulation results like force and steady state tool tip temperature have also been validated with the experimental results and found to be in good agreement. The advantages of UVAT process have been discovered in terms of reduction in the cutting forces and surface roughness for the used Ti-6Al-4V workpiece.

Tissue-engineered tubular scaffolds offer huge potential to heal or replace the diseased organ parts like blood vessels, trachea, oesophagus and ureter. However, manufacturing these scaffolds in various scales and shapes is always challenging and requires progressive technology. Developing a flexible and accurate manufacturing method is a major developmental direction in the field of tubular scaffold fabrication. In this context, the present work presents a novel solvent-based extrusion 3D printing which allows extruding over a rotating mandrel to fabricate tubular scaffolds of polycaprolactone (PCL) and polyurethane (PU). Experimental runs were planned as per the central composite design (CCD) to evaluate the effects of input parameters like infill density, layer thickness, print speed and percentage of PU on the output responses like printing quality and mechanical characteristics. The printing quality was quantified by measuring average surface roughness of the printed scaffolds and mechanical properties were evaluated by measuring radial compressive load, and percentage of elongation. The experimental investigations revealed that printing quality was improved at higher infill densities and was deteriorated at higher print speeds and layer thicknesses. Similarly, the radial compressive load was improved with the increase in infill density and was decreased with an increase in layer thickness, print speed and percentage of PU. The percentage of elongation was found to improve at higher infill densities and percentages of PU and was reduced with an increase in layer thickness and print speed. Additionally, a multi-objective optimization using Genetic Algorithm was used to evaluate the optimum conditions to minimize surface roughness and maximizing radial compression load and percentage of elongation. Finally, a case study was performed by comparing the mechanical properties of tubular organs and scaffolds from the existing reports and results of the present work.

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Tracheal implantation remains a major therapeutic challenge due to the unavailability of donors and the lack of biomimetic tubular grafts. Fabrication of biomimetic tracheal scaffolds of suitable materials with matched rigidity, enhanced flexibility and biocompatibility has been a major challenge in the field of tracheal reconstruction. In this study, customized tubular grafts made up of FDA-approved polycaprolactone (PCL) and polyurethane (PU) were fabricated using a novel solvent-based extrusion 3D printing. The printed scaffolds were investigated by various physical, thermal, and mechanical characterizations such as contact angle measurement, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), radial compression, longitudinal compression, and cyclic radial compression. In this study, the native goat trachea was used as a reference for the fabrication of different types of scaffolds (cylindrical, bellow-shaped, and spiral-shaped). The mechanical properties of the goat trachea were also compared to find suitable formulations of PCL=PU. Spiral-shaped scaffolds were found to be an ideal shape based on longitudinal compression and torsion load maintaining clear patency. To check the long-term implantation, in vitro degradation test was performed for all the 3D printed scaffolds and it was found that blending of PU with PCL reduced the degradation behavior. The printed scaffolds were further evaluated for biocompatibility assay, live/dead assay, and cell adhesion assay using bone marrow-derived human mesenchymal stem cells (hMSCs). From biomechanical and biological assessments, PCL70=PU30 of spiral-shaped scaffolds could be a suitable candidate for the development of tracheal regenerative applications.