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Bone defects in the skull often require cranioplasty, which has high complication rates. Implants combining a titanium (Ti) mesh and calcium phosphate (CP) tiles have reduced complications, but titanium is non-resorbable, interferes with imaging, and may require revision. In this study, it was hypothesized that fully degradable, printable polymers could replace titanium. Therefore, poly L-lactic acid (PLLA) was evaluated as support material in CP-based composite cranial implants.

Specimens consisting of a centered 3D-printed support beam (PLLA or Ti) embedded in molded brushitic CP were used to assess the hypothesis, with CP-only and PLLA-only controls. An accelerated degradation study was conducted at 37°C in NaOH (pH 13) for 24 h, 72 h, and 7 days, followed by mechanical, morphological, chemical, and thermal analyses.

Four-point bending showed that the thicker PLLA substantially reinforced the structure, similarly to titanium (failure load at t0: 250 N for PLLA-CP, 344 N for Ti-CP, vs 116 N for CP-only). First cracking occurred at lower loads after 72 h and 7 days, but DSC showed no detrimental polymer changes. Results indicated bulk CP degradation and surface polymer degradation, with no evidence of mutual interference. Overall, PLLA appears promising as a degradable substitute for titanium.

Hyaluronic acid (HA) derivatives are widely used to design biomaterials, but quantifying their degree of chemical modification (DoM) remains challenging with traditional analytical techniques. We present a counterion-based approach that determines DoM by measuring the loss of sodium counterions when carboxylate groups of HA are chemically modified. By focusing on the unmodified carboxylate fraction and its associated Na⁺, this method provides a universal, label-free readout of modifications. We implement the concept with two complementary techniques: thermogravimetric analysis (TGA) to quantify inorganic residue (sodium carbonate) after decomposition, and inductively coupled plasma optical emission spectroscopy (ICP-OES) to measure sodium content in solution. These methods applied to a series of HA derivatives (aldehyde, furan, thiol, and hydrazide-functionalized HA), yielded DoM consistent with nuclear magnetic resonance and ultraviolet-visible (UV-Vis) spectroscopy reference assays. Each method offers distinct advantages: TGA could analyze insoluble or cross-linked samples hands-free with lower user-induced uncertainty, while ICP-OES provides high sensitivity for soluble samples and multielement detection. Using both in parallel allowed cross-validation of results and highlighted the importance of controlling analysis conditions for certain functional groups. Overall, the counterion-counting strategy is simple, modification-agnostic, and broadly applicable, enabling accurate DoM measurements that support the development and quality control of biomaterials.

Ureteral stents are fundamental devices in urology but currently used stents are associated with adverse events such as encrustation and infections. Biodegradable magnesium yttrium (Mg-Y) has shown potential as base material for a next-generation biodegradable ureteral stent due to reported lower corrosion rates than pure Mg, homogeneous corrosion and associated antibacterial activity. In the present work, meshed tubes were produced via additive manufacturing (AM) and extruded, and coiled, wire tubes were fabricated. The corrosion behavior in dynamic conditions was studied, as well as the cytotoxicity and antibacterial activity. AM samples showed faster corrosion (associated with higher surface area and impurity level), while the extruded ones showed some localized corrosion points. Additionally, AM samples demonstrated lower toxicity compared with the extruded-coiled ones to urinary tract derived cell lines, at a low metal exposed surface area/volume ratio of 27.5 mm2/ml. AM samples also showed antibacterial activity against E. coli. This study highlights the potential of Mg-Y for the development of a biodegradable ureteral stent, an innovative concept with expected improved patient outcomes.

High-temperature ceramic compound Al₅C₃N belongs to the scarcely studied Al–C–N system. It was originally reported as an ordered compound in noncentrosymmetric space group P6₃mc and described as a nanolaminate with an –Al₂C–AlN–Al₂C₂– stacking sequence. The recently reported structural disorder in the related compound Al₄SiC₄ led us to question this proposed structure for Al₅C₃N and investigate the possibility of a disordered structure in the centrosymmetric space group P6₃/mmc. In the present work, we employed different synthesis routes to maximize the yield and quality of the desired phase, and applied a variety of techniques to probe the Al₅C₃N crystal structure. Our single-crystal X-ray diffraction analysis clearly indicates that noncentrosymmetric space group P6₃mc must be rejected. From a joint refinement of single-crystal X-ray and neutron powder diffraction data, the occupancies of C and N were refined at two sites in P6₃/mmc resulting in the stacking sequence –Al₂C–Al(C/N)–Al₂(C/N)₂–. Furthermore, DFT calculations show that a centrosymmetric disordered structure described in a supercell has the lowest energy, 0.2 eV per formula unit, relative to the previously reported P6₃mc structure. The calculated band structure shows both direct and indirect bandgaps, which leads to implications for the physical properties. Finally, STEM analysis provides additional evidence that the crystal structure of Al₅C₃N is better described in centrosymmetric space group P6₃/mmc.

The nonstoichiometric Fe₂P-type FeMn_(1-x)V_x(P_0.5Si_0.5)_1-x alloys (x = 0, 0.01, 0.02, and 0.03) have been investigated as potential candidates for magnetic refrigeration near room temperature. The magnetic ordering temperature decreases with increasing FeV concentration x, which can be ascribed to decreased ferromagnetic coupling strength between the magnetic atoms. The strong magnetoelastic coupling in these alloys results in large values of the isothermal entropy change (ΔS_M); 15.7 J/(kg K), at 2 T magnetic field for the x = 0 alloy. ΔS_M decreases with increasing x. Results from Mössbauer spectroscopy reveal that the average hyperfine field (in the ferromagnetic state) and average center shift (in the paramagnetic state) have the same decreasing trend as ΔS_M. The thermal hysteresis (ΔT_hyst) of the magnetic phase transition decreases with increasing x, while the mechanical stability of the alloys improves due to the reduced lattice volume change across the magnetoelastic phase transition. The adiabatic temperature change ΔT_ad, which highly depends on ΔT_hyst, is 1.7 K at 1.9 T applied field for the x = 0.02 alloy.

Powder Bed Fusion - Laser Beam (PBF - LB) is an additive manufacturing (AM) technique enables flexibility in material design. Ti6Al4V, a proven AM alloy, is widely used in the biomedical industry as an implant material. However, its typically poor wear behavior hampers its use. Often, increasing surface hardness can improve wear resistance, but orthopedic implants require low stiffness to minimize stress-shielding. Although pushing the stiffness of a metallic implant material close to the bone is a difficult task, PBF - LB offers potential solutions. This study aims to develop a Ti-alloy using PBF - LB with a lower stiffness while having a harder surface compared to common PBF - LB Ti6Al4V. A two-step strategy was applied, combining powder mixing and laser rescanning. We demonstrate that by employing laser rescanning to a mixed powder of Ti6Al4V and 316L stainless steel, we can print a Ti alloy with a graded microstructure. The resulting Ti alloy possesses harder (>5 GPa) α' microstructure on the surface while having a relatively low bulk stiffness (90 GPa) from a β-matrix microstructure. These findings show the combination of powder mixing and laser rescanning is effective in tailoring the mechanical properties of Ti6Al4V alloy.

LiFe₆Ge₄, with a theoretically predicted saturation magnetization of 1 T, a magnetocrystalline anisotropy energy of 1.78 MJ/m³ and a Curie temperature of 620 K was suggested to be a promising permanent magnet as an outcome of a data-mining search. Magnetic measurements of the synthesized sample are reported here. Unfortunately, experiments revealed a weak ferromagnetic behaviour with magnetization values much below that predicted by theory. This discrepancy is analyzed in detail, and is attributed to the trigonal crystal symmetry that was missed in the previous characterisation of the material. The correct crystal structure is R¯3 mH (space group 166) and it is found here to have an antiferromagnetic ground state, as opposed to a theoretically predicted ferromagnetic state of the previously reported monoclinic crystal structure. Theoretical calculations show that element substitution can stabilize a ferromagnetic state of the trigonal crystal structure, with high values of saturation magnetization and magnetocrystalline anisotropy. The best results are seen for the Al or Ga substitution for Ge of the LiFe₆ X₄ compound.

Magnesium alloy WE43 is desirable for biomedical implants due to its biocompatibility, degradability, and mechanical properties closely matching those of natural bone. Processing of WE43 by additive manufacturing (AM), such as powder bed fusion laser beam (PBF-LB), can further its potential for biomedical applications through improved customization (i.e., patient-specific implants) and fabrication of complex geometries. Nevertheless, AM-fabricated Mg implants have yet to reach clinical implementation. To enable this transition, while contributing to the global drive for more sustainable manufacturing, the aim of this research was to investigate the effect of powder reuse during PBF-LB processing of WE43. Specifically, we focus on the influence on both powder properties as well as bulk density and mechanical properties of printed components. Results indicate that repeated reuse alters the powder morphology and particle size distribution (PSD), through the formation of satellites and agglomerates, along with a preferential consumption of smaller particles (<20 mu m) during processing. In turn, powder flowability increased, but both spreadability, and layer density decreased. Only minor compositional changes were observed in both powders and printed samples. Despite these changes in the powder feedstock, the effect on the density of printed samples was minimal, as only small variations in porosity were observed between the initial (0.43 %) and final printing cycles (0.61 %), thereby resulting in a limited effect on sample hardness. The impact on sample density remained minimal despite introducing out-ofspec powder to the feedstock as a worst-case scenario. These findings demonstrate the potential for reducing material wastage when processing biomedical alloy WE43 by PBF-LB and can be used to support powder handling recommendations to ensure quality and sustainability for future commercial applications.

INTRODUCTION: Developing biodegradable implants is of growing interest to help fight antimicrobial resistance. Magnesium alloys are candidates for orthopaedic applications, but there is a need for improving their corrosion resistance[1]. Alloying reduces corrosion rates, but further improvement could be achieved by microstructural tuning using additive manufacturing (AM). However, process parameter optimization is time and resource consuming, motivating the use of numerical modelling to accelerate alloy development. The aim of this study was to predict the microstructure-temperature relationship for a MgCaZn alloy using the CALPHAD method as input for a classical nucleation and growth theory (CNGT) simulation. To achieve this, raw powder feedstock was characterized, along with a minimal number of printed samples.

METHODS: The powder composition was identified as Mg63.2Zn32Ca4.8 by Inductively Coupled Plasma – Optical Emission Spectroscopy (ICP-OES) and compared to the results of ToF-ERDA (Time-of-Flight Elastic Recoil Detection Analysis). The composition of printed samples was also measured to estimate evaporation rates during printing.

X-ray diffraction (XRD) was used for phase identification. Differential Scanning Calorimetry (DSC) was used to characterize phase transitions and generate Time-Temperature-Transformation (TTT) and Continuous-Heating-Transformation (CHT) diagrams.

RESULTS: Three cold crystallizations were distinguished (see Figure 1) and analysed by XRD. Kissinger analysis[2] was done on four heating rates and the results are shown in Table 1 together with the transformation onset temperatures. Metastable phases were formed at the first (Tp1, phase Mg51Zn20) and third crystallisation (Tp3, IM4). Thermodynamic data and unit cell parameters from experimental results and literature[3] were used in a Python code to simulate CHT and TTT diagrams for comparison with the experimental results. The experimental data was used to validate the numerical model.

DISCUSSION & CONCLUSIONS: The overall transitions and phases agreed with previous literature, with only significant differences in the obtained energies of activation. The first simulated TTT diagram to our knowledge has been generated for this composition and phases. Synchrotron studies and more compositions should be tested for proper validation of the methodology.

REFERENCES:

[1] Radha, R., & Sreekanth, D. (2017), J. Magnes. Alloy, 5(3), 286–312.

[2] Kissinger, H. E. (1957) Anal. Chem., 29(11), 1702–1706.

[3] Mezbahul-Islam, M. et al. (2014) Calphad, 46, 134–147.

ACKNOWLEDGEMENTS: This work was supported by the Wallenberg Initiative Materials Science for Sustainability (WISE) funded by the Knut and Alice Wallenberg Foundation and the Swedish Research Council (grant numbers 2019-00191 and 2023-00155) supporting the Ion Technology Center.

Introduction

The use of biodegradable alloys in orthopaedic implants can reduce secondary surgical interventions, including those resulting from infections caused by bacteria attachment to inert implants. Mg alloys are promising materials, but a main challenge lies in improving their corrosion resistance to ensure their safe and effective use as large implants [1]. A widely explored system is the Mg-Zn-Ca ternary alloy. To achieve a further improvement in corrosion resistance of additively manufactured (AM) Mg-Zn-Ca alloys, a better understanding of the thermodynamic and kinetic phase transformations is needed. Hence, the aim of this study was to model the crystal nucleation and growth in Mg-Zn-Ca powders used for powder bed fusion with laser beam (PBF-LB), thereby providing critical insight towards designing more corrosion-resistant microstructures, while reducing the trial-and-error process that usually accompanies process parameter development.

Materials and Methods

Classical nucleation and growth theory (CNGT) was applied through an in-house Python code. CALculation of PHAse Diagrams-based (CALPHAD) thermodynamic simulations of the Mg-Zn-Ca system were used to predict steady state nucleation rates. X-ray diffraction (XRD) and Rietveld refinement was used to calculate cell parameters to use in the model. To validate our simulations of time-temperature-transformation (TTT) diagrams with experimental data, an extensive differential scanning calorimetry (DSC) study was realized, studying isothermal and variable heating rate thermal histories for different sized powders. The powder groups were three; denominated fine, medium and coarse, where the medium powder group had a normal distribution between 20 to 63 μm in diameter, which is typically used for printing. The fine and coarse contained particles out-of-range, namely those below 20 μm (fine) and those above 63 μm in size (coarse), typically considered waste.

Results

Constant heating rate DSC results revealed a difference in phase formation between powders with different size distributions, as shown in Fig. 1. Three common partial crystallizations are observed at around 150, 192 and 245°C with an additional peak at 290°C in the coarse powder, as well as an incongruent melting from 335°C. The additional peak in the coarse powder is also present in cast material in the literature [2]. The kinetics of these transformations were studied using the Kissinger method and were found to be in accordance with literature [3]. The experimental enthalpies of fusion were between 6.5 and 7 KJ/mol for all powders, which were substantially higher than expected from theoretical predictions. Results from the Rietveld refinement of the XRD patterns (Fig. 2) at different temperatures were comparable to previous studies on cast alloys [4]. Experimental points from isothermal DSC measurements overlapped with the simulated TTT diagram.

Conclusions

Experimental values from DSC and XRD allowed for the identification of the stable phases and their crystallization. As compared to cast material, there was one less transformation detected by DSC in fine and medium powders. The CNGT simulations gave good initial indicative results, but experimental validation was necessary for calibration of the model and to improve the accuracy of the predictions.

Aknowledgements

This work was partially supported by the Wallenberg Initiative Materials Science for Sustainability (WISE) funded by the Knut and Alice Wallenberg Foundation.