Mid Sweden University

Applications of 3D printing in medicine are already well-established in relation to utilizing the shape freedom provided by additive manufacturing and capabilities of the digital pathway from the idea and clinical image to a product. Today's attention to designing 3D-printed parts for medicine and veterinary applications has shifted from pure “designing for defined shape” to the addition of “designing for demanded functionality.” Here additional properties or functionalities invoked into the final part beyond spatial ones (three dimensions), such as specific physical, biological, electrical, magnetic, or other functional parameters effectively that expand the design space toward the fourth functional dimension. In this chapter, the authors attempt to show the trends in functionalization of case- and patient-specific implants and supporting medical tools, including the specifics of the approaches (e.g., metamaterial), specific design modalities, and manufacturing methods. The chapter will cover materials, design, and manufacturing of porous structures (including variations of porosity, layered, and gradient structures), surface structuring, and functionalization. It has also focused on the integration of 3D printing into the surgery flow (parts for preoperational planning, customization of tools, physical modeling of human body parts), digital and physical modeling of the components functioning in the body, their stability, and longevity. 

Biomaterials play a crucial role in the long-term success of bone implant treatment. The accumulation of bacterial biofilm on the implants induces inflammation, leading to implant failure. Modification of the implant surface with bioactive molecules is one of the strategies to improve biomaterial compatibility and limit inflammation. In this study, whey protein isolate (WPI) fibrillar coatings were used as a matrix to incorporate biologically active phenolic compound phloroglucinol (PG) at different concentrations (0.1% and 0.5%) on titanium alloy (Ti6Al4V) scaffolds. Successful Ti6Al4V coatings were validated by X-ray photoelectron spectroscopy (XPS), showing a decrease in %Ti and increases in %C, %N, and %O, which demonstrate the presence of the protein layer. The biological activity of PG-enriched WPI (WPI/PG) coatings was assessed using bone-forming cells, human bone marrow-derived mesenchymal stem cells (BM-MSCs). WPI/PG coatings modulated the behavior of BM-MSCs but did not have a negative impact on cell viability. A WPI with higher concentrations of PG increased gene expression relative to osteogenesis and reduced the pro-inflammatory response of BM-MSCs after biofilm stimulation. Autoclaving reduced WPI/PG bioactivity compared to filtration. By using WPI/PG coatings, this study addresses the challenge of improving osteogenic potential while limiting biofilm-induced inflammation at the Ti6Al4V surface. These coatings represent a promising strategy to enhance implant bioactivity.

Head injury prevention is a crucial concern within the healthcare system and scientific community. Experimental and numerical trials play a key role, utilizing anthropomorphic test devices and human head numerical models to study impact scenarios. However, rigid headforms, Like Hybrid III or EN 960, lack biofidelity, suggesting a need for more refined physical models, such as NOCSAE standardized headform. Moreover, the direct development of human head numerical models relies on testing cadaveric tissues. Therefore, a biofidelic instrumented human head replica embedding synthetic simulants of cerebrospinal fluid, meninges, and brain was developed at the University of Padova in collaboration with Mid Sweden University. As part of this activity, the present study proposes an integrated experimental-numerical methodology for impact testing, involving the development of a finite element model of this replica. This also supports the future development of human head models having the same geometry as physical replicas. Preliminarily, the proposed workflow involves the mechanical characterization of the materials used for the replica and the geometry reconstruction for the subsequent numerical analysis. This was performed with an explicit dynamic algorithm to simulate impacts of the physical bare replica onto a flat anvil using a drop tower. An example of the collection and analysis of experimental and numerical data is presented as a preliminary validation of the model. The interpretation of these results is provided as a basis for refinements, before the study of helmeted impacts. The results show that the current model needs improvements in terms of coupling mechanisms and skin and fluid constitutive formulations.

Highlights Neck surrogates could be helpful tools to assess injury risk in simulated impacts but still can be perfectionated to capture the complexity and diversity of neck anatomy and behavior in different situations. The Biofidelic Instrumented Neck Surrogate (BINS) aims to offer a tool for the analysis of low-energy impacts and also to introduce a novel set of sensors to investigate neck movements without external equipment. This works explores the mechanical design of this surrogate as well as the working principle of the embedded sensors, providing comparison with literature data and proof of the sensor concept in static and dynamic tests. The BINS is still far from catching the whole complexity of the human neck behavior, but offers a valuable tool in low-energy scenarios, enriched by the possibility of getting quite accurate head/trunk relative kinematics by embedded sensors. What are the main findings? The BINS surrogate has similar flexural behavior to passive human subject. BINS embedded angular sensors return neck flexural and compressive measurements with similar performances with respect to motion capture cameras. What is the implication of the main finding? BINS neck could be used as a viable tool to obtain realistic head kinematics in low-energy impacts. The developed angular sensors could be used effectively to quantify BINS movements and could be adapted to future neck surrogates structurally designed to withstand high-energy impacts or crashes.Highlights Neck surrogates could be helpful tools to assess injury risk in simulated impacts but still can be perfectionated to capture the complexity and diversity of neck anatomy and behavior in different situations. The Biofidelic Instrumented Neck Surrogate (BINS) aims to offer a tool for the analysis of low-energy impacts and also to introduce a novel set of sensors to investigate neck movements without external equipment. This works explores the mechanical design of this surrogate as well as the working principle of the embedded sensors, providing comparison with literature data and proof of the sensor concept in static and dynamic tests. The BINS is still far from catching the whole complexity of the human neck behavior, but offers a valuable tool in low-energy scenarios, enriched by the possibility of getting quite accurate head/trunk relative kinematics by embedded sensors. What are the main findings? The BINS surrogate has similar flexural behavior to passive human subject. BINS embedded angular sensors return neck flexural and compressive measurements with similar performances with respect to motion capture cameras. What is the implication of the main finding? BINS neck could be used as a viable tool to obtain realistic head kinematics in low-energy impacts. The developed angular sensors could be used effectively to quantify BINS movements and could be adapted to future neck surrogates structurally designed to withstand high-energy impacts or crashes.Highlights Neck surrogates could be helpful tools to assess injury risk in simulated impacts but still can be perfectionated to capture the complexity and diversity of neck anatomy and behavior in different situations. The Biofidelic Instrumented Neck Surrogate (BINS) aims to offer a tool for the analysis of low-energy impacts and also to introduce a novel set of sensors to investigate neck movements without external equipment. This works explores the mechanical design of this surrogate as well as the working principle of the embedded sensors, providing comparison with literature data and proof of the sensor concept in static and dynamic tests. The BINS is still far from catching the whole complexity of the human neck behavior, but offers a valuable tool in low-energy scenarios, enriched by the possibility of getting quite accurate head/trunk relative kinematics by embedded sensors. What are the main findings? The BINS surrogate has similar flexural behavior to passive human subject. BINS embedded angular sensors return neck flexural and compressive measurements with similar performances with respect to motion capture cameras. What is the implication of the main finding? BINS neck could be used as a viable tool to obtain realistic head kinematics in low-energy impacts. The developed angular sensors could be used effectively to quantify BINS movements and could be adapted to future neck surrogates structurally designed to withstand high-energy impacts or crashes.Abstract Road accidents could result in severe or fatal neck injuries. A few surrogate necks are available to develop and test neck protectors as countermeasures, but each has its own limitations. The objective of this study was to develop a surrogate neck compatible with the Hybrid III dummy, focused on tunable flexural stiffness and integrated angular sensors for kinematic feedback during impact tests. The neck features six 3D-printed surrogate vertebral bodies interconnected by rubber surrogate discs, providing a baseline flexibility to the surrogate fundamental spinal units. An adjustable inner cable and elastic elements hooked on the sides of vertebral elements allow to increase the flexural stiffness of the surrogate and to simulate the asymmetric behavior of the human neck. Neck flexural angles and axial compression are measured using a novel system made of wires, pulleys, and rotary potentiometers embedded in the neck base. A motion capture system and a load cell were used to determine the bending and torsional stiffness of the neck and to calibrate the sensors. Results showed that the neck flexural stiffness can be tuned between 3.29 and 5.76 Nm/rad. Torsional stiffness was 1.01 Nm/rad and compression stiffness can be tuned from 39 to 193 N/mm. Sensor flexural angles were compared with motion capture angles, showing an RMSE error of 1.35 degrees during static testing and of 3 degrees during dynamic testing. The developed neck could be a viable tool for investigating neck braces from a kinematic and kinetic perspective due to its inbuilt sensing ability and its tunable stiffness.

The critical niobium content required to maintain the β phase in additively manufactured Ti–Nb alloys, preventing martensitic transformation, is still unclear. Our previous study showed that 42 wt% Nb was insufficient. Therefore, in this study, new pre-alloyed β-titanium alloys with high niobium percentage (56 wt%, Ti–56Nb) were successfully produced by Electron Beam Powder Bed Fusion (PBF-EB), and the effect of varying beam current (4 mA, 5 mA, and 7 mA) on microstructure and mechanical properties was studied. All processing regimes achieved proper fusion, with a uniform porosity distribution (∼0.3 %) and minimal niobium-enriched regions, attributed to powder heterogeneity. Beam current variations significantly affected melt pool dynamics, phase constitution, and heat distribution. Planar growth along layer boundaries and cellular structures within melt pools was observed, caused by high thermal gradients and high cooling rates. Texture analysis revealed that higher beam currents induced fiber-like textures due to zigzag beam movement and deep remelting, while 4 mA and 5 mA beam currents produced biaxial textures with minimal fiber contributions. TEM analysis indicated that higher energy input facilitated martensitic transformation, whereas lower energy enhanced β-phase stabilization. Mechanical testing identified the 4 mA regime as optimal, achieving the highest yield strength, favorable β-phase fraction, reduced elastic modulus, and enhanced wear resistance. This study demonstrates how varying beam energy inputs during PBF-EB printing can tailor the meso- and micro-scale structure and mechanical properties of Ti–56Nb alloys, providing valuable insights for optimizing densification, microstructure, texture, and mechanical performance in additive manufacturing applications. 

Orthopedic implant design increasingly aims to reduce the elastic modulus mismatch with bone and to mimic the native extracellular environment. However, achieving reliable osseointegration still remains a challenge. Herein, we report for the first time the fabrication and functionalization of Ti–xNb gyroid scaffolds with controlled porosity from pre-alloyed powders with different niobium content (x = 42 or 56 wt%) using powder bed fusion electron beam melting (PBF–EB) followed by strontium-substituted hydroxyapatite coating (Sr–HA) deposition via RF magnetron sputtering. Prior to coating, an optimized acid etching protocol effectively removed non-melted surface particles. Sr–HA coatings were initially deposited on flat Ti–Nb substrates to refine deposition parameters and facilitate detailed characterization using SEM, AFM, XRD, XPS, wettability measurements, and corrosion resistance testing in simulated body fluid. The resulting nanostructured, granular Sr–HA coatings (∼1000 nm thick) significantly improved both corrosion resistance and surface hydrophobicity. These coatings were subsequently applied to the gyroid scaffolds. In vitro studies assessing cytocompatibility, alkaline phosphatase (ALP) activity, calcium mineralization, and extracellular matrix production (collagen and glycosaminoglycans) revealed that the Sr–HA-coated Ti–xNb scaffolds substantially enhanced cell proliferation, nearly doubled ALP activity, promoted mineral deposition, and significantly increased collagen secretion compared to uncoated controls. This integrated approach highlights the potential of multiscale material design — combining architected porosity with nanoscale surface functionalization — to advance the development of next-generation load-bearing implants with superior osteointegration capabilities. 

The ability to control process parameters over time and build space in electron beam powder bed fusion (PBF-EB) opens up unprecedented opportunities to tailor the process and use materials of a different nature in the same build. The present investigation explored the various methods used to adapt the PBF-EB process for the production of functionally graded materials (FGMs). In this way, two pre-alloyed powders—a stainless steel (SS) powder and a highly alloyed cold work tool steel (TS) powder—were combined during processing in an S20 Arcam machine. Feasibility experiments were first carried out in a downscaled build setup, in which a single powder container was installed on top of the rake system. In the container, one powder was placed on top of the other (SS/TS) so that the gradient materials were produced as the powders were spread and intermixed during the build. The process was later scaled up to an industrial machine setup, where a similar approach was implemented using two configurations of powder disposal: SS/SS + TS/TS and TS/TS + SS/SS. Each configuration had an intermediate layer of powder blend. The FGMs obtained were characterized in terms of their microstructure and local and macromechanical properties. For the microstructural analysis, optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) were performed on the polished cross-sections. This provided evidence of gradual microstructural and compositional transitions in the samples, with a shift from SS to TS and vice versa. Nanoindentation experiments confirmed that there was a consequent gradient in the hardness, stiffness, and wear ratio from the softer and ductile SS to the harder and stiff TS. Scratch experiments revealed gradual evolution in the sliding wear behavior of the printed materials. A “progressive spring” and a “hardness-tailored punching tool” were fabricated as demonstrators. The results obtained demonstrate the great potential to gradually tailor the composition, microstructure, mechanical properties, and wear resistance by combining different powders, and they suggest that any PBF-EB system can be repurposed to build gradient materials without hardware modification. Potential applications include the tooling industry, where hard and wear-resistant materials are needed for the surfaces of tools, with tougher and more ductile materials used in the cores of tools.

Porous biomaterials based on triply periodic minimal surfaces (TPMS) are intensely studied and discussed in the literature. Manufacturing of these structures with a complex geometry became possible using additive manufacturing methods, having their own specifics and challenges. Previously, we demonstrated that sheet-based gyroids, one of TPMS structures, manufactured by electron beam powder bed fusion in Melt and Wafer themes could possess identical mechanical properties (quasi-elastic gradient). In the current research sheet-based gyroids were produced using Wafer Theme with five different settings, including electron beam current and scan speed variation with MultiBeam turned on and off, in attempt to obtain thin walls without losing mechanical performance. Mechanical tests revealed that the specimens manufactured with higher beam line energy on average show better mechanical properties. The specimens produced with MultiBeam showed slightly lower mechanical properties, and do not demonstrate significant improvement in the TPMS surface roughness. According to SEM studies, the average wall thickness was about 0.4 mm for specimens with high line energy, and 0.3 mm for low line energy. Through-hole defects on the horizontal surfaces, noticed and discussed by us previously, have larger average area of the hole and more irregular shape for increased beam line energy. TPMS surface morphology of the specimens produced with higher beam energy and no MultiBeam was on average more even. According to EBSD, α/α` martensite with laths oriented in a Widmanstätten basket-weave pattern was observed with no β phase in the resulting material. No significant differences in microstructure between specimens produced with different beam energy was detected. FEA modeling revealed the impact of the wall thickness, through holes size and orientation on quasi-elastic gradient of a gyroid. It was demonstrated that, through holes with small size located on the horizontal surfaces (layer plane) have only a minor impact on the mechanical properties of the samples if they are not extremely abundant. 

The scientific community is deeply concerned about the social impacts stemming from the consequences of Traumatic Brain Injuries (TBIs). Therefore, Anti-Rotational Technologies (ART) were designed to mitigate TBI severity. Advanced helmet testing, involving standard rigid headforms and numerical models of the human head, faces challenges regarding biofidelity and validation against rare cadaver data. The present study uses an innovative Instrumented Human Head Replica (IHHR), including cerebrospinal fluid (CSF), meninges, and brain simulants, to tackle biofidelity concerns. The IHHR assesses severity of impacts using embedded brain and skull pressure sensors, accelerometers, and gyros. Protected drop tests were conducted from three heights, incorporating ART and balaclava, onto an inclined anvil with a motorcycle helmet. A significant height-dependent reduction in Brain Injury Criterion (BrIC) with ART was shown (p-value≤0.001), while balaclava effects were not significant. The observed relative skull-brain motion was affected by ART (p-value≤0.001) and drop height (p-value=0.003). CSF pressures were significantly affected by ART and balaclava (p-values≤0.01), showing an increase in the coup duration and a decrease in pressure peaks with ART. These findings highlight the potential of the IHHR as a valuable tool for estimating the effect of ART on the severity of TBIs, allowing the calculation of injury criteria. 

Metal additive manufacturing technologies, such as electron beam powder bed fusion (PBF-EB), rely on layer heating to overcome the so-called “smoke” phenomenon. When scaled up for industrial manufacturing, PBF-EB becomes less productive due to the lengthy preheating process. Currently, only the electron beam (EB) is used for preheating in PBF-EB, resulting in increased manufacturing times, energy consumption, and in some cases limiting the applicability of the technology. In this study, a new preheating approach is suggested that incorporates a near-infrared radiation (NIR) emitter inside an PBF-EB system. The NIR unit eliminates the need for EB heating, reducing build time and powder charging. Successful builds using 316 L and Ti6Al4V precursor powders validate the feasibility of the proposed approach. The produced samples exhibit similar properties to those obtained by the standard PBF-EB process. The introduction of NIR technology also reduced build cost and increased the service intervals of the electron gun.