Nanoscale crystallinity modulates cell proliferation on plasma sprayed surfaces

Calcium phosphate coatings have been applied to the surface of metallic prostheses to mediate
hard and soft tissue attachment for more than 40 years. Most coatings are formed of high purity
hydroxyapatite, and coating methods are often designed to produce highly crystalline surfaces. It
is likely however, that coatings of lower crystallinity can facilitate more rapid tissue attachment
since the surface will exhibit a higher specific surface area and will be considerably more
reactive than a comparable highly crystalline surface. Here we test this hypothesis by growing a
population of MC3T3 osteoblast-like cells on the surface of two types of hip prosthesis with
similar composition, but with differing crystallinity. The surfaces with lower crystallinity
facilitated more rapid cell attachment and increased proliferation rate, despite having a less
heterogeneous surface topography. This work highlights that the influence of the crystallinity of
HA at the nano-scale is dominant over macro-scale topography for cell adhesion and growth.
Furthermore, crystallinity could be easily adjusted by without compromising coating purity.
These findings could facilitate designing novel coated calcium phosphate surfaces that more
rapidly bond tissue following implantation.