Title: Novel Nano-bioactive Glass /PLGA Composites: Preparation and
Study on the Repairing of Bone Defect Repair

Abstract:

Bone defect caused by trauma or tumor is a common problem in clinical
treatment. The state of the art in repairing, such as autologous or allogeneic bone
transplantation, has some drawbacks in varying degrees, respectively. For example,
although autologous bone substitution is by far the best option, however the amount
of autologous bone is extremely limited and the infection in donor site may further
intensify the pain of patients.While for the allogeneic bone, although the size and
amount of allogeneic bone could satisfy the requirement of bone transplant, its
applications are restricted sharply due to the suffering venture of inevitable immune
response and disease infection. In order to surmount the limitations mentioned
above, the design and development of novel artificial biomaterials as the substitute of
bone transplant has attracted the interests all over the world. This research field has
been an important emerging focus of medical and material even engineering sciences,
consequently.
Tissue engineering is the most prosperous one among the options technically
avialible for the bone repairs. The materials play a vital important role in the tissue
engineering since the bioabsorbable scaffolds is the bottleneck in tissue engineering
applications in clinical treatments.Till now several bioabsorbable scaffords have been
developed for the application of tissue engineeing, for instance, poly lactic acid(PLA),
polyglycolic acid(PGA) and polylactide-glycolide(PLGA). However, as far as bone
tissue engineering is concerned, the above mentioned materials have little thing to do
because of the apparent lack of bioactivities.
Bioactive Glass (BG) has been widely applied in plastic and oral surgery due to
its excellent abilities since its invention by Hench and his colleagues at the University
of Florida in 1971. As a kind of glass particles with high bioactivity, BG shows high
affinity towards bone tissue and could form a thick cement layer on the suface of bone,
thus the interface stress between transplant materials and tissue is significant
suppressed. Bioactive glass can be prepared through the formation of bioactive
apatites or phosphorites followed by the combination with hard (and in some cases
soft) tissues without encapsulations.
The soluble Si, Ca, P and Na ions released from the surfaces reaction of BG
could catalyze the intracellular and extracellular reaction of BG interface cell;
promote the proliferation and differentiation of osteoblast or its precursor. In addition,
its soluble product could modulate the expression of osteogenesis gene and produce
growth factor. This kind of materials will induce the bone tissue to the orientation
towards regeneration. Bone tissue shows rapid response to this kind of materials, thus
the bone-formation rate is fast and the quality of as-formed bone is relatively high.
Once repaired, these materials could be fused and further molted and/or corroded by
newly formed bone tissue.At last normal bone tissue will emerge, instead of the
physical mixture of materials and bone tissue.
The composition of bioactive BG and PLGA could improve the mechanical
strength and osteogenic activity of PLGA. The state of at method, i.e. simply physical
mixing of inorganic materials and polymers, suffer from the weak affinity of
interfaces. In additional, the poly dispersed inorganic particles may result in
aggregation and lower the mechanical response of the composition, thus application
of such composition is quite limited. In the present dissertation, we put the BG into
PLLA to form the polymer of PLLA-g-BG, and then polymerize it with PLGA to
obtain the novel composition of PLLA-g-BG/PLGA. This novel composition can
significantly overcome those drawbacks of trandtionals while maintaining
bioactivities, and would possess the characteritics of more applicable biomaterials for
clinics.
In the thesis, we have undertaken a quantitave aproach toward the design,
preparation, and the functional evaluation of a modified bioactive glass for the clinical
treatment of bone defect repair.