Download A Biphasic Biomaterial as Carrier for Bone Active Substances: Tibial

A Biphasic Biomaterial as Carrier for Bone Active Substances:
Tibial Bone Defect Reconstruction in Rats
Deepak Bushan Raina1, Peter Horstmann1,2, Hanna Isaksson1,3, Werner Hettwer2, Lars Lidgren1, Michael Mørk Petersen2, Magnus Tägil1
Department of Orthopedics1, Clinical Sciences, Lund University, Lund, Sweden, Department of Orthopedics2, Rigshospitalet, University of
Copenhagen, Denmark, Department of Biomedical Engineering3, Lund University, Lund, Sweden
Introduction
Treatment of bone defects is a challenging task in orthopedic surgery. Today most often bone grafts are used, either from the patient
(autograft) when bone formation and graft remodeling is required, or from donors (allografts) when simply void filling is sufficient.
Synthetic biomaterials may be an attractive alternative since biologically active substances can be added. In the present study, we used a
gentamicin containing biphasic calcium sulphate/hydroxyapatite biomaterial (GBM) to deliver ZA and bone morphogenic protein 2 (BMP-2)
in a tibial defect model in rats, in order to create an off the shelf bone inductive bone substitute for recalcitrant non-unions and infected bone
defects.
We hypothesized that:
- The bone defect would not be able to heal by itself (a critical bone defect).
- Fresh frozen allograft or GBM would result in higher mineral content compared to leaving the defect empty.
- The GBM as a carrier of active substances (ZA and BMP-2) would result in living remodeled tissue compared to filling the defect with
GBM alone.
Materials and Methods
The animals were randomly allocated to one of five groups (n=10 per group), and the defect
reconstruction was carried out with one of the following materials: 1) Empty defect (Empty), 2)
Allograft (Allograft), 3) GBM (GBM), 4) GBM and ZA (GBM+ZA), 5) GBM, ZA and BMP-2
(GBM+ZA+BMP-2).
At 4-weeks, in-vivo micro-CT imaging was performed (intermediate time).
At 8-weeks, all animals were sacrificed using an overdose of pentobarbital sodium. The tibiae were
harvested, cleaned from surrounding soft tissue, wrapped in wet gauze, and kept frozen. The defect
region was examined with plain radiography, histology, DEXA, and ex-vivo micro-CT.
Results
In-vivo Micro-CT images at 4-weeks showed significantly higher mineralized volume (MV) in the
defect in all GBM treated groups.
Ex-vivo micro-CT and DEXA at 8-weeks showed that addition of ZA (GBM+ZA) and BMP-2
(GBM+ZA+BMP-2) increased the cortical remodeling with the highest MV in the BMP-2 treated
group.
An increased cortical thickness by the addition of ZA and BMP-2 was seen by qualitative
histological analysis and trabecular bone was found in the all GBM treated groups.
Fig. 1 The three regions of interest (ROI)
were defined for the micro-CT analysis.
Fig. 2 Quantitative micro-CT results in the
tree regions: defect (MV/TV), cortex and
callus (MV), and 3mm whole bone.
section (MV).
In the Empty and the Allograft groups, normal cortical bone architecture was seen without
convincing signs of bone formation inside the defect area. Empty group appeared to be empty in the
middle, while specimens from the Allograft group were filled with marrow like tissue. The addition
of ZA increased cortical thickness but remnants of GBM were found inside the defect area and also
at the cortex. The defect was also filled with trabecular bone. Addition of BMP-2 further increased
callus size with a visible callus extending beyond the margins of the old cortex. The middle of the
defect contained viable trabecular bone integrating well with the GBM. GBM was also present near
the cortex.
Matched CT slices with the histology slices emphasize that the high-density mineral/tissue within
the defect not only represent remnants of the material entirely, but also appears to be new bone tissue.
Conclusion
The defect appeared to be non-critical as also the empty control bridged, but
left an empty interior of the defect after remodeling. GBM alone can be used
to also fill the defect with results comparable with bone allograft. The GBM
can further carry anabolic and anti-catabolic agents like BMP-2 and ZA, to
initiate bone regeneration when necessary, and not only void filling. Addition
of ZA in a metaphyseal defect can be beneficial, possibly due to the presence
of endogenous BMPs in the defect, which cause bone formation while ZA
blocks premature resorption. Moreover, in order to achieve accelerated bone
regeneration, it is also possible to combine the GBM with low dose rhBMP-2
along with ZA.
Fig. 3 Histology of the explants 8-weeks post-op (HE). Empty,
Allograft, GBM, GBM+ZA and GBM+ZA+BMP-2 groups. Lower
panel with matched CT images. Green lines show the middle of the
defect, orange lines the histology cut..
Clinical significance
The biomaterial alone, in combination with ZA, or both ZA and BMP-2 can
potentially be used as off-the-shelf alternative to currently used bone-grafting
materials for bone defects in orthopedic surgery.
Acknowledgements
We would like to thank the foundation for disabled people in Skåne, Sweden and the Medical Faculty, Lund University, Sweden. We also
acknowledge LBIC, Lund University for the Micro CT facility.
ORS 2017 Annual Meeting Poster No.1344