Lee, Thi Bang
(2013)
Substituted Apatite/Poly-Epsiloncaprolactone
Biocomposite As Substrates And Coating On Alphatricalcium
Phosphate Foams.
PhD thesis, Universiti Sains Malaysia.
Abstract
In this research, carbonate and silicon-substituted apatite/poly-ɛ-caprolactone
biocomposite were produced to be used as a porous biocomposite bone substitute.
Carbonate apatite/poly-ɛ-caproplactone (CO3Ap/PCL) was also used to coat on a
fully interconnected structure of α-tricalcium phosphate (α-TCP) foam to enhance the
mechanical and biological properties, and to mimic the structure of cancellous bone.
Carbonate apatite (CO3Ap) and silicon-substituted carbonate apatite (Si-CO3Ap)
were synthesized by a precipitation method. The results revealed that the silicate and
carbonate ions competed to occupy the phosphate site and also entered
simultaneously into the hydroxyapatite structure. The Si-substituted CO3Ap reduced
the powder crystallinity and promoted ion release which resulted in a better solubility
compared to that of Si-free CO3Ap. The silicon and carbonate co-substitution
appeared to have a better effect on the early stages of osteoblast behavior (cell
attachment and proliferation) rather than the immediate/late stages (proliferation and
differentiation). The fabrication of a biocomposite derived from an interconnected
porous Si-CO3Ap reinforced with molten poly-ε-caprolactone (PCL) was then
developed to mimic the composition and structure of bone coupled with enhanced
mechanical performance. Porous silicon-substituted carbonate apatite blocks were
produced using wax as a volatile agent. The interconnected porous Si-CO3Ap
obtained has a porosity of about 80% and a pore size of about 100-200 μm. The PCL
covered, and penetrated into the pores of, the porous Si-CO3Ap to form an excellent
bonding with Si-CO3Ap leading to a significant increase in diametral tensile strength
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from 0.23 MPa to a maximum of 2.04 MPa. However, although the porous
biocomposite meets the requirement of biological bone to some extent, it remains a
great challenge to make the ideal bone substitute materials that mimic the natural
structures, in which, a fully interconnected structure should be highly considered.
The mechanical behavior, microstructure and cell responses of CO3Ap/ PCL coated
α-tricalcium phosphate (α-TCP) foams were studied as an initial step for the
fabrication of a cancellous-type artificial bone replacement. The α-TCP foam was
obtained by sintering CaCO3 and CaHPO4•2H2O at 1500oC. It was then coated with
CO3Ap/PCL and its three dimensional, fully-interconnected porous structure was
found to be maintained. CO3Ap/PCL coating on α-TCP foam was proven to be very
effective in increasing the mechanical strength by 25 times and toughening the α-
TCP foam, in addition to excellent biocompatibility as proven by bone marrow cell
studies. The coated α-TCP specimens exhibited high porosity (80-85%) with large
pore size (500-700μm) that mimic the cancellous bone structure. The in vitro
biological evaluations indicated that CO3Ap/PCL used for coating improved cellular
attachment, accelerated proliferation and resulting in a greater alkaline phosphatase
(ALP) activity of both MC3T3-E1 cell-like and rat bone marrow cells.
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