title: Nanostructured calcium phosphates for biomedical applications: novel synthesis and characterization.
abstract: Materials play a key role in several biomedical applications, and it is imperative that both the materials and biological aspects are clearly understood for attaining a successful biological outcome. This paper illustrates our approach to implement calcium phosphates as gene delivery agents. Calcium phosphates (CaP) belong to the family of biocompatible apatites and there are several CaP phases, the most ubiquitous being hydroxyapatite (HAp, Ca(10)(PO(4))(6)(OH)(2). Other CaP structures include brushite (B, CaHPO(4).2H(2)O) and tricalcium phosphate (TCP, Ca(3)(PO(4))(2)). Several low and high temperature approaches have been reported for synthesizing HAp and brushite, while TCP is primarily synthesized using high temperature methods. Novel low temperature chemical methods have been developed by us to synthesize nanostructured HAp, brushite and TCP phases. The new low temperature approach results in the formation of stoichiometric and nanosized HAp under physiological conditions. Moreover, the synthesis methods were designed to be biocompatible with biological systems such as cells, DNA and proteins so that the CaP structures can be studied for gene delivery. The use of HAp type CaP phases for gene delivery is well known but to our knowledge, other forms of CaP have not been studied for gene delivery due to the lack of a biocompatible synthesis method. In addition to the biocompatible synthesis of CaP structures, we have also performed ion substitution that would provide us the appropriate tools to study the DNA-to-particle interactions and assess how these ionic substitutions would affect the level of DNA uptake by the cell and then its release to the cell nucleus. Substitution of calcium by 14% magnesium results in the formation of crystalline ( approximately 20 mum) brushite platelets that remains stable at pH 7.5. Further substitution results in unique nanostructured spherical morphologies of brushite from which rosette shaped high specific surface area ( approximately 200 m(2)/g) nanocrystals ( approximately 80 nm) of beta-TCMP phase can be grown. The novelty lies in the formation of stable phases of HAp, brushite and beta-TCMP under physiological conditions making them potential candidates for use as carriers for non-viral gene delivery or more generally in biological systems. The resultant nanocrystalline phosphates have been characterized for their structure, morphology, thermal stability, and composition. Results of the in vitro transfection are also described.
authors.affiliation: Department of Materials Science and Engineering, Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA. kumta@cmu.edu
authors.forename: Prashant N
authors.initials: PN
authors.lastname: Kumta
authors.forename: Charles
authors.initials: C
authors.lastname: Sfeir
authors.forename: Dong-Hyun
authors.initials: DH
authors.lastname: Lee
authors.forename: Dana
authors.initials: D
authors.lastname: Olton
authors.forename: Daiwon
authors.initials: D
authors.lastname: Choi
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001031:Apatites / Q000138:chemical synthesis; D001672:Biocompatible Materials / Q000138:chemical synthesis*; D002130:Calcium Phosphates / Q000138:chemical synthesis*; D016503:Drug Delivery Systems; D004355:Drug Stability; D017886:Durapatite / Q000138:chemical synthesis; D015316:Genetic Therapy; D006367:HeLa Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008274:Magnesium; D008422:Materials Testing; D051379:Mice; D008855:Microscopy, Electron, Scanning; D049329:Nanostructures; D017550:Spectroscopy, Fourier Transform Infrared; D014162:Transfection
chemical_list: D001031:Apatites; D001672:Biocompatible Materials; D002130:Calcium Phosphates; D017886:Durapatite; D008274:Magnesium; C494366:calcium phosphate, dibasic, dihydrate