Lensless imaging for simultaneous microfluidic sperm monitoring and sorting

Abstract

5.3 million American couples of reproductive age (9%) are affected by infertility, among which male factors account for up to 50% of cases, which necessitates the identification of parameters defining sperm quality, including sperm count and motility. In vitro fertilization (IVF) with or without intra cytoplasmic sperm injection (ICSI) has become the most widely used assisted reproductive technology (ART) in modern clinical practice to overcome male infertility challenges. One of the obstacles of IVF and ICSI lies in identifying and isolating the most motile and presumably healthiest sperm from semen samples that have low sperm counts (oligozoospermia) and/or low sperm motility (oligospermaesthenia). Microfluidic systems have shown potential to sort sperm with flow systems. However, the small field of view (FOV) of conventional microscopes commonly used to image sperm motion presents challenges in tracking a large number of sperm cells simultaneously. To address this challenge, we have integrated a lensless charge-coupled device (CCD) with a microfluidic chip to enable wide FOV and automatic recording as the sperm move inside a microfluidic channel. The integrated system enables the sorting and tracking of a population of sperm that have been placed in a microfluidic channel. This channel can be monitored in both horizontal and vertical configuration similar to a swim-up column method used clinically. Sperm motilities can be quantified by tracing the shadow paths for individual sperm. Moreover, as the sperm are sorted by swimming from the inlet towards the outlet of a microfluidic channel, motile sperm that reach the outlet can be extracted from the channel at the end of the process. This technology can lead to methods to evaluate each sperm individually in terms of motility response in a wide field of view, which could prove especially useful, when working with oligozoospermic or oligospermaesthenic samples, in which the most motile sperm need to be isolated from a pool of small number of sperm.

This journal is © The Royal Society of Chemistry 2011

Figures

Fig. 1

A schematic illustration of the CCD image platform. (A) The microfluidic chip consists of three layers: PMMA, DSA, and glass coverslip. (B) Lensless CCD image platform integrated with microfluidic chip for sperm tracking. When the light is incident on the microchip, the sperm inside the channel diffract and transmit light. Shadows of the sperm generated by diffraction can be imaged using CCD in one second. (C) Shadow image of the sperm in the microchip channel obtained by the lensless CCD platform. Scale bar is 100 μm. (D) Enlarged single shadow of the sperm from (C). Scale bar is 50 μm. (E) Microscope sperm images taken at 10 × objective. Scale bar is 50 μm.

Fig. 2

Bull's eye plot showing sperm motility vectors in the horizontal (left) and vertical (right) configurations. The distance between the adjacent concentric circles is 100 μm.

Fig. 3

Comparison of: (A) Average Path Velocity (VAP), Straight Line Velocity (VSL), (B) straightness (VSL/VAP), and (C) average acceleration for sperm cells imaged under horizontal and vertical configurations with a lensless microfluidic system developed in this study (p > 0.05).

Fig. 4

Comparison of Average Path Velocity (VAP) and Straight Line Velocity (VSL) of sperm for non-sorted condition, and at the inlet and outlet of the 7 mm long microfluidic channel. The VAP and VSL were observed to be significantly greater for the sperm cells imaged at the outlet of the microfluidic channel compared to non-sorted sperm and the sperm at the inlet. Therefore the microfluidic sperm tracking system presented here shows potential to be also used as a sorting platform. (n = 33–66, brackets indicate statistical significance with p < 0.01 between the groups).