Background: Intervertebral disc degeneration is a prevalent condition and a major risk factor for disc herniation. Mechanical overload, aging, injury, and disease contribute to the annulus fibrosus' structural failure, which allows nucleus pulposus material to escape and reduces the capacity to absorb shock. This study builds on previous investigations by evaluating additional thermoplastic polyurethane (TPU) filaments as potential materials for additively manufactured intervertebral disc replacements. Materials and Methods: Disc-shaped specimens (Ø50 × 10 mm) were fabricated using fused deposition modeling (FDM). A gyroid infill structure was employed with unit cell sizes ranging from 4 to 10 mm3 and wall thicknesses between 0.5 and 1.0 mm. The outer wall thickness varied from 0.4 to 0.8 mm. Four TPU filaments (Extrudr FlexSemiSoft, GEEE-TECH TPU, SUNLU TPU, and OVERTURE TPU) were tested, resulting in 36 parameter combinations per filament. Printed discs were examined via stereomicroscopy. Tensile testing was conducted according to DIN EN ISO 527-1 using Type 5A specimens. Mechanical performance under physiological loading was assessed through uniaxial compression tests, in which samples were compressed to 50% of their height while force-deformation curves were recorded. Target forces were defined as 4000-7500 N to maintain comparability with prior studies. Results: Across all filaments, a maximum of three parameter combinations per material achieved forces within the target range. Microscopy confirmed the dimensional accuracy of wall thicknesses with minimal deviation. Tensile strength values for GEEE-TECH, SUNLU, and FlexSemiSoft were comparable (10-11 MPa), while OVERTURE showed significantly lower strength (approximately 9 MPa). Tensile modulus values followed a similar trend: 25-30 MPa for three filaments and 17.5 MPa for OVERTURE. Conclusions: All four TPU filaments could be used to fabricate discs that met the mechanical requirements for compression. These results confirm that both the tested TPU materials and gyroid structures are suitable for potential intervertebral disc replacement applications.

The development of 4D-printing technology enables the fabrication of smart structures capable of transforming in response to external stimuli, offering potential for future minimally invasive biomedical applications. This study explores a direct 4D-printing approach for producing thermally actuated polylactic acid (PLA) components, focusing on self-expanding vascular stent prototypes. Unlike conventional 4D printing, which typically requires a separate post-printing programming step (e.g., heating, mechanical loading, cooling, and unloading), direct 4D printing embeds the programming phase directly into the layer-wise printing process by controlling the adjustment of process parameters, so that components are ready for shape transformation immediately after fabrication. A systematic experimental workflow was applied by combining a problem-solving methodology with action research and structured experimentation to identify and optimize the key parameters governing shape-shifting behavior. Bilayer plate structures were fabricated via fused filament fabrication (FFF) using multiple PLA material combinations and were thermally actuated under controlled conditions to characterize the influence of printing speed, printing temperature, and infill pattern on the magnitude and directionality of deformation. Building on these results, three functional demonstrators were developed, culminating in a grid-based cylindrical prototype that achieved approximately 5.8% radial expansion upon actuation at temperatures above 80 °C. Overall, the results suggest the fundamental technological feasibility of direct 4D printing as a manufacturing route for thermally actuated components, serving as a foundational proof-of-concept for future patient-specific, self-deploying medical devices.

OBJECTIVE:Degenerative disc disease remains a primary cause of chronic back pain, yet current surgical treatments are often limited by the mechanical mismatch between implants and native intervertebral disc (IVD) tissue. This study investigates additively manufactured functionally graded Gyroid structures based on thermoplastic polyurethane (TPU) as biomimetic IVD replacements, focusing on the influence of geometry and material gradients on mechanical performance.
Methods: Gyroid-based constructs were fabricated by multi-material fused filament fabrication using TPU filaments of different stiffness. Their mechanical performance was evaluated under static and dynamic compressive loading. Finite element analysis was performed to investigate stress distribution within the Gyroid architecture, while micro-computed tomography (µCT) was used to assess manufacturing-related defects and structural integrity before and after 700,000 loading cycles.
Results: All investigated structures exhibited stable and reproducible mechanical behavior. However, only a single geometric configuration reached the targeted physiological load range of 4000-8000 N, irrespective of the material combination. The incorporation of an additional compliant TPU phase did not significantly alter the global force-deformation response compared with two-material configurations, indicating that structural geometry predominantly governs the compressive mechanical behavior. Dynamic testing demonstrated consistent damping capacities of approximately 20% across all configurations together with stable stiffness, storage modulus, and loss modulus during fatigue loading. Finite element analysis revealed homogeneous load distribution with localized stress concentrations at the curved Gyroid junctions. Quantitative µCT analysis showed no measurable increase in micro-porosity, void fraction, or interfacial defects after 600,000 loading cycles.
Conclusion: The findings demonstrate that the mechanical performance of TPU-based Gyroid IVD constructs is primarily governed by architectural design rather than material gradients under compressive loading. The combined experimental, numerical, and µCT analyses confirm the mechanical robustness and structural stability of the proposed functionally graded Gyroid structures, highlighting architecture-driven design as a promising strategy for mechanically compatible intervertebral disc replacements.&#xD.

Background Disc degeneration is an increasingly common problem in modern society and is often a precursor to a herniated disc. Contributing factors include physical exertion, overuse, the natural aging process, and disease and injury. Over time, the fibrous ring of the disc develops cracks and small tears, allowing fluid from the nucleus pulposum to escape. As a result, the ability of the disc to absorb shock decreases, potentially leading to a bulging or herniated disc. In this work, previously initiated investigations are extended, and additional thermoplastic polyurethane (TPU) filaments are examined with respect to their suitability for additive manufacturing as potential disc replacement materials. Materials & Methods To remain comparable, the additive manufacturing in this work is also carried out with Fused Deposition Modeling (FDM) 3D printers and as a Ø50 mm x 10mm disc. The Gyroid was varied from 10 mm³ for the coarsest structure to 4 mm³ for the finest structure. The wall thickness of the Gyroid was also varied from 0.5 to 1.0 mm, as were the outer walls of the disc, whose wall thickness was varied from 0.4 to 0.8 mm. Four different TPU filaments (Extrudr FlexSemiSoft, GEEETECH TPU, SUNLU TPU and OVERTURE TPU) were used. This resulted in 36 different settings per filament. The 3D printed discs were analyzed using an Olympus SZ61 stereomicroscope. A tensile test according to DIN EN ISO 527-1 was performed on the 3D printed samples 5A. The aim was to investigate the difference between the different TPU filaments. To test the mechanical properties of the 3D printed discs, a uniaxial compression test was performed with at least three samples of each setting. The body was compressed to 50% of its total height and the force required was recorded as a force-deformation curve. To be comparable to a previous project, a maximum force of 4000–7500 N was used. Results Of the 36 different discs tested for each filament, only a maximum of three were within the target range of maximum force. Microscopy revealed that all wall thicknesses were within the target range with only minor variations. The tensile strengths of Geetech, SunLu, and SemiSoft were not significantly different and were in a similar range of 10-11 MPa, with Overture deviating significantly at 9 MPa. The tensile moduli exhibited a comparable distribution: 25-30 MPa for Geetech, SunLu, and SemiSoft, and 17.5 MPa for Overture. Conclusion For all of the filaments tested, it was possible to additively produce suitable discs that were within the specified range of 4000-7500 N at 50% compression. This would ensure that these discs would withstand the stresses they would be subjected to in a potential human disc replacement application. Thus, we were able to confirm the suitability of these four filaments, as well as the Gyroid structures, for use as a disc replacement.

The core/shell 3D printing process using CPC and alginate is intended to create biodegradable scaffolds that have a similar stability to bone tissue and also offer sufficient and continuous antibiotic release. In this way, a patient-specific and patient-friendly process will be established, which should optimally support the human organism in its regeneration. To generate the best possible strength values, the printed scaffolds underwent various post-treatments and were then tested in a material test. The test methods included self-setting, storage in a drying cabinet with a water-saturated atmosphere at 37°C, followed by incubation in PBS, freeze-drying, and coating the samples with alginate. Additionally, a degradation test at pH 7.4 and pH 5 was carried out to test stability under in vitro conditions. It was shown that the untreated and freeze-dried samples failed at a maximum load of 30–700 N, while the remaining scaffolds could withstand a load of at least 2,000 N. At this failure load, most of the test series showed an average deformation of 43.95%. All samples, therefore, remained below the strength of cancellous bone. However, based on a 20% load after surgery, the coated scaffolds represented the best possible alternative, with a Young’s modulus of around 1.71 MPa. We were able to demonstrate that self-setting occurs in core-shell printed CPC/alginate scaffolds after only 1 day, and that mass production is possible. By coating with alginate, the compressive strength could be increased without the need for additional post-treatment. The mechanical strength was sufficient to be available as a scaffold for bone regeneration and additionally as a drug delivery device for future applications and experiments.

IntroductionIntervertebral disk degeneration is a growing problem in our society. The degeneration of the intervertebral disk leads to back pain and in some cases to a herniated disk. Advanced disk degeneration can be treated surgically with either a vertebral body fusion or a disk prosthesis. Vertebral body fusion is currently considered the gold standard of surgical therapy and is clearly superior to disk prosthesis based on the number of cases. The aim of this work was the 3D printing of Gyroid structures and the determination of their mechanical properties in a biomechanical feasibility study for possible use as an intervertebral disc prosthesis.Material and methodsCreo Parametric 6.0.6.0 was used to create models with various Gyroid properties. These were printed with the Original Prusa i3 MK3s+. Different flexible filaments (TPU FlexHard and TPU FlexMed, extrudr, Lauterach, Austria) were used to investigate the effects of the filament on the printing results and mechanical properties of the models. Characterization was carried out by means of microscopy and tension/compression testing on the universal testing machine.ResultsThe 3D prints with the FlexHard and FlexMid filament went without any problems. No printing errors were detected in the microscopy. The mechanical confined compression test resulted in force-deformation curves of the individual printed models. This showed that changing the Gyroid properties (increasing the wall thickness or density of the Gyroid) leads to changes in the force-deformation curves and thus to the mechanical properties.ConlcusionThe flexible filaments used in this work showed good print quality after the printing parameters were adjusted. The mechanical properties of the discs were also promising. The parameters Gyroid volume, wall thickness of the Gyroid and the outer wall played a decisive role for both FlexMed and FlexHard. All in all, the Gyroid structured discs (Ø 50 mm) made of TPU represent a promising approach with regard to intervertebral disc replacement. We would like to continue to pursue this approach in the future.

In 4D printing, an additively manufactured component is given the ability to change its shape or function in an intended and useful manner over time. The technology of 4D printing is still in an early stage of development. Nevertheless, interesting research and initial applications exist in the literature. In this work, a novel methodical approach is presented that helps transfer existing 4D printing research results and knowledge into solving application tasks systematically. Moreover, two different smart materials are analyzed, used, and combined following the presented methodical approach to solving the given task in the form of recovering an object from a poorly accessible space. This is implemented by self-positioning, grabbing, and extracting the target object. The first smart material used to realize these tasks is a shape-memory polymer, while the second is a polymer-based magnetic composite. In addition to the presentation and detailed implementation of the methodical approach, the potentials and behavior of the two smart materials are further examined and narrowed down as a result of the investigation. The results show that the developed methodical approach contributes to moving 4D printing closer toward a viable alternative to existing technologies due to its problem-oriented nature.

Introduction The use of scaffolds in tissue engineering is becoming increasingly important as solutions need to be found to preserve human tissues such as bone or cartilage. Various factors, including cells, biomaterials, cell and tissue culture conditions, play a crucial role in tissue engineering. The in vivo environment of the cells exerts complex stimuli on the cells, thereby directly influencing cell behavior, including proliferation and differentiation. Therefore, to create suitable replacement or regeneration procedures for human tissues, the conditions of the cells’ natural environment should be well mimicked. Therefore, current research is trying to develop 3-dimensional scaffolds (scaffolds) that can elicit appropriate cellular responses and thus help the body regenerate or replace tissues. In this work, scaffolds were printed from the biomaterial polycaprolactone (PCL) on a 3D bioplotter. Biocompatibility testing was used to determine whether the printed scaffolds were suitable for use in tissue engineering. Material and Methods An Envisiontec 3D bioplotter was used to fabricate the scaffolds. For better cell-scaffold interaction, the printed polycaprolactone scaffolds were coated with type-I collagen. Three different cell types were then cultured on the scaffolds and various tests were used to investigate the biocompatibility of the scaffolds. Results Reproducible scaffolds could be printed from polycaprolactone. In addition, a coating process with collagen was developed, which significantly improved the cell-scaffold interaction. Biocompatibility tests showed that the PCL-collagen scaffolds are suitable for use with cells. The cells adhered to the surface of the scaffolds and as a result extensive cell growth was observed on the scaffolds. The inner part of the scaffolds, however, remained largely uninhabited. In the cytotoxicity studies, it was found that toxicity below 20% was present in some experimental runs. The determination of the compressive strength by means of the universal testing machine Z005 by ZWICK according to DIN EN ISO 604 of the scaffolds resulted in a value of 68.49 ± 0.47 MPa.

This article presents a comparative experimental study of the electrical, structural, and chemical properties of large‐format, 180 Ah prismatic lithium iron phosphate (LFP)/graphite lithium‐ion battery cells from two different manufacturers. These cells are particularly used in the field of stationary energy storage such as home‐storage systems. The investigations include 1) cell‐to‐cell performance assessment, for which a total of 28 cells are tested from each manufacturer; 2) electrical charge/discharge characteristics at different currents and ambient temperatures; 3) internal cell geometries, components, and weight analysis after cell opening; 4) microstructural analysis of the electrodes via light microscopy and scanning electron microscopy; 5) chemical analysis of the electrode materials using energy‐dispersive X‐ray spectroscopy; and 6) mathematical analysis of the electrode balances. The combined results give a detailed and comparative insight into the cell characteristics, providing the essential information needed for system integration. The study also provides complete and self‐consistent parameter sets for the use in cell models needed for performance prediction or state diagnosis.

The measurement of the active material volume fraction in composite electrodes of lithium-ion battery cells is difficult due to the small (sub-micrometer) and irregular structure and multi-component composition of the electrodes, particularly in the case of blend electrodes. State-of-the-art experimental methods such as focused ion beam/scanning electron microscopy (FIB/SEM) and subsequent image analysis require expensive equipment and significant expertise. We present here a simple method for identifying active material volume fractions in single-material and blend electrodes, based on the comparison of experimental equilibrium cell voltage curve (open-circuit voltage as function of charge throughput) with active material half-cell potential curves (half-cell potential as function of lithium stoichiometry). The method requires only (i) low-current cycling data of full cells, (ii) cell opening for measurement of electrode thickness and active electrode area, and (iii) literature half-cell potentials of the active materials. Mathematical optimization is used to identify volume fractions and lithium stoichiometry ranges in which the active materials are cycled. The method is particularly useful for model parameterization of either physicochemical (e.g., pseudo-two-dimensional) models or equivalent circuit models, as it yields a self-consistent set of stoichiometric and structural parameters. The method is demonstrated using a commercial LCO-NCA/graphite pouch cell with blend cathode, but can also be applied to other blends (e.g., graphite-silicon anode).