Electrospun fibers for fixation of implant to bone

Electrospun membrane has been explored as an aid in fixing implant to bone due to favorable cell response and bonding between dissimilar materials. This takes the advantage of nanofibers while circumventing its weakness as structural support.

In medical implants such as total hip implant and dental implant, bone cement is often used to secure the implant. Enhancement in the fracture toughness with nanofibers interlayers between two different materials has been demonstrated in composites as shown in Figure 1. This property may be used to improve the bonding between bone cement and metal implants. Khandaker et al (2014) used electrospun polycaprolactone fibers (diameter range from 919 nm to 1.25 µm) as interlayers between implant and cement. In this case, the implant was made of titanium (Ti) and the cement was poly methyl methacrylate (PMMA). The effect of fiber patterns was tested and it was found that fracture toughness of the device where unidirectional fibers were used was much better than Ti/PMMA without fibers. However, with bi-directional fibers, the fracture toughness was less than Ti/PMMA without fibers [Khandaker et al 2014a]. In general, the presence of the fibers increases the surface roughness of the metal implant and this decreases the micromovement of cracks at the interface of Ti/PMMA [Khandaker et al 2014b]. Further studies on the mechanical property of the Ti/PMMA with aligned interfacial fibers showed improvement in tensile strength, shear strength and mixed loading [Khandaker et al 2014b]. The difference in the fracture toughness may be due to the wetting and penetration of the PMMA within the fibers. With unidirectional fibers, PMMA may be better able to penetrate into the gaps between the fibers. However, with bidirectional fibers, the fibers may be more resistance to movement which reduces the ability of PMMA to penetrate between the pores. More tests will be needed verify and to determine cause for such differences in fracture toughness.

Electrospun membrane has been used to aid intra-medullary-fixation for fragile long bones. Nishizuka et al (2014) developed a new technique for strengthening severely weakened long bone metaphyses. This procedure require an intramedullary-fixation comprising of a poly(l-lactide) (PLLA) woven tube with calcium phosphate cement (CPC) based on a concept of reinforced concrete and an electrospun poly-3-hydroxybutyrate-co-4-hydroxybutyrate (PHA) membrane to prevent leakage of CPC from the core of the woven tube as shown in Figure 2. Mechanical studies showed that PLLA+CPC+PHA showed significantly higher fracture energy compared to CPC+PLLA, CPC+PHA and CPC only at 10 minute following CPC injection. In vivo study using New Zealand white rabbits showed no fracture displacement for the group with PLLA+CPC+PHA while such incidence were recorded for CPC only, PLLA+CPC and K-wire at 1 week.

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