Porous Nano-Fiber Structure of Modified Electrospun Chitosan GBR Membranes Improve Osteoblast Calcium Phosphate Deposition in Osteoblast-Fibroblast Co-Cultures.

Desirable characteristics of electrospun chitosan membranes (ESCM) for guided bone regeneration are their nanofiber structure that mimics the extracellular fiber matrix and porosity for the exchange of signals between bone and soft tissue compartments. However, ESCM are susceptible to swelling and loss of nanofiber and porous structure in physiological environments. A novel post-electrospinning method using di-tert-butyl dicarbonate (tBOC) prevents swelling and loss of nanofibrous structure better than sodium carbonate treatments. This study aimed to evaluate the hypothesis that retention of nanofiber morphology and high porosity of tBOC-modified ESCM (tBOC-ESCM) would support more bone mineralization in osteoblast-fibroblast co-cultures compared to Na2CO3 treated membranes (Na2CO3-ESCM) and solution-cast chitosan solid films (CM-film). The results showed that only the tBOC-ESCM retained the nanofibrous structure and had approximately 14 times more pore volume than Na2CO3-ESCM and thousands of times more pore volume than CM-films, respectively. In co-cultures, the tBOC-ESCM resulted in a significantly greater calcium-phosphate deposition by osteoblasts than either the Na2CO3-ESCM or CM-film (p < 0.05). This work supports the study hypothesis that tBOC-ESCM with nanofiber structure and high porosity promotes the exchange of signals between osteoblasts and fibroblasts, leading to improved mineralization in vitro and thus potentially improved bone healing and regeneration in guided bone regeneration applications.

Noninvasive optical monitoring of pulmonary embolism: a Monte Carlo study on visible Chinese human thoracic tissues.

Significance: In recent years, the incidence rate of pulmonary embolism (PE) has increased dramatically. Currently, the correct diagnosis rate of PE in China is relatively low, and the diagnosis error rate and missed diagnosis rate were as high as about 80%. The most standard method of PE detection is pulmonary artery digital subtraction angiography (DSA), but pulmonary artery DSA is an invasive examination, and patients can have certain risks and discomfort. Noninvasive monitoring of PE remains challenging in cardiovascular medicine. Aim: We attempt to study the light propagation in human thoracic tissues and explore the possibility of near-infrared spectroscopy (NIRS) in noninvasive detection of PE. Approach: In this study, by utilizing the Monte Carlo simulation method for voxelized media and the Visible Chinese Human dataset, we quantified and visualized the photon migration in human thoracic region. The influence of the development (three levels) of PE on the light migration was observed. Results: Results showed that around 4.6% light fluence was absorbed by the pulmonary tissue. The maximum signal sensitivity distribution reached 0.073% at the 2.8- to 3.1-cm light source-detector separation. The normalized light intensity was significantly different among different PE levels and formed a linear relationship ( r 2 = 0.998 , p < 10 - 5 ). Conclusions: The study found that photons could reach the pulmonary artery tissue, the light intensity was linearly related to the degrees of embolism, PE could be quantitatively diagnosed by NIRS. Meanwhile, the optimized distance in between the light source and detector, 2.8 to 3.1 cm, was recommended to be used in future potential noninvasive optical diagnosis of PE.

Dexmedetomidine treatment prevents cerebral ischemic reperfusion injury through HIF-1α/Beclin1-mediated autophagy.

OBJECTIVE: Cerebral ischemic reperfusion injury (CIRI) is a common cerebrovascular disorder with high disability and morbidity that threatens human health. Former investigations found that dexmedetomidine (DEX) has a protective effect against CIRI, but regulatory mechanism is unclear. METHODS: The current study utilized C57BL/6 mice to establish a focal cerebral ischemic reperfusion model. Cerebral infarct volume was defined by 2, 3, 5-triphenyltetrazolium chloride (TTC) staining. BV2 cells and primary neurons were utilized for molecular mechanism studies after treatment with DEX or autophagy inhibitor 3-Methyladenine (3-Ma). RESULTS: Data revealed that DEX pretreatment protected nerves against CIRI. In vitro studies also found that DEX pretreatment enhanced microglial M2 polarization and protected against neuronal apoptosis by autophagy activation. Downregulation of hypoxia inducible factor (HIF)-1α or Beclin-1 inhibited the promotional effects of DEX on microglial M2 polarization and inhibited the protective effects of DEX against neuronal apoptosis. CONCLUSION: The present study found that DEX treatment protects against CIRI by modulating microglial polarization via HIF-1α/Beclin1-mediated autophagy.

Non-invasive optical monitoring of human lungs: Monte Carlo modeling of photon migration in Visible Chinese Human and an experimental test on a human.

The human lung was quantified and visualized by photon transport in this paper. A Monte Carlo (MC) simulation of voxelized media was used with the visible Chinese human (VCH). This study theoretically explored the feasibility of non-invasive optical detection of pulmonary hemodynamics, and investigated the optimal location of the light source in the lung photon migration and optimized the source-detector distance. The light fluence intensity showed that the photon penetration depth was 6-8.4 mm in the human lung. The optimal distance from the light source to the detector was 2.7-2.9 cm, but the optimal distance of the superior lobe of right lung was 3.3-3.5 cm. We then conducted experiments on diffuse light reflectance using NIRS on 14 volunteers. These measurements agree well with the simulation results. All the results demonstrated the great potential of non-invasive monitoring of pulmonary hemodynamics and contribute to the study of human lungs in the biomedical optics community.

Long-Term Controlled Release of Simvastatin from Photoprinted Triple-Networked Hydrogels Composed of Modified Chitosan and PLA-PEG Micelles.

Local delivery of active agents using injectable or implantable hydrogels for tissue and bone regeneration is a promising therapy, but it remains challenging for controlling dose and duration of release. Simvastatin (SMV), a hydrophobic drug, has shown potential for osteogenic stimulation. Secure loading of hydrophobic drugs by physical interactions is particularly difficult to establish in hydrophilic polymer matrices, and their sustained release over several months for long-term regeneration has rarely been reported. Additionally, mechanical properties of hydrogels must be improved for a sufficient support while maintaining eventual biodegradability. This study assesses the effect of controlled SMV release from 3D-printed triple-network hydrogels for osteogenic stimulation and characterizes their mechanical and biological properties as an implant. SMV is loaded into polymeric micelles of polylactide/poly(ethylene glycol) triblock copolymers (PLA-PEG-PLA) and mixed with N-methacryloyl chitosan and PEG dimethacrylate to fabricate hydrogels by photo-cross-linked 3D printing. The hydrogel properties and drug release profiles have shown significant dependance on the polymer compositions. The SMV release from the triple-polymer-network hydrogel has continued for 17 weeks of observation. Cytocompatibility of hydrogels with various formulations is confirmed. The tunable triple-network hydrogels loaded with SMV provide a potential therapeutic value for bone regeneration.

A Study of Combining Elastin in the Chitosan Electrospinning to Increase the Mechanical Strength and Bioactivity.

While electrospun chitosan membranes modified to retain nanofibrous morphology have shown promise for use in guided bone regeneration applications in in vitro and in vivo studies, their mechanical tear strengths are lower than commercial collagen membranes. Elastin, a natural component of the extracellular matrix, is a protein with extensive elastic property. This work examined the incorporation of elastin into electrospun chitosan membranes to improve their mechanical tear strengths and to further mimic the native extracellular composition for guided bone regeneration (GBR) applications. In this work, hydrolyzed elastin (ES12, Elastin Products Company, USA) was added to a chitosan spinning solution from 0 to 4 wt% of chitosan. The chitosan-elastin (CE) membranes were examined for fiber morphology using SEM, hydrophobicity using water contact angle measurements, the mechanical tear strength under simulated surgical tacking, and compositions using Fourier-transform infrared spectroscopy (FTIR) and post-spinning protein extraction. In vitro experiments were conducted to evaluate the degradation in a lysozyme solution based on the mass loss and growth of fibroblastic cells. Chitosan membranes with elastin showed significantly thicker fiber diameters, lower water contact angles, up to 33% faster degradation rates, and up to seven times higher mechanical strengths than the chitosan membrane. The FTIR spectra showed stronger amide peaks at 1535 cm-1 and 1655 cm-1 in membranes with higher concentrated elastin, indicating the incorporation of elastin into electrospun fibers. The bicinchoninic acid (BCA) assay demonstrated an increase in protein concentration in proportion to the amount of elastin added to the CE membranes. In addition, all the CE membranes showed in vitro biocompatibility with the fibroblasts.

A comparison of two types of electrospun chitosan membranes and a collagen membrane in vivo.

BACKGROUND: Electrospun chitosan membranes subjected to post-spinning processes using either triethylamine/tert-butyloxycarbonyl (TEA/tBOC) or butyryl-anhydride (BA) modifications to maintain nanofiber structure have exhibited potential for use in guided bone regeneration applications. The aim of this study was to evaluate ability of the modified membranes to support healing of bone-grafted defects as compared to a commercial collagen membrane. METHOD: TEA/tBOC-treated and BA-treated chitosan membranes were characterized for fiber morphology by electron microscopy, residual trifluoroacetic acid by19F NMR and endotoxin level using an endotoxin quantitation kit (ThermoScientific, US). Chitosan membranes were cut into 12 mm diameter disks. An 8 mm calvarial defect was created in each of 48 male rats and then filled with Bio-Oss (Geistlich, US) bone graft. The grafted defects were covered with either (1) TEA/tBOC-treated chitosan membrane (2) BA-treated chitosan membrane or (3) the control BioMend Extend (Zimmer Biomet, US) collagen membrane. After 3 and 8 weeks, the rats were euthanized and calvaria was retrieved for microCT and histological analyses (n = 8/group/time points). RESULTS: Both TEA/tBOC-treated and BA-treated membranes were composed of nanofibers in the ∼231 to ∼284 nm range respectively, exhibited no TFA salt residue and low endotoxin levels (≤0.1 ± 0.01 EU/membrane). All membranes supported increased bone growth from 3 weeks to 8 weeks though there was no significant difference among the membrane types. However, TEA/tBOC treated and BA treated chitosan membranes both showed significantly greater bone density (∼6% greater at 3 weeks and ∼8% greater at 8 weeks) as compared to BioMend Extend collagen membrane at both time points (p = 0.0002). CONCLUSIONS: Chitosan membranes supported better bone healing based on bone density than the collagen membrane.

Mechanically stable surface-hydrophobilized chitosan nanofibrous barrier membranes for guided bone regeneration.

The use of chitosan based nanofiber membranes in guided bone regeneration (GBR) is limited by its uncontrolled swelling and mechanical instability in aqueous environments. This paper describes the significantly improved stability and properties of surface butyrylated chitosan nanofiber (BCSNF) membranes that greatly enhance their potential in GBR. The BCSNF membranes exhibited an overall degree of substitution of 1.61, an average diameter of 99.3 ± 33.7 nm, and a 75% decrease in swelling with an approximate doubling in suture pull out strengths as compared to unmodified fibers in aqueous environment. In a five week phosphate-buffered saline-lysozyme degradation study, it was found that the remaining mass fraction of BCSNF membranes was 11.5% more than that of unmodified fibers. In vitro, the BCSNF membranes were found to support the adhesion and proliferation of fibroblasts and were cell occulusive. In vivo, the BCSNF membranes were found to significantly improve the regeneration of a rat calvarial critical size defect in a 12 week healing period and showed better barrier function than commercially available collagen membranes with little soft tissue penetration through the membranes. Taken together, these data provide strong scientific evidence for use of BCSNF membranes in GBR applications.

In vitro and in vivo evaluations of a novel post-electrospinning treatment to improve the fibrous structure of chitosan membranes for guided bone regeneration.

Electrospun chitosan membranes have been investigated for guided bone regeneration but are susceptible to swelling, dissolution, and loss of biomimetic nanofiber structure due to residual acid salts. A novel process was investigated for acidic salt removal from chitosan electrospun in 70% trifluoroacetic acid (TFA) by treating with triethylamine (TEA)/acetone and di-tert-butyl dicarbonate (tBOC) instead of the common Na2CO3 treatment. TFA salt removal and nanofiber structure stabilization were confirmed by EDS, FTIR, 19F NMR and electron microscopy before and after soaking in water. Membrane degradation after 4 weeks in PBS with 100 µg ml-1 lysozyme and osteoblastic proliferation were similar between TEA/tBOC-treated and Na2CO3-treated membranes. A simulated surgical tear test using surgical tacks showed that the peak tensile tear strength of the TEA/tBOC-treated chitosan membranes (62.1 ± 1.9 N mm-1) was significantly greater than a commercial polylactic acid (PLA) membrane (13.4 ± 0.4 N mm-1), similar to one commercial collagen membrane (55.3 ± 7.5 N mm-1) but lower than another commercial collagen membrane (133.9 ± 21.5 N mm-1). Rat 8 mm critical-sized calvarial defects covered with TEA/tBOC-treated chitosan membranes prevented soft tissue infiltration and supported new bone growth (15.76 ± 10.28%) similar to a commercial collagen membrane (16.08 ± 10.69%) at 12 weeks based on microCT analyses. Hence our novel TEA/tBOC process significantly improved nanofiber structure and mechanical strengths of electrospun chitosan membranes as compared to Na2CO3 treated membranes, without affecting in vitro degradation or cytocompatibility, improved membrane mechanical properties to be greater than a commercial PLA membrane and to be in range of commercial collagen membranes and supported calvarial bone defect healing similar to collagen. Thus TEA/tBOC-treated chitosan membranes exhibit many characteristics and properties that strongly support their potential for use in guided bone regeneration.