Towards hydrophilic piezoelectric poly-L-lactide films: optimal processing, post-heat treatment and alkaline etching

Active, hydrophilic, piezoelectric PLLA surface is formed by correlating processing parameters with etching and annealing as post-processing steps. Optimal design is obtained after uniaxial drawing of films for five times their length at 90 degrees C with 40 mm min(-1) drawing rate and post-processing heat treatment at 140 degrees C followed by surface alkaline etching. We designed active PLLA film with high potential for intensive interactions with cells, very important for further biomedical applications, including exploring the effect of piezoelectricity on cell proliferation. Piezoelectric poly-L-lactide (PLLA) films are highly applicable for designing soft electronics in biomedicine. However, due to a lack of reactive side-chain groups, PLLA is characterized by a chemically inert and hydrophobic surface. Although compatible with biological environments, this polymer has very poor interactions with cells. This work is the first report on piezoelectric PLLA films with hydrophilic surfaces. We performed a systematic study that correlated processing parameters (drawing ratio, drawing temperature, drawing rate) with postprocessing steps (annealing and etching) to produce active, hydrophilic, piezoelectric PLLA surfaces. During processing, the optimal drawing ratio, temperature and rate increase the crystallinity and crystallite size and provide chain orientation. Postprocessing annealing and etching afford further improvements in structural properties and optimized surface characteristics. Consequently, the resulting PLLA films possess piezoelectric properties in combination with hydrophilic surfaces and specifically patterned topography. Using this approach, we designed active PLLA films with high potential for strong interactions with cells in further biomedical applications, including exploring the effect of piezoelectricity on cell proliferation. This study provides novel insight into designing synthetic piezoelectric polymers with significantly improved interactions with cells and tissues, which are particularly important for their application in biomedicine.