‘Laser spinning’ technique aids in bone regeneration

Gary Boas, gary.boas@photonics.com

Researchers have devoted considerable effort to developing materials for bone regeneration in the wake of damage or disease. Their studies have focused on producing tissue scaffolds that can mimic the natural extracellular matrix, often exploring the potential of bioactive glass fibers for directing and mediating cell growth.

A variety of techniques for generating these fibers have been described. In the Oct. 19, 2009, issue of Advanced Functional Materials, investigators from the University of Vigo, from Rutgers University in Piscataway and from Imperial College London reported a “laser spinning” method that yields a mesh of disordered intertwined freestanding fibers. The technique offers several important advantages over other approaches to producing bioactive glass fibers.

Developed by Félix Quintero and colleagues in the applied physics department at the University of Vigo, the technique begins with a small volume of precursor ceramic material that is melted at very high temperatures using a high-power laser (in the current study, a Rofin DC 035 CO₂ emitting at 10,600 nm with 2.5 kW of power). At the same time, a high-velocity gas jet blows the molten ceramic, stretching and cooling it very quickly. Because this process occurs at such high speeds, the final structure is amorphous and, thus, essentially bioglass. Also, the extremely rapid stretching of the material leads to considerable length-to-diameter ratios – as much as 1,000,000:1.

Researchers have developed a method with which to produce glass nanofibers for use in bone regeneration applications. The technique yields fibers that more closely mimic the natural extracellular matrix and, furthermore, can be used with the bioactive glass known as 45S5, which is widely used clinically but is not readily drawn into fibers.

Controlling the melting of the precursor and simultaneous elongation of the fluid filaments – so as to achieve minimum breakup of the filaments into spheroidal droplets – proved challenging, Quintero said, but a detailed study of the process helped address this objective.

Using the technique, the researchers obtained fibers from materials that cannot be formed into fibers using more conventional methods. Thanks to its ability to produce fibers from very fragile melts, Quintero said, the investigators succeeded in generating fibers with the BioGlass composition. BioGlass, a commercially available bioactive glass also known as 45S5, is widely used clinically but not easily drawn into fibers because of devitrification – a process in which a material is rendered crystalline and brittle – which often takes place during the fiber drawing.

At the same time, the researchers reduced the diameter of the fibers down to the nanometer scale; bioactive glass fibers generated by other means typically are in the range of 200 to 300 nm. The smaller fibers more closely resemble the collagen fibers in the extracellular matrix. Tissue scaffolds incorporating the fibers therefore will elicit the same or similar behavior from cells.

The researchers now are working to scale up the technology to produce an industrial prototype. They also are performing in vitro and in vivo animal studies in preparation for the approval processes required before it can be used clinically for bone regeneration applications.

Beyond this, they are looking into using the technique for various materials and applications. “We are working on other functional compositions, such as alumina-based nanofibers, useful to produce new fire-resistant fabrics,” Quintero said.