The process at the heart of the review is dark fermentation, a biotechnology in which anaerobic bacteria dismantle organic matter, sugars, and waste streams such as food waste, palm oil mill effluent, and agricultural residues, in the absence of light and oxygen. During this microbial dismantling, hydrogen gas is released as a byproduct of the bacteria’s energy metabolism. The appeal is obvious: the feedstock is often waste that would otherwise rot in landfills, the reaction proceeds at ambient to moderately warm temperatures without light energy, and the gas produced is pure energy carrier rather than a carbon-containing fuel. Yet the technology has struggled to escape the laboratory. Yields remain stubbornly low relative to the theoretical maximum, and the microbial communities that do the work are notoriously sensitive to disturbance, swinging between productive and unproductive metabolic states as conditions drift.

The review’s first pillar is a systematic account of the physicochemical and operational variables that govern microbial performance. pH emerges as perhaps the most decisive lever. Fermentative hydrogen producers operate best in a mildly acidic window, typically around pH 5 to 6, where the hydrogenase enzymes responsible for releasing hydrogen gas remain active and where competing microbes that channel carbon into methane or other reduced products are suppressed. Let the pH drift too low and acid accumulation crashes the culture; let it rise and methanogens invade, consuming the hydrogen that the fermenters worked to produce. Temperature is the second master variable, with mesophilic and thermophilic regimes each selecting for distinct microbial consortia and distinct metabolic end products. Thermophilic operation, the authors note, often supports higher hydrogen yields and faster kinetics, but demands more energy input and careful reactor management.

Beyond pH and temperature, the review examines the characteristics of the inoculum itself, the starting microbial community seeded into the reactor. Heat treatment of seed sludge is a common strategy to kill off hydrogen-consuming methanogens while sparing spore-forming hydrogen producers such as Clostridium species. Organic loading rate, the amount of substrate fed per unit reactor volume per day, must be balanced carefully: push it too high and volatile fatty acids accumulate faster than the microbes can process them, acidifying the reactor and stalling hydrogen production; run it too low and the process becomes economically unattractive. Reactor configuration adds another layer of control. Immobilized-cell systems, upflow anaerobic sludge blanket reactors, packed bed biofilm reactors, and membrane bioreactors all retain biomass more effectively than simple suspended-growth tanks, allowing higher cell densities, faster throughput, and greater resilience to washout during shock loads.

Into this well-mapped landscape, the review introduces its genuinely novel perspective: multifunctional green materials, with hydroxyapatite as the star. Hydroxyapatite, with the chemical formula reflecting its calcium, phosphate, and hydroxide components, is the mineral that gives bones and teeth their rigidity. In a fermenter, it performs several jobs at once. Its surfaces serve as attachment sites for bacteria, promoting cell immobilization and the formation of dense, stable granules that resist washout in continuous operation. Its mineral chemistry buffers pH, absorbing and releasing ions in ways that damp the acidification that so often kills hydrogen-producing cultures. And through the controlled release of calcium and phosphate ions, it appears to support microbial metabolic stability, keeping the community locked into hydrogen-producing pathways for longer stretches of operation.

The evidence for this approach is not merely theoretical. The review’s own authors have published experimental work showing that eggshell-derived hydroxyapatite enhanced thermophilic hydrogen production, with the material promoting the formation of biogranules, compact microbial aggregates in which cells packed closely together exchange metabolites efficiently and maintain favorable microenvironments. Other studies cited in the review report that hydroxyapatite fabrication improved hydrogen output from glucose dark fermentation, and that graphene-hydroxyapatite composites boosted productivity from duckweed biomass. The mechanism is elegantly circular: the material that stabilizes the microbes is itself made from waste, so a discarded eggshell becomes the scaffold on which bacteria convert discarded food into fuel.

How the hydroxyapatite is made matters enormously, and the review devotes detailed attention to synthesis routes. Physical methods include pyrolysis and spray techniques that produce fine, well-defined particles. Chemical routes encompass wet chemical precipitation, sol-gel synthesis, hydrothermal treatment, sonochemical processing, and microwave-assisted reactions, each offering control over crystal size, morphology, and surface area, properties that directly determine how well the material buffers pH and hosts bacterial attachment. Biological and green synthesis routes use plant extracts, microbial activity, or biogenic templates to direct mineral formation under mild conditions, avoiding harsh reagents and high energy demands. Most compelling from a sustainability standpoint are the waste-based routes: eggshells, cow and fish bones, mussel and oyster shells, sea urchin spines, calcified algae, and even industrial byproducts such as phosphogypsum and carbide slag have all been converted into hydroxyapatite. Calcination temperature during processing, the review notes, strongly influences the crystallinity and purity of the final product, and higher specific surface area enhances the release of calcium ions, the very property that makes the material useful in fermentation.

This waste-to-material-to-energy chain is where the review’s conceptual contribution becomes clearest. By linking bioprocess engineering with materials science, the authors construct a framework for what they describe as more efficient, resilient, and environmentally friendly biohydrogen systems. The circular economy logic runs in both directions: organic waste feeds the fermenters, and inorganic waste supplies the additives that make the fermenters work better. Nothing in the chain requires virgin mined minerals or energy-intensive synthetic chemistry if biogenic sources are chosen. The review also situates hydroxyapatite within a broader family of additives, from carbonaceous materials and magnetite nanoparticles to nickel and cobalt ferrites, that have been explored to enhance fermentative hydrogen yields, but argues that hydroxyapatite’s combination of buffering capacity, immobilization support, biocompatibility, and waste-derived availability gives it a distinctive edge.

Challenges remain before the vision reaches industrial scale. The review is candid that low yield and process instability still limit the scalability of dark fermentation, and the integration of a solid additive introduces new variables: optimal dosing, particle size selection, long-term material stability, and the economics of recovering or disposing of spent mineral. Techno-economic assessments of dark fermentation systems generally conclude that profitability hinges on cheap feedstock, high productivity, and valorization of the fermentation effluent, which can itself be converted to biomethane, bioplastics, or microbial lipids in cascading processes. Hydroxyapatite strengthens two of those three pillars, feedstock flexibility and productivity, but the full chain must be demonstrated at pilot scale. The review’s framework, mapping process parameters onto material design, gives researchers a structured way to run those demonstrations, and it signals a broader shift in bioenergy thinking: the microbes may be the engine, but increasingly, the materials around them are the engineering that keeps the engine running.

Subject of Research: Enhancement of dark fermentative biohydrogen production using waste-derived hydroxyapatite additives

Article Title: Integrating process parameters and green hydroxyapatite (HAP) strategies for sustainable dark fermentative biohydrogen production

Article References: Zisha, S. Z., Che Man, H., Omar, R., Abdul Rashid, S., Tan, J. P., Abdul Manaf, S. F., Mumtaz, T., & Jamali, N. S. (2026). Integrating process parameters and green hydroxyapatite (HAP) strategies for sustainable dark fermentative biohydrogen production. Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-026-38274-x

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38274-x

Keywords: biohydrogen, dark fermentation, hydroxyapatite, waste valorization, circular economy, bioprocess optimization, cell immobilization, pH buffering, anaerobic digestion, sustainable energy, green synthesis, microbial consortium

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

Now, a study published in the Journal of Cellular and Molecular Medicine proposes a molecularly grounded strategy for upgrading these coatings. A research team from King Khalid University and collaborating institutions investigated what happens at the atomic scale when graphene oxide (GO), a chemically functionalised derivative of graphene, is combined with hydroxyapatite in a nanocomposite surface. Using an integrated suite of computational techniques—molecular docking, molecular dynamics simulations, three-dimensional pharmacophore mapping, and in silico toxicity screening—the researchers systematically compared how extracellular matrix (ECM) proteins and integrin receptors engage with pure HA, pure GO, and the combined GO–HA surface. Their central question: does graphene oxide genuinely enhance the molecular dialogue that sparks bone formation at the implant interface?

The choice of biological players was deliberate and biologically grounded. The team assembled a panel of twelve ECM proteins central to bone regeneration, including fibronectin, collagen type I, laminin, periostin, vitronectin, osteocalcin, osteonectin, bone sialoprotein, osteopontin, biglycan, decorin, and tenascin-C. Each plays a defined role in osseointegration—fibronectin drives osteoblast adhesion and migration through its RGD peptide motifs, collagen type I forms the primary organic scaffold of bone, and proteoglycans such as decorin and biglycan orchestrate collagen fibril assembly and growth factor activity. On the receptor side, six integrins were modelled, including α5β1, the principal fibronectin receptor, αvβ3, which binds RGD-rich bone proteins, and α2β1, the major collagen receptor. These transmembrane molecules are the mechanistic gateway through which cells sense a biomaterial surface and launch the signalling cascades leading to survival, proliferation, and osteogenic differentiation.

The docking results delivered a clear message. While hydroxyapatite showed respectable binding to laminin—its best-performing complex, with a HADDOCK score of −19.7 and a binding free energy of −4.95 kcal/mol—the graphene oxide-containing systems outperformed HA alone by a wide margin. The GO–α5β1 integrin complex posted a HADDOCK score of −56.0 and a striking binding affinity of −10.53 kcal/mol, driven by powerful van der Waals (−33.7 kcal/mol) and electrostatic (−53.3 kcal/mol) contributions and the largest buried surface area in the study at 745.4 square angstroms. GO complexes with α6β1 and laminin were similarly strong. The investigators attribute this enhanced interaction potential to GO’s exceptional mechanical strength, vast surface area, and dense array of oxygen-containing functional groups—hydroxyl, carboxyl, and epoxide moieties—that fuel hydrogen bonding and polar contacts with target proteins.

The most impressive performance came from the hybrid surface. The GO_HA_α5β1 complex achieved the strongest docking score of the entire study, −71.4 ± 2.2, with a binding free energy of −12.33 kcal/mol and the largest buried surface area recorded, 915.3 square angstroms. Specific atomic contacts helped explain the synergy: a hydrogen bond formed between a GO hydroxyl group and the Tyr287 residue of the integrin, reinforced by attractive charge interactions with Arg350, van der Waals forces, and π–π stacking against the aromatic carbon backbone. Complexes with periostin and vitronectin reached ΔG values of −11.63 and −10.93 kcal/mol, respectively, both exceeding anything achieved with pure hydroxyapatite. Intermolecular contact analysis reinforced the picture, with the GO_HA_α5β1 system registering thousands of carbon-carbon and carbon-oxygen atom-pair contacts—markers of extensive hydrophobic and polar interaction networks across a broad molecular interface.

Pharmacophore mapping added chemical nuance to the binding story. For the α5β1 complex, clusters of hydrogen-bond acceptors gathered around GO’s epoxide and hydroxyl groups, while a dense web of hydrogen-bond donors—traced largely to HA’s phosphate and calcium-bound hydroxyl sites—lined the opposite side of the interface. The periostin complex displayed a balanced, evenly distributed network of donors and acceptors that the authors describe as an effective molecular anchor, while vitronectin’s β-sheet regions aligned with hydrophobic patches along the GO aromatic framework. In essence, the two materials divide the labour: graphene oxide supplies electron-rich acceptor chemistry and hydrophobic surface anchoring, while hydroxyapatite contributes polar donor sites, producing a reactive, dual-function surface that ECM proteins grip more firmly than either component alone.

Molecular dynamics simulations running 100 nanoseconds under physiological conditions—310 K, 1 bar, explicitly solvated—tested whether these docked encounters survive thermal motion. Across three flagship complexes (α5β1 integrin, periostin, and vitronectin), the GO–HA assemblies consistently showed the highest numbers of hydrogen bonds and the lowest residue-level fluctuations. The GO_HA_periostin complex, for instance, formed 20 hydrogen bonds—double the count of the HA-only equivalent—and recorded the lowest root-mean-square fluctuation among all periostin systems at 0.852 nm, indicating that individual residues were held more tightly in place. Similarly, GO_HA_vitronectin stabilised the functionally important Ser180–Phe210 region and maintained 19 hydrogen bonds. While the hybrid complexes exhibited larger radii of gyration, reflecting an extended conformation that embraces more surface contact, the combined evidence points to a surface that holds proteins in stable, potentially more bioactive orientations rather than merely sticking them down loosely.

Safety, inevitably, complicates the enthusiasm. In silico toxicity screening painted a stark contrast between the two components: hydroxyapatite showed no predicted mutagenicity, tumorigenicity, irritancy, or reproductive toxicity, consistent with its long clinical record in bone grafting, whereas graphene oxide triggered high-risk flags across all four endpoints. GO’s intermediate lipophilicity, large hydrophobic surface area, and predicted capacity to cross cellular barriers underlie these warnings. Experimental literature offers both caution and a remedy: smaller GO nanosheets can be internalised by cells, provoking oxidative stress and membrane damage, yet embedding GO within a calcium phosphate matrix may neutralise its excessive negative surface charge, mask reactive oxygen functionalities, and temper reactive oxygen species generation. The authors are explicit that this protective effect remains a theoretical postulate requiring cytotoxicity assays and in vivo validation before any clinical claim can be made.

The team is equally candid about the boundaries of computational prediction. Their model represents GO and HA as component-level molecular structures within a simplified interfacial assembly—it does not validate a covalent GO–HA bond, coating morphology, or crystallinity, and it cannot capture competitive serum protein adsorption, immune responses, biomechanical loading, or the messy temporal dynamics of living bone. The findings are framed as a framework for generating testable hypotheses rather than proof of clinical efficacy. The validation roadmap is nonetheless concrete: surface characterisation by atomic force microscopy, electron microscopy, and X-ray photoelectron spectroscopy; protein adsorption assays; osteoblast cell-culture experiments measuring adhesion, viability, and osteogenic differentiation; macrophage and cytokine profiling to rule out adverse immunological reactions; and eventually animal implantation studies assessed by micro-computed tomography, histomorphometry, and pull-out testing.

If those experiments confirm what the simulations suggest, the implications extend well beyond dentistry. A coating that simultaneously strengthens the mechanical integrity of the implant interface, amplifies protein adsorption, exposes integrin-binding domains in adsorbed fibronectin, and passes biological safety screening would address the central weakness of titanium implants: their silence in the molecular language of bone. The study’s real contribution is a rigorous, multi-method template for evaluating next-generation biomaterial surfaces before a single laboratory experiment is run—accelerating the search for implant coatings that coax bone to embrace metal not reluctantly, but eagerly.

Subject of Research: Computational analysis of graphene oxide–hydroxyapatite nanocomposite coatings and their interactions with extracellular matrix proteins to improve dental implant osseointegration.

Article Title: Graphene Oxide–Hydroxyapatite Nanocomposite Coatings and Extracellular Matrix Protein Interactions for Enhanced Osseointegration in Dental Implants

Article References: Saini, R. S., Binduhayyim, R. I. H., Dermawan, D., Kanji, M. A., Quadri, S. A., & Heboyan, A. (2026). Graphene Oxide–Hydroxyapatite Nanocomposite Coatings and Extracellular Matrix Protein Interactions for Enhanced Osseointegration in Dental Implants. Journal of Cellular and Molecular Medicine, 30(17), Article e71352. https://doi.org/10.1111/jcmm.71352

Image Credits: AI Generated

DOI: 10.1111/jcmm.71352

Keywords: dental implants, osseointegration, graphene oxide, hydroxyapatite, nanocomposite coatings, extracellular matrix proteins, molecular docking, molecular dynamics simulation, integrin receptors, biomaterials, in silico toxicity, titanium implants