Colloids and Surfaces B: Biointerfaces 133 (2015) 140–147 Contents lists available at ScienceDirect Colloids and Surfaces B: Biointerfaces jo ur nal ho me p ag e: www.elsevier.com/locate/colsurfb Diatom-inspired skeletonisation of insulin – Mechanistic insights into crystallisation and extracellular bioactivity Diosángeles Soto Véliz a , Catharina Alam b , Thiago Nietzel a , Rebecca Wyborski a , Adolfo Rivero-Müller c,d , Parvez Alam a,∗ a Laboratory of Paper Coating and Converting, Centre for Functional Materials, Abo Akademi University, Porthaninkatu 3, 20500 Turku, Finland b Biomedical Science Research, Turku, Finland c Department of Physiology, Institute of Biomedicine, University of Turku, Turku, Finland d Department of Biochemistry and Molecular Biology, Medical University of Lublin, 20-093 Lublin, Poland a r t i c l e i n f o Article history: Received 26 March 2015 Received in revised form 24 May 2015 Accepted 31 May 2015 Available online 9 June 2015 Keywords: Calcium carbonate Crystallisation Direct encapsulation Insulin Diatom Diabetes a b s t r a c t In this paper, we encage insulin within calcium carbonate by means of a biomineralisation process. We find that both dogbone and crossbone morphologies develop during the crystallisation process. The crystals break down into small nanocrystals after prolonged immersion in phosphate buffer solution, which adhere extracellularly to mammalian cells without causing any observable damage or early cell- death. The mechanisms behind calcium carbonate encaging of single insulin monomers are detailed. This communication elucidates a novel, diatom-inspired approach to the mineral skeletonisation of insulin. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Insulin dependent diabetes mellitus, commonly known as diabetes type 1, has been described as the immune-mediated destruction of endocrine -cells located in the pancreatic islets of Langerhans [1]. The selective destruction of -cells results in insulin deficiency in the body and induces specific microvascular pathologies such as neuropathies, nephropathies and cardiovascu- lar diseases increasing the risk of mortality [2–8]. Therefore, insulin treatments are needed in order to control blood glucose levels and prevent further complications due to hyperglycaemia [9]. To date, the most common treatment has been daily subcu- taneous injections of insulin which disrupts a normal life. As a result, in the past decade, pharmaceutical companies have been attempting to develop non-invasive delivery systems capable of mimicking the insulin secretion of -cells [10]. Breakthroughs in short-term diabetic treatment include technologies such as ∗ Corresponding author at: Adjunct Professor of Composite Materials and Biostructures, Laboratory of Paper Coating and Converting, Centre for Func- tional Materials, Abo Akademi University, Porthaninkatu 3, 20500 Turku, Finland. Tel.: +358 22154858. E-mail addresses: parvez.alam@abo.fi, shantanou@gmail.com (P. Alam). Exubera ® , a commercialised pulmonary delivery system, later removed from the market [11], and Eligen TM (Emisphere technolo- gies), an ongoing project for oral insulin delivery based on the use of synthetic non-acylated amino acids as carriers [12]. 1.1. Biomineralisation Drug delivery systems should ideally be designed as functional carriers with specific sizes, morphologies and with desired chemi- cal characteristics, whilst retaining the functionality and bioactivity of the drug. One way this can be achieved may be through deriv- ing inspiration from natural processes of biomineralisation [14]. Biomineralisation gives birth to a broad range of minerals with functional patterns and diverse properties. It does so by tailoring the formation of complex inorganic–organic structures, where the organic component acts as a template to control mineral nucleation and crystal growth [15,16]. Diatoms are inspirational models for biomineralisation. These are a group of eukaryotic algae characterised by their unmatched and so far, irreproducible hierarchical frustules (silica exoskele- tons). Their beautiful shells are a result of genetically guided biomineralisation where the cell is encaged within a protective skeleton [17]. These skeletons are amorphous, species-specific http://dx.doi.org/10.1016/j.colsurfb.2015.05.047 0927-7765/© 2015 Elsevier B.V. All rights reserved.