coatings Article Plasma Surface Engineering to Biofunctionalise Polymers for β-Cell Adhesion Clara Tran 1, *, Nicole Hallahan 2 , Elena Kosobrodova 1 , Jason Tong 2 , Peter Thorn 2 and Marcela Bilek 1   Citation: Tran, C.; Hallahan, N.; Kosobrodova,E.; Tong, J.; Thorn, P.; Bilek, M. Plasma Surface Engineering to Biofunctionalise Polymers for β-Cell Adhesion. Coatings 2021, 11, 1085. https://doi.org/10.3390/ coatings11091085 Academic Editor: Alenka Vesel Received: 29 July 2021 Accepted: 6 September 2021 Published: 8 September 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 School of Physics and School of Biomedical Engineering, The University of Sydney, Sydney, NSW 2006, Australia; kosobrodova@fastmail.com.au (E.K.); marcela.bilek@sydney.edu.au (M.B.) 2 Charles Perkins Centre, School of Medical Sciences, The University of Sydney, Sydney, NSW 2006, Australia; nic.hallahan@gmail.com (N.H.); jason.tong@rdm.ox.ac.uk (J.T.); p.thorn@sydney.edu.au (P.T.) * Correspondence: clara.tran@sydney.edu.au Abstract: Implant devices containing insulin-secreting β-cells hold great promise for the treatment of diabetes. Using in vitro cell culture, long-term function and viability are enhanced when β-cells are cultured with extracellular matrix (ECM) proteins. Here, our goal is to engineer a favorable environment within implant devices, where ECM proteins are stably immobilized on polymer scaf- folds, to better support β-cell adhesion. Four different polymer candidates (low-density polyethylene (LDPE), polystyrene (PS), polyethersulfone (PES) and polysulfone (PSU)) were treated using plasma immersion ion implantation (PIII) to enable the covalent attachment of laminin on their surfaces. Surface characterisation analysis shows the increased hydrophilicity, polar groups and radical density on all polymers after the treatment. Among the four polymers, PIII-treated LDPE has the highest water contact angle and the lowest radical density which correlate well with the non-significant protein binding improvement observed after 2 months of storage. The study found that the radical density created by PIII treatment of aromatic polymers was higher than that created by the treatment of aliphatic polymers. The higher radical density significantly improves laminin attachment to aromatic polymers, making them better substrates for β-cell adhesion. Keywords: beta cells; polymer membrane; plasma immersion ion implantation 1. Introduction Microencapsulation of insulin secreting β-cells is a promising approach to treating diabetes. The construction of a microencapsulation device requires that the cells within the implant are protected from immune attack but also that it is permeable to glucose and nutrient inflow as well as insulin outflow. There has been a focus of work on prevention of the foreign body response to an implant and we have recently shown a benefit in coating with IL4 to modify macrophage responses [1]. However, there has been less attention on the internal environment of these devices which, in principle, could be engineered to optimise the support of β-cell function. The approach we favor is the use of an internal polymer scaffold that is bioactivated with extracellular matrices (ECM) proteins that are recognized by β-cells to cause cell adhesion and trigger a range of beneficial cell responses. To this end, we aim to develop methods of stably immobilizing ECM proteins on candidate polymers. It has long been recognized that β-cells function optimally when situated within their native functional unit—the islets of Langerhans, with the support of ECM. The presence of collagen and laminin has been observed to promote β-cell functions including proliferation, survival, identity, insulin gene expression and protein synthesis, and exocytosis [2,3]. Human β-cells, however, are not known to express or secrete their own ECM proteins and may potentially be dependent on external sources [4,5]. The myriad roles and importance of the native micro-environment in β-cell function as well as current limitations in the islet encapsulation field are the impetus to facilitate reconstruction of a replicating key components of the native micro-environment within synthetic capsules to improve current Coatings 2021, 11, 1085. https://doi.org/10.3390/coatings11091085 https://www.mdpi.com/journal/coatings