electrospinning-ceramic nanofiber

2015-10-06 05:12

ES-3-caramic nanofiber.pdf


Hydroxyapatite is the dominant inorganic phase in natural bone. Synthetic
hydroxyapatite particles, films, coatings, fibers and porous skeletons are used extensively
in various biomedical applications. This bioceramic, Ca10(PO4)6(OH)2, can be
synthesized by many wet chemical and mechano-chemical methods. The sol-gel route is
becoming a unique low-temperature technique to produce ultra fine and pure ceramic
powders. Recently, hydroxyapatite powders and coatings have been successfully
synthesized by the sol gel method. The process parameters have been optimized to
produce high purity hydroxyapatite.
Porous calcium phosphate based scaffolds are used in a wide range of applications in
tissue engineering, controlled drug delivery systems and in the treatment of bone disease.
Various methods have been developed to introduce porosity in calcium phosphate
scaffolds including incorporation of volatile organic particles, gel casting, replication of a
polymer sponge or reticulation and salt leaching. A more recent approach to developing
ceramic fibers and porous structures is the use of electrospinning. In this case, the
inorganic solution that acts as a precursor to the ceramic (e.g. sol) may be mixed with a
polymer solution and the mixture is electrospun at voltages between 10 to 30 kV. Several
researchers have used electrospinning for the production of micro-porous ceramic
structures containing a network of submicron fibers. A variety of ceramic fibers, with
average diameters in the sub-micron range, have been produced by this
technique. Typically, the sol is electrospun with a polymer solution and the resultant
structure is calcined at temperatures on the order of 600oC to remove the polymer.
During electrospinning, the breakup of solution jets into droplets and fibers is strongly
influenced by rheological properties of the solution. The molecular weights (MW) of the
polymer and concentration (c) have significant influences on solution rheology. In
particular, MW plays a vital role in controlling solution viscosity. In this work, the
feasibility of producing hydroxyapatite fibrous networks by calcination of an electrospun
polymer-sol mixture has been studied. The effects of polymer molecular weight and of
the volume fraction of the inorganic sol on the structures obtained after calcination have
been examined.


Hydroxyapatite (HA) is the principal inorganic phase in bone. Synthetic hydroxyapatite particles, films, coatings, fibers and porous skeletons are used extensively in various biomedical applications. In this contribution, sol-gel processing and electrospinning have been used to develop a technique to produce fibrous structures. Poly(vinyl alcohol) (PVA) with an average molecular weight (MW) between 40,500 g/mol and 155,000 g/mol was electrospun with a calcium phosphate based sol. The sol was prepared by reacting triethyl phosphite and calcium nitrate and was directly added to an aqueous solution of PVA. This mixture was electrospun at a voltage of 20 - 30 kV. The results indicate that the sol particles were distributed uniformly within the PVA fibers. This electrospun structure was calcined at 600oC for 6 hr to obtain a residual inorganic, sub-micron fibrous network. The fibrous structure after electrospinning is retained after calcination. A variety of structures including solid fibers, micro-porous fibers and interconnected networks could be obtained after calcination. A bead-on-string structure was obtained after electrospinning for MW = 40,500 g/mol. X-Ray diffraction of this fibrous structure indicated that it consisted predominantly of hydroxyapatite with an average crystal size of almost 10-30 nm. The final morphologies of the ceramic fibers were found to depend on polymer molecular weight and sol volume fraction. Average fiber diameters were on the order of 200 nm and 800 nm for molecular weight of 67,500 g/mol and 155,000 g/mol, respectively. By judiciously controlling these material and process variables, non-woven mats of sub-micron fibers with varying degrees of interconnectivity and porosity have been produced. Such novel structures can be useful in drug delivery, tissue engineering and related biomedical applications.

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