Title: A novel electrictive biodegradable polymeric nano-composite for
bone repair: preparation and experimental study on the biological
activity

Abstract:
Bone defection and nonunion induced by trauma or tumor are still the puzzles of
reconstructive orthopaedic surgery nowadays. Although autologous and allogeneic
bone substitute materials, as the common replaceable materials, play important role in
treatments, they still have many intrinsic disadvantages and do not meet the demands
in all situations. Autologous bone grafts are considered to be the optimal selection, but
the morbidity at donor sites, limited shape, size and amount of graft are the major
drawbacks of this technique. Furthermore, the additional surgery makes patient
undergo more body injuries, including pain and infection. Allogeneic bone material
can be prepared with any shape, size needed in surgery without the limits of amount,
however the inevitable immune response and the risk of virus disease transmission
make it limit with application. In order to overcome the limitation of the two methods,
it is important task to develop the better man-made biological material to repair bone
defect.
Hydroxyapatite (HA), a major in component of bone organic, has been used
extensively for biomedical implant applications and bone regeneration dueing to its
bioactive, biodegradable and osteoconductive properties. The microstructure of nano
Hydroxyapatite (n-HA）is the same as natural bone matrix, it can be adsorbed by
bone matrix, therefore it can enhance the biological activity. The n-HA can release
more calcium and phosphor for inducing the formation of new bone. The mechanical
properties of n-HA can not be fixed and repaired to meet the orthopedic needs,
limiting its clinical application. The biodegradable material of poly
（lactic-co-glycolic acid）(PLGA) have been permitted by FDA of USA for clinical
application. PLGA used in tissue engineering bone and cartilage of the building and
tissue repairing, there must be a prerequisite for uniform stent planted in a sufficient
number of seed cells. Construction of tissue engineering will take some time and
conditions, which limit its clinical application.
In order to overcome the above shortcomings, a new type of n-HA and PLGA
composite materials will be prepared in this study. The n-HA particles will be
transplanted to the surface of grafted oligomeric lactic acid (LAc oligomer),
then,modified n-HA (op-HA) blends with composite material made of PLGA.
Thus ,op-HA/PLGA. is formatted. Modified op-HA particles in the PLGA matrix
has more uniform dispersion, and op-HA surface oligomeric lactic acid chains into
the PLGA matrix can be internal, it can enhance both the organic and inorganic
phase of adhesion, increase the mechanical strength of composite materials. PLGA
matrix material can be adjusted degradation of the material by adjusting the the ratio
of the composition of lactic acid (LA) and glycolic acid (GA). The biological
activity of the op-HA and PLGA degradation characteristics of the combination of
polymer materials will enhance the biocompatibility and osteoinductive capabilities,
making it more suitable for clinical need for bone defection repairing.
To further enhance the biological activity and intelligent of materials, on the
baseis on op-HA/PLGA materials, a conductive polymer materia will be introduced.
Polyaniline (PA) is a synthetic polymer materials, commonly known as conductive
plastics. As a medical biological materials, there is poor biocompatibility,
non-degradable and difficult to process, poor solubility of defects, thus affecting its
medical applications. A biodegradable aliphatic polyester and aniline oligomer block
copolymer of (PAP) will be prepared in this study. By aliphatic polyester and the
introduction of natural bio-polymer, can not only greatly improve the electrical
activity of the soluble material, but also improve the biocompatibility of materials.
The introduction of the aniline oligomer, which has the similar electrical activity as
Polyaniline.
Combined with pulsed electrical stimulation, a new type of electrical activity of
nano-composite bone repairing material PAP/op-HA/PLGA, reflects the intelligence,
induces bone formation and shortens the bone healing process, provides a basis for
clinical applications.
Conclusion: Op-HA/PLGA bone repair composite material has better cell
adhesion, proliferation and osteogenic activity. The proportion of 85% porogen
scaffolds has the best bone repairing. PAP/op-HA/PLGA has better biocompatibility,
osteoblast adhesion, proliferation and osteogenic activity of gene expression. Under

the pulse electrical stimulation, material properties has a better reflection.

Key words: Nano-hydroxyapatite; Poly(lactide-co-glycolide); Polyaniline; Conducting
polymer; Composite; Tissue engineering scaffold; Biocompatibility; Electrica