Investigation of albumin-derived perfluorocarbon-based capsules by holographic optical trapping

Abstract

Albumin-derived perfluorocarbon-based capsules are promising as artificial oxygen carriers with high solubility. However, these capsules have to be studied further to allow initial human clinical tests. The aim of this paper is to provide and characterize a holographic optical tweezer to enable contactless trapping and moving of individual capsules in an environment that mimics physiological (in vivo) conditions most effectively in order to learn more about the artificial oxygen carrier behavior in blood plasma without recourse to animal experiments. Therefore, the motion behavior of capsules in a ring shaped or vortex beam is analyzed and optimized on account of determination of the optical forces in radial and axial direction. In addition, due to the customization and generation of dynamic phase holograms, the optical tweezer is used for first investigations on the aggregation behavior of the capsules and a statistical evaluation of the bonding in dependency of different capsule sizes is performed. The results show that the optical tweezer is sufficient for studying individual perfluorocarbon-based capsules and provide information about the interaction of these capsules for future use as artificial oxygen carriers.

Keywords: (000.1430) Biology and medicine; (090.2890) Holographic optical elements; (140.7010) Laser trapping; (160.1435) Biomaterials; (350.4855) Optical tweezers or optical manipulation.

Fig. 1

Chemical structure of PFD (C₁₀F₁₈).

Fig. 2

The used hologram on the SLM is a combination of the phase and amplitude patterns, which leads to a ring shaped intensity profile and enables trapping of the PBCs.

Fig. 3

A combination of the vortex phase pattern and a changing amplitude leads to presented intensity distributions and opening of the vortex beam. The topological charge of the vortex is ℓ = 19 and the diameter is d_v = 5 µm, respectively. The MATLAB code is available in the supplementary information, see Code 1 [40].

Fig. 4

(a) The critical velocity v_c is determined by moving a capsule on a circular path while gradually increasing the velocity. (b)–(d) A capsule with a diameter of 5.2 µm is moved with a velocity of 3.5 µm/s.

Fig. 5

(a) The optimal ratio of the vortex-to-capsule diameter where the critical velocity can be maximized is d_v/d_c = 1. (b) Using this value, a linear correlation between velocity and laser power can be determined. (c) The radial optical force F_rad can be calculated by Equation 2.

Fig. 6

The acting forces on a capsule must be balanced for stably trapping in axial direction. The equilibrium position is slightly above the imaging plane (I). The laser power is reduced until the capsule falls out of the trap onto the cover glass (II).

Fig. 7

(a) The minimal laser power to stably trap different capsules augments with increasing diameter. The black lines correspond to fits by Equation 3 $\left(P_{\text{min}}\propto d_c^3\right)$. (b) The axial force F_ax can be calculated by Equation 3 (black lines are linear fits through the origin).

Fig. 8

Two vortex beams are generated to simultaneously trap two PBCs. By moving and opening the vortices, the capsules were joined.

Fig. 9

A number of 168 capsules were optically joined and the presented probability of bonding was determined.