title: Controlled Release from Zein Matrices: Interplay of Drug Hydrophobicity and pH.
abstract: OBJECTIVE
  In earlier studies, the corn protein zein is found to be suitable as a sustained release agent, yet the range of drugs for which zein has been studied remains small. Here, zein is used as a sole excipient for drugs differing in hydrophobicity and isoelectric point: indomethacin, paracetamol and ranitidine.
  
  
  METHODS
  Caplets were prepared by hot-melt extrusion (HME) and injection moulding (IM). Each of the three model drugs were tested on two drug loadings in various dissolution media. The physical state of the drug, microstructure and hydration behaviour were investigated to build up understanding for the release behaviour from a zein based matrix for drug delivery.
  
  
  RESULTS
  Drug crystallinity of the caplets increases with drug hydrophobicity. For ranitidine and indomethacin, swelling rates, swelling capacity and release rates were pH dependent as a consequence of the presence of charged groups on the drug molecules. Both hydration rates and release rates could be approached by existing models.
  
  
  CONCLUSIONS
  The drug state and pH dependant electrostatic interactions are hypothesised to influence release kinetics. Both factors can potentially be used to influence release kinetics release, thereby broadening the horizon for zein as a tuneable release agent.
authors.affiliation: Laboratory of Physical Chemistry and Soft Matter, Wageningen University, Wageningen, The Netherlands. jacob.bouman@wur.nl.|Laboratory of Physics and Physical Chemistry of Foods, Wageningen University, Wageningen, The Netherlands. jacob.bouman@wur.nl.|School of Pharmacy, University of East Anglia, Norwich, UK. jacob.bouman@wur.nl.
authors.forename: Jacob
authors.identifier: http://orcid.org/0000-0002-1713-6006
authors.initials: J
authors.lastname: Bouman
authors.affiliation: School of Chemistry, University of East Anglia, Norwich, UK.
authors.forename: Peter
authors.initials: P
authors.lastname: Belton
authors.affiliation: Laboratory of Physics and Physical Chemistry of Foods, Wageningen University, Wageningen, The Netherlands.
authors.forename: Paul
authors.initials: P
authors.lastname: Venema
authors.affiliation: Laboratory of Physics and Physical Chemistry of Foods, Wageningen University, Wageningen, The Netherlands.
authors.forename: Erik
authors.initials: E
authors.lastname: van der Linden
authors.affiliation: Laboratory of Physical Chemistry and Soft Matter, Wageningen University, Wageningen, The Netherlands.|Department of Biomedical Engineering, University of Groningen and University Medical Centre Groningen, Groningen, The Netherlands.
authors.forename: Renko
authors.initials: R
authors.lastname: de Vries
authors.affiliation: School of Pharmacy, University of East Anglia, Norwich, UK.
authors.forename: Sheng
authors.initials: S
authors.lastname: Qi
mesh_terms: D000082:Acetaminophen / Q000737:chemistry; D003692:Delayed-Action Preparations / Q000737:chemistry*; D004337:Drug Carriers / Q000737:chemistry; D004339:Drug Compounding / Q000379:methods; D016503:Drug Delivery Systems / Q000379:methods; D005079:Excipients / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D007213:Indomethacin / Q000737:chemistry; D007700:Kinetics; D011899:Ranitidine / Q000737:chemistry; D055672:Static Electricity; D013607:Tablets / Q000737:chemistry; D015028:Zein / Q000737:chemistry*
chemical_list: D003692:Delayed-Action Preparations; D004337:Drug Carriers; D005079:Excipients; D013607:Tablets; D000082:Acetaminophen; D011899:Ranitidine; D015028:Zein; D007213:Indomethacin
keywords: Zein; controlled release; diffusion mechanism; dissolution kinetics modelling; extrusion-injection moulding