title: Microfabricated silicon microneedles for nonviral cutaneous gene delivery.
abstract: BACKGROUND
  The skin represents an accessible somatic tissue for therapeutic gene transfer. The superficial lipophilic layer of the skin, the stratum corneum, however, constitutes a major obstacle to the cutaneous delivery of charged macromolecules such as DNA.
  
  
  OBJECTIVE
  To determine whether silicon-based microneedles, microfabricated via a novel isotropic etching/BOSCH reaction process, could generate microchannels in the skin of sufficient dimensions to facilitate access of lipid : polycation : pDNA (LPD) nonviral gene therapy vectors.
  
  
  METHODS
  Scanning electron microscopy was used to visualize the microconduits created in heat-separated human epidermal sheets after application of the microneedles. Following confirmation of particle size and particle surface charge by photon correlation spectrocopy and microelectrophoresis, respectively, the diffusion of fluorescent polystyrene nanospheres and LPD complexes through heat-separated human epidermal sheets was determined in vitro using a Franz-type diffusion cell. In-vitro cell culture with quantification by flow cytometry was used to determine gene expression in human keratinocytes (HaCaT cells).
  
  
  RESULTS
  The diffusion of 100 nm diameter fluorescent polystyrene nanospheres, used as a readily quantifiable predictive model for LPD complexes, through epidermal sheets was significantly enhanced following membrane treatment with microneedles. The delivery of LPD complexes either into or through the membrane microchannels was also demonstrated. In both cases considerable interaction between the particles and the epidermal sheet was observed. In-vitro cell culture was used to confirm that LPD complexes mediated efficient reporter gene expression in human keratinocytes in culture when formulated at the appropriate surface charge.
  
  
  CONCLUSIONS
  These studies demonstrate the utility of silicon microneedles in cutaneous gene delivery. Further studies are required to elucidate fully the influence of the physicochemical characteristics of gene therapy vectors, e.g. particle diameter and surface charge, on their diffusion through microchannels and to quantify gene expression in vivo.
authors.affiliation: Welsh School of Pharmacy, Cardiff University, Cardiff, UK.
authors.forename: F
authors.initials: F
authors.lastname: Chabri
authors.forename: K
authors.initials: K
authors.lastname: Bouris
authors.forename: T
authors.initials: T
authors.lastname: Jones
authors.forename: D
authors.initials: D
authors.lastname: Barrow
authors.forename: A
authors.initials: A
authors.lastname: Hann
authors.forename: C
authors.initials: C
authors.lastname: Allender
authors.forename: K
authors.initials: K
authors.lastname: Brain
authors.forename: J
authors.initials: J
authors.lastname: Birchall
mesh_terms: D000279:Administration, Cutaneous; D001940:Breast / Q000648:ultrastructure; D002478:Cells, Cultured; D004817:Epidermis / Q000648:ultrastructure; D004867:Equipment Design; D005260:Female; D015870:Gene Expression; D018014:Gene Transfer Techniques / Q000295:instrumentation*; D005822:Genetic Vectors / Q000008:administration & dosage*; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism; D008845:Microinjections / Q000295:instrumentation; D008855:Microscopy, Electron, Scanning; D036103:Nanotechnology / Q000379:methods; D043942:Nanotubes; D009339:Needles; D010316:Particle Size; D011137:Polystyrenes; D012825:Silicon
chemical_list: D011137:Polystyrenes; D012825:Silicon