1. 3D printed fibroblast-laden alginate-cellulose scaffolds support extracellular matrix formation and angiogenic growth factor secretionJernej Vajda, Dragana Bjelić, Boštjan Vihar, Matej Vesenjak, Polona Dobnik-Dubrovski, Lidija Gradišnik, Monika Belak, Uroš Maver, Marko Milojević, 2025, original scientific article Abstract: Effective microvascular tissue engineering requires fibroblasts that remain phenotypically stable and secrete extracellular matrix (ECM) proteins and growth factors relevant for vascularization. This study evaluated 3D printed hydrogels based on sodium alginate (ALG) and carboxymethyl cellulose (CMC) to assess their ability to sustain fibroblast phenotype, ECM deposition, and angiogenic growth factor secretion during long-term culture. Seven formulations – including one with nanofibrillated cellulose – were compared by encapsulating fibroblasts and crosslinking with CaCl₂ or SrCl₂. All scaffolds were printable and exhibited comparable degradation profiles. Mechanical testing indicated stable compressive response, with Sr2+-crosslinked hydrogels generally showing higher apparent compressive modulus, while Ca2+-crosslinked scaffolds supported slightly higher cell viability. Encapsulated fibroblasts retained their phenotype for 30 days, evidenced by steadily increasing collagen I/III and fibronectin deposition, alongside sustained expression of specific fibroblast markers. After 30 days, all groups produced comparable levels of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (FGF-2), with one formulation yielding a significantly higher FGF-2 output. This multiparametric study demonstrates that scaffold composition and crosslinker chemistry influence fibroblast phenotype maintenance, ECM deposition, and growth factor secretion. To our knowledge, this is the first systematic, 30-day screening of ALG-CMC hydrogels – tuned by polymer content, NFC addition, and Ca2+/Sr2+ crosslinking – specifically for their ability to sustain fibroblast phenotype, extracellular matrix deposition, and growth factor secretion, providing design considerations to guide bioink development for microvascular models.
Keywords: 3D bioprinting, alginate, cellulose, skin fibroblast, microvasculature, angiogenesis
Published in DKUM: 18.12.2025; Views: 0; Downloads: 2
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2. Deformation behaviour of optimised three-dimensional axisymmetric chiral auxetic structuresNejc Novak, Alen Grebo, Matej Borovinšek, Lovre Krstulović-Opara, Zoran Ren, Matej Vesenjak, 2025, original scientific article Abstract: Background/Objectives: Developing functional tissue constructs via 3D bioprinting relies heavily on scaffold architecture, demanding precise mechanical tunability and highresolution feature fidelity. Methods: This paper presents a novel approach utilising photocurable resins and resin 3D printing to fabricate auxetic axisymmetric chiral structures (ACSs), which can be used for advanced scaffold engineering. Results: The experimental tests showed that the optimised ACS (optACS) possess superior mechanical properties compared to their non-optimised counterpart. Both analysed structures possess an auxetic behaviour up to 40% longitudinal strain, with a Poisson’s ratio of about −0.1. Conclusions: This auxetic capability is promising for biomedical applications, particularly in developing enhanced stents or tissue scaffolds.
Keywords: auxetic, axisymmetric chiral structures, 3D printing, mechanical testing, deformation behaviour, optimisation
Published in DKUM: 10.12.2025; Views: 0; Downloads: 6
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3. Integrated design, simulation, and experimental validation of advanced cellular metamaterialsNejc Novak, Zoran Ren, Matej Vesenjak, 2025, original scientific article Abstract: Cellular metamaterials offer supreme properties for engineering, medicine, and defence, but their transition to industrial use faces design, fabrication, and characterisation challenges. This review provides an overview of 20 years of advancements in cellular structures, from open-cell foams to triply periodic minimal surfaces (TPMS), presenting novel fabrication techniques (e.g., explosive compaction for UniPore structures) and demonstrating validated computational models for optimising graded auxetic and hybrid TPMS lattices. The study indicates that porosity and base material primarily govern energy absorption, with closed-cell foams and TPMS outperforming other geometries. Additive manufacturing enables spatially graded designs with tailored mechanical properties. This work accelerates the development of next-generation metamaterials for crash absorption, blast protection, and biomedical devices.
Keywords: cellular structures, metamaterials, experimental testing, computational simulations, mechanical properties
Published in DKUM: 09.12.2025; Views: 0; Downloads: 3
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4. Fatigue of triply periodic minimal surface (TPMS) metamaterials – a reviewŽiga Žnidarič, Branko Nečemer, Matej Vesenjak, Srečko Glodež, 2025, review article Abstract: A review of the fatigue behavior of triply periodic minimal surface (TPMS) metamaterials with consideration for their fabrication is presented in this paper. The review analyses the most common TPMS geometries used due to their mechanical characteristics. Production methods and the base materials used are presented with the key advantages and drawbacks. Furthermore, the mechanical characteristics of cellular structures with emphasis on TPMS geometries are described. Lastly, the state-of-the-art findings of their fatigue behavior are analyzed and explained. Based on the findings in this article, cellular geometries based on TPMS are superior to conventional cellular structures when comparing their fatigue life. Because of the smooth transitions between struts or surfaces, the stress distribution is much more uniform without stress concentration zones.
Keywords: cellular structures, TPMS metamaterials, production technologies, mechanical characterization, fatigue behavior
Published in DKUM: 09.12.2025; Views: 0; Downloads: 5
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5. Editorial : special issue of the Faculty of Mechanical Engineering, University of MariborMatej Vesenjak, Matej Borovinšek, Simon Klančnik, 2025, other scientific articles Abstract: This editorial introduces the Special Issue of the Strojniški vestnik - Journal of Mechanical Engineering dedicated to the 30th anniversary of the Faculty of Mechanical Engineering as an independent member of the University of Maribor, and the 50th anniversary of the University of Maribor. The Faculty of Mechanical Engineering is one of the most successful members at the University of Maribor and is recognised for its excellence in education, research and collaboration with industry. Its history of development, from its early beginnings in 1959 to becoming an internationally active and research-driven institution, reflects a continuous commitment to technological progress and societal impact. The Special Issue presents a selection of articles covering applied fluid mechanics, advanced materials and metamaterials, manufacturing science, and biomedical modelling. The collected works combine experimental, numerical, and review-based approaches to address contemporary challenges in mechanical engineering. This publication not only highlights the scientific excellence achieved at the Faculty of Mechanical Engineering, University of Maribor, but also celebrates its enduring mission to connect knowledge, innovation and human creativity in shaping a sustainable and technologically advanced future.
Keywords: applied fluid mechanics, computational fluid dynamics (CFD), hydropower systems, advanced materials, metamaterials, triply periodic minimal surfaces (TPMS), biomedical modelling, inverse bioheat problem, intelligent toolpath generation, artificial intelligence in manufacturing
Published in DKUM: 08.12.2025; Views: 0; Downloads: 7
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6. Quasi-static and impact behaviour of polymer-metal interpenetrating phase TPMS compositesNejc Novak, Oraib Al-Ketan, Anja Mauko, Lovre Krstulović-Opara, Shigeru Tanaka, Matej Borovinšek, Boštjan Vihar, Uroš Maver, Kazuyuki Hokamoto, Matej Vesenjak, Zoran Ren, 2025, original scientific article Abstract: Interpenetrating phase composites (IPC) are materials with two or more mutually continuous, interconnected phases. This structure allows each phase to retain its properties, while together they exhibit enhanced synergistic properties. In this work, polymer-metal IPCs with Triply Periodical Minimal Surface (TPMS) structures were fabricated and tested for their mechanical properties at different impact velocities (ranging from 0.1 mm/s to 250 m/s). Samples. The samples comprise a stainless steel reinforcement phase and two polymeric matrices (silicone and epoxy). Computed tomography was used to evaluate the internal structure and the fabrication quality. The results showed that the samples were thoroughly infiltrated with polymeric filler, achieving a high degree of homogeneity in the composite. The compression tests of silicone-filled IPCs showed an increase in stiffness. Still, the Specific Energy Absorption (SEA) was not improved due to the non-optimal stiffness ratio between the polymeric matrix and the metallic reinforcement phase. However, using epoxy as the matrix resulted in the SEA enhancement of 38 %. This is attributed to the interlocking mechanism between the two phases, which improved the macroscopic mechanical properties. The compression tests showed significant strain rate hardening due to the base material’s strain rate sensitivity and the inertia effects.
Keywords: TPMS, interpenetrating phase composite, polymer filler, hybrid structure, experimental testing, mechanical properties, strain rate effect
Published in DKUM: 26.05.2025; Views: 0; Downloads: 16
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7. Primerjava med 1d in 3d cfd numerično simulacijo motornega prostora delovnega stroja : diplomsko deloTomaž Rejc Zagožen, 2024, undergraduate thesis Abstract: Namen zaključnega dela je primerjava med 1D in 3D CFD numerično simulacijo kompleksnega motornega prostora delovnega stroja. Zanima nas, ali je 1D CFD simulacija smiselna in dovolj natančna za nadaljni razvoj hladilnega sistema. CAD model delovnega stroja je bil uvožen v GEM3D ter primerno obdelan za izvoz v 1D model. 1D model je bil izdelan in simuliran v programski opremi GT-SUITE.
Končna ugotovitev je, da trenutno GT-SUITE še ne premore obdelovati tako kompleksnih modelov, vendar ima zelo dobro podlago za obdelavo modelov v začetni fazi razvoja modela.
Keywords: motorni prostor, delovni stroj, 1D CFD, primerjava med 1D in 3D CFD simulacijo, GT-SUITE, GEM3D, GT-ISE, CFD, 1D model, 3D model, numerična simulacija
Published in DKUM: 06.05.2025; Views: 0; Downloads: 26
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8. In-plane deformation behavior and the open area of rotating squares in an auxetic compound fabricPolona Dobnik-Dubrovski, Nejc Novak, Matej Borovinšek, Matej Vesenjak, Zoran Ren, 2022, original scientific article Abstract: A conventional compound fabric was used to develop a modern, multifunctional material
with an auxetic behaviour and a tailored open area for particle filtration. Such material was produced
using traditional textile technology and laser cutting, to induce a rotating squares unit geometry. The
behaviour was investigated of three different rotating unit cell sizes. The laser slit thickness and the
length of the hinges were equal for all three-unit cells. The tensile properties, Poisson’s ratio and
auxetic behaviour of the tested samples were investigated, especially the influence of longitudinal
displacement on the fabric’s open area and the filtered particle sizes (average and maximum). Results
show that the developed compound fabric possesses an average negative Poisson’s ratio of up to
−1, depending on the applied auxetic geometry. The larger rotating cell size samples offer a higher
average negative Poisson’s ratio and a higher breaking strength due to the induced slits. The findings
highlight the usefulness of patterned cuts in conventional textile materials to develop advanced
auxetic textile materials with tailored geometrical and mechanical properties.
Keywords: compound textile material, auxetic structure, open area, filtration, mechanical properties, Poisson’s ratio
Published in DKUM: 25.03.2025; Views: 0; Downloads: 14
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9. Mechanism elucidation of high-pressure generation in cellular metal at high-velocity impactMasatoshi Nishi, Shigeru Tanaka, Akihisa Mori, Matej Vesenjak, Zoran Ren, Kazuyuki Hokamoto, 2022, original scientific article Abstract: Cellular metals exhibit diverse properties, depending on their geometries and base materials. This study investigated the mechanism of high-pressure generation during the high-velocity
impact of unidirectional cellular (UniPore) materials. Cubic UniPore copper samples were mounted
on a projectile and subjected to impact loading using a powder gun to induce direct impact of samples.
The specimens exhibited a unique phenomenon of high-pressure generation near the pores during
compression. We elucidate the mechanism of the high-pressure phenomenon and discuss the pore
geometries that contribute to the generation of high pressures.
Keywords: cellular metal, high-pressure, high-velocity impact, computational simulation, metal jet
Published in DKUM: 24.03.2025; Views: 0; Downloads: 7
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