Date Published: January 17, 2019
Publisher: Public Library of Science
Author(s): Salvatore Montesanto, Natalie P. Smithers, Fabio Bucchieri, Valerio Brucato, Vincenzo La Carrubba, Donna E. Davies, Franco Conforti, Mária A. Deli.
Development of biocompatible and functional scaffolds for tissue engineering is a major challenge, especially for development of polarised epithelia that are critical structures in tissue homeostasis. Different in vitro models of the lung epithelial barrier have been characterized using non-degradable polyethylene terephthalate membranes which limits their uses for tissue engineering. Although poly-L-lactic acid (PLLA) membranes are biodegradable, those prepared via conventional Diffusion Induced Phase Separation (DIPS) lack open-porous geometry and show limited permeability compromising their use for epithelial barrier studies. Here we used PLLA membranes prepared via a modification of the standard DIPS protocol to control the membrane surface morphology and permeability. These were bonded to cell culture inserts for use in barrier function studies. Pulmonary epithelial cells (H441) readily attached to the PLLA membranes and formed a confluent cell layer within two days. This was accompanied by a significant increase in trans-epithelial electrical resistance and correlated with the formation of tight junctions and vectorial cytokine secretion in response to TNFα. Our data suggest that a structurally polarized and functional epithelial barrier can be established on PLLA membranes produced via a non-standard DIPS protocol. Therefore, PLLA membranes have potential utility in lung tissue engineering applications requiring bio-absorbable membranes.
The epithelial barrier of the skin, gastrointestinal and respiratory tract are the main interfaces between our body and the outside environment. Their function is to protect the body from environmental agents including pathogens and pollutants, dehydration, and heat loss. Moreover, the epithelial barriers are essential for the physiological functioning of tissues and organs permitting the formation and maintenance of tissue sub-compartments with different composition. Establishment of specialized cell adhesion complexes, especially tight junctions, are crucial to epithelial barrier integrity and function [1–3]. Conversely, the disruption of tight junction structure, due to specific mutations or altered regulatory signals can result in the development of a range of different diseases . For example, in the lung, disruption of epithelial barrier function has been linked to asthma, COPD and cystic fibrosis [3, 5]. In the 2017 report from the Forum of International Respiratory Societies, respiratory diseases were highlighted as being among the principal causes of severe illness and death worldwide and consequently there is a great need for new and more effective treatments. Furthermore, since the lung epithelium offers a non-invasive and efficient route for the delivery of medical compounds, there is a critical need for methods and models in order to enable investigators to test drugs safety and effectiveness [6, 7].
Development of biomaterials suitable for both in vivo and in vitro tissue engineering applications offers opportunities not only for regenerative medicine, but also for target discovery, preclinical evaluation, drug transport and toxicology studies. In our work we show that a functional epithelial barrier can be established on biodegradable PLLA membranes that have enhanced surface porosity and permeability through use of a modification of the standard DIPS protocol. Our results show that the epithelial barrier properties are comparable to those using more conventional PET membranes, however PLLA may be a more suitable material for development of more complex tissue mimetic models because of its biodegradable properties and the possibility of controlling membrane structure. Moreover, PLLA polymers, which are Federal Drug Administration (FDA)-approved, offer an excellent biocompatible and biodegradable scaffold for tissue engraftment in vivo where, after its initial role as a cellular support, it can be degraded by physiological processes. This is especially relevant for pulmonary patients with permanent damage, stenosis or a tumour in the trachea; these patients have a poor quality of life because only limited reconstruction options are currently available. However, tissue engineering and regenerative medicine in the lung offers considerable potential  and will require establishment of an effective epithelial tissue barrier.