Researchers at the University of Veterinary Medicine in Vienna, working with the Agricultural Research and Education Center Raumberg-Gumpenstein in Austria, followed 66 Fleckvieh, Holstein-Friesian, and New Zealand Friesian cows and heifers through 85 calvings between November 2022 and March 2024. Blood samples were collected at a dense series of time points: roughly 21, 14, and 7 days before the expected calving date, just hours before and after parturition, and then at 1, 3, 7, and 14 days postpartum. From each sample, the team measured serum total calcium alongside a panel of osteoimmunological markers, proteins and enzymes that reflect the ongoing dialogue between the immune system and bone tissue.

The central focus was the RANK/RANKL/OPG signaling system, a triad of molecules from the tumor necrosis factor superfamily that governs bone remodeling. RANK ligand, produced by osteoblasts and activated T cells, binds to the RANK receptor on osteoclast precursor cells and drives their differentiation into mature bone-resorbing cells. Osteoprotegerin acts as a soluble decoy receptor, neutralizing RANKL and thereby restraining osteoclast formation. This regulatory axis responds to hormonal and cytokine signals, including interleukin-6, tumor necrosis factor-alpha, and interleukin-17, which are known to shift during the inflammatory events of pregnancy and calving. Because parturition itself is an inflammatory process, involving detachment and expulsion of the fetal membranes, the researchers reasoned that immune activation around calving might perturb bone turnover and influence systemic calcium availability.

To track bone resorption directly, the team measured C-terminal cross-linked telopeptide of type I collagen, or CTX-I, a fragment released when type I collagen is degraded, widely accepted as a sensitive marker of osteoclastic activity in both human and veterinary medicine. They also measured osteocalcin, a marker of osteoblast formation activity, and alkaline phosphatase, an enzyme long used in human medicine to evaluate bone diseases such as osteomalacia and Paget’s disease. After calving, cows were retrospectively classified by their serum calcium concentrations as normocalcemic, above 2.20 millimoles per liter; subclinical hypocalcemic, between 1.80 and 2.20; or low-calcium, below 1.80 millimoles per liter.

The distribution of calcium status revealed how widespread the problem is even in a well-managed research herd. Of the 85 calvings, only about 39 percent remained normocalcemic, while 54 percent fell into the subclinical hypocalcemic range and 7 percent into the low-calcium category. Notably, the burden fell disproportionately on older animals: among cows in their fourth or later lactation, 18 of 27 calvings were subclinical and 5 were frankly low-calcium, whereas most heifers maintained normal calcium concentrations.

CTX-I emerged as the standout marker. Its concentrations rose after parturition, peaked in early lactation, and then gradually declined, consistent with a transient stimulation of bone resorption to meet the demands of lactation. Crucially, first-lactation animals showed significantly higher CTX-I concentrations than multiparous cows at every examination time, and cows that went on to develop low calcium had the lowest CTX-I concentrations at nearly all time points, with significant differences from normocalcemic cows stretching from two weeks before calving through two weeks after. The interpretation is striking: cows that could not mobilize calcium from their skeletons effectively were the ones that became hypocalcemic, and their impaired resorptive capacity was visible in the blood before calving.

The predictive power was quantified using receiver operating characteristic analysis, which evaluates how well a biomarker separates two groups across all possible threshold values. Prepartum CTX-I achieved area under the curve values between 0.75 and 0.90, with Youden indices between 0.75 and 0.82 at several time points. At 14 days before calving, a cut-off of 0.17 nanograms per milliliter yielded 100 percent specificity and roughly 81 percent sensitivity for identifying cows that would later become hypocalcemic. In practical terms, a single blood test in late gestation could flag most at-risk cows while essentially never falsely accusing a cow that would remain healthy. Alkaline phosphatase showed moderate predictive value before calving, and RANK, whose concentrations declined in all parity groups before calving and then remained low, was more useful for tracking postpartum regulatory processes than for prepartum prediction. No reliable models could be built for osteocalcin, RANKL, or osteoprotegerin, likely because RANKL and OPG act predominantly within the local bone microenvironment and are not fully reflected in circulating concentrations.

The parity findings carry their own biological weight. The consistently lower CTX-I concentrations in older cows suggest an age-related decline in bone remodeling, echoing human studies showing that osteoclast precursors become less responsive to RANKL stimulation with age. This diminished capacity to activate osteoclast-mediated calcium mobilization offers a mechanistic explanation for why older cows are far more susceptible to milk fever: when the sudden calcium drain of lactation begins, their skeletons simply cannot respond as vigorously as those of younger animals. Markers of bone formation, by contrast, showed far less pronounced age-related variation, indicating that the parity effect is concentrated on the resorptive side of skeletal metabolism.

The authors are careful to frame the findings appropriately. The low-calcium group contained only six calvings, limiting statistical power, and the study was conducted under specific herd and management conditions without controlled nutritional factors, which are known to influence calcium metabolism. The commercial ELISA kits used may introduce analytical variability, and the observational design precludes causal inference. The proposed cut-off values require validation in independent cohorts before any clinical application, and the researchers explicitly caution that biomarker screening should complement, not replace, established herd-level prevention strategies such as dietary calcium management around calving.

Even with those caveats, the study opens a genuinely new window on an old problem. Milk fever has been managed for decades through nutritional strategies, yet individual risk prediction has remained crude. The demonstration that a bone resorption marker measured weeks before calving can identify cows destined for hypocalcemia suggests that the disease process begins long before the calcium crash, rooted in the skeleton’s diminished ability to respond. If validated at scale, CTX-I testing in late gestation could allow farmers and veterinarians to target preventive interventions precisely at the cows that need them most, turning a metabolic emergency into a manageable prediction problem.

Subject of Research: Osteoimmunological biomarkers for predicting periparturient hypocalcemia in dairy cows

Article Title: Periparturient changes in osteoimmunological markers and their association with hypocalcemia in dairy cows

Article References: Gleissenberger, J., Gleissenberger, M., Becker, S., Schraml, M., Eingang, D., Khol, J. L., & Wittek, T. (2026). Periparturient changes in osteoimmunological markers and their association with hypocalcemia in dairy cows. Journal of Veterinary Internal Medicine, 40(5), Article aalag244. https://doi.org/10.1093/jvimsj/aalag244

Image Credits: AI Generated

DOI: 10.1093/jvimsj/aalag244

Keywords: dairy cows, hypocalcemia, bone resorption, CTX-I, RANK/RANKL/OPG, osteocalcin, alkaline phosphatase, transition period, milk fever, osteoimmunology, biomarkers, veterinary medicine

The review, led by Yunhe Zhang of Dalian Medical University with colleagues from China Medical University and Haicheng Orthopedics Hospital, examines how the quantity, identity, orientation, conformation, and exchange kinetics of adsorbed proteins collectively determine what cells actually see when they encounter an implant. The authors introduce the term interfacial protein state to describe this measurable combination, and they propose that researchers report all five dimensions together under matched conditions rather than relying on total protein mass alone. Their central argument is that two surfaces carrying identical amounts of fibronectin can produce entirely different biological outcomes depending on whether the integrin-binding RGD motif and the PHSRN synergy site remain accessible to cellular receptors.

The evidence for this principle is strongest in defined laboratory systems. In one frequently cited comparison, fibronectin adsorbed onto poly(ethyl acrylate) and poly(methyl acrylate) surfaces reached similar surface densities of approximately 340 nanograms per square centimeter when exposed to a 20 microgram per milliliter coating solution for ten minutes. Yet atomic force microscopy revealed fibrillar assembly on one polymer and a more globular organization on the other, and an antibody-based accessibility assay showed that the fraction of fibronectin molecules presenting their integrin-binding domain differed between the two surfaces. The protein was there in equal amounts on both materials, but it was not equally available to the cells that needed to read it.

This distinction between quantity and functional presentation has direct consequences for how bone implants are designed and evaluated. The review emphasizes that increasing the amount of an adsorbed protein does not restore signaling if the critical domain is turned toward the material or sterically blocked by neighboring molecules. Orientation, the authors argue, can change function even when protein identity and abundance remain unchanged. Receptor-binding regions that face the surrounding fluid remain available to cells, while the same regions become biologically silent when they lie against the material surface. This principle applies not only to fibronectin and vitronectin but also to the Fc region of immunoglobulins and to receptor-recognition sites on complement fragments.

Conformation presents an equally complex picture. The review distinguishes between limited structural extension that can preserve or even enhance physiological function and deeper denaturation that exposes nonphysiological epitopes and triggers inflammatory pathways. Fibronectin illustrates the potentially beneficial side: after adsorption onto certain surfaces, it can transition from a compact form toward an extended or fibrillar organization that makes integrin-binding and growth-factor-binding regions more accessible. Fibrinogen demonstrates the opposite direction. When adsorption unfolds this coagulation protein excessively, the gamma-chain region recognized by the Mac-1 integrin on leukocytes becomes exposed, driving inflammatory-cell adhesion and cytokine release. Albumin, often assumed to be a passive blocking agent, can acquire affinity for scavenger receptors when sufficiently denatured.

The temporal dimension adds another layer of complexity. The review documents that the protein layer is not frozen after implantation but continuously evolves through competitive exchange, enzymatic cleavage, cell-mediated remodeling, and deposition of new matrix. In nanoparticle systems, a complex plasma protein corona has been detected within less than thirty seconds of exposure. Human serum albumin dissociation from a specific particle type showed a half-life of approximately thirty minutes, though the authors stress this is a protein-and-material-specific result rather than a universal timescale. By the time immune cells, endothelial cells, and osteoprogenitors reach the implant surface, they are contacting a material-protein composite that has already undergone multiple rounds of exchange and restructuring.

One of the most clinically relevant sections addresses autologous blood-product precoatings. Platelet-rich plasma and platelet-rich fibrin are widely used to deliver patient-derived proteins and growth factors to implant surfaces before insertion. The review acknowledges that these preparations differ substantially in their growth-factor release profiles depending on centrifugation protocol, anticoagulation, activation state, and fibrin organization. However, it also notes that a randomized split-mouth trial involving fifteen patients and thirty dental implants found no statistically significant between-group differences in assessed outcomes after one year when liquid platelet-rich fibrin was applied to implant surfaces. The authors interpret this as limiting unqualified efficacy claims rather than excluding benefits under other protocols, and they emphasize that neither growth-factor content nor clinical application alone validates a particular protein-state mechanism.

The review also confronts an uncomfortable reality about bacterial competition. Staphylococcal fibronectin-binding proteins can exploit adsorbed fibronectin to engage host alpha-5 beta-1 integrins, while fibrinogen-binding adhesins support bacterial attachment to conditioned surfaces. The very protein features that support mammalian-cell attachment may simultaneously facilitate bacterial colonization and biofilm development. The authors argue that host-cell adhesion alone cannot establish resistance to bacterial attachment and that protein-conditioned materials require parallel assessment with clinically relevant bacterial species. They cite an experimental system that combined fibronectin and BMP-2 presentation on coated titanium nanotopography with examination of both mesenchymal stromal cells and Pseudomonas aeruginosa in the same material platform, demonstrating that host-cell support and biofilm inhibition can be evaluated together.

Perhaps the most sobering section of the review addresses what remains unvalidated. The authors are explicit that predicting bone-healing outcomes across different materials, guiding patient-specific implant selection, and replacing growth-factor delivery through endogenous protein capture all remain unproven hypotheses. They distinguish carefully between evidence obtained with purified protein coatings, recombinant growth factors, and dispersed nanoparticles versus evidence of endogenous protein recruitment at a bone-contacting implant. A mechanism supported only by in vitro systems, non-bone animal models, or nanoparticle studies is not described as clinically established without cross-scale validation. The review proposes a six-level evidence ladder ranging from interface formation through receptor translation to human translation, with each level requiring progressively stronger causal evidence.

The authors conclude that the interfacial protein state framework is a reporting and comparison scheme rather than a validated predictor or clinical score. They call for future studies to connect measurements on the final sterilized product to causal perturbations, disease-relevant biofluids, safety endpoints, and indication-matched outcomes. Patient-specific implant selection and programmed endogenous protein exchange remain research proposals until prospective validation demonstrates added clinical value beyond conventional variables. What the review does establish is that the protein layer acquired by a bone implant within minutes of insertion is not a passive footnote to material design but an active biological interface that determines whether the body builds bone, mounts inflammation, or invites bacterial colonization at the site of repair.

Subject of Research: How endogenous protein adsorption and functional presentation at bone-regenerative biointerfaces control receptor recognition, inflammation, and bone healing outcomes

Article Title: Endogenous protein adsorption and functional presentation at bone-regenerative biointerfaces

Article References: Zhang, Y., Xu, Y., Zhang, C., & Lu, B. (2026). Endogenous protein adsorption and functional presentation at bone-regenerative biointerfaces. Frontiers in Bioengineering and Biotechnology, 14, Article 1965344. https://doi.org/10.3389/fbioe.2026.1965344

Image Credits: AI Generated

DOI: 10.3389/fbioe.2026.1965344

Keywords: protein corona, bone regeneration, biointerface, fibronectin, fibrinogen, integrin signaling, BMP-2, titanium implants, osteogenesis, protein adsorption, biomaterials, osteoimmunology

The study, published in BMC Cancer, set out to answer a deceptively simple question: do patients actually feel better, and do their bones fare better, when they are being treated with proteasome inhibitors? These drugs—which include bortezomib, carfilzomib, and ixazomib—block the proteasome, a cellular waste-disposal complex that myeloma cells depend on to clear misfolded proteins. When the proteasome is inhibited, toxic protein accumulation builds up inside the malignant cells and triggers their death. This mechanism has transformed myeloma survival over the past two decades, and proteasome inhibitors are now embedded in nearly every modern treatment regimen, from newly diagnosed patients to those with relapsed and refractory disease.

But proteasome inhibitors may do more than kill myeloma cells. Laboratory studies have long suggested they carry bone-modulating effects that go beyond their anticancer activity, potentially suppressing the overactive osteoclasts that chew away at bone while influencing the osteoblasts that should rebuild it. If those biological effects were meaningful in real patients, you might expect to see the benefits show up in the clinic—in less bone pain, fewer osteolytic lesions, and better patient-reported quality of life. The Freiburg team wanted to know whether this theoretical promise survives contact with routine clinical practice, where treatment decisions are anything but random.

That caveat is crucial, and it shaped the study’s design. In routine care, physicians preferentially assign proteasome inhibitor-based therapy to patients with more active or more symptomatic disease. This means patients on these drugs are, by definition, likely sicker to begin with—a classic case of confounding by indication that would make naive comparisons deeply misleading. To address this, the researchers prospectively enrolled 209 patients with multiple myeloma during routine interdisciplinary follow-up, stratifying them by whether they were currently receiving proteasome inhibitor-based treatment or a non-PI-based regimen. Of the cohort, 78 patients, or 37 percent, were on proteasome inhibitor-based therapy at the time of assessment. Sixty-nine patients were reassessed after at least six months, allowing the team to track changes over time.

The investigators deployed multivariable regression and sensitivity analyses designed specifically to address baseline imbalances and the treatment selection problem. Patient-reported outcomes were captured using validated instruments measuring overall quality of life and health-related functional status, while skeletal symptoms were assessed through structured evaluation of bone pain and imaging-documented osteolytic lesions. This combination of subjective, patient-centered measures and objective skeletal endpoints is what makes the study unusual—it bridges hematology, orthopedics, and trauma surgery in a way that reflects how myeloma patients actually experience the disease.

The headline result is one of careful null findings. After adjustment, current proteasome inhibitor-based treatment status was not associated with meaningful differences in quality of life, with a standardized effect estimate of −0.08 and a 95 percent confidence interval spanning −0.45 to 0.29 and a p-value of 0.662. Health-related status told the same story, at −0.06 with a confidence interval of −0.42 to 0.30 and a p-value of 0.740. Bone pain showed no significant association either, with an odds ratio of 0.92 and a confidence interval of 0.48 to 1.74, and neither did the prevalence of osteolytic lesions, at an odds ratio of 1.26. During the six-month follow-up period, quality of life and health-related status remained comparable between the groups, suggesting no divergence in how patients felt over time depending on their current treatment class.

There was one signal worth watching, even if it fell short of statistical significance. Myeloma-related bone pain was numerically more frequent among patients currently receiving proteasome inhibitor-based treatment—46 percent versus 33 percent in the non-PI group. After multivariable adjustment, the association yielded an odds ratio of 1.80 with a confidence interval of 0.93 to 3.48 and a p-value of 0.081, hovering just above the conventional threshold for significance. The authors are careful here, and rightly so: this is precisely the pattern you would expect from confounding by indication, since clinicians reserve these potent drugs for patients with more active, more symptomatic disease. The excess pain likely reflects why those patients were on proteasome inhibitors in the first place, not a harmful effect of the drugs themselves.

What the study does not claim is nearly as important as what it does. The team explicitly states that these findings provide a real-world description of patient-reported and skeletal outcomes according to current treatment status, but they do not establish whether the biological effects of proteasome inhibitors on bone remodeling translate into clinically meaningful patient-reported or structural skeletal benefits. This is the persistent gap between bench and bedside that the study illuminates so clearly. Preclinical data on proteasome inhibition and osteoclast biology remain biologically plausible, yet the messy realities of clinical medicine—physician judgment, patient selection, concurrent antiresorptive therapy, and disease heterogeneity—obscure any signal that might exist. A randomized comparison, which would be ethically and practically difficult given the established efficacy of proteasome inhibitors against the cancer itself, would be needed to isolate the skeletal effects specifically.

For patients and clinicians, the practical message is one of reassurance with nuance. Being on a proteasome inhibitor was not associated with worse quality of life or health status in this cohort, which matters because these drugs carry well-known side effect profiles, including peripheral neuropathy that can compound a patient’s symptom burden. At the same time, patients on these drugs should not expect them to deliver measurable bone-protective benefits beyond their antimyeloma activity. Skeletal protection in multiple myeloma still rests on established pillars: bisphosphonates and other antiresorptive agents, orthopedic management of lytic lesions and fracture risk, and prompt control of the underlying disease. The study underscores that quality of life and bone pain in myeloma are shaped by many forces beyond a single drug class.

The research also highlights the value of prospective, interdisciplinary cohort designs in oncology. By following patients through routine hematology and orthopedic follow-up simultaneously, the Freiburg team captured a picture of myeloma care that is closer to everyday practice than most clinical trials can offer. As proteasome inhibitors become a permanent fixture of myeloma therapy, studies like this one serve as an essential reality check—reminding the field that biological promise, statistical adjustment, and the lived experience of patients with aching bones do not always align. The next challenge is to determine, with better-designed comparisons, whether the bone-modulating potential of these drugs can ever be converted into tangible relief for the patients who need it most.

Subject of Research: Patient-reported outcomes and skeletal symptoms in multiple myeloma patients receiving proteasome inhibitor-based versus non-PI-based therapy

Article Title: Patient-reported outcomes and skeletal symptoms in multiple myeloma stratified by proteasome inhibitor-based therapy: a prospective interdisciplinary cohort study

Article References: Patient-reported outcomes and skeletal symptoms in multiple myeloma stratified by proteasome inhibitor-based therapy: a prospective interdisciplinary cohort study. (n.d.). https://doi.org/10.1186/s12885-026-17177-7

Image Credits: AI Generated

DOI: 10.1186/s12885-026-17177-7

Keywords: multiple myeloma, proteasome inhibitors, patient-reported outcomes, quality of life, bone pain, osteolytic lesions, bone remodeling, antiresorptive therapy, hematology-oncology, prospective cohort study, osteoimmunology, real-world evidence

The team, led by researchers including Tianhao Wang and Xiaoxiang Ren, defines its constructs as scaffold-guided engineered bone organoids, meaning the biomaterial establishes the initial three-dimensional architecture while the encapsulated cells progressively take over, depositing bone-specific extracellular matrix and driving mineralization. This dynamic remodeling is what separates a true organoid from a passive cell-laden scaffold. Conventional bone organoid platforms are largely built to push stem cells toward osteogenic differentiation, but they rarely incorporate immune components, a significant drawback given that macrophages must typically shift from a pro-inflammatory M1 state to a pro-regenerative M2 state to resolve inflammation, induce new vessel formation, and facilitate matrix remodeling during healing.

The new bioink blends three components in a carefully optimized ratio of 10 percent gelatin methacryloyl (GelMA), 1 percent Laponite synthetic nanoclay, and 40 percent aloe vera gel. Each ingredient earns its place through a defined function. GelMA, a photocrosslinkable derivative of gelatin, carries the arginine-glycine-aspartic acid cell-adhesion motif and offers tunable mechanics through rapid UV cross-linking. Laponite forms what materials scientists describe as a house-of-cards microstructure, imparting strong shear-thinning behavior that makes the ink extrusion-printable while boosting elastic modulus and toughness; its degradation products, magnesium and silicon ions, have independently been shown to foster a pro-regenerative microenvironment. Aloe vera serves as the immunologically active component, delivering bioactive polysaccharides such as acemannan along with phytosphingosine- and polyphenol-related metabolites identified by liquid chromatography-mass spectrometry.

Reaching that sweet-spot formulation required systematic trade-off analysis. Lower GelMA concentrations produced weak mechanical support and structural collapse, while higher levels restricted cell migration and matrix remodeling. Laponite at 1 percent elevated shape fidelity to a printability coefficient near 1.0, but higher loadings clogged nozzles and pushed cell viability below 80 percent through elevated shear stress. Aloe vera below the optimal threshold weakened immunomodulatory efficacy, whereas excess diluted the precursor and compromised cross-linking. The final formulation, seeded with rat bone marrow mesenchymal stem cells at one million cells per milliliter, yielded continuous filament deposition, precise architecture, and post-printing viability exceeding 90 percent, all without a single exogenous cytokine such as IL-4.

The printing parameters themselves are a study in delicacy. Constructs were extruded at 8 degrees Celsius to preserve gel consistency and prevent filament deformation, under pneumatic pressure of 0.2 to 0.3 megapascals at a speed of 4 millimeters per second, using a 21-gauge metal nozzle. A rectangular, eight-layer porous grid of 5 by 5 millimeters was built with 1.5-millimeter infill spacing and 90-degree interlayer rotation. Cross-linking used 365-nanometer UV light at just 5 percent intensity, applied for 10 seconds per layer with brief post-curing, enough to lock in shape without damaging the stem cells. Printed precursors then spent 24 hours in growth medium before switching to osteogenic induction medium supplemented with beta-glycerophosphate, ascorbic acid, and dexamethasone for up to 28 days.

In vitro, the organoids behaved as hoped. Alkaline phosphatase and Alizarin Red S staining documented progressive osteogenic differentiation and mineral deposition, confirmed by elevated expression of the master osteogenic markers OCN, RUNX2, and OPN and by micro-computed tomography detection of mineralized matrix. On the immune side, the constructs increased macrophage recruitment, invasion, and adhesion, and shifted the cells toward a CD206-positive, iNOS-low phenotype characteristic of pro-regenerative M2 macrophages, accompanied by reduced IL-1beta and increased IL-10 expression. Bulk RNA sequencing of implanted constructs revealed broad immune remodeling across Th1/Th2/Th17-related pathways and alterations in STAT6, NF-kappaB, PI3K/AKT, and RANKL-related signaling, consistent with enhanced pro-regenerative responses and dampened inflammation, though the authors caution these associations do not yet establish direct causality.

The in vivo results are where the platform becomes genuinely striking. When implanted subcutaneously into nude mice, the organoid precursors matured into bone-like tissue, organizing type 1 collagen and periostin into structured extracellular matrix, forming vinculin-positive focal adhesions, and sprouting prominent surface capillaries alongside internal CD31-positive microvascular networks. The team then moved to the decisive test: bilateral 5-millimeter critical-sized calvarial defects in rats, wounds too large to heal on their own. By eight weeks, the aloe-containing organoids had promoted more robust bone regeneration than GelMA-only or GelMA/Laponite control scaffolds, with improved mineralized bone formation, closer integration with host tissue, and CD206-positive macrophages populating the repair site. Histology of major organs and routine blood biochemistry revealed no obvious systemic toxicity.

The authors are candid about the platform’s limits. The protocol models macrophage-mediated regulation only; neutrophils, osteoclasts, T cells, and other stromal populations were not systematically incorporated, and the use of immunodeficient nude mice precludes assessment of adaptive immunity. Late-stage osteocyte maturation and lacuno-canalicular network organization remain uncharacterized, and the eight-week observation window captures only early-to-intermediate regeneration, leaving scaffold degradation kinetics, vascular stabilization, and biomechanical load-bearing integration for future studies extending to 12 to 24 weeks and, ultimately, large-animal models. Batch-to-batch consistency of aloe vera gel also emerges as a critical quality-control point, since variability in its bioactive constituents could weaken macrophage polarization.

Even so, the implications extend well beyond the skull. The researchers envision adapting the bioink to model immune-dysregulated orthopedic diseases such as rheumatoid arthritis and osteoporosis by incorporating patient-derived macrophages, synovial fibroblasts, or osteoclast precursors. Adding chondrogenic factors like TGF-beta3 could generate cartilage organoids, while the same immunoregulatory chemistry might improve wound repair and reduce scarring in skin models. Because the constructs simultaneously promoted bone formation and vascularization in vivo, the system could also help solve the vascularization bottleneck that plagues the engineering of many other tissues. Multi-nozzle bioprinting and microfluidic culture could eventually arrange bone-forming, vascular, and marrow-like compartments in spatially organized, immunocompetent constructs. For a field long tethered to an ill-defined gel extracted from mouse tumors, a printable, plant-powered alternative that teaches immune cells to heal rather than inflame marks a genuinely consequential turn in the organoid revolution.

Subject of Research: Fabrication of immune-regulatory bone organoids using a plant-based GelMA/Laponite/Aloe vera bioink

Article Title: Protocol for fabricating immune-regulatory bone organoids via plant-based bioinks

Article References: Wang, T., Gao, G., Zhang, X., Huo, K., Liu, C., Geng, Z., Bai, L., Zhang, H., Liu, H., Xu, K., Lai, Y., Wang, J., Jing, Y., He, C., Wang, G., Su, J., & Ren, X. (2026). Protocol for fabricating immune-regulatory bone organoids via plant-based bioinks. iScience, 29(11), Article 117866. https://doi.org/10.1016/j.isci.2026.117866

Image Credits: AI Generated

DOI: 10.1016/j.isci.2026.117866

Keywords: bone organoids, bioink, Aloe vera, GelMA, Laponite, 3D bioprinting, macrophage polarization, osteoimmunology, bone regeneration, Matrigel-free, tissue engineering, calvarial defect

The team, led by immunologist Susanna Mandruzzato of the Veneto Institute of Oncology and the University of Padua, focused on a family of cells known as myeloid-derived suppressor cells, or MDSCs. These immature cells of the myeloid lineage, which includes precursors of granulocytes and monocytes, are best known from cancer research, where they accumulate in tumors and suppress the T cell responses that would otherwise attack malignant tissue. But MDSCs are not exclusive to cancer. They expand during infection, sepsis, and chronic inflammatory diseases, and recent work has implicated them in bone pathologies ranging from osteoporosis to inflammatory arthritis, where they can even act as dysfunctional osteoclast progenitors that contribute directly to bone destruction.

What made the question urgent for osteoarthritis is the disease’s peculiar inflammatory profile. Hip osteoarthritis is not an autoimmune condition like rheumatoid arthritis, yet it features a persistent, smoldering inflammation marked by elevated levels of cytokines such as IL-1β, TNF-α, and IL-6 in the joint environment. This inflammatory milieu promotes synovial activation, disrupts subchondral bone remodeling, enhances osteoclast formation, and accelerates cartilage breakdown through catabolic enzymes like metalloproteinases. In parallel, aging itself drives a phenomenon called inflammaging, a chronic low-grade inflammatory state that biases hematopoietic stem cells in the bone marrow toward producing myeloid cells at the expense of lymphoid lineages. The Padua team asked whether these two forces, aging and disease-associated inflammation, converge in the bone marrow of osteoarthritis patients.

To find out, the researchers collected fresh bone marrow aspirates from 13 patients undergoing total hip arthroplasty for osteoarthritis and 13 patients undergoing surgery for proximal femoral fracture, all recruited at the University-Hospital of Padova. The samples were drawn from the medullary canal of the femur during the earliest stage of surgical preparation, before any broaching of the canal, ensuring that the cellular composition reflected the living marrow environment. Patients with active malignancies, autoimmune diseases, infections, or hematological disorders were excluded. The two cohorts were not identical: the fracture patients were, on average, older than the osteoarthritis group, a difference the authors acknowledge as a potential confounder, but it makes the direction of their key finding all the more remarkable.

Using multiparametric flow cytometry, the team quantified the myeloid and lymphoid compartments in each sample. Despite being younger on average, the osteoarthritis patients showed a significantly higher proportion of myeloid cells in their bone marrow than the fracture patients, a difference that reached statistical significance at p = 0.0036. Lymphoid cell frequencies, by contrast, did not differ between the groups. This selective myeloid enrichment could not be explained by advanced age alone, suggesting that the chronic inflammation associated with hip osteoarthritis actively amplifies the age-related skewing of hematopoiesis toward the myeloid lineage. In other words, the disease may be superimposing its own inflammatory signature on top of the normal immunological remodeling of aging.

The researchers then drilled down into the maturation stages of these myeloid cells, using the surface markers CD11b and CD16 to distinguish granulocytic precursors at different points along their developmental path. Here a specific subset stood out. Cells with a CD11b-positive, CD16-low phenotype, which correspond to metamyelocytes, an intermediate stage of granulocyte maturation, were significantly enriched in the osteoarthritis samples, both when analyzed directly ex vivo and after the cells were cultured for four days with the growth factors G-CSF and GM-CSF to drive myeloid expansion. After cytokine stimulation, this metamyelocyte-like fraction reached a median of 31.5 percent in the osteoarthritis cultures versus 20.3 percent in the fracture cultures, a persistent difference indicating that the osteoarthritic marrow environment favors the production of these intermediate myeloid cells even under standardized laboratory conditions.

The functional heart of the study, however, lay in the suppressive capacity of these cells. In earlier work, the same group had established that the immunosuppressive power of bone marrow-derived MDSCs resides almost entirely in the most immature fraction, a CD11b-negative or low, CD16-negative population with promyelocyte-like features. In the new experiments, the researchers co-cultured these myeloid fractions with T cells from healthy donors that had been labeled with a fluorescent proliferation dye and activated with anti-CD3 and anti-CD28 antibodies. The result was unambiguous: only the immature fraction significantly inhibited T cell proliferation, in both osteoarthritis and fracture samples, while the more differentiated CD11b-positive fractions and unsorted bulk cultures had little or no effect. Suppression was accompanied by a marked downregulation of CD3 expression on the T cell surface, a well-established indicator of impaired T cell receptor signaling.

Crucially, the degree of suppression did not differ between the two patient groups. Even though the osteoarthritic marrow was more myeloid-skewed and richer in intermediate metamyelocyte-like cells, the core immunoregulatory machinery of the immature MDSC fraction remained intact and functionally equivalent to that of the fracture donors. This extends the team’s earlier observation that MDSC suppressive function is preserved during aging, from comparisons between pediatric and elderly donors, into the specific context of chronic osteoarthritis-associated inflammation. Morphological analysis by May-Grünwald-Giemsa staining of sorted populations confirmed the phenotypic story: the suppressive CD11b-low fraction showed uniform promyelocyte-like morphology with prominent nucleoli, while the more mature fractions contained myelocytes, metamyelocytes, band cells, and even macrophage-like cells with cytoplasmic vacuolation.

The authors are careful to frame these findings as an association rather than proof of a disease-specific mechanism. The fracture cohort, they note, is not a healthy control group; femoral fracture triggers its own acute, time-limited inflammatory response, and no ethically defensible route exists for harvesting bone marrow from truly healthy elderly volunteers. Differences in age and sex distribution between the cohorts, along with the modest sample size, particularly for the correlation analyses, further limit statistical power. The study also did not assess whether the osteoarthritic MDSCs can differentiate into osteoclasts, a question of obvious importance given evidence from breast cancer and inflammatory arthritis models that MDSCs can drive pathological bone resorption while simultaneously suppressing T cells. Whether the same dual function operates in hip osteoarthritis remains an open question for future work.

Even with those caveats, the study reframes osteoarthritis as a systemic immunological condition rather than a purely local joint disease. If the bone marrow of osteoarthritis patients is chronically pumping out expanded myeloid populations, those cells could feed the synovial inflammation, cartilage degradation, and aberrant subchondral bone remodeling that characterize disease progression, while their preserved suppressive activity simultaneously holds immune activation in check. The authors suggest this balance between heightened myelopoiesis and conserved immunoregulation may define the distinctive low-grade, persistent inflammatory state of osteoarthritis, setting it apart from overt autoimmune arthritis. It also raises a therapeutic possibility worth taking seriously: modulating myeloid responses, rather than broadly suppressing the immune system, might one day offer a way to slow joint degeneration in the elderly without compromising host defense. For a disease affecting hundreds of millions of people worldwide and currently treatable only with pain management and, ultimately, joint replacement, that would be a genuinely transformative shift in perspective.

Subject of Research: Bone marrow myeloid cell remodeling and myeloid-derived suppressor cell function in elderly patients with hip osteoarthritis

Article Title: Bone marrow myeloid skewing and preserved immunoregulation in hip osteoarthritis of elderly patients

Article References: Tushe, A., Binatti, E., Belluzzi, E., Pozzuoli, A., Francescato, S., Buldini, B., Biz, C., Ruggieri, P., & Mandruzzato, S. (2026). Bone marrow myeloid skewing and preserved immunoregulation in hip osteoarthritis of elderly patients. GeroScience. https://doi.org/10.1007/s11357-026-02578-0

Image Credits: AI Generated

DOI: 10.1007/s11357-026-02578-0

Keywords: hip osteoarthritis, bone marrow, myeloid-derived suppressor cells, inflammaging, myelopoiesis, immunosenescence, T cell suppression, osteoimmunology, flow cytometry, granulopoiesis, chronic inflammation, GeroScience

Bone is not the static scaffold it appears to be on an X-ray. Throughout life, the skeleton undergoes continuous renewal through the coordinated activity of bone-forming osteoblasts, bone-resorbing osteoclasts, mechanosensing osteocytes, mesenchymal stem cells, immune cells and endothelial cells lining the vasculature. When this balance tips, the consequences are familiar and debilitating: osteoporosis, delayed fracture healing, and failed bone grafts. The Guangzhou team argues that ApoEVs sit at a previously underappreciated control point in this system, ferrying RNA molecules, proteins and lipids between the cell types that build and break down bone, and thereby shaping the communication networks that keep skeletal tissue in homeostasis.

Technically, ApoEVs are a heterogeneous category. The review distinguishes several subtypes based on size and biogenesis, including large apoptotic bodies, apoptotic microvesicles shed from the plasma membrane, apoptotic exosome-like vesicles, and smaller apoptotic small extracellular vesicles. What unites them is their origin in programmed cell death and their cargo: they encapsulate messenger RNAs, microRNAs, long noncoding RNAs and ribosomal RNAs, together with proteins and lipids that often reflect the identity of the parent cell. A vesicle released by a bone marrow mesenchymal stem cell carries a different molecular inventory than one shed by a mature osteoclast, and that identity matters for the message the vesicle delivers to its recipient.

Two signaling circuits dominate the review’s mechanistic analysis. The first is the RANKL/RANK/OPG axis, the central lever of osteoclast biology. RANKL, expressed on osteoblasts and osteocytes, binds RANK on osteoclast precursors and drives their differentiation into bone-resorbing giants, while osteoprotegerin acts as a decoy receptor that dampens the process. ApoEVs can modulate this axis from multiple directions, influencing the ratio of RANKL to OPG in the local microenvironment and thereby tuning how aggressively bone is broken down. The second circuit is the Wnt/β-catenin pathway, the master switch for osteoblast differentiation. When Wnt ligands engage their receptors, β-catenin accumulates and translocates to the nucleus, switching on genes such as RUNX2 and Osterix that commit stem cells to the bone-forming lineage. ApoEVs have been shown to carry Wnt pathway components and microRNAs that either amplify or suppress this cascade depending on their cargo.

The cargo story is where the biology becomes genuinely striking. In preclinical studies summarized by the review, apoptotic vesicles derived from mesenchymal stem cells delivered microRNAs that activated the AKT and ERK signaling cascades in recipient cells, promoting osteogenic differentiation marked by elevated alkaline phosphatase activity and expression of osteocalcin and bone sialoprotein. Vesicles from other sources carried insulin-like growth factor binding proteins, bone morphogenetic protein pathway components, or stanniocalcin 1, each steering recipient cells along distinct trajectories. Even the surface of the vesicle participates: the abundant phosphatidylserine on the outer leaflet of apoptotic membranes is recognized by receptors such as MerTK and TIM-4 on phagocytes, linking vesicle uptake to the same engulfment machinery that clears dying cells during normal tissue turnover.

Immune regulation emerges as a third pillar. Macrophage-derived apoptotic vesicles and T cell-derived vesicles can shift the inflammatory tone of the bone microenvironment, and the review highlights interactions with the STING pathway, a cytosolic DNA sensor that drives inflammatory signaling when activated. By modulating tumor necrosis factor alpha, interleukins and cyclooxygenase-2 signaling, ApoEVs appear to help resolve inflammation after injury, creating a permissive environment for regeneration. This osteoimmunological dimension matters clinically, because excessive inflammation is a hallmark of osteoporotic bone loss and a major obstacle to fracture healing and implant integration.

The translational implications are already being tested in animal models. In studies of critical-sized bone defects, scaffolds loaded with mesenchymal stem cell-derived ApoEVs accelerated regeneration, with the vesicles promoting both new bone formation and angiogenesis through vascular endothelial growth factor signaling. In ovariectomized rodents, the standard model of postmenopausal osteoporosis, ApoEV-based treatments improved bone microarchitecture and partially reversed the resorption-heavy imbalance. Vesicles derived from dental pulp stem cells and periodontal ligament stem cells have shown promise in periodontal and craniofacial repair, while platelet-derived and red blood cell-derived apoptotic vesicles have been explored for their regenerative and immunomodulatory properties. Mature osteoclast-derived vesicles, intriguingly, appear to feed back on osteoblasts, suggesting that even the bone-destroying cells contribute building materials to the renewal cycle.

What makes ApoEVs attractive as therapeutic vehicles is structural as much as chemical. Their lipid bilayer protects fragile RNA cargo from degradation by serum nucleases, their phosphatidylserine-rich surface promotes uptake by target cells, and their size allows them to penetrate the extracellular matrix of bone tissue. The review describes engineering strategies that exploit these properties: surface functionalization with the aspartic acid-serine-serine peptide to confer bone-targeting ability, incorporation into gelatin methacryloyl hydrogels or poly(lactic-co-glycolic acid) scaffolds for local, sustained delivery, and preconditioning of parent cells with agents such as strontium or 1,25-dihydroxyvitamin D3 to load vesicles with pro-osteogenic cargo before they are harvested.

Significant hurdles remain before ApoEVs reach the clinic. The review notes that standardization of isolation and characterization protocols is still immature, that the heterogeneity of vesicle subpopulations complicates dose definition, and that scalable production under good manufacturing practice conditions has yet to be demonstrated for skeletal applications. Questions about biodistribution, immunogenicity across donors, and the long-term fate of vesicle cargo in recipients also await rigorous answers. The authors frame these as the field’s next frontier rather than disqualifying obstacles, pointing out that the same challenges confronted and were largely resolved for the broader extracellular vesicle field now advancing through early clinical trials.

The conceptual shift, however, may prove as important as any therapy. For decades, apoptosis was taught as a one-way street ending in silent disposal. The Guangzhou review makes the case that the dying cell’s final act is communicative: it packages its regulatory contents into vesicles that instruct neighboring stem cells, immune cells and vascular cells on how to rebuild. In the skeleton, where the stakes include osteoporosis affecting hundreds of millions of people worldwide, that reframing turns cellular death from a passive endpoint into an active resource, and it positions apoptotic extracellular vesicles as candidates for a new generation of regenerative treatments built from the body’s own demolition byproducts.

Subject of Research: Roles of apoptotic extracellular vesicles in bone remodeling and regeneration

Article Title: Emerging roles of apoptotic extracellular vesicles in bone remodeling: mechanisms and applications

Article References: Wu, S., Chen, Z., Yuan, Q., Chen, H., Zhang, B., & Lin, T. (2026). Emerging roles of apoptotic extracellular vesicles in bone remodeling: mechanisms and applications. Journal of Translational Medicine. https://doi.org/10.1186/s12967-026-08921-5

Image Credits: AI Generated

DOI: 10.1186/s12967-026-08921-5

Keywords: apoptotic extracellular vesicles, bone remodeling, osteoporosis, bone regeneration, RANKL/RANK/OPG axis, Wnt/beta-catenin pathway, mesenchymal stem cells, osteoblasts, osteoclasts, osteoimmunology, extracellular vesicles, bone tissue engineering

The clinical problem is formidable. Bone defects caused by trauma, infection, tumour resection and congenital abnormalities are common, and while small injuries heal spontaneously, defects exceeding the local regenerative capacity, so-called critical-sized defects, often fail to close on their own. Autologous bone grafting remains the gold standard because it delivers osteogenic cells, inductive growth factors and a conductive matrix simultaneously, but it is limited by donor-site morbidity and restricted availability. Allografts are more available yet carry risks of immune rejection, infection and variable efficacy. What is needed, the review contends, are regenerative strategies that remain stable and reproducible inside the messy, inflamed microenvironment of a real defect.

Bioprinting offers an unusual degree of control over that environment. Unlike conventional fabrication, printing allows multiple materials, cells and bioactive signals to be arranged in three dimensions with defined pore architecture, compositional gradients and localised mechanical properties. Composite bioinks built from printable hydrogels such as gelatin methacryloyl (GelMA), alginate and hyaluronic acid methacrylate can be blended with inorganic phases including calcium phosphate, hydroxyapatite, beta-tricalcium phosphate and bioactive glass, balancing printability with an osteogenic milieu. Crucially, these same components release ions and present surface chemistry that shape the earliest host immune recognition of the implant, making the printer a tool for immunology as much as for structural engineering.

The biological rationale comes from the now well-established field of osteoimmunology. Bone repair unfolds in overlapping phases: an inflammatory phase dominated by neutrophils and pro-inflammatory M1-like macrophages that clear debris and pathogens; a proliferative phase in which macrophages shift toward reparative M2-like states, releasing factors such as TGF-beta and VEGF that recruit mesenchymal stem cells and drive angiogenesis; and a remodeling phase in which osteoblasts and osteoclasts, governed by the RANKL/OPG axis, convert woven bone into mechanically adapted lamellar bone. Simply suppressing the early inflammatory burst, the review stresses, can starve the repair process of the very signals that initiate cell recruitment and vascularisation. The goal instead is controlled, resolvable inflammation.

Material composition is one of the three main levers the authors identify. Strontium-substituted calcium silicate hydrate nanowires incorporated into a GelMA bioink, for example, released Sr, Ca and Si ions that nudged macrophages toward a repair-associated phenotype while supporting bone marrow stromal cell differentiation, producing substantial regeneration in rat critical-sized calvarial defects. Silicon-substituted calcium phosphate combined with methacrylated bone-derived extracellular matrix showed a striking temporal immune transition in vivo, from early pro-inflammatory activation to later anti-inflammatory resolution, linked to suppression of p38 MAPK signalling. Zinc-releasing ZIF-8 metal-organic framework particles delivered the anti-inflammatory polyphenol luteolin alongside Zn2+ ions, integrating immunomodulation, antioxidation and antibacterial action in a single printed construct.

Geometry itself can be immunologically active. Using digital light processing, researchers fabricated hydroxyapatite scaffolds identical in composition but differing only in pore size, and found that 600-micrometre pores best regulated macrophage behaviour through IFN-beta and HIF-1alpha-related signalling while improving vascularisation and bone formation. Even curvature matters: beta-tricalcium phosphate scaffolds engineered with negative Gaussian curvature suppressed macrophage Ras-MAPK/HIF-1alpha signalling and increased secretion of BMP-2 and VEGF, promoting vascularised bone ingrowth in a rabbit segmental defect model. Melt electrowriting adds another dimension, with ordered PCL microfibres and calcium phosphate coatings steering macrophages toward repair-associated states via PI3K/AKT and cAMP-PKA signalling, demonstrating that physical microarchitecture can substitute for exogenous drugs.

The most sophisticated strategies deliver bioactive cargo in stage-matched sequences. One printed system used coaxial bioprinting with sequential crosslinking to release interferon-gamma first, preserving the early inflammatory activation needed for repair initiation, before Laponite-derived magnesium and silicon ions gradually drove macrophages toward a reparative state, ultimately enhancing vascularised bone regeneration in calvarial defects. Interleukin-4 delivered from graphene oxide/black phosphorus nanointerfaces promoted CD206-positive macrophages while the materials themselves supported angiogenesis and osteogenesis. Exosome-based approaches add further nuance: macrophage-derived vesicles from mixed functional states outperformed those from purely M2-like macrophages in stimulating osteogenic signalling, underscoring the review’s warning that the simplified M1/M2 dichotomy cannot capture the continuum of immune states that real healing involves.

The authors are candid about translational hurdles. Every added component, whether living cells, recombinant cytokines, exosomes or decellularised matrix, increases batch variability, manufacturing complexity and regulatory burden. Sterilisation methods can silently alter hydrogel mechanics and even macrophage gene expression, while endotoxin contamination at low levels can confound the interpretation of a material’s intrinsic immunological effects. Degradation kinetics must be synchronised with tissue ingrowth: too fast and the scaffold loses support prematurely, too slow and the foreign-body response persists. The review advocates defining critical quality attributes that reflect immunomodulatory potency, not just scaffold geometry and compressive strength, and pursuing standardised platforms with patient-specific variation confined to a validated design space.

Looking forward, the field is moving toward spatiotemporal and even intelligent regulation. Microenvironment-responsive hydrogels that release therapeutic ions only under pathological acidity or oxidative stress, four-dimensional printing that changes scaffold architecture over time, and machine-learning frameworks that optimise bioink composition against immune as well as mechanical endpoints all feature in the review’s roadmap. Pathology-specific design receives particular emphasis: infected defects need preserved antimicrobial inflammation before resolution, diabetic defects require correction of hyperglycaemia-driven oxidative stress, and aged or osteoporotic bone demands restoration of senescence-impaired immune function rather than generic osteogenic stimulation. The overarching message is that the next generation of bone scaffolds should not simply contain more ingredients, but should speak the immune system’s own temporal language, guiding inflammation, vascularisation and remodeling in the order that nature intended.

Subject of Research: Immunoregulatory biomaterials and 3D bioprinting strategies for bone regeneration

Article Title: Advances in 3D bioprinting of immunoregulatory biomaterials for bone regeneration

Article References: Wang, X., & Zhang, A. (2026). Advances in 3D bioprinting of immunoregulatory biomaterials for bone regeneration. Materials Today Bio, 41, Article 103714. https://doi.org/10.1016/j.mtbio.2026.103714

Image Credits: AI Generated

DOI: 10.1016/j.mtbio.2026.103714

Keywords: 3D bioprinting, bone regeneration, osteoimmunology, macrophage polarization, bioinks, GelMA, biomaterials, critical-sized bone defects, exosomes, cytokine delivery, scaffold architecture, tissue engineering