The review, authored by M. Mutharasu and J. Joel at the School of Mechanical Engineering, Vellore Institute of Technology in India, synthesizes a sprawling body of literature on additive manufacturing (AM) of metallic implants and proposes a unified design framework. Rather than optimizing biomaterials, architectures, printing processes, and bioactive coatings as separate silos — a fragmentation the authors identify as a persistent weakness in the field — the framework links patient anatomy, material selection, architected porosity, AM technology, and hybrid surface engineering into a single development pathway. The stakes are high: implants that are too stiff relative to bone can trigger stress shielding, a phenomenon in which the metal carries so much of the load that the surrounding bone resorbs and weakens over time, ultimately leading to loosening and revision surgery.

At the heart of the review is a deceptively simple engineering problem. Human bone is not a uniform material. Cortical bone, the dense outer shell, has an elastic modulus of roughly 15 to 20 gigapascals, while trabecular bone, the spongy interior, sits far lower at around 0.01 to 3 gigapascals. Fatigue strength follows a similar split, with cortical bone tolerating roughly 40 to 60 megapascals and trabecular bone only about 0.3 to 3 megapascals. Conventional dense metallic implants — titanium alloys, cobalt-chromium, stainless steel — are dramatically stiffer than any of these. Ti-6Al-4V, the workhorse of the industry, has an elastic modulus of approximately 130 gigapascals, more than six times that of cortical bone. The review’s proposed solution is to use topology-optimized lattice structures, printed via powder bed fusion, to bring the effective stiffness of the implant down into the physiological range of 0.01 to 20 gigapascals, targeting volumetric porosity levels between 50 and 85 percent.

But the review is candid about the trade-offs. Increasing porosity does reduce effective modulus and can improve tissue ingrowth, yet it simultaneously erodes fatigue resistance. At high porosity levels, the lattice relies on ultra-thin struts that shift the primary failure mechanism from bulk compression to localized elastoplastic bending. Under cyclic loading, micro-defects at nodal junctions act as severe stress concentrators, leading to rapid crack initiation, progressive strut rupture, and sudden macroscopic fatigue collapse long before the theoretical yield strength is reached. Retaining fatigue strength above the cortical bone threshold of 40 to 60 megapascals while simultaneously achieving bone-matching stiffness remains, in the authors’ assessment, a profound manufacturing challenge. The review emphasizes that compressive strength alone is insufficient to establish the mechanical suitability of a lattice implant; fatigue behavior is governed by a complex interplay of porosity, pore morphology, strut thickness, surface roughness, residual stress, internal defects, and loading mode.

The material landscape itself is evolving. Titanium alloys remain the most studied, prized for their low density, high specific strength, and corrosion resistance, but the review highlights a shift toward novel beta-phase titanium compositions engineered with non-toxic stabilizers such as niobium, tantalum, zirconium, and molybdenum. These alloys can drive the elastic modulus down toward 50 to 60 gigapascals without any porous structuring at all, and compositions like Ti-25Nb reach as low as 19 gigapascals — approaching cortical bone directly. Copper-containing titanium alloys, such as Ti-0.3Cu, add antibacterial functionality alongside high tensile strength. Cobalt-chromium-molybdenum alloys, meanwhile, remain the gold standard for wear resistance in articulating environments, thanks to high hardness and stable passive oxide films, though their high stiffness and susceptibility to micro-galvanic corrosion at grain boundaries present their own challenges. 316L stainless steel, when printed via laser powder bed fusion, develops a refined sub-micron cellular austenitic microstructure with dense dislocation networks that breaks the traditional strength-ductility tradeoff — a property the review notes is particularly valuable for porous scaffolds that must dissipate physiological loads through progressive plastic bending rather than catastrophic brittle fracture.

Magnesium alloys occupy a different niche entirely. Unlike titanium or cobalt-chromium, magnesium is biodegradable: it dissolves in the body over months to years, potentially eliminating the need for secondary removal surgery. The review catalogs a growing clinical portfolio, from BIOmag coronary stents launched in 2024 to WE43 bone screws and high-purity magnesium vascular closure devices. But the same reactivity that makes magnesium attractive also makes it dangerous. Rapid corrosion generates hydrogen gas faster than the body can transport it away, and accumulation can produce local cavities, alter tissue-implant contact, and interfere with healing. The review cites a frequently discussed reference level of approximately 0.01 milliliters per square centimeter per day for tolerable hydrogen evolution, while cautioning that this is not a universal clinical threshold — tolerance depends on anatomical site, vascularization, implant geometry, and degradation kinetics.

Surface engineering emerges as the third pillar of the integrated framework. Hydroxyapatite, a calcium phosphate ceramic that closely mimics the mineral component of natural bone, has long been the go-to bioactive coating, but the review details its limitations: inherent brittleness, thermal expansion mismatch with metallic substrates that causes residual stress and microcracking, and dissolution behavior that varies with crystalline phase. Ion-substituted variants — incorporating zinc, magnesium, or strontium — offer improved antibacterial properties, corrosion resistance, and osteogenic activity. Bioactive glasses, both silicate-based and the newer borate compositions, release therapeutic ions that promote bone regeneration; borate glasses like 13-93B3 can degrade 85 percent within 7 to 14 days, far outpacing silicate counterparts, though this rapid dissolution risks compromising mechanical integrity before bone has fully healed. Hybrid hierarchical coatings that combine ceramic, polymeric, and biomolecular layers — such as polydopamine, zinc oxide nanoparticles, chitosan, and nanocrystalline hydroxyapatite — represent the current frontier, achieving adhesion strengths exceeding 50 megapascals in some configurations.

The review also confronts a manufacturing reality that is easy to overlook: the machines themselves wear out. In directed energy deposition systems, the continuous flow of abrasive metallic powders induces significant wear on entry nozzles, altering powder focus and causing spatial inaccuracies in the melt pool. In laser powder bed fusion, abrasive wear of the re-coater blade against the powder bed can induce subtle variations in layer thickness. This machine-level tribological degradation translates directly into metallurgical defects, heterogeneous porosity, and diminished fatigue life in the final biomedical component — a feedback loop that the authors argue must be accounted for in any robust quality-control framework.

On the clinical side, the pathway from computed tomography or magnetic resonance imaging scans to a printed, patient-specific implant involves segmentation, computer-aided design, finite element analysis, and build preparation. The review notes that patient-specific implants currently cost five to ten times more than conventional standard implants, a premium driven by imaging software, prolonged CAD processing, specialized machine usage, and tailored post-processing. This economic reality confines their routine use to complex revision procedures, cancer resections, or critical trauma where conventional implants would fundamentally fail. Regulatory qualification, manufacturing reproducibility, and coating durability on complex lattice geometries are identified as the leading barriers to broader clinical translation.

Ultimately, the review’s central message is that no single material-architecture-coating combination can be considered universally optimal. The authors argue that implant performance emerges from the combined effects of alloy properties, architectural design, manufacturing-induced defects, surface characteristics, and post-processing conditions — and that future research must simultaneously consider mechanical compatibility, fatigue performance, corrosion and degradation, coating durability, biological response, powder removal from complex architectures, and economic and regulatory requirements. The era of treating the implant as a monolithic object, they suggest, is over; what replaces it is a design philosophy in which every layer, from the atomic arrangement of the alloy to the nanometer-scale chemistry of the outermost surface, is treated as a coupled variable in a single, interconnected system.

Subject of Research: Additive manufacturing of metallic implants integrating material selection, porous lattice architecture, and hybrid surface engineering

Article Title: Additive manufacturing of metallic implants: a comprehensive review of material selection, porous architecture, and hybrid surface engineering

Article References: Mutharasu, M., & Joel, J. (2026). Additive manufacturing of metallic implants: a comprehensive review of material selection, porous architecture, and hybrid surface engineering. Frontiers in Mechanical Engineering, 12, Article 1978898. https://doi.org/10.3389/fmech.2026.1978898

Image Credits: AI Generated

DOI: 10.3389/fmech.2026.1978898

Keywords: additive manufacturing, metallic implants, porous lattice, stress shielding, titanium alloys, cobalt-chromium, magnesium alloys, hydroxyapatite, bioactive glass, surface engineering, powder bed fusion, biodegradable implants

The central idea behind the new platform is that tissue regeneration is not only a matter of biochemistry. Mineralized tissues such as bone and dentin are rich in collagen, and collagen-bearing matrices exhibit piezoelectric behavior, generating electrical signals under physiological mechanical loading. These endogenous bioelectrical cues are known to influence cell migration, differentiation, extracellular matrix organization, and the growth of new blood vessels. Conventional bioactive glasses, which have long been favored in regenerative dentistry for their tunable degradation and their release of calcium and silicate ions that promote mineralization, exploit only the biochemical side of this picture. They lack any externally controllable physical or electromechanical signal that could be switched on or off to steer cellular behavior on demand.

Piezoelectric biomaterials offer a way to close that gap, because they can convert external mechanical stimulation into localized electrical signals that modulate cell activity. Low-intensity pulsed ultrasound, or LIPUS, is particularly attractive as the trigger: it is noninvasive, wireless, and capable of reaching deep tissues. But the most established piezoelectric ceramics come with drawbacks. Barium titanate and lead-based ceramics are poorly biodegradable and raise long-term biosafety concerns, while polymeric options such as polyvinylidene fluoride are biocompatible but produce relatively weak piezoelectric responses. Zinc oxide has emerged as a compelling alternative, combining useful piezoelectric properties with biodegradability and intrinsic biological activity, and the zinc ions released as it degrades have been reported to promote both angiogenesis and odonto/osteogenic differentiation. The catch is that zinc oxide degrades rapidly under physiological conditions, and excessive zinc ion release induces oxidative stress and cytotoxicity that have seriously limited its biomedical use.

The research team’s solution was a confinement-based nanocomposite they call Z-MBGNs: zinc oxide nanoparticles incorporated into mesoporous bioactive glass nanospheres. The nanospheres were synthesized through a sol–gel templating method in which cetyltrimethylammonium bromide served as the mesoporous template, tetraethyl orthosilicate supplied the silica, and calcium nitrate provided the calcium. Zinc species were then deposited under alkaline conditions and converted to crystalline zinc oxide by calcination at 600 degrees Celsius. By varying the zinc precursor concentration, the researchers produced three formulations containing 5.28, 10.24, and 15.22 weight percent zinc oxide, designated 5Z-, 10Z-, and 15Z-MBGNs. Transmission electron microscopy showed uniform spheres roughly 87 nanometers in diameter, and elemental mapping confirmed homogeneous co-distribution of zinc, silicon, calcium, and oxygen throughout the particles, supporting the interpretation that the zinc-containing phases are predominantly incorporated within the mesoporous matrix rather than simply sitting on the surface.

The mesoporous glass matrix plays a double role. It acts as a carrier for sustained ionic release, and it moderates the degradation of the embedded zinc oxide, taming the burst of zinc ions that makes the bare nanoparticles toxic. The safety advantage was striking in direct comparisons: in standardized L929 fibroblast cytotoxicity testing, cell viability in the 10Z-MBGN group reached 84.9 percent, whereas bare zinc oxide nanoparticles at equivalent zinc concentration dropped viability to 51.8 percent. At the highest loading, the nanocomposite still outperformed the bare nanoparticles by a wide margin, 48.3 percent versus 19.0 percent. Proliferation assays with human dental pulp stem cells and human umbilical vein endothelial cells showed that the 5Z and 10Z formulations significantly promoted growth, while the 15Z formulation inhibited it, likely because of excessive zinc ion exposure. The 10Z formulation was selected as the lead candidate because it balanced biological compatibility with the strongest ultrasound-responsive functionality.

That functionality was verified at two scales. Piezoresponse force microscopy revealed the characteristic signatures of a nanoscale electromechanical response, including a butterfly-shaped amplitude loop and phase switching under a DC bias sweep from minus ten to plus ten volts. More importantly, when the nanoparticle suspension was stimulated with LIPUS at 1 megahertz and a nominal 400 milliwatts per square centimeter with a 50 percent duty cycle, the 10Z-MBGN suspension generated a distinct electrical signal with a peak-to-peak voltage of about 600 millivolts, while plain buffer and zinc-free nanospheres showed only background fluctuations. Autoclave sterilization, a prerequisite for biological use, did not diminish this response, and it likewise preserved the mesoporous architecture, colloidal stability, and the sustained, burst-free release of calcium and zinc ions observed over 14 days.

With the material characterized, the team tested its effects on human dental pulp stem cells under a carefully optimized ultrasound protocol of 1 megahertz, 400 milliwatts per square centimeter, 50 percent duty cycle, and five minutes per day. Ultrasound-treated 10Z-MBGNs dramatically enhanced cell migration, closing 57.3 percent of a scratch wound within 12 hours compared with 26.7 percent for the nanospheres alone and 23.6 percent for untreated controls, a result that held even when proliferation was chemically suppressed with mitomycin C. Alkaline phosphatase activity, an early marker of odontogenic differentiation, was strongest in the ultrasound-treated group after 7 days. After 21 days of induction, Alizarin Red S staining and calcium quantification confirmed significantly greater mineralized matrix deposition. Gene expression analysis showed that the dentin matrix proteins DSPP and DMP-1 were significantly upregulated, with DMP-1 at day 14 roughly threefold higher than with nanospheres alone and ninefold higher than in controls. Western blotting additionally revealed increased expression of the mitochondrial calcium uniporter, MCU, hinting that mitochondrial calcium handling may participate in the cellular response, although the authors caution this remains a molecular readout rather than proof of a causal mechanism.

The angiogenic side of the story proved equally compelling. Human umbilical vein endothelial cells cultured with ultrasound-treated 10Z-MBGNs formed denser, more interconnected capillary-like networks on Matrigel, with significantly more branch points and greater total tube length. Expression of the angiogenic genes VEGF, bFGF, and CD31 rose over 7 days, and enzyme-linked immunosorbent assays confirmed increased secretion of VEGF and bFGF protein. To test whether these effects translate into tissue formation, the researchers implanted tooth-root-shaped beta-tricalcium phosphate scaffolds loaded with dental pulp stem cells, Matrigel, and 10Z-MBGNs subcutaneously in nude mice, applying LIPUS daily for the first 7 days. At 2 weeks, the ultrasound-treated constructs showed markedly larger VEGF- and bFGF-positive areas. At 6 weeks, they displayed increased DSPP and DMP-1 expression, and Masson’s trichrome staining revealed a collagen-positive area approximately 56-fold larger than in controls and 11-fold larger than in the non-ultrasound nanosphere group, alongside more organized tissue, odontoblast-like cells, mineralized tissue-like structures, and the greatest histologically identified vascular area.

The authors are appropriately measured about what these results do and do not establish. Because LIPUS-only and zinc-free nanosphere-plus-ultrasound control groups were not included, the relative contributions of direct ultrasound mechanotransduction and zinc oxide-associated electromechanical stimulation cannot yet be quantitatively separated, and phenomena such as acoustic streaming or electrokinetic effects may contribute to the measured electrical signal. The ectopic model is a proof of concept rather than a recapitulation of the native pulp–dentin complex, the vascular structures cannot yet be considered fully mature or perfused, and the animal sample size was small with no formal power analysis. Even so, the work demonstrates the feasibility of a growth-factor-free platform in which externally controllable ionic and electromechanical cues are combined in a single degradable nanomaterial. Before clinical translation, tooth-specific studies must determine how ultrasound transmits through enamel, dentin, and periodontal tissues, and how transducer design, coupling, intensity, and exposure should be tailored. If those hurdles are cleared, a five-minute daily ultrasound session activating piezoelectric nanospheres inside a treated tooth could one day offer a genuinely regenerative alternative to the root canal.

Subject of Research: Ultrasound-responsive piezoelectric zinc oxide bioactive glass nanospheres for dental pulp–dentin tissue regeneration

Article Title: Piezoelectric ZnO-incorporated bioactive glass nanospheres for enhanced odontogenic differentiation and angiogenesis

Article References: Wu, Z., Diao, J., Zhang, H., & Zhao, N. (2026). Piezoelectric ZnO-incorporated bioactive glass nanospheres for enhanced odontogenic differentiation and angiogenesis. Materials Today Bio, 41, Article 103731. https://doi.org/10.1016/j.mtbio.2026.103731

Image Credits: AI Generated

DOI: Not provided

Keywords: piezoelectric biomaterials, zinc oxide, bioactive glass, mesoporous nanospheres, low-intensity pulsed ultrasound, dental pulp stem cells, odontogenic differentiation, angiogenesis, regenerative endodontics, pulp-dentin complex, tissue engineering, VEGF

Tribocatalysis has been quietly building momentum as one of the more surprising entries in the clean energy and environmental remediation playbook. The principle is deceptively simple: when certain materials are subjected to friction, abrasion, or repeated mechanical contact, charges are generated and separated on their surfaces, much as they are in piezoelectric and triboelectric phenomena. Those separated charges can drive electrochemical reactions at the material surface, splitting water and dissolved oxygen into reactive species that are powerful enough to shred stubborn organic molecules. Over the past several years, laboratories around the world have demonstrated this effect in a growing roster of ceramics and nanomaterials, including bismuth tungstate, barium titanate, titanium dioxide, cadmium sulfide nanowires, zinc oxide nanorods, and even natural tourmaline. What has been missing is a material that combines strong tribocatalytic output with genuine biological functionality, opening applications beyond wastewater treatment.

The Lucknow team’s candidate material is a bioactive glass ceramic, a family of substances first famous for a different trick entirely. Bioactive glasses, pioneered by Larry Hench in the late 1960s, are prized because when placed in contact with physiological fluids they grow a layer of hydroxyapatite, the same mineral that constitutes human bone. That bonding ability has made them staples of bone tissue engineering and dentistry. The Indian researchers reasoned that if such a material could also harvest mechanical energy efficiently, a single substance might serve double duty: scrubbing dye-laden industrial wastewater in one context and potentially supporting bone regeneration in another. To get there, they prepared their glass ceramic by a hydrothermal method, a synthesis route that uses aqueous chemistry under elevated temperature and pressure, and doped it with varying concentrations of strontium oxide.

Strontium is a deliberate and well-motivated choice. In the biomaterials world, strontium ions are celebrated for their role in bone metabolism, since strontium ranelate has historically been prescribed to combat osteoporosis, and strontium substitution in bioactive glasses has been shown to influence degradation rates, ion release, and apatite formation. But strontium also matters for the catalytic side of the story. Introducing strontium oxide into a glass network modifies the balance between bridging oxygens, which link network-forming units together, and non-bridging oxygens, which break that continuity. This disruption of the glass network alters local electronic structure, defect chemistry, and charge transport, all of which feed directly into how efficiently a material can separate and mobilize charge under mechanical stimulation. In other words, the same compositional tweak that boosts bioactivity can, if tuned correctly, boost tribocatalytic performance too.

To verify that their synthesis had produced what they intended, the team deployed a standard but rigorous characterization arsenal. X-ray diffraction confirmed the crystalline phases in the glass ceramic and later verified the formation of a hydroxyapatite layer after bioactivity testing. Scanning electron microscopy revealed the surface morphology and mesoporous texture, while energy dispersive X-ray spectroscopy mapped the elemental composition and confirmed the incorporation of strontium. Ultraviolet-visible spectroscopy provided optical information relevant to charge generation, and the researchers additionally drew on facilities at IIT Kanpur and IIT Delhi, using atomic absorption spectroscopy and electron paramagnetic resonance to support their analysis of ion release and radical formation. The in vitro bioactivity assessment followed a well-established protocol: samples were immersed in Hank’s balanced salt solution at body temperature, 37 degrees Celsius, for seven days, and the growth of a hydroxyapatite layer was tracked by diffraction, microscopy, and elemental analysis.

The headline result concerns dye degradation. Using methylene blue, a common model pollutant and a genuine industrial contaminant, the researchers ran tribocatalytic experiments under regular magnetic stirring, with no light source and no applied voltage. Among the compositions tested, the sample designated SrO-5, doped with an intermediate strontium oxide concentration, emerged as the clear champion. Stirring at 700 revolutions per minute, it degraded 97.14 percent of the dye within 180 minutes. That figure is notable not merely for its magnitude but for its provenance: the energy input was nothing more than the friction and mechanical agitation of ordinary stirring, energy that would otherwise be simply dissipated as heat. The mesoporosity of the glass ceramic likely contributes as well, since a high surface area with abundant active sites gives mechanically generated charges more opportunities to reach pollutant molecules.

Of course, a high degradation number means little without a mechanism. The team probed which reactive species were doing the destructive work through active species quenching experiments, in which specific scavengers are added to intercept particular radicals or charge carriers. Isopropanol served to trap hydroxyl radicals, while ascorbic acid and ethylenediaminetetraacetic acid disodium salt were used to target other species. The verdict was clear: superoxide radicals and photogenerated-analogous holes, the positively charged sites left behind when electrons are excited, were the principal active species driving the tribocatalytic process. This mechanistic picture aligns with the broader literature on friction-driven catalysis, in which mechanical contact generates charge separation, electrons reduce dissolved oxygen to superoxide, and holes directly oxidize organic molecules or water, together producing a cascade of reactive oxygen species that dismantle dye chromophores.

Durability matters as much as performance for any real-world water purification technology, and the researchers addressed it directly with reusability testing. The SrO-5 glass ceramic was cycled through repeated degradation runs to verify that its catalytic effectiveness persisted rather than collapsing after first use, a crucial check for materials intended for practical deployment in wastewater streams. Combined with the fact that the catalyst works under ambient stirring conditions without lamps, electrodes, or chemical additives, the reusability results bolster the case that friction-powered catalysis could be engineered into low-cost, low-energy treatment systems, particularly in settings where electricity is scarce but mechanical agitation, flowing water, or vibration is freely available.

The bioactivity results give the material its second identity. After seven days of soaking in Hank’s balanced salt solution at physiological temperature, the formation of a hydroxyapatite layer on the glass ceramic was confirmed by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy, the classic triad of evidence for in vitro bioactivity. Because hydroxyapatite formation in simulated physiological solutions is widely used as a predictor of how a biomaterial will bond to living bone, this finding positions the strontium-doped glass ceramic as a credible candidate for bone tissue engineering scaffolds and dental applications. The researchers note that the combination of exceptional tribocatalytic activity and confirmed bioactivity gives SrO-5 potential in biomedical contexts as well as environmental ones, a synergy that few single materials can claim.

The wider significance of the study lies less in one record-breaking percentage and more in the design philosophy it demonstrates. Rather than treating mechanical energy harvesting and biological function as separate engineering goals, the Lucknow team shows they can be tuned together in a single glass composition, with strontium oxide acting as the lever that raises both. As researchers worldwide refine tribocatalysis mechanisms, exploring charge transfer, friction pair design, and defect engineering across systems from strontium titanate nanofibers to co-doped nickel oxide catalysts, materials that are simultaneously catalytically potent, mechanically simple to operate, and biocompatible could define a next generation of multifunctional ceramics. A glass that purifies water on a Tuesday and mends a fracture on a Wednesday may sound like science fiction, but the underlying chemistry reported here suggests it is simply good materials design, waiting for engineers to scale it up.

Subject of Research: Strontium-modified mesoporous bioactive glass ceramic for tribocatalytic dye degradation and bioactivity

Article Title: Synergistic Enhancement of Tribocatalytic Activity and Bioactivity in Strontium-Modified Mesoporous Bioactive Glass Ceramic

Article References: Gupta, A., Srivastava, A., & Shukla, R. K. (2026). Synergistic Enhancement of Tribocatalytic Activity and Bioactivity in Strontium-Modified Mesoporous Bioactive Glass Ceramic. Catalysis Letters, 156(9), Article 264. https://doi.org/10.1007/s10562-026-05512-3

Image Credits: AI Generated

DOI: 10.1007/s10562-026-05512-3

Keywords: tribocatalysis, bioactive glass, strontium oxide, methylene blue, hydroxyapatite, water purification, biomaterials, bone tissue engineering, reactive oxygen species, mesoporous ceramics, mechanical energy harvesting, Synergistic