Advances in Surface Engineering and Biocompatible Coatings for Biomedical Applications Egemen Avcu, Yasemin Yıldıran Avcu, Berzah Yavuzyegit, Mert Guney Coatings, 2025 The two-volume Special Issue “Advances in Surface Engineering and Biocompatible Coatings for Biomedical Applications” has brought together a comprehensive collection of 26 peer-reviewed articles, reflecting the rapid scientific progress and sustained global interest in advanced surface modification strategies for biomaterials [...]
Estimating Demolition Waste Recoverable Fractions in Rapidly Transforming Urban Zones Aslan Nauyryzbay, Aiganym Kumisbek, Arna Amangeldiyeva, Jong Ryeol Kim, Mert Guney Sustainability Switzerland, 2025 The construction sector is a major contributor to global solid waste generation, with demolition waste posing substantial environmental and economic challenges. The present study introduces a demolition waste estimation tool and applies it to a rapidly transforming city: Astana, the capital of Kazakhstan. The approach is also readily applicable to cities in transformation with similar characteristics, e.g., those in the Commonwealth of Independent States region and beyond. The key materials of interest were identified as those that can be efficiently extracted from buildings slated for demolition. A comprehensive analysis of current building stocks and demolition plans (2023–2029) was then conducted. Based on the height, purpose, and main material of the building, the main types and subtypes of the building stock in Astana were created. The results for Astana showed that 67.52% or 1736.5 thousand tons of all demolition waste could be recovered. Concrete had the highest recovery potential by mass (162.42 thousand tons annually) and by percent (91%). The economic analysis of construction and demolition waste illustrated a financial potential from construction and demolition waste recovery in Astana at USD 4600 million per year, with concrete having the highest potential among fractions (56% of total).
Towards Sustainable Air Quality in Coal-Heated Cities: A Case Study from Astana, Kazakhstan Akmaral Agibayeva, Aiganym Kumisbek, Aslan Nauyryzbay, Egemen Avcu, Kuanysh Zhalgasbayev, Ferhat Karaca, Mert Guney Sustainability Switzerland, 2025 Despite severe particulate matter (PM) pollution in Central Asia, limited air composition and health impact data are hindering sustainable air quality management and resilient urban planning. This study provides the first comprehensive assessment of PM2.5 and PM2.5–10 in the urban environment of Astana, Kazakhstan, a rapidly expanding city with intense winter heating demands. We characterized PM and atmospheric precipitation and assessed health risks using bioaccessible fractions of PM-bound potentially toxic elements (PTEs). Among 388 samples, PM2.5 and PM2.5–10 concentrations peaked at 534 and 1564 μg·m−3, respectively. Scanning electron microscopy (SEM) identified soot and coal fly ash, indicating fossil fuel combustion as a major source. Precipitation characterization also showed elevated SO42− (17.8 μg⋅L−1), V (108 μg⋅L−1), Ni (84.0 μg⋅L−1), and Mn (63.2 μg⋅L−1). Bioaccessibility tests showed high solubility for Fe (16,229 mg·kg−1) followed by V: key indicators of combustion emissions. Non-carcinogenic risk for Ni and V exceeded acceptable limits for adults and children (e.g., HQ: 6.07 for V for adults). Carcinogenic risk exceeded the threshold 10−6 for Cd (adults), Co, Cr, and Ni. These findings may help advance urban air quality management via integrating bioaccessibility-based health risk assessment and source apportionment, supporting evidence-driven policies for environmentally responsible development in rapidly urbanizing cold-climate regions.
Effect of cholesterol and other selected physiological parameters on in vitro lung bioaccessibility of particle-bound potentially toxic elements Akmaral Agibayeva, Mert Guney, Aruzhan Merekeyeva, Ferhat Karaca, Egemen Avcu Air Quality Atmosphere and Health, 2025 In recent years, the number of studies on in vitro lung bioaccessibility of potentially toxic elements (PTEs) has increased; however, physiological parameters for these tests have yet to be optimized. This study aims to (1) evaluate the effect of adding cholesterol to synthetic lung fluid on PTEs bioaccessibility, and to (2) assess the effect of other selected test parameters on bioaccessibility. The bioaccessibility of Cd, Co, Cr, Cu, Mn, Ni, Pb, Sb, V, and Zn have been investigated using seven formulations of Gamble’s solution (GS, with/without cholesterol/DPPC) and one artificial lysosomal fluid (ALF) on two reference materials (SRM 2691, BGS 102). The bioaccessibility of certain PTEs increased in GS modified with 5% DPPC (e.g., V in BGS 102 from 2.87 to 8.35%), 0.25% cholesterol (e.g., Cr in SRM 2691 from 27.3 to 31.5%), and 2% DPPC + 0.25% cholesterol (e.g., Cu in BGS 102 from 43.9 to 46.2%). Using DPPC + cholesterol may be recommended for bioaccessibility testing. The effect of the tested solid-to-liquid ratio (S/L) was sample/element-specific. Overall, lower S/L led to higher bioaccessibility in ALF (e.g., for Pb: 94.8% at 1/500 vs. 36.5% at 1/100). The peak bioaccessibility was reached at a 4-week extraction, suggesting a longer testing duration when feasible. Higher agitation (100 vs. 20 rpm) increased the bioaccessibility of some PTEs (e.g., 91.0% vs. 79.7% for Cd in BGS 102). Method modifications would prove valuable when used together with highly needed in vivo validation studies for in vitro lung bioaccessibility.
Comparative Effects of Fine and Conventional Shot Peening on Surface Morphology, Topography, Wettability, and Antibacterial Activity of Biomedical Ti6Al4V Alloy Egemen Avcu, Mert Guney, Yasemin Yıldıran Avcu, Mine Sulak, Hüseyin Uzuner, Meltem İlçe Bahadır, Eray Abakay, Mustafa Armağan, Rıdvan Yamanoğlu, Cagatay Elibol, Martin F.-X. Wagner Coatings, 2025 Interest in textured surfaces for biomaterials and implants is increasing, with shot peening emerging as a promising method for surface modification. This study investigates the influence of conventional and fine shot peening on the surface morphology, topography, wettability, and antibacterial properties of biomedical-grade Ti6Al4V alloy. Peening was conducted using a custom-built, fully automated system, employing fine (100–200 µm) and coarse (700–1000 µm) shots using well-controlled sets of parameters. Both treatments introduced severe plastic deformation on the surface, resulting in increased roughness. Conventionally shot-peened samples exhibited deeper and wider dimples compared to finely peened ones. Surface wettability shifted from hydrophilic (contact angle: ~4°, untreated) to hydrophobic, reaching contact angles of ~91° and ~100° for fine and conventional shot peening, respectively. Antibacterial assays against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) were evaluated by normalizing colony counts to the untreated Ti6Al4V surface. The inherent antibacterial response of Ti6Al4V against E. coli was preserved after both shot peening treatments, showing no notable increase in bacterial proliferation. In contrast, adhesion of S. aureus increased, more notably on fine shot-peened surfaces, indicating a strain-specific response influenced by surface roughness and wettability. In summary, both fine and conventional shot peening altered the surface morphology, topography, and wettability of Ti6Al4V. At the same time, their antibacterial influence was strain-dependent, underscoring the need for careful parameter selection in biomedical applications.
Use of steel slag and recycled concrete in GeoBarrier system for slope stabilization Rezat Abishev, Alfrendo Satyanaga, Mert Guney, Aswin Lim, Jong Kim Frontiers in Built Environment, 2025 Improving slope stability against rainfall-induced slope collapses is a current area of study interest in geotechnical structure design for climate change mitigation. The GeoBarrier system (GBS) concept used recycled concrete and steel slag to avoid these kinds of failures. The present study investigated the practicability of incorporating recycled concrete and steel slag, two types of recycled materials, into the GBS design. Extensive experimental investigations were conducted to determine the index properties and hydraulic characteristics, including permeability functions, soil-water characteristic curves (SWCCs), and unsaturated shear strength parameters of steel slag and recycled concrete. A finite element transient seepage analysis and limit equilibrium slope stability study were conducted to evaluate the impact of precipitation on the pore water pressure profile of the slope and its stability under rainfall circumstances, respectively. According to the findings, no breakthrough into the steel slag, a coarse-grained layer within the GBS, was observed. Based on the pore-water pressure profiles and the variation in the factor of safety (FOS) over time, steel slag and recycled concrete were found to be applicable for use as coarse- and fine-grained layers in the GBS, respectively. The incorporation of these waste materials facilitated the slope protection against infiltrated rainwater into the slope and increased the FOS for a slope with a height of 10 m and a slope angle of 70°.
Editorial: Tribological behavior of biomaterials Egemen Avcu, Yasemin Yıldıran Avcu, Mustafa Armağan, Eray Abakay, B. F. Yousif, Mert Guney Frontiers in Materials, 2025 IntroductionStents, joint and dental implants, orthopedic fixation devices, internal support, and the replacement of biological tissues are only a few of the many medical applications that depend extensively on biomaterials. In these applications, biomaterials frequently experience mechanical forces that entail tribological interactions. One of the main factors affecting these materials' long-term performance and durability is their tribological characteristics, which include frictional behavior, lubrication, and wear resistance. Numerous studies have been carried out to comprehend the mechanical properties of the innovative biomaterials that have developed in the current context. However, there is an urgent necessity to further investigate their tribological properties to confirm their suitability for medical applications. The literature on the tribological evaluation of biomaterials under various functioning conditions (including load, counter body properties, duration, and especially lubricating media) is insufficient. The primary aim of this Research Topic is to elucidate recent developments in the study of the tribological properties of biomaterials, providing a forum for researchers to share their latest findings, thorough reviews, methodological advancements, and illustrative case studies in the specific field of "tribological behavior of biomaterials". The present Research Topic focuses on (1) the current understanding of the wear of biomaterials, (2) the relationship between their mechanical-microstructural and tribological behaviours, and (3) recent advances in the tribological behaviour of biomaterials. The topic is structured to offer a platform for researchers in biomaterials, featuring three core contributions (1-3). Contribution highlightsThe review “Advances in improving tribological performance of titanium alloys and titanium matrix composites for biomedical applications: a critical review” presents recent advancements and strategies for enhancing wear resistance in metallic implants for biomedical applications. Life expectancy has been globally rising, and more patients require biomedical implants. Consequently, permanent implants serving for extended durations require rigorously engineered tribological properties. Additionally, today’s patients stay younger and more active, putting higher demands on the implants (4). In case of failure, implants need more challenging and painful revisions than the initial replacement. Revision surgeries place an economic burden on both patients and healthcare systems. Therefore, introducing novel concepts and technological innovations to improve the tribological performance of metallic biomaterials is essential for patient well-being and economic reasons. The longevity of metallic biomaterials, especially those employed in tribological applications, is dictated by their tribological performance. Titanium alloys and their composites are among the most widely used biomaterials among metallic implants (e.g., stainless steel, Co-Cr-Mo alloys) in tribological applications. According to this critical review, the current cutting-edge research on enhancing tribological behaviour of titanium implants focuses on i. developing new titanium alloys and their composites; ii implementing mechanical surface treatment methods; iii. developing biomedical coatings; iv. developing functional (e.g., self-lubricating, self-adaptive, self-healing) materials; v. implementing new tribological testing/characterization methods; and vi. the application of tribo-informatics (e.g., machine learning, deep learning, data-driven methodologies). The prevailing challenges in this domain are: i. achieving precise control over the alloy's microstructure to attain the required mechanical and biological properties, ii. reducing wear debris generation, iii. employing advanced instruments such as electron microscopy and optical profilometry to clarify the fundamental causes of the tribological behavior of these materials, iv. rectifying defects, such as porosity and cracks, arising from surface modification techniques (e.g., biomedical coatings and chemical/mechanical treatments), and v. modeling studies aimed at predicting tribological properties, including the coefficient of friction and wear rate (1). The original research “Electrophoretic deposition of polyetheretherketone/polytetrafluoroethylene on 316L SS with improved tribological and corrosion properties for biomedical applications” focuses on the implementation of polyetheretherketone (PEEK) and polytetrafluoroethylene (PTFE) coatings on metallic implants (i.e., stainless steel) to improve their tribological properties. When tested in a physiological setting with phosphate-buffered saline (PBS), 316L stainless steel (316L SS) exhibits lower corrosion and wear resistance than Cp-Ti and Ti-6Al-4V implants. However, they are reasonably priced. The application of biocompatible coatings could enhance their resistance to wear and corrosion. This study utilises electrophoretic deposition to apply a polymer coating of PEEK and PTFE on 316L SS at optimal processing conditions. They investigated the performance of PEEK and hybrid PEEK/PTFE coatings through scratch testing, corrosion testing, and scanning electron microscopy. Their adhesion strength and wear resistance tests verified that the PEEK/PTFE coating is appropriate for coating orthopedic implants and can withstand implementation loading (2).The original research “Rheological behavior of the synovial fluid: a mathematical challenge” presents solutions to the governing equations for the partial differential equations pertaining to the synovial fluid (SF), which sheds lights on the viscous flow along the articular surfaces of the knee joints. SF is frequently utilized for diagnostic and research objectives as it mirrors the local inflammatory environment. Due to its intricate composition, particularly the inclusion of hyaluronic acid, SF is viscous and heterogeneous. The presence of high-molecular-weight hyaluronan in this fluid imparts the necessary viscosity for its role as a lubricant. Viscosity is the predominant hydraulic property of the SF in articular cartilage. This work examined the flow of a non-Newtonian fluid applicable for modeling SF flow. The study concludes that the rheological behavior of SF transitions gradually from non-Newtonian to a Newtonian profile. The results of this study may provide novel insights for diagnosis, criteria, and prediction of diseased case types by comparing new parameter values subjected to identical experimental settings as hyaluronidase injection (3). Concluding remarksThis Research Topic addresses challenges in the field of tribological behavior of biomaterials and offers a summary of some of the most promising developments with diverse publications. The published work shows that an effective translation of new biomaterials into clinically successful implants strongly depends on overcoming the challenges related to wear and friction. This requires a change in our comprehension of tribological interactions within the complex biological context. Addressing the tribological challenges encountered by biomaterials in biomedical applications often necessitates a multidisciplinary approach crucial for transforming innovative solutions into clinically viable advancements. Research is needed with a focus on developing new metallic biomaterials and biomedical coatings with improved wear resistance and biocompatibility, investigating advanced surface modification methods, and enhancing predictive models that properly represent the in vivo tribological performance of these biomaterials.
Modification of surface and subsurface properties of cold-rolled Ti6Al4V sheets through water jet shot peening Egemen Avcu, Mustafa Armağan, Yasemin Yıldıran Avcu, Eray Abakay, Emirhan Çalım, Funda Gül Koç, Mert Guney, Rıdvan Yamanoğlu Materials Research Express, 2025 Titanium alloys possess remarkable properties, such as high strength, biocompatibility, and resistance to corrosion. Nonetheless, both their surface and subsurface properties require improvements, particularly for applications where surface contact is unavoidable. The present study utilises an emerging mechanical surface treatment technique (water jet shot peening) for modifying the surface and subsurface characteristics of cold-rolled Ti6Al4V sheets. Water jet shot peening was applied on Ti6Al4V samples following an L18 full factorial experimental design, focusing on the variable parameters of process time, standoff distance, and shot mass flow rate. ANOVA indicated that the shot mass flow rate had the greatest impact on the roughness parameters (p < 0.0001). The roughness values of Ra, Rp, and Rv decreased as the shot’s mass flow rate increased, and this decrease was more pronounced as the standoff distance diminished. The surface morphologies of the samples were notably modified by plastic deformation resulting from the repeated impact of shots. The water jet shot peening method modified the grains within the microstructure near the surface region. The grains in the microstructure were oriented perpendicularly to the peening direction to a depth of 5.36 μm beneath the surface, even at minimal peening levels. The surface hardness increased by approximately 64% relative to the hardness of untreated Ti6Al4V alloy (512.43 Hv versus 311.52 Hv), attributed to significant plastic deformation and strain hardening induced by the high kinetic energy of the impacting shots during water jet peening.
Cavitation erosion behaviour of MAB-CU4 alloy: influences of cavitation number, attack angle, time, and stand-off distance Sedat Can Tini, Adalet Zeren, Yasemin Yıldıran Avcu, Eray Abakay, Mert Guney, Egemen Avcu Materials Research Express, 2024 The present study comprehensively examines the cavitation erosion behaviour of a manganese aluminium bronze alloy (MAB-CU4 alloy) as a function of several parameters (i.e., cavitation angle, cavitation number, time, and stand-off distance), particularly focusing on the influences of cavitation angle on the surface morphology and topography of the alloy. According to the design of experiment (Taguchi experimental design) analysis, mass loss increased with cavitation number and attack angle, while increasing the stand-off distance resulted in a decrease in mass loss and an increase in the surface area affected by cavitation erosion. Cavitation erosion behaviour was most affected by the cavitation attack angle, with the cavitation attack angle contributing 69.1% to total erosion, according to variance analysis. At 90° cavitation attack angle, MAB-CU4’s erosion rate was 64% greater than that at 30°. Scanning electron microscopy and optical profilometry revealed that cavitation erosion damage at 90° occurred mostly in the grain interiors as cavitation pits due to severe plastic deformation and surface corrosion, whereas pit formation was restricted around the hard secondary phases at the grain boundaries. At 30°, deep cavitation pits were limited, the erosion crater expanded, and the number of pits was reduced. Overall, finer microstructures with more grain boundaries and secondary phases may improve cavitation erosion resistance at 90°. The present study is the first to comprehensively capture erosion damage at the microstructural scale and analyse the impact of microstructural features on the erosion damage during the cavitation erosion of MAB-CU4 alloy.
In-situ soil carbon dioxide flux measurement from forest floor in Karasu Forests in Western Black Sea Region of Turkey 12th International Conference on Computer Methods and Advances in Geomechanics 2008, 2008
