Solar Microcells Wirelessly Align Cells for Bioprinting

Researchers at Penn State have demonstrated that miniature solar cells can wirelessly control the alignment of biological cells, offering a potential method to shape 3D-printed tissues without the need for invasive wiring. The team, led by engineering professor Ibrahim T. Ozbolat, published their findings in Advanced Functional Materials, describing how they used light-activated photovoltaic microcells to influence the orientation of fibroblasts grown on computer chips. This approach eliminates the bulky electronic interfaces and tethered electrodes traditionally required to apply electrical currents to cells, marking a significant step toward more flexible bioprinting techniques.

Bioprinting involves using living cells and molecular signals to construct biological tissues and organs layer by layer in a laboratory setting. A critical challenge in this process is maintaining the correct alignment of the bioink, a blend of cells and materials, to ensure the resulting tissue grows in the desired structure. Historically, researchers have used electricity to guide this alignment, but the method typically relies on wired connections that can be cumbersome and invasive. The new study introduces a wireless alternative that uses light energy to generate the necessary electrical influence directly at the cell interface.

The study was an experimental investigation focused on the interaction between photovoltaic cells and biological samples. The researchers utilized commercially sourced lung and dermal fibroblasts, which are common cell types found in connective tissue throughout the body. These cells were placed on silicon wafers, the fundamental base used to build computer chips, that had been patterned with arrays of tiny solar cells. By varying the configuration of these solar cells, the team aimed to observe how different electrical fields affected cell behavior over time.

The experimental design involved two primary strategies for adjusting the layout of the photovoltaic cells on the chips. In the first strategy, the researchers varied the diameters of the individual solar cells, ranging from just smaller than a millimeter to a mere 80 micrometers, which is less than the width of a human hair. In the second strategy, the diameters remained constant, but the overall shape of the patterned array was altered. These variations allowed the team to test how changes in size, shape, and spacing between the individual solar cells influenced the electric field generated by the array.

During the experiment, the chips were exposed to various intensities of light for seven days, allowing the fibroblasts to grow. The light was captured by the photovoltaic cells and converted into an electrical current, which in turn influenced the cells. At the conclusion of the seven-day period, the researchers compared the alignment of the cells on the illuminated chips to those grown on chips that did not receive light exposure. This comparison served as a control to isolate the effect of the photovoltaic-generated electrical fields on cell orientation.

The results indicated a strong correlation between the patterning of the solar cells and the alignment of the fibroblasts. In the control chips that were not exposed to light, the cell alignment was largely random, with no specific directional preference. However, in the illuminated chips, the cells aligned in a manner that clearly mirrored the underlying pattern of the photovoltaic cells. This finding suggests that the electrical fields generated by the solar cells are sufficient to guide cell orientation without the need for direct physical wiring or external electrodes.

Yifan Tao, the first author of the paper and a doctoral candidate in engineering science and mechanics, noted that the intensity of the illumination also played a role in the process. The testing showed that the activity of the photovoltaic cells was influenced by the brightness of the light source. This means that researchers can adjust cell alignment not only by changing the physical pattern of the solar cells but also by modifying the light intensity or the distance of the light source from the sample.

Ozbolat explained that while scientists have known for years that weak electrical currents can influence cell alignment, the traditional methods have been limited by the need for bulky systems and invasive wiring. Photovoltaic cells, the same materials used in solar panels, have previously been shown to offer a wireless approach to electrically influencing biological cells. However, it was previously unclear whether manipulating the layout of a photovoltaic cell array could effectively align larger clusters of cells into specific shapes. This study provides evidence that such manipulation is possible and effective for the cell types tested.

The researchers acknowledged that the method does not offer complete control over cell alignment, as cell-to-cell interactions can still play a role in the final structure. Nevertheless, the findings light the path toward wirelessly influencing tissue growth, which could have significant implications for the field of regenerative medicine.

Future work will focus on testing more sensitive cell types, such as cardiac or muscle cells, to understand how the electrical influence may impact cell function alongside alignment. The current study was conducted on a flat, planar surface, but the researchers hope to extend the method to three-dimensional spaces in the future.

The study was supported by chair funds from the Huck Institutes of the Life Sciences at Penn State, as well as grants from the National Institutes of Health’s National Institute of Biomedical Imaging and Bioengineering and the National Institute of Allergy and Infectious Diseases. The research team included several doctoral candidates and postdoctoral researchers from engineering science and mechanics.

Subject of Research: Wireless cell alignment control using photovoltaic microcells for bioprinting

Article Title: Microscopic solar panels could help shape 3D-printed biological tissue

Article References: Microscopic solar panels could help shape 3D-printed biological tissue. Original publication (Bibliographic details unavailable.)

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Keywords: bioprinting, photovoltaic cells, cell alignment, fibroblasts, tissue engineering, wireless control, light-activated, silicon wafers, electrical fields, regenerative medicine, microcell arrays, bioink, cell migration, 3D printing, connective tissue, optical stimulation, material science, biomedical engineering, light intensity, cell orientation