Tuning Pore Size in Graphene in the Angstrom Regime for Highly Selective Ion-Ion Separation.

Zero-dimensional pores spanning only a few angstroms in size in two-dimensional materials such as graphene are some of the most promising systems for designing ion-ion selective membranes. However, the key challenge in the field is that so far a crack-free macroscopic graphene membrane for ion-ion separation has not been realized. Further, methods to tune the pores in the Å-regime to achieve a large ion-ion selectivity from the graphene pore have not been realized. Herein, we report an Å-scale pore size tuning tool for single layer graphene, which incorporates a high density of ion-ion selective pores between 3.5 and 8.5 Å while minimizing the nonselective pores above 10 Å. These pores impose a strong confinement for ions, which results in extremely high selectivity from centimeter-scale porous graphene between monovalent and bivalent ions and near complete blockage of ions with the hydration diameter, DH, greater than 9.0 Å. The ion diffusion study reveals the presence of an energy barrier corresponding to partial dehydration of ions with the barrier increasing with DH. We observe a reversal of K+/Li+ selectivity at elevated temperature and attribute this to the relative size of the dehydrated ions. These results underscore the promise of porous two-dimensional materials for solute-solute separation when Å-scale pores can be incorporated in a precise manner.

[Correlation Analysis of the Number of Hemophagocytes and Peripheral Blood Cells in Bone Marrow].

OBJECTIVE: To study the correlation between the number of hemophagocytes and peripheral blood cells in bone marrow of patients with fever of unknown origin. METHODS: A total of 465 patients with fever of unknown origin in our hospital from January 2019 to December 2021 were selected as the research objects, which was to reviewed retrospectively the correlation between the number of hemophagocytes and peripheral blood cells in bone marrow. RESULTS: The positive rates of hemophagocytes detected in the three lines decreased group, the two lines decreased group, the one line decreased group, normal group of the three lines and at least one of the three lines increased group were 86.4%, 62.1%, 38.3%, 34.6% and 33.3%, respectively. The number of hemophagocytes per unit area in the three lines decreased group was significantly higher than that in the other four groups ( P < 0.001). The number of hemophagocytes per unit area in the two lines decreased group was higher than that in the one line decreased group, normal group of three lines and at least one of the three lines increased group ( P < 0.01). There was no significant difference in the number of hemophagocytes per unit area between the group with a decreased number of one line and the other two groups with a normal number of three lines and the group with at least one increased number of three lines (P >0.05). The missed rates of hemophagocytes in the five groups were 15.78%, 22.03%, 62.22%, 77.78% and 53.84%, respectively. CONCLUSION: For patients with fever of unknown origin, especially those with obvious decrease in the number of three lines and two lines in peripheral blood cells, which should pay attention to the detection of hemophagocytes in bone marrow. Meanwhile, if the number of three lines was normal even at least one of the three lines increased, the presence of hemophagocytes in the bone marrow slice should be also carefully observed.

Enhancing cross-Kerr coupling via mechanical parametric amplification.

We present a proposal to enhance the cross-Kerr coupling between the cavity and the mechanical oscillator significantly. Specifically, the periodic modulation of the mechanical spring constant induces strong mechanical parametric amplification, which leads to the cross-Kerr nonlinear enhancement. Also, we discuss its application in photon-phonon blockade and phonon-number measurement. We find that under the strong cross-Kerr coupling condition, not only the photon-phonon blockade effect is dramatically enhanced but also different phonon number is clearly distinguished. Our results offer an alternative approach to perform quantum manipulation between photon and phonon.

Parthenolide ameliorates colon inflammation through regulating Treg/Th17 balance in a gut microbiota-dependent manner.

Inflammatory bowel disease (IBD) is a global health problem in which gut microbiota dysbiosis plays an important pathogenic role. However, the current drugs for IBD treatment are far from optimal. Previous researches indicated that parthenolide (PTL) had not only anti-cancer properties but also strong anti-inflammatory activities. Rationale: To investigate the protective effect of PTL on colon inflammation and demonstrate the underlying gut microbiota-dependent mechanism. Methods: Colon inflammation severity in mouse model was measured by body weight change, mortality, colon length, disease activity index (DAI) score, H&E staining and colonoscopy evaluation. Gut microbiota alteration and short-chain fatty acids (SCFAs) production were analyzed through 16S rRNA sequencing and targeted metabolomics. Luminex cytokine microarray and Enzyme-linked immunosorbent assay (ELISA) were conducted to measure the colon cytokines profile. The frequency of immune cells in lamina propria (LP) and spleen were phenotyped by flow cytometry. Results: The PTL-treated mice showed significantly relieved colon inflammation, as evidenced by a reduction in body weight loss, survival rate, shortening of colon length, DAI score, histology score and colonoscopy score. Notably, when the gut microbiota was depleted using antibiotic cocktails, the protective effect of PTL on colon inflammation disappeared. PTL treatment downregulated the level of proinflammatory cytokines, including IL-1ß, TNF-α, IL-6, and IL-17A and upregulated the immunosuppressive cytokine IL-10 in colon tissue. 16S rRNA sequencing indicated that PTL-treated mice exhibited much more abundant gut microbial diversity and flora composition. Targeted metabolomics analysis manifested the increased SCFAs production in PTL-treated mice. Additionally, PTL administration selectively upregulated the frequency of colonic regulatory T (Treg) cells as well as downregulated the ratio of colonic T helper type 17 (Th17) cells, improving the Treg/Th17 balance to maintain intestinal homeostasis. Gut microbiota depletion and fecal microbiota transplantation (FMT) was performed to confirm this gut microbiota-dependent mechanism. Conclusions: PTL ameliorated colon inflammation in a gut microbiota-dependent manner. The underlying protective mechanism was associated with the improved Treg/Th17 balance in intestinal mucosa mediated through the increased microbiota-derived SCFAs production. Collectively, our results demonstrated the role of PTL as a potential gut microbiota modulator to prevent and treat IBD.

Long intergenic non­protein coding RNA 00460 predicts a poor prognosis and promotes tumorigenesis of human osteosarcoma.

Osteosarcoma (OS) is the most common type of primary malignant bone tumor, which has a high incidence rate in children and adolescents. This research aims to reveal the role of long intergenic non­protein coding RNA 00460 (LINC00460) in OS by the loss­of­function experiment. LINC00460 is involved in the development of multiple types of tumor, but the role of LINC00460 in OS is unclear. To discover more effective molecular targets for the treatment of OS, the association between LINC00460 and OS prognosis was analyzed using the Gene Expression Profiling Interactive Analysis database. Additionally, small interfering RNA was used to knockdown LINC00460 gene expression in vitro to verify its biological effects on the viability, invasive and migratory potential of OS cells. LINC00460 knockdown significantly reduced the viability of OS cells and initiated cell cycle arrest within the G0/G1 phase through the decreased expression of cyclin D1 and CDK4/CDK6. In addition, LINC00460 knockdown promoted apoptosis of OS cells, and inhibited the migratory and invasive abilities of OS cells through the inhibition of the epithelial­mesenchymal transition pathway. In conclusion, the present study reported that LINC00460 may predict OS prognosis, and may serve an important role in mediating the viability, invasive and migratory potential of OS cells. Based on these findings, LINC00460 demonstrated promising potential as a future therapeutic target for OS treatment.

Generation of H11-albumin-rtTA Transgenic Mice: A Tool for Inducible Gene Expression in the Liver.

The modification of the mouse genome by site-specific gene insertion of transgenes and other genetic elements allows the study of gene function in different developmental stages and in the pathogenesis of diseases. Here, we generated a "genomic safe harbor" Hipp11 (H11) locus-specific knock-in transgenic mouse line in which the albumin promoter is used to drive the expression of the reverse tetracycline transactivator (rtTA) in the liver. The newly generated H11-albumin-rtTA transgenic mice were bred with tetracycline-operator-Histone-2B-green fluorescent protein (TetO-H2BGFP) mice to assess inducibility and tissue-specificity. Expression of the H2BGFP fusion protein was observed exclusively upon doxycycline (Dox) induction in the liver of H11-albumin-rtTA/TetO-H2BGFP double transgenic mice. To further analyze the ability of the Dox-inducible H11-albumin-rtTA mice to implement conditional DNA recombination, H11-albumin-rtTA transgenic mice were crossed with TetO-Cre and Ai14 mice to generate H11-albumin-rtTA/TetO-Cre/Ai14 triple transgenic mice. We successfully confirmed that the Cre-mediated recombination efficiency was as strong in Dox-induced H11-albumin-rtTA /TetO-Cre/Ai14 mice as in the control albumin-Cre/A14 mice. Finally, to characterize the expression-inducing effects of Dox in H11-albumin-rtTA/TetO-H2BGFP mice in detail, we examined GFP expression in embryos at different developmental stages and found that newly conceived H11-albumin-rtTA/TetO-H2BGFP embryos of Dox-treated pregnant female mice were expressing reporter GFP by E16.5. Our study demonstrates that these new H11-albumin-rtTA transgenic mice are a powerful and efficient tool for the temporally and spatially conditional manipulation of gene expression in the liver, and illustrates how genetic crosses with these new mice enable the generation of complex multi-locus transgenic animals for mechanistic studies.

Molecular mechanism of viscoelastic polymer enhanced oil recovery in nanopores.

Polymer flooding is a promising chemical enhanced oil recovery (EOR) method, which realizes more efficient extraction in porous formations characterized with nanoscale porosity and complicated interfaces. Understanding the molecular mechanism of viscoelastic polymer EOR in nanopores is of great significance for the advancement of oil exploitation. Using molecular dynamics simulations, we investigated the detailed process of a viscoelastic polymer displacing oil at the atomic scale. We found that the interactions between polymer chains and oil provide an additional pulling effect on extracting the residual oil trapped in dead-end nanopores, which plays a key role in increasing the oil displacement efficiency. Our results also demonstrate that the oil displacement ability of polymer can be reinforced with the increasing chain length and viscoelasticity. In particular, a polymer with longer chain length exhibits stronger elastic property, which enhances the foregoing pulling effect. These findings can help to enrich our understanding on the molecular mechanism of polymer enhanced oil recovery and provide guidance for oil extraction engineering.

Identification of G2/M phase transition by sequential nuclear and cytoplasmic changes and molecular markers in mice intestinal epithelial cells.

Although the regulatory network of G2/M phase transition has been intensively studied in mammalian cell lines, the identification of morphological and molecular markers to identify G2/M phase transition in vivo remains elusive. In this study, we found no obvious morphological changes between the S phase and G2 phase in mice intestinal epithelial cells. The G2 phase could be identified by Brdu incorporation resistance, marginal and scattered foci of histone H3 phosphorylated at Ser10 (pHH3), and relatively intact Golgi ribbon. Prophase starts with nuclear transformation in situ, which was identified by a series of prophase markers including nuclear translocation of cyclinB1, fragmentation of the Golgi complex, and a significant increase in pHH3. The nucleus started to move upwards in the late prophase and finally rounded up at the apical surface. Then, metaphase was initiated as the level of pHH3 peaked. During anaphase and telophase, pHH3 sharply decreased, while Ki67 was obviously bound to chromosomes, and PCNA was distributed throughout the whole cell. Based on the aforementioned markers and Brdu pulse labeling, it was estimated to take about one hour for most crypt cells to go through the G2 phase and about two hours to go through the G2-M phase. It took much longer for crypt base columnar (CBC) stem cells to undergo G2-prophase than rapid transit amplifying cells. In summary, a series of sequentially presenting markers could be used to indicate the progress of G2/M events in intestinal epithelial cells and other epithelial systems in vivo.

[Analysis of Relationship between Serum Total Light Chain κ/λ Ratio and Proportion of Bone Marrow Plasma Cells in Patients with IgG type and IgA type Multiple Myeloma].

OBJECTIVE: To explore the relationship between serum total light chain κ/λ ratio (sTLC-κ/λ) and proportion of bone marrow plasma cells (BMPC) in patients with IgG type and IgA type multiple myeloma (MM) and its clinical significance. METHODS: The levels of serum IgG, IgA, κ type and λ type total light chain were detected in 79 newly diagnosed patients with IgG type (n=52) and IgA type (n=27) MM by immuno-nephelometric assay and the sTLC-κ/λ ratio was calculated. The proportion of BMPC was determined by bone marrow smears in the corresponding period, and the changes in sTLC-κ/λ ratio and the proportion of BMPC were observed in 19 patients with IgG type(n=16) and IgA type (n=3) MM undergoing treatment, 26 cases of non-phasmocytic proliferative diseases were enrolled in control group. RESULTS: In MM patients with IgGκ type and IgAκ type, the sTLC-κ/λ ratio was significantly higher than that in the control group (P<0.01), while in MM patients with IgGλ type and IgAλ type, the sTLC-κ/λ ratio was significantly lower than that in the control group (P<0.01). In MM patients with IgGκ, the sTLC-κ/λ ratio was significantly higher than that in MM patients with IgAκ(P<0.01), while the sTLC-κ/λ ratio in MM patients with IgGλ was significantly lower than that in MM patients with IgAλ. The sTLC-κ/λ ratios in MM patients with IgGκ and IgAκ were positively correlated with the concentrations of IgG (r=0.778,P=0.000) and IgA (r=0.601,P=0.039), while the sTLC-κ/λ ratios of patients with IgGλ and IgAλ were negativily correlated with the IgG(r=-0.586,P=0.01) and IgA level(r=-0.718,P=0.003). In addition, a correlation between each type MM was not found except the IgGκ type MM which had a positive correlation between the sTLC-κ/λ ratio and proportion of BMPC (r=0.579,P=0.002). Nonetheless, 18 of 19 patients with IgG type and IgA type MM undergoing treatment showed concordance between the sTLC-κ/λ ratio and proportion of BMPC change. CONCLUSION: There is a lower correlation between the sTLC-κ/λ ratio and the proportion of BMPC in MM patients with IgG type and IgA type, but there is a high concordance between the sTLC-κ/λ ratio and the proportion of BMPC change in the same patient and it suggests that the sTLC-κ/λ ratio plays an important role in the diagnosis and monitoring of IgG type and IgA type MM.

Morroniside protects SK-N-SH human neuroblastoma cells against H2O2-induced damage.

Oxidative stress-induced cell injury has been linked to the pathogenesis of neurodegenerative disorders such as spinal cord injury, Parkinson's disease, and multiple sclerosis. Morroniside is an antioxidant derived from the Chinese herb Shan-Zhu-Yu. The present study investigated the neuroprotective effect of morroniside against hydrogen peroxide (H2O2)-induced cell death in SK-N-SH human neuroblastoma cells. H2O2 increased cell apoptosis, as determined by flow cytometry and Hoechst 33342 staining. This effect was reversed by pretreatment with morroniside at concentrations of 1-100 µM. The increase in intracellular reactive oxygen species (ROS) generation and lipid peroxidation induced by H2O2 was also abrogated by morroniside. H2O2 induced a reduction in mitochondrial membrane potential, increased caspase-3 activity, and caused downregulation of B cell lymphoma-2 (Bcl-2) and upregulation of Bcl-2-associated X protein (Bax) expression. These effects were blocked by morroniside pretreatment. Thus, morroniside protects human neuroblastoma cells against oxidative damage by inhibiting ROS production while suppressing Bax and stimulating Bcl-2 expression, thereby blocking mitochondrial-mediated apoptosis. These results indicate that morroniside has therapeutic potential for the prevention and treatment of neurodegenerative diseases.

Super-elastic and fatigue resistant carbon material with lamellar multi-arch microstructure.

Low-density compressible materials enable various applications but are often hindered by structure-derived fatigue failure, weak elasticity with slow recovery speed and large energy dissipation. Here we demonstrate a carbon material with microstructure-derived super-elasticity and high fatigue resistance achieved by designing a hierarchical lamellar architecture composed of thousands of microscale arches that serve as elastic units. The obtained monolithic carbon material can rebound a steel ball in spring-like fashion with fast recovery speed (∼580 mm s-1), and demonstrates complete recovery and small energy dissipation (∼0.2) in each compress-release cycle, even under 90% strain. Particularly, the material can maintain structural integrity after more than 106 cycles at 20% strain and 2.5 × 105 cycles at 50% strain. This structural material, although constructed using an intrinsically brittle carbon constituent, is simultaneously super-elastic, highly compressible and fatigue resistant to a degree even greater than that of previously reported compressible foams mainly made from more robust constituents.

PDGF-AA mediates B104CM-induced oligodendrocyte precursor cell differentiation of embryonic neural stem cells through Erk, PI3K, and p38 signaling.

The conditioned medium from B104 neuroblastoma cells (B104CM) induces neural stem cells (NSCs) to differentiate into OPCs in vitro, which indicates that certain factor(s) contained within the B104CM must give instructional signals that direct OPC differentiation of NSCs. However, the OPC-inductive factor(s) present within the B104CM has not been well identified yet. Platelet-derived growth factor AA (PDGF-AA) was not only known to be a potent mitogen for OPC proliferation but also to act as a regulator of oligodendrocyte differentiation from multipotent embryonic NSCs. This raises the possibility that B104CM induces OPC differentiation of NSCs through secretion of PDGF-AA. In the present study, we detected the expression of PDGF-AA mRNA in B104 cells and the high level of PDGF-AA protein in B104CM. Most importantly, B104CM-induced OPC differentiation of NSCs could be completely blocked by AG1295, a specific inhibitor of PDGFR signal pathway, suggesting that the PDGF-AA in B104CM is the key factor that induces NSCs to differentiate into OPCs. Moreover, such B104CM-induced OPC differentiation appears to be mediated by the extracellular signal-regulated kinases 1 and 2 (Erk1/2), phosphatidylinositol-3 kinase (PI3K), and p38 signal pathway because B104CM elicited the activation of Erk1/2, PI3K, and p38, which could be markedly blocked by U0126, LY294002, and SB203580, several specific inhibitors of these signal pathway, respectively. These inhibitors also abolished OPC differentiation of NSCs completely. Together our study suggests that PDGF-AA contained in B104CM is the key regulating molecule that instructs OPC differentiation from embryonic NSCs through the activation of Erk, PI3K, and p38 signal pathway in vitro.

Effects of SCR-3 on the immunosuppression accompanied with the systemic inflammatory response syndrome.

Steroid receptor coactivator-3 (SRC-3) is a multifunctional protein that plays an important role in mammary gland growth, development, and tumorigenesis. In this study, SCR-3 gene knockout mice were used to study the effects of SCR-3 on the immunosuppression accompanied with systemic inflammatory response syndrome (SIRS). Bacterial clearance assay was performed by blood culture and frozen sections, and the results showed that the absence of SCR-3 protein serious damaged the innate immune system and the body's ability to inactivate or phagocytosis of bacteria was significantly decreased, and the absence of SCR-3 protein also weakened phagocytes' ability to degrade bacteria and their metabolites. Furthermore, animal model of inflammatory reaction was established and the immune function was determined, and the results revealed that SRC-3 protein may play an important role in maintenance of T-cells' immune function, and severe T-cell immune function disorder would be resulted once SRC-3 protein is missing. In addition, the results of our study showed the steady-state of lymphocyte subsets was destroyed after SIRS, leading the suppression of cellular immune function, and the absence of SCR-3 protein may aggravate the suppression of T-lymphocyte function. Therefore, the present study demonstrated that the absence of SCR-3 protein would aggravate immunosuppression. In addition, SRC-3 protein is a significant regulator of infection and inflammation, and SRC-3 protein play an essential role in the development of immunosuppression accompanied with SIRS.

Differential gene expression in oligodendrocyte progenitor cells, oligodendrocytes and type II astrocytes.

Oligodendrocyte precursor cells (OPCs) are bipotential progenitor cells that can differentiate into myelin-forming oligodendrocytes or functionally undetermined type II astrocytes. Transplantation of OPCs is an attractive therapy for demyelinating diseases. However, due to their bipotential differentiation potential, the majority of OPCs differentiate into astrocytes at transplanted sites. It is therefore important to understand the molecular mechanisms that regulate the transition from OPCs to oligodendrocytes or astrocytes. In this study, we isolated OPCs from the spinal cords of rat embryos (16 days old) and induced them to differentiate into oligodendrocytes or type II astrocytes in the absence or presence of 10% fetal bovine serum, respectively. RNAs were extracted from each cell population and hybridized to GeneChip with 28,700 rat genes. Using the criterion of fold change > 4 in the expression level, we identified 83 genes that were up-regulated and 89 genes that were down-regulated in oligodendrocytes, and 92 genes that were up-regulated and 86 that were down-regulated in type II astrocytes compared with OPCs. The up-regulated genes, such as activating transcription factor 3 and myelin basic protein in oligodendrocytes or claudin 11 in type II astrocytes, might contribute to OPC differentiation and represent constitutive components of oligodendrocytes or type II astrocytes. The down-regulated genes in both oligodendrocytes and type II astrocytes, such as transcription factor 19, might be involved in maintaining self-renewal and/or represent the property of OPCs. These results provide new insights into the elucidation of the molecular mechanisms, by which OPCs differentiate to oligodendrocytes or type II astrocytes.

Cyclosporin A increases recovery after spinal cord injury but does not improve myelination by oligodendrocyte progenitor cell transplantation.

BACKGROUND: Transplantation of oligodendrocyte precursor cells (OPCs) is an attractive therapy for demyelinating diseases. Cyclosporin A (CsA) is one of the foremost immunosuppressive agents and has widespread use in tissue and cell transplantation. However, whether CsA affects survival and differentiation of engrafted OPCs in vivo is unknown. In this study, the effect of CsA on morphological, functional and immunological aspects, as well as survival and differentiation of engrafted OPCs in injured spinal cord was explored. RESULTS: We transplanted green fluorescent protein (GFP) expressed OPCs (GFP-OPCs) into injured spinal cords of rats treated with or without CsA (10 mg/kg). Two weeks after cell transplantation, more GFP-positive cells were found in CsA-treated rats than that in vehicle-treated ones. However, the engrafted cells mostly differentiated into astrocytes, but not oligodendrocytes in both groups. In the CsA-treated group, a significant decrease in spinal cord lesion volume along with increase in spared myelin and neurons were found compared to the control group. Such histological improvement correlated well with an increase in behavioral recovery. Further study suggested that CsA treatment could inhibit infiltration of T cells and activation of resident microglia and/or macrophages derived from infiltrating monocytes in injured spinal cords, which contributes to the survival of engrafted OPCs and repair of spinal cord injury (SCI). CONCLUSIONS: These results collectively indicate that CsA can promote the survival of engrafted OPCs in injured spinal cords, but has no effect on their differentiation. The engrafted cells mostly differentiated into astrocytes, but not oligodendrocytes. The beneficial effect of CsA on SCI and the survival of engrafted cells may be attributed to its neuroprotective effect.

Activation of PKC-alpha is required for migration of C6 glioma cells.

The PKC signaling pathway has been implicated in diverse cellular functions. Here, we sought to investigate the role of PKC-alpha÷beta in C6 glioma cell migration. We found that both PKC-alpha and PKC-beta were expressed by C6 glioma cells, but only PKC-alpha was markedly activated in serum-treated C6 cells. Go6976, a PKC-alpha÷beta specific inhibitor, was found to cause a dose-dependent reduction of PKC-alpha activation and cell migration induced by serum in C6 cells. These results collectively indicated that the PKC-alpha signaling pathway is necessary for glioma cell migration. Our findings may provide an insight into a better understanding to the malignant progression of gliomas.

Electrowetting on a lotus leaf.

Electrowetting on dielectrics has been widely used to manipulate and control microliter or nanoliter liquids in micro-total-analysis systems and laboratory on a chip. We carried out experiments on electrowetting on a lotus leaf, which is quite different from the equipotential plate used in conventional electrowetting. This has not been reported in the past. The lotus leaf is superhydrophobic and a weak conductor, so the droplet can be easily actuated on it through electrical potential gradient. The capillary motion of the droplet was recorded by a high-speed camera. The droplet moved toward the counterelectrode to fulfill the actuation. The actuation speed could be of the order of 10 mms. The actuation time is of the order of 10 ms.

Down-regulation of alphav integrin by retroviral delivery of small interfering RNA reduces multicellular resistance of HT29.

Since multicellular resistance (MCR) has been shown to be as adhesion-dependent, the role of alphav integrin in MCR of HT29 was investigated in this paper. Down-regulation of alphav integrin reduced MCR to oxaliplatin, but did not detectably change the drug sensitivity of monolayers. Down-regulation of alphav integrin decreased phosphorylated NF-kappaB p65 and increased phosphorylated JNK2 in multicellular spheroids. Cell-cell adhesion and cell-cell junctions in multicellular spheroids resembled the in vivo situation. Since force, including adhesion, can activate alphav integrin, cell-cell contact may contribute to activation of alphav integrin, through which increasing phosphorylated p65 and decreasing phosphorylated JNK2 takes part in MCR.

The head-on colliding process of binary liquid droplets at low velocity: high-speed photography experiments and modeling.

The experimental and theoretical studies are reported in this paper for the head-on collisions of a liquid droplet with another of the same fluid resting on a solid substrate. The droplet on the hydrophobic polydimethylsiloxane (PDMS) substrate remains in a shape of an approximately spherical segment and is isometric to an incoming droplet. The colliding process of the binary droplets was recorded with high-speed photography. Head-on collisions saw four different types of response in our experiments: complete rebound, coalescence, partial rebound with conglutination, and coalescence accompanied by conglutination. For a complete rebound, both droplets exhibited remarkable elasticity and the contact time of the two colliding droplets was found to be in the range of 10-20 ms. With both droplets approximately considered as elastic bodies, Hertz contact theory was introduced to estimate the contact time for the complete rebound case. The estimated result was found to be on the same order of magnitude as the experimental data, which indicates that the present model is reasonable.