Synthesis and investigation of desalinating,antibacterial, and mechanical properties of tetraethylorthosilicate crosslinked chitosan/polyethylene glycol (PEG-300) membranes for reverse osmosis

Solution casting method was used to synthesize chitosan (CS)-based membranes for reverse osmosis (RO) using PEG-300 and tetraethylorthosilicate as a crosslinker. Their salt rejection (%) and permeate flux (mL/h.m²) was measured by using lab scale RO plant. FTIR spectroscopy reveals interactions between CS and PEG by shifting of  OH peak from 3237 cm⁻¹ to lower wavenumber in modified membranes. SEM results showed pores in modified membranes while pure CS membranes had uniform nonporous and dense microstructure. DMA results demonstrated that the addition of PEG lowers the T_g value up to 6.5%. Water content of membranes increases up to 82.63% as the amount of PEG increases owing to its hydrophilic nature. The bacterial killing ability showed that the modified membranes possess good antibacterial activity against Escherichia coli in comparison to the control film. The permeation results revealed that salt rejection and flux of the modified membranes increased up 60% and 86.36 mL/h.m², respectively. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48870.     

Chitosan-Based Functional Films Integrated with Magnolol: Characterization,Antioxidant and Antimicrobial Activity and Pork Preservation

The aims of this study were to develop the magnolol–chitosan films and study the positive effect of the combination of magnolol and chitosan. The addition of magnolol made the magnolol–chitosan films exhibit higher density (1.06–1.87 g/cm³), but the relatively lower water vapor permeability (12.06–7.36 × 10⁻¹¹·g·m⁻¹·s⁻¹·Pa⁻¹) and water content (16.10–10.64%). The dense and smooth surface and cross-section of magnolol–chitosan films were observed by environmental scanning electron microscopy (ESEM) images. The interaction of magnolol and chitosan was observed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). After the addition of magnolol, the antioxidant capacity of magnolol–chitosan films was increased from 18.99 to 82.00%, the growth of P. aeruginosa was inhibited and the inhibition percentage of biofilm formation was increased from 30.89 to 86.04%. We further verified that the application of magnolol–chitosan films on chilled pork significantly reduced the increases in pH value, inhibited the growth of microorganisms and extended the shelf life. Results suggest that magnolol had a positive effect on magnolol–chitosan films and could be effectively applied to pork preservation.     

A High Redox Potential Laccase from Pycnoporus sanguineus RP15: Potential Application for Dye Decolorization

Laccase production by Pycnoporus sanguineus RP15 grown in wheat bran and corncob under solid-state fermentation was optimized by response surface methodology using a Central Composite Rotational Design. A laccase (Lacps1) was purified and characterized and the potential of the pure Lacps1 and the crude culture extract for synthetic dye decolorization was evaluated. At optimal conditions (eight days, 26 °C, 18% (w/w) milled corncob, 0.8% (w/w) NH₄Cl and 50 mmol·L⁻¹ CuSO₄, initial moisture 4.1 mL·g⁻¹), the laccase activity reached 138.6 ± 13.2 U·g⁻¹. Lacps1 was a monomeric glycoprotein (67 kDa, 24% carbohydrate). Optimum pH and temperature for the oxidation of 2,2’-azino-bis(3-ethylbenzthiazoline-6-sulfonate) (ABTS) were 4.4 and 74.4 °C, respectively. Lacps1 was stable at pH 3.0–8.0, and after two hours at 55–60 °C, presenting high redox potential (0.747 V vs. NHE). ABTS was oxidized with an apparent affinity constant of 147.0 ± 6.4 μmol·L⁻¹, maximum velocity of 413.4 ± 21.2 U·mg⁻¹ and catalytic efficiency of 3140.1 ± 149.6 L·mmol⁻¹·s⁻¹. The maximum decolorization percentages of bromophenol blue (BPB), remazol brilliant blue R and reactive blue 4 (RB4), at 25 or 40 °C without redox mediators, reached 90%, 80% and 60%, respectively, using either pure Lacps1 or the crude extract. This is the first study of the decolorization of BPB and RB4 by a P. sanguineus laccase. The data suggested good potential for treatment of industrial dye-containing effluents.     

Pervaporation characteristics and structure of poly(vinyl alcohol)/poly(ethylene glycol)/tetraethoxysilane hybrid membranes

Poly(vinyl alcohol) (PVA) blended with poly(ethylene glycol) (PEG) was crosslinked with tetraethoxysilane (TEOS) to prepare organic–inorganic PVA/PEG/TEOS hybrid membranes. The membranes were then used for the dehydration of ethanol by pervaporation (PV). The physicochemical structure of the hybrid membranes was studied with Fourier transform infrared spectra (FT‐IR), wide‐angle X‐ray diffraction WXRD, and scanning electron microscopy (SEM). PVA and PEG were crosslinked with TEOS, and the crosslinking density increased with increases in the TEOS content, annealing temperature, and time. The water permselectivity of the hybrid membranes increased with increasing annealing temperature or time; however, the permeation fluxes decreased at the same time. SEM pictures showed that phase separation took place in the hybrid membranes when the TEOS content was greater than 15 wt %. The water permselectivity increased with the addition of TEOS and reached the maximum at 10 wt % TEOS. The water permselectivity decreased, whereas the permeation flux increased, with an increase in the feed water content or feed temperature. The hybrid membrane that was annealed at 130°C for 12 h exhibited high permselectivity with a separation factor of 300 and a permeation flux of 0.046 kg m^?2 h^?1 in PV of 15 wt % water in ethanol. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Studies on fouling by natural organic matter (NOM) on polysulfone membranes: Effect of polyethylene glycol (PEG)

Polysulfone membranes were prepared via phase inversion technique by using polyethylene glycol with molecular weights of 400, 1500 and 6000 Da as pore forming agent in dope formulation. The performance of membrane was characterized using humic acid and water sample taken from Sembrong River, Johor, Malaysia was used as natural organic matter sources. Membrane properties were also characterized in terms of mean pore radius, pure water flux, humic acid rejection and fouling resistance. The results indicated that the pure water flux and mean pore radius of membranes increased with the increase of PEG content. Fourier transform infrared spectroscopy results revealed the presence of hydrophilic component in PSf/PEG blend with the significant appearance of O–H peak at 3418.78 cm^− 1. Scanning electron microscopy analysis revealed the presence of finger-like structure for all membranes and the structure intensified as PEG content was increased. The results obtained from the fouling study indicated that the membrane with the lowest PEG content and molecular weight has an excellent performance in mitigating fouling.     

Chitosan-Coated Magnetic Nanoparticles Prepared in One Step by Reverse Microemulsion Precipitation

Chitosan-coated magnetic nanoparticles (CMNP) were obtained at 70 °C and 80 °C in a one-step method, which comprises precipitation in reverse microemulsion in the presence of low chitosan concentration in the aqueous phase. X-ray diffractometry showed that CMNP obtained at both temperatures contain a mixture of magnetite and maghemite nanoparticles with ≈4.5 nm in average diameter, determined by electron microscopy, which suggests that precipitation temperature does not affect the particle size. The chitosan coating on nanoparticles was inferred from Fourier transform infrared spectrometry measurements; furthermore, the carbon concentration in the nanoparticles allowed an estimation of chitosan content in CMNP of 6%–7%. CMNP exhibit a superparamagnetic behavior with relatively high final magnetization values (≈49–53 emu/g) at 20 kOe and room temperature, probably due to a higher magnetite content in the mixture of magnetic nanoparticles. In addition, a slight direct effect of precipitation temperature on magnetization was identified, which was ascribed to a possible higher degree of nanoparticles crystallinity as temperature at which they are obtained increases. Tested for Pb²⁺ removal from a Pb(NO₃)₂ aqueous solution, CMNP showed a recovery efficacy of 100%, which makes them attractive for using in heavy metals ion removal from waste water.     

Is Dialdehyde Chitosan a Good Substance to Modify Physicochemical Properties of Biopolymeric Materials?

The aim of this work was to compare physicochemical properties of three dimensional scaffolds based on silk fibroin, collagen and chitosan blends, cross-linked with dialdehyde starch (DAS) and dialdehyde chitosan (DAC). DAS was commercially available, while DAC was obtained by one-step synthesis. Structure and physicochemical properties of the materials were characterized using Fourier transfer infrared spectroscopy with attenuated total reflectance device (FTIR-ATR), swelling behavior and water content measurements, porosity and density observations, scanning electron microscopy imaging (SEM), mechanical properties evaluation and thermogravimetric analysis. Metabolic activity with AlamarBlue assay and live/dead fluorescence staining were performed to evaluate the cytocompatibility of the obtained materials with MG-63 osteoblast-like cells. The results showed that the properties of the scaffolds based on silk fibroin, collagen and chitosan can be modified by chemical cross-linking with DAS and DAC. It was found that DAS and DAC have different influence on the properties of biopolymeric scaffolds. Materials cross-linked with DAS were characterized by higher swelling ability (~4000% for DAS cross-linked materials; ~2500% for DAC cross-linked materials), they had lower density (Coll/CTS/30SF scaffold cross-linked with DAS: 21.8 ± 2.4 g/cm³; cross-linked with DAC: 14.6 ± 0.7 g/cm³) and lower mechanical properties (maximum deformation for DAC cross-linked scaffolds was about 69%; for DAS cross-linked scaffolds it was in the range of 12.67 ± 1.51% and 19.83 ± 1.30%) in comparison to materials cross-linked with DAC. Additionally, scaffolds cross-linked with DAS exhibited higher biocompatibility than those cross-linked with DAC. However, the obtained results showed that both types of scaffolds can provide the support required in regenerative medicine and tissue engineering. The scaffolds presented in the present work can be potentially used in bone tissue engineering to facilitate healing of small bone defects.     

Selective Isolation of Trypsin Inhibitor and Lectin from Soybean Whey by Chitosan/Tripolyphosphate/Genipin Co-Crosslinked Beads

Selective isolation of Kunitz trypsin inhibitor (KTI) and lectin from soybean whey solutions by different types of chitosan beads was investigated. The chitosan beads were co-crosslinked with tripolyphosphate/genipin in solutions at pH 5, 7 or 9 (CB5, CB7, CB9). The maximum adsorption ratios of chitosan beads to KTI and lectin were observed at pH 4.4 and 5.4, respectively; highly selective separation was also demonstrated at these pHs. The adsorption ratios increased with temperature, rising between 5 and 25 °C. CB9 produced the best adsorption ratio, followed by CB7 then CB5. The critical interaction governing absorption of chitosan beads to KTI and lectin could be hydrogen bonding. At pH 9, KTI and lectin desorbed efficiently from CB7 with desorption ratios of 80.9% and 81.4%, respectively. The desorption was most likely caused predominantly by electrostatic repulsion. KTI and lectin can effectively be selectively isolated from soybean whey using this novel separation technique.     

Preparation and Characterization of a Chloroperoxidase-like Catalytic Antibody

The small molecule, meso-tetra(α,α,α,α-o-phenylacetamidophenyl) porphyrin (Mr1147.0) was used as complete antigen to elicit MAb through the immunization and cell fusion techniques. The MAb 1F2 obtained was demonstrated to be very pure by MALDI/TOFMS. The subtype of MAb 1F2 is IgG2a, which has a relative molecular weight of 156,678.8 Da.No significant change in the intensity of absorption peaks in UV and CD spectra was observed over a pH range between 6 and 12. The high stability of the abzyme and the tight binding between Fe porphyrin and antibody were also demonstrated. V_max, K_m, κcat, κcat/K_m for abzyme are 5.18 × 10⁻⁸ Ms⁻¹, 1.50 × 10⁻⁸ M, 0.518 s⁻¹, 3.45 × 10⁷ M⁻¹s⁻¹, respectively. The data obtained indicate that catalytic antibody has high catalytic activity. The chloroperoxidase activity of MAb 1F2-Fe porphyrin complex is stable from 10 °C to 60 °C.     

Nanofiltration membranes based on poly(vinyl alcohol) and ionic polymers

Nanofiltration membranes based on poly(vinyl alcohol) (PVA) and ionic polymers, such as sodium alginate (SA) and chitosan, were prepared by casting the respective polymer solutions. The membranes prepared from PVA or PVA–ionic polymer blend were crosslinked in a isopropanol solution using glutaraldehyde as a crosslinking agent. The membranes were characterized with Fourier transform infrared spectroscopy and X‐ray diffractometry and swelling test. The membranes crosslinked through the acetal linkage formation between the  OH groups of PVA and the ionomer and glutaraldehyde appeared to be semicrystalline. To study the permeation properties, the membranes were tested with various feed solutions [sodium sulfate, sodium chloride, poly(ethylene glycol) with 600 g/mol of molecular weight (PEG 600), and isopropyl alcohol]. For example, the permeance and the solute rejection of the 1000 ppm sodium sulfate at 600 psi of upstream pressure through the PVA membrane were 0.55 m³/m² day and over 99%, respectively. The effects of the ionomers on the permeation properties of the PVA membranes were studied using the PVA–SA and PVA–chitosan blend membranes. The addition of small amount of ionic polymers (5 wt %) made the PVA membranes more effective for the organic solute rejection without decrease in their fluxes. The rejection ratios of the PEG 600 and isopropanol were increased substantially. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1755–1762, 1999     

Novel photo-crosslinkable polymeric electrolyte system based on poly(ethylene glycol) and trimethylolpropane triacrylate for dye-sensitized solar cell with long-term stability

Polyethylene glycol (PEG) and trimethylolpropane triacrylate (TMPTA) were used as photo-crosslinkable polymer electrolytes for dye-sensitized solar cells (DSSCs). PEG and trifunctional TMPTA formed a crosslinked structure upon light illumination, as confirmed by the solubility test and FTIR spectroscopy. In order to make close contact with the TiO₂ porous film, the polymeric electrolyte was prepared by photo-polymerization after injecting the monomer electrolyte solution into the porous film. The cross-sectional FE-SEM images showed the penetration of the electrolyte into the porous TiO₂ layer. Under AM 1.5 (100 mW/cm²) light irradiation for up to 30 min, a maximum 21% increase in the photo-conversion efficiency (η%) was observed. The electrolyte containing PEG and 20 wt% TMPTA showed a maximum increase in the photo-conversion efficiency from 2.75% to 3.35% with 30 min of light illumination. Also, the DSSCs with the novel crosslinkable PEG/TMPTA based polymer electrolyte showed improved long-term stability in comparison to those with electrolytes containing only PEG.     

Preparation and characterization of poly(ethylene glycol) crosslinked chitosan films

Poly(ethylene glycol) (PEG) crosslinked chitosan films with various PEG to chitosan ratio and PEG molecular weight were successfully prepared via the epoxy‐amine reaction between chitosan and PEG‐epoxy. The thermal and mechanical properties and swelling behavior were studied for the PEG crosslinked chitosan films. The mechanical strength of chitosan films were greatly enforced by the introduction of PEG‐epoxy, achieving an elongation of about 80%. It was found that the crosslinked chitosan films form hydrogel in water, achieving a swelling ratio higher than 20 times of original weight. The swelling behavior of chitosan films relied greatly on the molecular weight of the crosslinker PEG‐epoxy and the weight percent of PEG‐epoxy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Optimization of Blood Handling and Peripheral Blood Mononuclear Cell Cryopreservation of Low Cell Number Samples

Background: Rural/remote blood collection can cause delays in processing, reducing PBMC number, viability, cell composition and function. To mitigate these impacts, blood was stored at 4 °C prior to processing. Viable cell number, viability, immune phenotype, and Interferon-γ (IFN-γ) release were measured. Furthermore, the lowest protective volume of cryopreservation media and cell concentration was investigated. Methods: Blood from 10 individuals was stored for up to 10 days. Flow cytometry and IFN-γ ELISPOT were used to measure immune phenotype and function on thawed PBMC. Additionally, PBMC were cryopreserved in volumes ranging from 500 µL to 25 µL and concentration from 10 × 10⁶ cells/mL to 1.67 × 10⁶ cells/mL. Results: PBMC viability and viable cell number significantly reduced over time compared with samples processed immediately, except when stored for 24 h at RT. Monocytes and NK cells significantly reduced over time regardless of storage temperature. Samples with >24 h of RT storage had an increased proportion in Low-Density Neutrophils and T cells compared with samples stored at 4 °C. IFN-γ release was reduced after 24 h of storage, however not in samples stored at 4 °C for >24 h. The lowest protective volume identified was 150 µL with the lowest density of 6.67 × 10⁶ cells/mL. Conclusion: A sample delay of 24 h at RT does not impact the viability and total viable cell numbers. When long-term delays exist (>4 d) total viable cell number and cell viability losses are reduced in samples stored at 4 °C. Immune phenotype and function are slightly altered after 24 h of storage, further impacts of storage are reduced in samples stored at 4 °C.     

Structure and ionic conductivity of a series of di‐o‐butyrylchitosan membranes

Di‐o‐butyrylchitosan was prepared by reacting chitosan with butyric acid anhydride in the presence of perchloric acid as a catalyst. ¹³C‐NMR and IR spectra of the modified chitosan suggested that both hydroxyl groups, at the C‐6 and C‐3 positions, in the chitosan molecules were substituted. The maximum degree of substitution was found to be less than 28%. The results of X‐ray diffractograms revealed that, in comparison with the unmodified chitosan membrane, the crystallinity of di‐o‐butyrylchitosan membranes was remarkably decreased. Meanwhile, it was also observed that the swelling indices of modified membranes were increased significantly in direct proportion to the degree of substitution. Thermogravimetric analysis indicated that the modified membranes exhibited a slightly increased thermal stability compared to the unmodified membrane. The ionic conductivity of di‐o‐butyrylchitosan membranes after hydration was investigated using impedance spectroscopy. Compared to the unmodified chitosan membrane, the hydrated di‐o‐butyrylchitosan membrane with a relatively high degree of the substitution showed an increased ionic conductivity of more than one order of magnitude. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2309–2323, 2004     

Removal of lipopolysaccharide from protein solution using nanostructured porous supports bearing lipid membranes

Polymeric lipid membranes of N-octadecylchitosan, which consists of 70 mol% of 2-(octadecylamino)-2-deoxy-d-glucopyranose, 17 mol% of 2-amino-2-deoxy-d-glucopyranose, and 13 mol% of 2-acetamido-2-deoxy-d-glucopyranose, were covalently immobilized to carboxylated porous supports composed of chitosan and used for the adsorption of pyrogenic lipopolysaccharide. When human serum albumin solution, including 5 mg mL^-1 of albumin and 5.6 ng mL^-1 of lipopolysaccharide, was passed through a column packed with the resulting porous supports bearing lipid membranes assembled in nanoscale, lipopolysaccharide was removed to as low as a detection limit of 0.020 ng mL^-1 with a quantitative recovery of protein. On the other hand, in the case of directly N-octadecylated porous supports having cationic and hydrophobic ligands which are not assembled as lipid membranes, lipopolysaccharide could not be removed to the detection limit and protein recovery was lower than the porous supports bearing lipid membranes. The difference above as well as difference from conventional adsorbents suggested that the selectivity was attributable to an interaction between the cationic lipid membranes of N-octadecylchitosan and lipopolysaccharide as well as protein. The porous supports bearing lipid membranes were stable in 0.5 M NaOH and 0.1 M HCl at ambient temperature. Considering the confirmed excellent selectivity and chemical stability, their practical use as separation media in the pharmaceutical manufacturing can be expected.     

Polydimethylsiloxane-modified chitosan I. Synthesis and structural characterisation of graft and crosslinked copolymers

Graft and crosslinked polydimethylsiloxane (PDMS)-chitosan copolymers were prepared through the reaction between mono and difunctional glycidoxypropyl-terminated PDMSs and chitosan. The transformation of amino groups of chitosan through the reaction with epoxy groups was confirmed by FT-IR and ¹³C cross-polarization (CP) magic-angle spinning (MAS)-NMR analysis. Chitosan-based materials modified with about 40% and 60% hydrophobic polydimethylsiloxane were obtained, respectively. As proved by wide angle X-ray analysis, the crystallinity of chitosan was strongly decreased through the incorporation of PDMS sequences. However, both graft and crosslinked copolymers still present a partial crystalline structure. Their X-ray patterns are not only different as compared to chitosan but also as compared to each other. For the graft copolymer, three diffraction peaks were observed at 2θ = 8.4°, 11.2° and 21.2°, indicating the formation of a new partially crystalline phase and the modification of the interplanar distances for the phases similar to chitosan. The crosslinked copolymer is even less crystalline, the peak around 2θ = 20° being strongly decreased. Different thermal behaviour of siloxane modified chitosan was registered for graft and crosslinked copolymers; the graft sample is less stable than chitosan, while the crosslinked copolymer showed an intermediate stability between chitosan and polydimethylsiloxane precursors.     

Synthesis and characterization of photo-crosslinkable hydrogel membranes based on modified chitosan

In order to develop a non toxic and biocompatible hydrogel system with potential ability in biotechnology, modified photo-crosslinkable hydrogel membranes based on chitosan were prepared. Using an EDC/NHS conjugation method, chitosan was chemically modified to incorporate a photosensitive α-cyano-4-hydroxycinnamic acid moiety with various degrees of substitutions. Fourier transform infrared spectra (FTIR), proton nuclear magnetic resonance (¹H NMR) and ultraviolet-visible light spectra (UV-vis) were used for structural characterization of modified chitosan, The obtained membranes were crosslinked by irradiation in the ultraviolet region, where the photosensitive monomers showed maximum sensitivity. The prepared photo-crosslinked hydrogel membranes were investigated by thermal gravimetric analysis (TGA) and wide angle X-ray diffraction (WAXD). The swelling behaviors were investigated in terms of pH, time of swelling, and degree of substitution. Also, mechanical properties of the different photo-crosslinked hydrogel membranes were studied in both dry and wet conditions.     

Surface modification and preparation of nanofiltration membrane from polyethersulfone/polyimide blend—Use of a new material (polyethyleneglycol‐triazine)

Blends of polyethersulfone/polyimide (PES/PI) were prepared by dissolving in dimethylformamide/dioxane (DMF/DO) to manufacture nanofiltration membranes by using polyvinylpirrolidone (PVP) as a pore former. The membrane modification was carried out by adding ethylenediamine (EDA) to open the imide group ring of PI and by using polyethyleneglycol (PEG)‐triazine, as a new modifier material, that was produced in the laboratory. This modification involves the formation of a covalence ‐C‐N‐ bound between PEG‐triazine and amine groups (according to addition‐elimination reactions) at different temperatures. After functionalizing the membranes, diethanolamine (DA) was utilized as a hydrophilic modifier to change the membranes properties. SEM, AFM, FTIR‐ATR, EDS (X‐ray analysis) and contact angle tests were carried out to characterize modified membranes. The hydrophilicity of PES/PI membranes was improved by modification. An increase in pure water flux (up to 195 kg/m² h) and a decline in NaCl rejection (from 25 to 16%) are largely influenced by diminishing the PES/PI ratio in L₁‐L₅ membranes (Category 1). In L₆, L₇, and L₈ membranes (Category 2), by introducing PEG‐triazine into the membrane recipe, salt rejection increased from 75 to 80%. Addition of DA further enhances the salt rejection up to 93%. Fluxes were approximately similar for membranes in Category 2. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Temperature-Responsive Poly(?-caprolactone) Cell Culture Platform with Dynamically Tunable Nano-Roughness and Elasticity for Control of Myoblast Morphology

We developed a dynamic cell culture platform with dynamically tunable nano-roughness and elasticity. Temperature-responsive poly(ɛ-caprolactone) (PCL) films were successfully prepared by crosslinking linear and tetra-branched PCL macromonomers. By optimizing the mixing ratios, the crystal-amorphous transition temperature (T_m) of the crosslinked film was adjusted to the biological relevant temperature (~33 °C). While the crosslinked films are relatively stiff (50 MPa) below the T_m, they suddenly become soft (1 MPa) above the T_m. Correspondingly, roughness of the surface was decreased from 63.4–12.4 nm. It is noted that the surface wettability was independent of temperature. To investigate the role of dynamic surface roughness and elasticity on cell adhesion, cells were seeded on PCL films at 32 °C. Interestingly, spread myoblasts on the film became rounded when temperature was suddenly increased to 37 °C, while significant changes in cell morphology were not observed for fibroblasts. These results indicate that cells can sense dynamic changes in the surrounding environment but the sensitivity depends on cell types.