CHARACTERISTICS AND MECHANICAL PROPERTIES OF ACRYLOLPAMIDRONATE TREATED
STRONTIUM CONTAINING BIOACTIVE BONE CEMENT
ZY Li1, C Yang2, WW Lu1, B Xu2, WM Lam1, GX Ni1, SA Abbah1, F Yang1, KMC Cheung1 and KDK Luk1
1Department of Orthopaedics and Traumatology, The University of Hong Kong, Hong Kong, China
2Department of Chemistry, Hong Kong University of Science and Technology, Hong Kong, China
Previously we developed an injectable strontium-containing
hydroxyapatite bioactive bone cement (Sr-HAC) system
composed of Sr-HA powders and bisphenol A
diglycidylether dimethacrylate (Bis-GMA) . The outcome
of clinical trials for vertebroplasty was very satisfactory with
a lower setting temperature, good osteointegration and with
no evidence of toxicity . However, the Sr-HAC was
primarily designed for osteoporotic bone fracture and has
not yet been optimized for other orthopaedic applications
such as total hip replacement surgery, implant augmentation
etc, which require the improved mechanical properties.
The aim of the present study was to determine the influence
of surface treatment on the mechanical properties and
biocompatibility of Sr-HA bioactive bone cement.
The Sr-HA powder was subjected to surface treatment using
acrylolpamidronate, a bisphosphonate derivative which has a
polymerizable group, to improve the interface between
inorganic filler and organic matrix by binding Sr-HA and
copolymerizing into the matrix. After surface treatment, the
compression strength, bending strength and stiffness (Fig. 1)
of the resulting composites were defined by using a material
testing machine (MTS) according to ISO 5833. The fracture
surface of the bone cement specimen was observed with a
scanning electron microscope (SEM). In vitro cytotoxicity of
surface treated SrHAC was also studied using a tetrazolium
based cell viability assay (MTS/pms) on human
osteoblast-like cells, the SaOS-2 cell line. Cells were seeded
at a density of 104/ml and allowed to grow in an incubator
for 48hrs at 37°C.
Fig.1: Bending test curves of original Sr-HAC
RESULTS AND DISCUSSION
After surface treatment, the compression strength and
stiffness significantly improved by 22.68% and 14.51%,
respectively. The bending strength and stiffness of the
bioactive bone cement also showed 19.06% and 8.91%
improvements via three-point bending test.
The fracture surface micromorphology after compression
and bending revealed that the bonding between the resin to
surface treated filler considerably improved. Results of the
morphology after compression suggest that there was better
integration between acrylolpamidronate treated SrHAC (Fig.
2B) than pristine SrHAC (Fig. 2A). The increase in the
compressive strength and stiffness can be explained by the
Sr-HA treatment with acrylolpamidronate, which promoted
a better adhesion between the Sr-HA filler and the Bis-GMA
matrix . For untreated Sr-HA bone cement, a typical
smooth Type I brittle fracture surface was observed (Fig.
2C), which meant that there was no or little plastic
deformation when bending, while a rougher Type II/III
brittle fracture surface was observed in treated Sr-HA bone
cement (Fig. 2D). The morphology of treated SrHAC after
bending testing showed that the fracture surface was much
more jagged, irregular, and rough (Fig. 2D). As a result, the
bending strength and stiffness of the bioactive bone cement
Fig. 2: SEM micrographs of the Sr-HAC fracture surface
The cell viability indicated that the treated particles were
nontoxic and did not inhibit cell growth.
This study demonstrated a new surface chemistry route to
enhance the covalent bonds between inorganic fillers and
polymer matrix for improving the mechanical properties of
bone cement. This method not only improves the overall
mechanical performance, but also increases osteoblastic
1. Li YW, et al. J Biomed Mater Res 52, 164-170, 2000.
2. Cheung KM, et al. Spine 30, S84-S91, 2005.
3. Mekraldi S, et al. J Bone Miner Res 20, 1365-1371, 2005.
This study was partially supported by Hong Kong ITF Fund