**3.3 Optical rotation and deformation of human red blood cells**

Except for the bidirectional transportation of the RBC chain, FPs were also investigated to conduct the multifunctional rotation and deformation of human red blood cells, which were of great physiological and pathological significance. As shown in **Figure 6**, one RBC was bound to the tip of TFP 1 at *θ* = 0° due to the optical gradient force and the Van der Waals force. At *t* = 0 s, the laser beam at a wavelength of 980 nm was injected into TFP 2 at *P*2 = 24 mW (**Figure 6a1**). Meanwhile, the upper part of the RBC was trapped by TFP 2. By shifting TFP 2 along the −*y* direction, the cell rotated around the *x*-axis with *θ* increased (**Figure 6a2–5**). At *t* = 10 s, TFP 2 was shifted along the +*y* direction, and *θ* decreased to be 0° (**Figure 6a6–10**).

To quantitatively analyze the above rotation process, *y*TFP2 and *θ* were achieved as shown in **Figure 6b**. In the region I (from *t* = 0 to 3.8 s), TFP 2 was shifted along the −*y* direction with a distance of 3.3 μm, and *θ* increased from 0 to 90°. Then, *θ* remained to be 90° from 3.8 to 5 s (region II), which indicated a certain orientation of cell can be realized by manipulating TFP 2. After that, *θ* increased from 90 to 172° (region III) with TFP 2 shifted along the −*y* direction again, and then it remained to be 172° from *t* = 7 to 9.5 s (region VI). From *t* = 9.5 to 15 s, TFP 2 was shifted along the −*y* direction so that *θ* decreased from 172 to 0° (region V). Thus, a controllable rotation and orientation of the RBC around *x*-axis can be realized by manipulating TFP 2. In addition, the shift velocity of TFP 2 (*V*TFP2) and angular velocity of the RBC (*ω*RBC) were also calculated. As shown in **Figure 6c**, the value of *ω*RBC monotonously varied with *V*TFP2, with a maximum of 4.7 rad/s. Notably, the trapped part can be changed by adjusting TFP 2 along the *z* direction. For example,

#### **Figure 6.**

*RBC rotation around x-axis. (a) Optical microscopic images for rotating an RBC around x-axis. Scale bar: 5 μm. (b) Calculated yTFP2 and θ in the rotation process. (c) Calculated VTFP2 and ωRBC in the rotation process [40].*

**19**

**Figure 7.**

*Optical Fiber Probe-Based Manipulation of Cells DOI: http://dx.doi.org/10.5772/intechopen.81423*

realize the multifunctional rotation around different axes.

by trapping the left part of the cell, the cell will rotate around z-axis, which can

Further, a stretch of single or multiple RBCs can also be realized by using two TFPs. As schematically shown in **Figure 7a**, after the laser beams injected into both TFPs 1 and 2, three RBCs are trapped and then stretched along the optical axis of TFPs. The experiments were then conducted to demonstrate the above stretch mechanism. At *t* = 0 s, two RBCs were located between two TFPs, with diameters of 5.6 and 6.4 μm, respectively (**Figure 7b1**). Then, two laser beams at the wavelength of 980 nm were injected into the TFPs with the power of *P*1 = *P*2 = 20 mW. After that, the RBCs moved toward each other and finally became contacted due to the optical force (**Figure 7b2**). Meanwhile, they were gradually stretched till reaching an equilibrium at *t* = 10 s (**Figure 7b3**). The deformation degree of RBCs can be described by the shear strain (*γ*) which was defined as *γ* = *Δl*/*l*, where *Δl* and *l* are the cell stretch length and original length, respectively. At *t* = 10 s (**Figure 7b3**), the shear strain of two cells reached the maximum of 0.14 and 0.12, respectively. Then, they kept stretched until the laser was turned off at *t* = 35 s (**Figure 7b4**). After that, the RBCs were gradually resumed their original shapes (**Figure 7b5, 6**).

Similarly, the simultaneous stretch of three RBCs was also conducted, as shown in **Figure 7c**. The diameters of RBCs 1, 2, and 3 were 6.7, 5.7, and 6.9 μm, respectively. At *t* = 2 s, the RBCs began to be trapped and then stretched after the laser turned on (**Figure 7c2**). Meanwhile, the distance between the cells was decreased, while *γ* were increased. They gradually became contacted with each other. At *t* = 5 s,

*The stretch of multiple RBCs with light from two TFPs. (a) Schematic of stretching multiple RBCs with two TFPs. (b) Optical microscopic images of stretching two RBCs. (c) Optical microscopic images of stretching three RBCs. (d) Stress distribution on the surfaces of two RBCs. (e) Stress distribution on the surfaces of three RBCs [40].*

### *Optical Fiber Probe-Based Manipulation of Cells DOI: http://dx.doi.org/10.5772/intechopen.81423*

*Fiber Optics - From Fundamentals to Industrial Applications*

transported by adjusting the laser power or flow velocity.

decreased to be 0° (**Figure 6a6–10**).

**3.3 Optical rotation and deformation of human red blood cells**

kept stationary with *D* remained at 35.2 μm (**Figure 5c4**). Besides, the distance can also be changed by adjusting the flow velocity, which was similar to the case of yeast cell chain. These results demonstrated that various cell chains can be dynamically

Except for the bidirectional transportation of the RBC chain, FPs were also investigated to conduct the multifunctional rotation and deformation of human red blood cells, which were of great physiological and pathological significance. As shown in **Figure 6**, one RBC was bound to the tip of TFP 1 at *θ* = 0° due to the optical gradient force and the Van der Waals force. At *t* = 0 s, the laser beam at a wavelength of 980 nm was injected into TFP 2 at *P*2 = 24 mW (**Figure 6a1**). Meanwhile, the upper part of the RBC was trapped by TFP 2. By shifting TFP 2 along the −*y* direction, the cell rotated around the *x*-axis with *θ* increased (**Figure 6a2–5**). At *t* = 10 s, TFP 2 was shifted along the +*y* direction, and *θ*

To quantitatively analyze the above rotation process, *y*TFP2 and *θ* were achieved as shown in **Figure 6b**. In the region I (from *t* = 0 to 3.8 s), TFP 2 was shifted along the −*y* direction with a distance of 3.3 μm, and *θ* increased from 0 to 90°. Then, *θ* remained to be 90° from 3.8 to 5 s (region II), which indicated a certain orientation of cell can be realized by manipulating TFP 2. After that, *θ* increased from 90 to 172° (region III) with TFP 2 shifted along the −*y* direction again, and then it remained to be 172° from *t* = 7 to 9.5 s (region VI). From *t* = 9.5 to 15 s, TFP 2 was shifted along the −*y* direction so that *θ* decreased from 172 to 0° (region V). Thus, a controllable rotation and orientation of the RBC around *x*-axis can be realized by manipulating TFP 2. In addition, the shift velocity of TFP 2 (*V*TFP2) and angular velocity of the RBC (*ω*RBC) were also calculated. As shown in **Figure 6c**, the value of *ω*RBC monotonously varied with *V*TFP2, with a maximum of 4.7 rad/s. Notably, the trapped part can be changed by adjusting TFP 2 along the *z* direction. For example,

*RBC rotation around x-axis. (a) Optical microscopic images for rotating an RBC around x-axis. Scale bar: 5 μm. (b) Calculated yTFP2 and θ in the rotation process. (c) Calculated VTFP2 and ωRBC in the rotation process [40].*

**18**

**Figure 6.**

by trapping the left part of the cell, the cell will rotate around z-axis, which can realize the multifunctional rotation around different axes.

Further, a stretch of single or multiple RBCs can also be realized by using two TFPs. As schematically shown in **Figure 7a**, after the laser beams injected into both TFPs 1 and 2, three RBCs are trapped and then stretched along the optical axis of TFPs. The experiments were then conducted to demonstrate the above stretch mechanism. At *t* = 0 s, two RBCs were located between two TFPs, with diameters of 5.6 and 6.4 μm, respectively (**Figure 7b1**). Then, two laser beams at the wavelength of 980 nm were injected into the TFPs with the power of *P*1 = *P*2 = 20 mW. After that, the RBCs moved toward each other and finally became contacted due to the optical force (**Figure 7b2**). Meanwhile, they were gradually stretched till reaching an equilibrium at *t* = 10 s (**Figure 7b3**). The deformation degree of RBCs can be described by the shear strain (*γ*) which was defined as *γ* = *Δl*/*l*, where *Δl* and *l* are the cell stretch length and original length, respectively. At *t* = 10 s (**Figure 7b3**), the shear strain of two cells reached the maximum of 0.14 and 0.12, respectively. Then, they kept stretched until the laser was turned off at *t* = 35 s (**Figure 7b4**). After that, the RBCs were gradually resumed their original shapes (**Figure 7b5, 6**).

Similarly, the simultaneous stretch of three RBCs was also conducted, as shown in **Figure 7c**. The diameters of RBCs 1, 2, and 3 were 6.7, 5.7, and 6.9 μm, respectively. At *t* = 2 s, the RBCs began to be trapped and then stretched after the laser turned on (**Figure 7c2**). Meanwhile, the distance between the cells was decreased, while *γ* were increased. They gradually became contacted with each other. At *t* = 5 s,

#### **Figure 7.**

*The stretch of multiple RBCs with light from two TFPs. (a) Schematic of stretching multiple RBCs with two TFPs. (b) Optical microscopic images of stretching two RBCs. (c) Optical microscopic images of stretching three RBCs. (d) Stress distribution on the surfaces of two RBCs. (e) Stress distribution on the surfaces of three RBCs [40].*

the three cells reached the equilibrium with *γ* = 0.15, 0.1, and 0.12 (**Figure 7c3**). After that, RBCs started to resume their original shapes by turning off the laser at *t* = 9 s (**Figure 7c4–6**). Further, the normalized stress distribution on the RBC surfaces was also investigated, as indicated by the red arrows in **Figure 7e** and **f**. The stress was mainly distributed along the *x*-axis, and the stress direction was toward the outside of cells. Therefore, the RBCs were stretched and further became contacted with each other.
