Objective: To analyze the characteristics of latent classes of dietary patterns among children and adolescents in Qinghai Province, and their association with overweight and obesity, so as to provide a scientific basis for conducting targeted nutritional interventions and weight management for the local population. Methods: From May to October 2025, a multi stage stratified cluster random sampling method was employed to recruit 1 611 children and adolescents aged 6-17 years from Chengdong District of Xining City and Gonghe County of Hainan Tibetan Autonomous Prefecture in Qinghai Province. Questionnaire survey was conducted using a questionnaire developed by the Chinese Center for Disease Control and Prevention, and physical examination was conducted by using unified measurement standards. Latent class analysis (LCA) was performed on the food intake frequency of the participants. The χ 2 test and Logistic regression analysis were applied to explore the relationship between dietary patterns and overweight/obesity. Results: The detection rates of overweight, obesity, and overall overweight/obesity among the participants were 10.4%, 5.8%, and 16.2%, respectively. Latent class analysis identified three dietary patterns: modern mixed pattern ( n =399, 24.8%), low diversity pattern ( n =476, 29.5%), and traditional dietary pattern ( n =736, 45.7%). The potential category distribution differences of three dietary patterns among children and adolescents with and without overweight or obesity were statistically significant (non overweight and obesity: 22.5%, 29.1%, 48.4%; overweight and obesity: 36.4%, 31.8%, 31.8%) ( χ 2=30.69, P <0.01). Logistic regression showed that, compared with the traditional dietary pattern, the modern mixed pattern was associated with a higher risk of overweight and obesity ( OR =1.68, 95% CI =1.13-2.49); female sex was associated with a lower risk of overweight/obesity compared with male sex ( OR =0.66, 95% CI =0.50-0.86) (both P <0.05). Conclusions A positive association exists between the modern mixed dietary pattern and obesity in children and adolescents. It is recommended to reduce the intake of grains and unhealthy foods among overweight and obese children and adolescents, while increasing the consumption of legumes, fish, and shrimp, in order to cultivate healthy and rational dietary habits.

Multidrug-resistant (MDR) bacterial infections have emerged as a serious challenge of global public health crisis. The overuse and misuse of conventional antibiotics have dramatically accelerated the emergence, evolution and worldwide spread of drug-resistant bacterial strains, necessitating urgent exploration of novel antibacterial strategies. Bacteriophages serve as natural bacterial predators offering distinct advantages including high host specificity, autonomous self-replication capabilities and cost-effective large-scale production. However, wild-type phages present significant clinical limitations due to their narrow host ranges, susceptibility to rapid immune clearance and poor penetration of bacterial biofilms, which severely restrict their therapeutic applications. The convergence of synthetic biology, nanotechnology and advanced gene editing technologies has accelerated the development of engineered bacteriophage platforms, providing programmable, scalable and clinically translatable pathways to overcome these inherent biological constraints. Here, we systematically delineate four fundamental strategies for engineered bacteriophage development. Chemical modification utilizes reactive functional groups such as amino, carboxyl and thiol moieties on capsid proteins through esterification, amidation or click chemistry reactions to achieve precise drug conjugation and surface functionalization. In vivo editing encompasses ultraviolet or chemical mutagenesis for random mutation induction, homologous recombination for targeted genetic alterations, recombineering methodologies including electroporation-mediated bacteriophage recombination engineering, and CRISPR-Cas systems for precise genome editing to enable exact genetic reconstruction and host range reprogramming. In vitro synthesis leverages genome engineering platforms where intact phage genomes are transferred into yeast or host bacteria to facilitate highly efficient homologous recombination, enabling large DNA fragment assembly and cross-gene host range expansion without bacterial toxicity constraints. Directed evolution combines artificial selection through mutation library screening with rational design approaches involving chimeric receptor binding protein construction or site-specific mutagenesis, effectively balancing the discovery of unknown adaptive pathways with targeted host specificity modification. Moreover, we comprehensively discuss therapeutic applications across diverse clinical scenarios. Engineered bacteriophage effectively disrupt bacterial biofilms through sophisticated functionalized delivery platforms including nanozyme-conjugated phages, phage-liposome nanoconjugates and bio-responsive hydrogels, demonstrating significantly enhanced bactericidal efficiency compared to unmodified free phages. These bioengineered vectors attenuate bacterial virulence and resensitize pathogens to antibiotics by delivering CRISPR-Cas systems or base editors to disrupt critical virulence factors such as pili, capsule synthesis machineries and quorum sensing systems, or by inactivating antibiotic resistance determinants including beta-lactamase genes. As an intelligent nanomedicine delivery platform, engineered bacteriophage enable precise pathogen elimination an through photocatalytic reactive oxygen species generation, immunomodulatory interventions, or controlled release of antibacterial drugs. Furthermore, oral administration of engineered bacteriophage facilitates microbiota modulation, which selectively eliminate intestinal pathogens while preserve beneficial commensal microbiota, thereby restoring microbial community balance and preventing complications associated with dysbiosis. Finally, we critically analyze persistent challenges including host strain matching complexity, evolution of bacterial resistance mechanisms, pharmacokinetic optimization requirements, optimal administration route selection, large-scale production quality control standards and clinical dosing determination protocols. Through multidisciplinary integration of synthetic biology, infectious disease medicine and immunology, future translational medicine studies of bacteriophage should establish comprehensive technical platforms encompassing rapid phage screening, intelligent rational design, rigorous in vivo evaluation and standardized clinical validation processes, ultimately advancing engineered bacteriophage from laboratory innovations to clinically approved therapeutics for effectively combating MDR bacterial infections.

ObjectiveStroke poses a heavy burden due to its high mortality and morbidity rates. Accurate and real-time detection of lesions is pivotal for prompt clinical intervention and favorable prognosis. Electrical impedance tomography (EIT) and microwave tomography (MWT) have emerged as compelling alternatives for stroke screening, owing to their non-ionizing, non-invasive and portable nature. EIT provides information on tissue conductivity, and MWT offers high sensitivity to changes in dielectric properties. However, single-modality imaging is inherently limited, EIT suffers from low sensitivity to deep-seated tissues and severe ill-posedness of inverse problems, whereas MWT is challenged by strong nonlinearity in inverse scattering and susceptibility to modeling errors. Consequently, the clinical utility of standalone EIT or MWT for stroke diagnosis remains constrained by poor spatial resolution and imaging artifacts. To improve the accuracy and robustness of stroke imaging, a dual-modality fusion conditional denoising diffusion probabilistic model (DM-DDPM) was proposed for high-precision dual-modality image reconstruction. MethodsA dual-encoder network with a symmetric architecture and independently trained parameters was constructed to extract heterogeneous features separately from EIT boundary voltage measurements and MWT scattered field signals. Attentional feature fusion (AFF) is employed to integrate complementary information from the two modalities adaptively, generating robust fused priors that suppress redundant noise while preserving key physical characteristics. Subsequently, the fused priors are embedded into a Transformer-based diffusion model via a cross attention mechanism to guide the reverse denoising process. This approach effectively reduces artifacts and enhances the stability of conductivity distribution reconstruction. Time step embedding is introduced to enable the network to perceive the diffusion stage and further improve the accuracy of noise prediction. ResultsSimulated experiments demonstrated that DM-DDPM significantly outperforms single-modality and multi-modality networks under various noise levels. A head model simulation dataset was constructed based on COMSOL Multiphysics, and tests were carried out under 50 dB, 40 dB and 30 dB signal-to-noise ratio levels. At 30 dB, the average relative error (RE) was below 0.20, while the structural similarity index measure (SSIM) and correlation coefficient (CC) remained above 0.90 and 0.89, respectively. Compared with single-modality and multi-modality networks, artifacts were significantly reduced, lesion edges were clearer, and localization was more accurate. The model maintains high reconstruction quality and strong robustness for single, double, and triple lesions simultaneously. Furthermore, physical experiments were conducted using a 16-electrode EIT system and a 16-antenna MWT system with asynchronous data acquisition. These experiments confirmed the feasibility of the method in real-world scenarios and demonstrated that it can robustly reconstruct simulated lesions despite environmental interference and measurement noise, validating its reliability for practical clinical applications. ConclusionThe proposed method effectively combines complementary dual-modality information with a conditional diffusion model. Low accuracy and poor noise resistance in single-modality imaging were effectively addressed, while the noise amplification issue caused by direct multimodal data fusion was avoided. The proposed algorithm exhibits strong anti-noise interference ability and high imaging stability in both simulation and physical experiments. Precise localization of stroke lesions with different quantities was achieved, providing a high-precision, and practical technical support for clinical stroke detection.

ObjectiveTranscranial magneto-acoustic stimulation (TMAS) is an emerging non-invasive neuromodulation technique that may provide a novel non-pharmacological intervention strategy for Parkinson's disease (PD). PD is characterized by the progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNc), leading to motor impairments such as bradykinesia, tremor, and rigidity. Increasing evidence indicates that mitochondrial dysfunction and impaired mitochondrial quality control are central mechanisms underlying dopaminergic neuronal loss. In particular, abnormalities in mitophagy and mitochondrial fission-fusion balance contribute substantially to oxidative stress, energy metabolic failure, and neuronal injury. At present, most clinical treatments for PD mainly alleviate symptoms but do not effectively halt disease progression. Therefore, exploring new interventions targeting the core pathological mechanisms is of considerable significance. This study aims to investigate whether TMAS can improve neural damage and motor dysfunction in PD mice by regulating mitophagy and the fission/fusion dynamic balance, thereby providing theoretical and experimental support for its application in PD treatment. MethodsMale C57BL/6 mice were used in this study. A PD model was established by intraperitoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) for 7 consecutive days. After model induction, mice in the intervention group received TMAS once daily for 14 consecutive days, whereas the corresponding control group received sham stimulation. The stimulation target was positioned over the primary motor cortex (M1). Motor performance was evaluated using the pole test and the open-field test. To verify the activation effect of TMAS on the target cortical region, c-Fos immunohistochemistry was performed in the M1. To assess nigral dopaminergic neuronal injury, tyrosine hydroxylase (TH) immunohistochemistry was used to quantify TH-positive neurons in the SNc. Mitochondrial function was evaluated by measuring reactive oxygen species (ROS) levels and adenosine triphosphate (ATP) content in the SNc. Western blot was further performed to determine the expression of mitophagy-related proteins, including PINK1, Parkin, LC3-II, and p62, as well as mitochondrial dynamics-related proteins, including Drp1 and Opa1. ResultsTMAS significantly increased the number of c-Fos-positive cells in M1 (P<0.000 1), indicating effective activation of neurons in the targeted cortical region. Compared with the control group, MPTP-treated mice exhibited marked motor dysfunction, including a significant reduction in total distance traveled in the open-field test (P<0.000 1) and mean speed (P=0.000 1), as well as significant prolongation of turn time and total climbing time in the pole test (P<0.000 1). These behavioral impairments were accompanied by a substantial loss of TH-positive dopaminergic neurons in the SNc, whereas TMAS significantly increased TH-positive neuron survival (P<0.000 1). In parallel, MPTP induced a pronounced increase in ROS levels and a significant reduction in ATP content, indicating severe mitochondrial dysfunction and energy metabolism impairment (P<0.01). TMAS treatment significantly improved motor performance, as reflected by the reversal of MPTP-induced impairment in the open-field and pole tests, and significantly reduced ROS accumulation (P<0.01) while restoring ATP production (P<0.001). At the molecular level, MPTP markedly downregulated PINK1 and Parkin, decreased p62 expression, increased LC3-II accumulation, elevated Drp1 expression, and reduced Opa1 expression, whereas TMAS significantly reversed these abnormalities, suggesting restoration of mitophagy-related mitochondrial quality control and re-establishment of mitochondrial fission-fusion balance. Collectively, these findings indicate that TMAS ameliorates MPTP-induced neurotoxicity and restores mitochondrial homeostasis and energy metabolism. ConclusionTMAS effectively attenuates neural damage and improves motor dysfunction in MPTP-induced PD mice. Its neuroprotective effects are closely associated with multidimensional regulation of the mitochondrial quality control system, including restoration of PINK1/Parkin-mediated mitophagy and rebalancing of Drp1/Opa1-related mitochondrial dynamics. Rather than acting only as a symptomatic neuromodulatory intervention, TMAS may influence a key pathological axis of PD by improving mitochondrial homeostasis in SNc and protecting nigral dopaminergic neurons. These findings provide experimental evidence supporting TMAS as a promising non-invasive physical intervention for PD.

OBJECTIVE To establish a method for simultaneous determination of plasma concentration of lamotrigine（LTG）， levetiracetam（LEV） and perampanel（PER） in children with epilepsy and apply this method in clinical practice. METHODS Plasma proteins were precipitated with acetonitrile. Using PER-D 5 as internal standard， ultra-high performance liquid chromatography-tandem mass spectrometry （UPLC-MS/MS） method was adopted. The determination was performed on ACQUITY UPLC HSS T3 C 18 column with mobile phase consisted of 0.1% formic acid with 5 mmol/L ammonium acetate-acetonitrile （gradient elution） at the flow rate of 0.3 mL/min. The column temperature was 40 ℃， and sample size was 5 μL. The analysis time was 5 min. The electrospray ionization source and multiple reaction monitoring mode were used for positive ion scanning. The ion pairs used for quantitative analysis of LTG， LEV， PER and internal standard were m / z 255.9→144.9， m / z 171.1→126.1， m / z 350.1→219.0 and m / z 354.9→220.2， respectively. The steady-state trough concentrations of the aforementioned drugs in the plasma of 14 pediatric epilepsy patients receiving combination therapy were determined using the same UPLC-MS/MS method as above. RESULTS The linear ranges of LTG， LEV and PER were 0.15-24 μg/mL （ R 2 ＞0.993）， 0.312 5-50 μg/mL （ R 2 ＞0.997） and 6.25-1 000 ng/mL （ R 2 ＞0.997）， respectively. The lower limits of quantification were 0.15 μg/mL， 0.312 5 μg/mL and 6.25 ng/mL， respectively. RSDs of intraday and interday precision tests of the three drugs were no more than 9.83%， and the accuracies （relative errors） were between －9.33% and 13.72%（ n ＝6 or n ＝18）； the average extraction recovery rates were 86.4%-97.9%， and the average matrix effects were 86.9%-110.0% （ n ＝6）. The absolute values of the relative errors in the stability tests were all below 15%. The steady-state trough concentrations of LTG， LEV and PER were （5.64±4.03）μg/mL， （10.67±8.78）μg/mL and（450.20±251.27）ng/mL， respectively； the rates of achieving target trough concentrations were 71.4%， 37.5% and 84.6%， respectively. CONCLUSIONS The established UPLC-MS/MS method is specific， rapid and suitable for the plasma concentration monitoring in epileptic children receiving combination therapy.

ObjectiveTo investigate the effects of metformin on the immune functions of immature dendritic cells （imDCs） and the underlying mechanisms. MethodsMouse bone marrow-derived imDCs were treated with different concentrations of metformin. The working concentration and treatment time of metformin in this study were determined based on the results of cell apoptosis and cell viability assays. The effects of metformin on the phagocytic capacity of imDCs was evaluated using an antigen endocytosis assay. The expression of cluster of differentiation 205 （CD205）， the polymerization of filamentous actin （F-actin）， and the underlying regulatory mechanisms were investigated through flow cytometry， laser confocal fluorescence microscopy， and Western blot. ResultsThe working concentrations of metformin were 1， 2， 4 mmol/L for 24 h determined by the apoptosis and cell viability assays.Metformin significantly suppressed the phagocytic capacity of imDCs， down-regulated the expression of the mannose receptor CD205 on the cell surface， which was closely associated with phagocytic function； metformin inhibited the RhoA-ROCK1-LIMK1-Cofilin signaling pathway， which inhibited the polymerization of F-actin and disturbed its dynamic remodeling of imDCs. ConclusionMetformin can inhibit the expression of CD205 and disrupt the remodeling of F-actin， thereby suppressing the antigen-capturing capacity of imDCs.

ObjectiveTo analyze the risk factors for long-term cardiovascular events in patients undergoing long-term peritoneal dialysis （PD）， and to construct and validate a visual nomogram prediction model based on multiple parameters. MethodsA prospective cohort study was conducted， consecutively enrolling 248 maintenance PD patients （dialysis duration ≥ 3 months）. Demographic characteristics， clinical indicators， laboratory parameters， and echocardiographic indices （including left ventricular ejection fraction ［LVEF］， ratio of early diastolic mitral inflow velocity to early diastolic mitral annular velocity （E/e’）， etc.） were collected. The composite endpoint was defined as the occurrence of cardiovascular events or cardiovascular death， with non-cardiovascular death as the competing risk and loss to follow-up or the end of follow-up as censoring events. Fine-Gray competing risks model was used to screen independent predictors， based on which a nomogram model was constructed. Internal validation was performed using the Bootstrap method （1 000 resamplings）， and the concordance index （C-index） and time-dependent receiver operating characteristic （time-dependent ROC） curve were calculated to evaluate the model performance. ResultsWith a median follow-up of 29 months （interquartile range： 24–35 months）， 88 patients （35.48%） reached the composite endpoint， including 80 cases of cardiovascular events and 8 cases of cardiovascular death， and 4 patients died of non-cardiovascular causes. Multivariate Fine-Gray analysis revealed that age， diabetes mellitus， hemoglobin （HGB） level and E/e' ratio were independent influencing factors of the composite endpoint. Specifically， each 1-year increase in age was associated with a 3.0% increase in the risk of the composite endpoint （HR=1.030， P=0.006）； patients with diabetes mellitus had a 167.9% higher risk compared with non-diabetic patients （HR=2.679， P=0.007）； each 1g/L increase in HGB level contributed to a 1.5% reduction in the risk （HR=0.985， P=0.003）； and each 0.1 increase in E/e' ratio led to a 7.2% increase in the risk （HR=1.072， P=0.045）. The nomogram model had a C-index of 0.76 （95% CI： 0.698–0.820）， and the AUC of the time-dependent ROC curve reached 0.849 at 23 months of follow-up. ConclusionIncreased age， complicated with diabetes mellitus， decreased HGB， and elevated E/e' ratio are independent risk factors of long-term occurrence of cardiovascular events and cardiovascular death in patients undergoing long-term PD. The nomogram model constructed based on the above variables has good predictive value and clinical applicability， which can provide a reference for cardiovascular risk stratification and individualized intervention in long-term PD patients.

Objective To investigate the prevalence, distribution characteristics, and influencing factors of mental health problems among the elderly, and to provide a scientific basis for policy-making.  Methods A convenience sampling method was used to investigate depression, anxiety, and cognitive function among permanent residents aged 65 and older at 59 mental health care sites for the elderly in Hubei Province. Multinomial logistic regression was employed to analyze influencing factors. Results The screening rates for depression, anxiety, and cognitive function at critical/high-risk levels among the elderly in Hubei Province were 9.7%, 5.4%, and 12.2%, respectively. Urban elderly had lower risks of depression and cognitive function at critical/high-risk levels compared to rural elderly (OR for critical depression = 0.640, P < 0.001; OR for high-risk depression = 0.595, P = 0.012; OR for critical cognitive function = 0.448, P < 0.001; OR for high-risk cognitive function = 0.188, P < 0.001). Six key population groups had higher risks of depression, anxiety, and cognitive function at critical/high-risk levels than others (OR for critical depression = 1.463, P < 0.001; OR for high-risk depression = 1.912, P < 0.001; OR for critical anxiety = 1.462, P < 0.001; OR for high-risk anxiety = 2.882, P < 0.001; OR for critical cognitive function = 1.381, P < 0.001; OR for high-risk cognitive function = 2.345, P < 0.001). A higher number of chronic diseases was associated with increased risks of critical and high-risk depression (OR for critical = 1.316, P < 0.001; OR for high-risk = 3.677, P < 0.001) and cognitive impairment (OR for critical depression = 1.316, P < 0.001; OR for high-risk depression = 3.677, P < 0.001; OR for critical anxiety = 1.512, P < 0.001; OR for high-risk anxiety = 1.801, P < 0.001). Conclusion It is recommended to expand mental health care sites in rural areas, improve the layout of mutual-support elderly care facilities, and explore sustainable models for rural elderly care. Efforts should also focus on enhancing social participation among the elderly through community-based activities, and strengthening cognitive screening and emotional regulation interventions, with particular attention to the mental health needs of older, isolated, and chronically ill individuals.

ObjectiveA mouse model of vaccinia virus Tiantan strain (VTT)-induced encephalopathy was developed using AG6 mice. MethodsVTT was amplified by infecting Vero cells at a multiplicity of infection (MOI) of 0.01, followed by concentration and titration. After 72 h of incubation, virus-containing cells were collected and subjected to concentration. The concentrated viral suspension was serially diluted (10-fold dilutions) and added to 6-well plates containing confluent Vero cell monolayers for plaque assay. The number of plaques formed in each well was counted, and the virus titer was calculated based on the dilution factor. Fourteen 5-6-week-old AG6 mice (half male and half female, housed separately by sex) were randomly divided into a control group (n=3, PBS), a low-dose group (n=6, 1×10⁵ PFU), and a high-dose group (n=5, 5×10⁵ PFU). The mice were anesthetized by isoflurane inhalation and then infected via intranasal instillation. The mental state of the mice in each group was observed daily, and the body weight and mortality were recorded. On day 13 post-infection, 2% Evans Blue (4 mL/kg body weight) was administered via tail vein injection to assess blood-brain barrier (BBB) disruption. Subsequently, brain tissue samples were collected for immunofluorescence analysis to evaluate the activation of astrocytes and microglia. ResultsThe titer of purified VTT was 1×10⁷ PFU/mL. Compared with the control group, mice in the low-dose group showed no significant change in body weight, and no lethality was observed. In contrast, mice in the high-dose group exhibited significant weight loss starting on day 5 post-infection (P<0.05), accompanied by lethality. On day 13 post-infection, no Evans Blue extravasation was detected in the brain tissues of the low-dose group, while the olfactory bulb region of the high-dose group displayed distinct blue staining, indicating disruption of the BBB. Immunofluorescence analysis revealed no significant proliferation of astrocytes and microglia in the olfactory bulb region of the low-dose group on day 13 post-infection. In contrast, marked activation of glial cells was observable in the high-dose group. ConclusionAn animal model of VTT-induced encephalopathy in AG6 mice is successfully established, characterized by BBB disruption and reactive gliosis specifically localized to the olfactory bulb region, manifested as astrocytic and microglial proliferation.

Background Carbendazim (CBZ), a widely used benzimidazole fungicide, has raised increasing concerns regarding the health risks associated with its residues. However, the toxic effects and associated mechanisms of CBZ on the skeletal system have not been reported. Objective To elucidate the effects of carbendazim on osteogenic differentiation and its underlying mechanisms. Methods MC3T3-E1 mouse pre-osteoblastic cells were treated with 1, 10, and 100 μmol·L⁻¹ CBZ for 24 h to examine cell viability, alkaline phosphatase (ALP) activity, bone nodule formation, reactive oxygen species (ROS) level, malondialdehyde (MDA) content, and nitric oxide synthase (NOS) activity. Transcriptomics was used to identify differentially expressed genes (DEGs) in osteoblasts exposed to CBZ. Kyoto Encyclopedia of Genes and Genomes (KEGG) and gene set enrichment analysis (GSEA) were employed to analyze the potential biological pathways of DEGs. Real-time polymerase chain reaction (RT-PCR) and Western blot were used to validate changes in gene and protein expression. Results Exposure to 10 and 100 μmol·L⁻¹ CBZ significantly reduced osteoblast viability, ALP activity, bone nodule formation, and NOS activity, while increasing intracellular ROS levels. CBZ at 100 μmol·L⁻¹ concentration significantly elevated MDA level (P < 0.05). The transcriptomic analysis revealed that 1 μmol·L⁻¹ CBZ treatment resulted in 385 significantly DEGs. The KEGG enrichment analysis revealed that CBZ significantly affects hormone regulation pathways (including parathyroid hormone, growth hormone, dopamine, and oxytocin), mitogen-activated protein kinase (MAPK) and cyclic GMP-dependent protein kinase G (cGMP-PKG) signaling pathways, focal adhesion and adherens junction, as well as the NOD-like receptor signaling pathway and the mRNA surveillance (NMD) pathway. The results of GSEA showed that CBZ significantly inhibited the bile acid metabolism and the Wnt/β-catenin pathway in osteoblasts. The validation results demonstrated that CBZ significantly suppressed the mRNA expression of Wnt3a and β-catenin, as well as the protein expression of Runx2 and Osterix in the Wnt/β-catenin pathway. Conclusion CBZ exposure exhibits potential skeletal toxicity, and its mechanism is through promoting oxidative stress, interfering with the Wnt/β-catenin pathway in osteogenic differentiation, thereby inhibiting the bone formation function of osteoblasts.