Picture of piezoelectric scaffolds. Scale bar = 2 mm (A). Scanning electron microscope (SEM) image of piezoelectric scaffold showing fibrous structure at 2000 magnification. Scale bar = 20 microns (B).Tissue engineering promises the regeneration of damaged or diseased parts of the body by providing a scaffold on which cells can regrow. Ideally, scaffold materials should mimic the characteristics of native tissue as closely as possible. Now researchers have created scaffolds from piezoelectric materials, which generate electrical activity when mechanically deformed, that harness the body’s own natural movements to stimulate the repair of damaged tissue [Damaraju et al., Biomaterials 149 (2017) 51-62].
“Tissues, such as bone and cartilage, and their extracellular matrix (ECM) components, collagen and glycosaminoglycans, have been known to display electrical behavior when subjected to loading or deformation,” explains Treena Livingston Arinzeh of New Jersey Institute of Technology, who led the research with colleagues from the University of Washington and Shenzen Institutes of Advanced Technology in China.
Despite this knowledge, piezoelectricity has been largely overlooked in the design of scaffold materials for tissue engineering. Arinzeh and her colleagues set out to address this shortcoming by investigating how piezoelectric activity affects the differentiation of stem cells into cartilage and bone cells.
“We developed a three-dimensional piezoelectric fibrous scaffold and demonstrated, for the first time, that it could stimulate stem cell differentiation and tissue formation,” she says.
The scaffold is made from the piezoelectric polymer poly(vinylidene fluoride-triflouroethylene) (PVDF-TrFE) using electrospinning in which an electric field is applied to the ejected polymer solution.
“We have a unique setup that differs from conventional electrospinning so we can create large three-dimensional fibrous scaffolds,” explains Arinzeh.
The tangled fibers, which are a few microns in diameter, are separated by large spaces that allow cells access and tissues to grow. Heat-treating (or annealing) the scaffolds, the researchers found, increases the level of piezoelectric activity. When the scaffold is deformed mechanically, electrical activity is generated without the need for any external power source or electrodes.
“This is a unique property that imitates natural tissues or extracellular components,” points out Arinzeh. “Electrical stimulation has been shown to stimulate both cell growth and differentiation.”
Indeed, the research shows that, in a bioreactor the as-spun piezoelectric PVDF-TrFE scaffolds promote the differentiation of stem cells into cartilage cells. The more strongly piezoelectric annealed scaffolds, by contrast, promote differentiation into bone cells.
“This is the first time that piezoelectric materials have been fabricated into a 3-D scaffold and shown feasibility for tissue engineering applications,” Arinzeh told Materials Today. “In fibrous form, PVDF-TrFE has soft/flexible mechanical properties so it can be used for a variety of tissue engineering applications.”
She is now undertaking preclinical studies of the PVDF-TrFE scaffolds for spinal cord repair with the University of Miami.