Glass micropipettes with silanized inner walls can be filled with an organic solvent for voltammetric measurements in an aqueous solution. This arrangement was employed to investigate systematically the mechanism of f...Glass micropipettes with silanized inner walls can be filled with an organic solvent for voltammetric measurements in an aqueous solution. This arrangement was employed to investigate systematically the mechanism of facilitated potassium ion transfer by an ionophore dibenzo 18 crown 6(DB18C6) across a micro water/1,2 dichloroethane(W/DCE) interface supported at the tip of a silanized micropipette. Our experimental results verify that this facilitated ion transfer across the liquid/liquid interface did occur by an interfacial complexation dissociation process(TIC TID mechanism). The ratio of the diffusion coefficient of DB18C6 to that of its complexed ion in the DCE phase was calculated to be 1.74±0.07.展开更多
Background The mechanical properties are related with many biological functions of cells. Accurate quantification of the mechanical properties of living cells require the combined use of experimental techniques and th...Background The mechanical properties are related with many biological functions of cells. Accurate quantification of the mechanical properties of living cells require the combined use of experimental techniques and theoretical models. Micropipette aspiration (MPA) is one of common techniques in determining mechanical properties of the living cells. The halfspace model (HSM) is employed in MPA technique. However,in the conditions of linear constitutive relations and small deformations,the HSM is inadequate for characterizing the MPA of a spherical cell in two respects. Firstly,the cell size is fairly finite other than semi-infinite to the inner radius of a micropipette;Secondly,cells are compressible,with a Poisson’s ratioνvarying from 0. 2 to 0. 4 (23-25) instead of incompressible (ν=0. 5). Thus,a more accurate model is necessary.In this study,the viscoelastic expressions were derived from our previous MPA test. Then,a sphere model (SM) employed to analyze mechanical properties of rabbit chondrocytes combined with the experimental data. Differences in mechanical properties estimated by different mechanical models were evaluated.Methods A sphere model (SM) was employed. The relative dimension of cell to micropipette and the compressibility of the cell were taken into account,as shown in Fig. 1a.■Fig.1 Sphere model of the MPA of a single cell employing different constitutive relationships The approximate expression for the aspirated length was obtained from our previous study as follows:■Furthermore,assuming that the cell behaves as a homogeneous and isotropic standard linear solid (Fig. 1b),two viscoelastic creep expressions of the aspirated length for incompressible sphere model (ICSM) and for compressible sphere model (CSM) were derived by elastic-viscoelastic correspondence principle and integral transformation as Eqs.(2) and (3)respectively.■Results(1) Comparisons of models The elastic modulus from the ICSM was 47. 4%higher than that of the half-space model (HSM)(P<0. 001). For the CSM,the percentage increase in E over the value for the HSM was 87. 7%,78. 9%,and 64. 9%when the Poisson’s ratio was set to 0. 2,0. 3,and 0. 4,respectively.For the viscoelasticity,the parameters for the ICSM and CSM were significantly larger than those of the HSM (P <0. 001). The k1,k2,andμfor the ICSM were 37. 8%,37. 9%,and 39. 0%higher,respectively,than those of the HSM. For the CSM,the viscoelastic parameters decreased with the increase ofν. Whenν=0. 3,k1,k2,andμincreased by 71. 0%,200%,and 157%,respectively,compared to those of the ICSM (P<0. 001);For the cases ofν=0. 2 andν=0. 4,the above parameters were respectively 102%,243%,and 209%and 35. 3%,97. 5%,and 79%higher than those of the ICSM.(2) Predictions for the relative errors of mechanical parameters caused by HSM e is defined as the relative change of elastic moduli (or relative error) between the HSM and SM. As shown in Fig. 2,when Poisson’s ratioνis 0. 3,in order to let the e less than 30%,relative dimension between the cell and the micropipetteξneeds to be at least 5. 0. Whenνequals 0. 5 (ICSM),ξis about 3. 3 to make the e reach 20%. However,ξis rarely larger than 5. 0 in general MPA experiments,thus the relative error of modulus will exceed 30%. The above results are independent of cell types,thus they are applicable to other spherical solid-like cells.■Fig.2 Thresholds ofξvarying withνwhen e was 10%,20%,and 30%,respectively Another parameter VR was introduced to represent the relative errors of viscoelastic parameters between HSM and SM.With regard to ICSM (Fig. 3a),whenξis 3,VRis nearly 22%. If theξis larger than 8. 0,the relative error will be reduced to less than 10%. For the CSM,the viscoelastic parameters of a typical chondrocyte varying withξandνwere obtained,as shown from Figs. 3b to 3d. Whenνtends to 0. 5,the parameters tend to those of ICSM. When theξexceeds 10,each parameter changes very little. For a certain Poisson’s ratio (ν=0. 3),whenξis 3,the VR of k1,k2,andμare 47. 1%,70. 8%,and 68. 2%,respectively. Whenξequals 5 and 10,the above values are 42. 3%,68. 8%,65%,and 38. 4%,66. 0%,63. 2%,respectively. For a givenξ(ξ=3),whenνis 0. 2,the VR of k1,k2,andμare 53. 6%,73. 3%,and 75. 0%,respectively.Whenνis taken as 0. 3 and 0. 4,the above errors are 47. 7%,71. 1%,68. 2%,and 38. 4%,58. 8%,54. 8%,respectively.Thus,the VR also decreases with the increase ofξandν.Conclusions The effects of the relative dimension between the cell,and micropipette and the Poisson’s ratio of cell were remarkable and should be taken into consideration in the pursuit of more accurate mechanical parameters of cells.展开更多
The erythrocytes play an important role in the human body. The healthy erythrocytes can undergo extremely large deformation while passing through small capillaries. Their infection by Malaria Plasmodium falcipurum （P...The erythrocytes play an important role in the human body. The healthy erythrocytes can undergo extremely large deformation while passing through small capillaries. Their infection by Malaria Plasmodium falcipurum （P.f.） will lead to capillary blockage and blood flow obstruction. Many experimental and computational methods have been applied to study the increase in stickiness and decrease in deformability of the Malaria （P.f.） infected erythrocytes. The novelty of this paper lies in the establishment of an multi-component model for investigating mechanical properties of Malaria （P.f.） infected erythrocytes, especially of their enclosed parasites. Finite element method was applied to simulate the erythrocytes＇ deformation in micropipette aspiration and optical tweezers stretching using the computational software ABAQUS. The comparisons between simulations and experiments were able to quantitatively conclude the effects of stiffness and stickiness of the parasitophorous vacuole membrane on the cells＇ deformation, which could not be obtained from experiments directly.展开更多
A new PVC matrix membrane double-barreled calcium ion-selective microelectrode based on liquid ion exchanger has been designed and constructed.The tip diameter of about 2.5μm as well as lower selectivity coefficients...A new PVC matrix membrane double-barreled calcium ion-selective microelectrode based on liquid ion exchanger has been designed and constructed.The tip diameter of about 2.5μm as well as lower selectivity coefficients for K+,Na and Mg2+are adequate for in-tracellular measurements of Ca activities.The inner wall of the selective channel was made to be hydrophobic by treatment withalkyl-alcohols.By means of this microelectrode some physiologicalphenomena related to Ca2+activities have been studied,and Caconcentrations in clinical microsamples have also been determined.展开更多
基金Supported by Chinese Academ y of Sciences(CAS) National Natural Science Foundation of China(No. 2 982 5 111) andthe Third World Academ y of Science(TWAS) and the State Key L aboratory of Electroanalytical Chem istry of the CAS.
文摘Glass micropipettes with silanized inner walls can be filled with an organic solvent for voltammetric measurements in an aqueous solution. This arrangement was employed to investigate systematically the mechanism of facilitated potassium ion transfer by an ionophore dibenzo 18 crown 6(DB18C6) across a micro water/1,2 dichloroethane(W/DCE) interface supported at the tip of a silanized micropipette. Our experimental results verify that this facilitated ion transfer across the liquid/liquid interface did occur by an interfacial complexation dissociation process(TIC TID mechanism). The ratio of the diffusion coefficient of DB18C6 to that of its complexed ion in the DCE phase was calculated to be 1.74±0.07.
文摘Background The mechanical properties are related with many biological functions of cells. Accurate quantification of the mechanical properties of living cells require the combined use of experimental techniques and theoretical models. Micropipette aspiration (MPA) is one of common techniques in determining mechanical properties of the living cells. The halfspace model (HSM) is employed in MPA technique. However,in the conditions of linear constitutive relations and small deformations,the HSM is inadequate for characterizing the MPA of a spherical cell in two respects. Firstly,the cell size is fairly finite other than semi-infinite to the inner radius of a micropipette;Secondly,cells are compressible,with a Poisson’s ratioνvarying from 0. 2 to 0. 4 (23-25) instead of incompressible (ν=0. 5). Thus,a more accurate model is necessary.In this study,the viscoelastic expressions were derived from our previous MPA test. Then,a sphere model (SM) employed to analyze mechanical properties of rabbit chondrocytes combined with the experimental data. Differences in mechanical properties estimated by different mechanical models were evaluated.Methods A sphere model (SM) was employed. The relative dimension of cell to micropipette and the compressibility of the cell were taken into account,as shown in Fig. 1a.■Fig.1 Sphere model of the MPA of a single cell employing different constitutive relationships The approximate expression for the aspirated length was obtained from our previous study as follows:■Furthermore,assuming that the cell behaves as a homogeneous and isotropic standard linear solid (Fig. 1b),two viscoelastic creep expressions of the aspirated length for incompressible sphere model (ICSM) and for compressible sphere model (CSM) were derived by elastic-viscoelastic correspondence principle and integral transformation as Eqs.(2) and (3)respectively.■Results(1) Comparisons of models The elastic modulus from the ICSM was 47. 4%higher than that of the half-space model (HSM)(P<0. 001). For the CSM,the percentage increase in E over the value for the HSM was 87. 7%,78. 9%,and 64. 9%when the Poisson’s ratio was set to 0. 2,0. 3,and 0. 4,respectively.For the viscoelasticity,the parameters for the ICSM and CSM were significantly larger than those of the HSM (P <0. 001). The k1,k2,andμfor the ICSM were 37. 8%,37. 9%,and 39. 0%higher,respectively,than those of the HSM. For the CSM,the viscoelastic parameters decreased with the increase ofν. Whenν=0. 3,k1,k2,andμincreased by 71. 0%,200%,and 157%,respectively,compared to those of the ICSM (P<0. 001);For the cases ofν=0. 2 andν=0. 4,the above parameters were respectively 102%,243%,and 209%and 35. 3%,97. 5%,and 79%higher than those of the ICSM.(2) Predictions for the relative errors of mechanical parameters caused by HSM e is defined as the relative change of elastic moduli (or relative error) between the HSM and SM. As shown in Fig. 2,when Poisson’s ratioνis 0. 3,in order to let the e less than 30%,relative dimension between the cell and the micropipetteξneeds to be at least 5. 0. Whenνequals 0. 5 (ICSM),ξis about 3. 3 to make the e reach 20%. However,ξis rarely larger than 5. 0 in general MPA experiments,thus the relative error of modulus will exceed 30%. The above results are independent of cell types,thus they are applicable to other spherical solid-like cells.■Fig.2 Thresholds ofξvarying withνwhen e was 10%,20%,and 30%,respectively Another parameter VR was introduced to represent the relative errors of viscoelastic parameters between HSM and SM.With regard to ICSM (Fig. 3a),whenξis 3,VRis nearly 22%. If theξis larger than 8. 0,the relative error will be reduced to less than 10%. For the CSM,the viscoelastic parameters of a typical chondrocyte varying withξandνwere obtained,as shown from Figs. 3b to 3d. Whenνtends to 0. 5,the parameters tend to those of ICSM. When theξexceeds 10,each parameter changes very little. For a certain Poisson’s ratio (ν=0. 3),whenξis 3,the VR of k1,k2,andμare 47. 1%,70. 8%,and 68. 2%,respectively. Whenξequals 5 and 10,the above values are 42. 3%,68. 8%,65%,and 38. 4%,66. 0%,63. 2%,respectively. For a givenξ(ξ=3),whenνis 0. 2,the VR of k1,k2,andμare 53. 6%,73. 3%,and 75. 0%,respectively.Whenνis taken as 0. 3 and 0. 4,the above errors are 47. 7%,71. 1%,68. 2%,and 38. 4%,58. 8%,54. 8%,respectively.Thus,the VR also decreases with the increase ofξandν.Conclusions The effects of the relative dimension between the cell,and micropipette and the Poisson’s ratio of cell were remarkable and should be taken into consideration in the pursuit of more accurate mechanical parameters of cells.
基金supported by the National Natural Science Foundation of China (11072178,11172214)the Scientific Research Foundation for the Returned Overseas Chinese Scholars,State Education Ministry,and Shanghai Leading Academic Discipline Project (B302)
文摘The erythrocytes play an important role in the human body. The healthy erythrocytes can undergo extremely large deformation while passing through small capillaries. Their infection by Malaria Plasmodium falcipurum （P.f.） will lead to capillary blockage and blood flow obstruction. Many experimental and computational methods have been applied to study the increase in stickiness and decrease in deformability of the Malaria （P.f.） infected erythrocytes. The novelty of this paper lies in the establishment of an multi-component model for investigating mechanical properties of Malaria （P.f.） infected erythrocytes, especially of their enclosed parasites. Finite element method was applied to simulate the erythrocytes＇ deformation in micropipette aspiration and optical tweezers stretching using the computational software ABAQUS. The comparisons between simulations and experiments were able to quantitatively conclude the effects of stiffness and stickiness of the parasitophorous vacuole membrane on the cells＇ deformation, which could not be obtained from experiments directly.
基金Projects supported by the science Fund of the Chinese Academy of Sciences.
文摘A new PVC matrix membrane double-barreled calcium ion-selective microelectrode based on liquid ion exchanger has been designed and constructed.The tip diameter of about 2.5μm as well as lower selectivity coefficients for K+,Na and Mg2+are adequate for in-tracellular measurements of Ca activities.The inner wall of the selective channel was made to be hydrophobic by treatment withalkyl-alcohols.By means of this microelectrode some physiologicalphenomena related to Ca2+activities have been studied,and Caconcentrations in clinical microsamples have also been determined.
