title: Physicochemical characterization of solid lipid nanoparticles (SLNs) prepared by a novel microemulsion technique.
abstract: OBJECTIVE
  Solid lipid nanoparticles (SLNs) produced by conventional microemulsion techniques using thermal heat have specific limitations (e.g. high polydispersity, instability and low encapsulation). Replacing thermal heat with microwave heat may produce SLNs which overcome some of these limitations.
  
  
  METHODS
  Stearic acid-based SLNs prepared with Tween® 20 as the emulsifier were chosen as the optimum formulation to encapsulate and potentially deliver the antibacterial drug tetracycline. All formulations were characterized for their particle size, zeta potential, encapsulation efficiency, loading capacity, thermal and X-ray diffraction analyses. Short-term stability and in vitro drug studies were also performed.
  
  
  RESULTS
  Microwave heating helps to overcome several disadvantages associated with thermal heating (nonuniform, inefficient and slow) and results in improved particle characteristics. There is thus the potential for new opportunities in the development of colloidal carriers. The particle sizes of microwave-produced SLNs were in the desired nanometer range (200-250 nm) with both lower size and lower polydispersity than the conventional SLNs. We take this as an indication of improved stability; however zeta potential measurements were not different, indicating similar stability. True stability testing (visual observation with time) did show that the microwave-induced SLNs were found to be more stable, particularly when refrigerated. The microwave-produced SLNs also demonstrated improved encapsulation efficiency and loading capacity. Thermal and diffraction analysis confirmed a lowered crystallinity of stearic acid with successful incorporation of tetracycline into the SLNs. In vitro release studies indicated that, after an initial burst release, SLNs could provide prolonged release of tetracycline. The presence of tetracycline and non-toxicity of carriers towards microbes was confirmed by antimicrobial susceptibility tests.
authors.affiliation: Faculty of Science, Engineering and Technology, Swinburne University of Technology, Melbourne, Victoria, Australia. Electronic address: rshah@swin.edu.au.
authors.forename: Rohan M
authors.initials: RM
authors.lastname: Shah
authors.affiliation: Faculty of Science, Engineering and Technology, Swinburne University of Technology, Melbourne, Victoria, Australia. Electronic address: fmalherbe@swin.edu.au.
authors.forename: François
authors.initials: F
authors.lastname: Malherbe
authors.affiliation: Faculty of Science, Engineering and Technology, Swinburne University of Technology, Melbourne, Victoria, Australia. Electronic address: deldridge@swin.edu.au.
authors.forename: Daniel
authors.initials: D
authors.lastname: Eldridge
authors.affiliation: Faculty of Science, Engineering and Technology, Swinburne University of Technology, Melbourne, Victoria, Australia. Electronic address: epalombo@swin.edu.au.
authors.forename: Enzo A
authors.initials: EA
authors.lastname: Palombo
authors.affiliation: Faculty of Science, Engineering and Technology, Swinburne University of Technology, Melbourne, Victoria, Australia. Electronic address: iharding@swin.edu.au.
authors.forename: Ian H
authors.initials: IH
authors.lastname: Harding
mesh_terms: D000900:Anti-Bacterial Agents / Q000008:administration & dosage* / Q000494:pharmacology; D004337:Drug Carriers / Q000737:chemistry*; D004655:Emulsions / Q000737:chemistry*; D004926:Escherichia coli / Q000187:drug effects; D004927:Escherichia coli Infections / Q000188:drug therapy; D006801:Humans; D008872:Microwaves; D053758:Nanoparticles / Q000737:chemistry*; D011136:Polysorbates / Q000737:chemistry; D013203:Staphylococcal Infections / Q000188:drug therapy; D013211:Staphylococcus aureus / Q000187:drug effects; D013229:Stearic Acids / Q000737:chemistry*; D013752:Tetracycline / Q000008:administration & dosage* / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D004337:Drug Carriers; D004655:Emulsions; D011136:Polysorbates; D013229:Stearic Acids; C031183:stearic acid; D013752:Tetracycline
keywords: Encapsulation efficiency; In vitro release; Loading capacity; Microwave; Polydispersity; Solid lipid nanoparticles; Stability; Stearic acid; Tetracycline