Three dimensional (3D) printing technology has been widely evaluated for the fabrication of various anthropomorphic phantoms during the last couple of decades. The demand for such high quality phantoms is constantly rising and gaining an ever-increasing interest. Although, in a short time 3D printing technology provided phantoms with more realistic features when compared to the previous conventional methods, there are still several aspects to be explored. One of these aspects is the further development of the current 3D printing methods and software devoted to radiological applications. The current 3D printing software and methods usually employ 3D models, while the direct association of medical images with the 3D printing process is needed in order to provide results of higher accuracy and closer to the actual tissues’ texture. Another aspect of high importance is the development of suitable printing materials. Ideally, those materials should be able to emulate the entire range of soft and bone tissues, while still matching the human’s anatomy. Five types of 3D printing methods have been mainly investigated so far: (a) solidification of photo-curing materials; (b) deposition of melted plastic materials; (c) printing paper-based phantoms with radiopaque ink; (d) melting or binding plastic powder; and (e) bio-printing. From the first and second category, polymer jetting technology and fused filament fabrication (FFF), also known as fused deposition modelling (FDM), are the most promising technologies for the fulfilment of the requirements of realistic and radiologically equivalent anthropomorphic phantoms. Another interesting approach is the fabrication of radiopaque paper-based phantoms using inkjet printers. Although, this may provide phantoms of high accuracy, the utilized materials during the fabrication process are restricted to inks doped with various contrast materials. A similar condition applies to the polymer jetting technology, which despite being quite fast and very accurate, the utilized materials are restricted to those capable of polymerization. The situation is better for FFF/FDM 3D printers, since various compositions of plastic filaments with external substances can be produced conveniently. Although, the speed and accuracy of this 3D printing method are lower compared to the others, the relatively low-cost, constantly improving resolution, sufficient printing volume and plethora of materials are quite promising for the creation of human size heterogeneous phantoms and their adaptation to the treatment procedures of patients in the current health systems.

A couple of fused deposition modeling (FDM) three-dimensional (3D) printers using variable infill density patterns were employed to simulate human muscle, fat, and lung tissue as it is represented by Hounsfield units (HUs) in computer tomography (CT) scans. Eleven different commercial plastic filaments were assessed by measuring their mean HU on CT images of small cubes printed with different patterns. The HU values were proportional to the mean effective density of the cubes. Polylactic acid (PLA) filaments were chosen. They had good printing characteristics and acceptable HU. Such filaments obtained from two different vendors were then tested by printing two sets of cubes comprising 10 and 6 cubes with 100% to 20% and 100% to 50% infill densities, respectively. They were printed with different printing patterns named “Regular” and “Bricks,” respectively. It was found that the HU values measured on the CT images of the 3D-printed cubes were proportional to the infill density with slight differences between vendors and printers. The Regular pattern with infill densities of about 30%, 90%, and 100% were found to produce HUs equivalent to lung, fat, and muscle. This was confirmed with histograms of the respective region of interest (ROI). The assessment of popular 3D-printing materials resulted in the choice of PLA, which together with the proposed technique was found suitable for the adequate simulation of the muscle, fat, and lung HU in printed patient-specific phantoms.

Three-dimensional (3D) printing technology has emerged as a promising tool for meticulously fabricated scaffolds with high precision and accuracy, resulting in intricately detailed biomimetic 3D structures. Producing magnetic scaffolds with the aid of additive processes, known as 3D printing, reveals multitude and state-of-the-art areas of application such as tissue engineering, bone repair and regeneration, drug delivery and magnetic hyperthermia. A crucial first step is the development of innovative polymeric composite magnetic materials. The current work presents a fabrication protocol of 3D printed polymer-bonded magnets using the Fused Deposition Modeling 3D printing method. Polymer-bonded magnets are defined as composites with permanent-magnet powder embedded in a polymer binder matrix. By using a low-cost mixing extruder, four (4) different filament types of 1.75 mm were fabricated using commercial magnetite magnetic nanoparticles mixed with a pure polylactic acid powder (PLA) and a ferromagnetic PLA (Iron particles included) filaments. The powder mixture of the basic filaments was compounded mixed with the nanoparticles (NPs), and extruded to fabricate the 3D printing filament, which is subsequently characterized structurally and magnetically before the printing process. Magnetic polymer scaffolds are finally printed using composite filaments of different concentration in magnetite. Our results demonstrate that the heating efficiency (expressed in W g⁻¹) of the 3D printed magnetic polymer scaffolds (ranging from 2 to 5.5 W g⁻¹ at magnetic field intensity of 30 mT and field frequency of 365 kHz) can be tuned by choosing either a magnetic or a non-magnetic filament mixed with an amount of magnetite NPs in different concentrations of 10 or 20 wt%. Our work opens up new perspectives for future research, such as the fabrication of complex structures with suitable ferromagnetic custom-made filaments adjusting the mixing of different filaments for the construction of scaffolds aimed at improving the accuracy of magnetic hyperthermia treatment.

The aim of this study is the development of a methodology for manufacturing 3D printed anthropomorphic structures, which mimic the X-ray properties of the human bone tissue. A mixing approach of two different materials is proposed for the fabrication of a radiologically equivalent hip bone for an anthropomorphic abdominal phantom. The materials employed for the phantom were polylactic acid (PLA) and Stonefil, while a custom-made dual motor filament extrusion setup and a custom-made software associating medical images directly with the 3D printing process were employed. Three phantoms representing the hip bone were 3D printed utilizing two filaments under three different printing scenarios. The phantoms are based on a patient's abdominal CT scan images. Histograms of CT scans of the printed hip bone phantoms were calculated and compared to the original patient's hip bone histogram, demonstrating that a constant mixing composition of 30% Stonefil and 70% PLA with 0.0375 extrusion rate per voxel (93.75% flow for fulfilling a single voxel) for the cancellous bone, and using 100% Stonefil with 0.04 extrusion rate per voxel (100% flow) for the cortical bone results in a realistic anatomy replication of the hip bone. Reproduced HU varied between 700 and 800, which are close to those of the hip bone. The study demonstrated that it is possible to mix two different filaments in real-time during the printing process to obtain phantoms with realistic and radiographically bone tissue equivalent attenuation. The results will be explored for manufacturing a CT-compatible abdominal phantom.