CELL - BASED NANOCOMPOSITES AND BIOMOLECULES FOR BONE TISSUE ENGINEERING - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 550

based materials is incorporated into the synthetic materials to aid in bone integra-
tion of the graft material to the native host tissue.
16.3.3 Nano-HA/Collagen-Based Composites
Calcium phosphate (CaP) coatings are commonly deposited on orthopedic
implants to improve on the biological properties, especially at the bone-implant
interface. Plasma spraying, laser deposition and ion beam deposition are some of
the methods used to coat CaP on implants 68 . Studies have shown that nanoscale
topography of materials favor cellular response. As such, the fabrication of nano-
phase HA has been evident in recent years. Electrostatic spray deposition, or
electrospraying of nano-HA, is one such method, whereby nano-HA particles
were fi rst synthesized via a precipitation reaction using calcium hydroxide
(Ca(OH) 2 ) and orthophosphoric acid (H 3 PO 4 ) with a Ca/P ratio of 1.67, similar to
natural bone. Subsequently, the nano-HA particles were suspended in ethanol to
form a ceramic slurry for electrospraying 69 .
As natural bone is a nanocomposite, investigators explore the possibilities of
fabricating nanocomposite materials to marry the properties of at least two indi-
vidual materials. In the author's previous work, the auhtors have successfully fab-
ricated a composite that can act as a guided tissue regeneration (GTR) membrane
for periodontal therapy. This three-layered graded membrane consists of one face
of the material made of 8% nano-carbonated hydroxyapatite/collagen/polylactic-
co-glycolic acid (nCHAC/PLGA) porous membrane, the non-porous opposite
face made of pure PLGA and the middle layer made of 4% nCHAC/PLGA. The
porous membrane allowed cellular penetration and the non-porous side of the
membrane inhibited cellular adhesion. The composite was fabricated via a layer-
by-layer casting method. As all three layers consisted of PLGA, the composite
exhibited suffi cient fl exibility and mechanical strength. The nCHAC had the
same constituent and had a nano crystal size that was similar to that of natural
bone. As such, it can act as a template for mineralization to take place, attracting
bone cells to the bone graft site during bone remodeling. PLGA was the choice
of polymer because it is biodegrabable in vivo, and bone cells can deposit the
osteoblastic components within the porous, degradable polymer over time, allow-
ing it to be a suitable bone tissue engineered material, improving bone-biomate-
rial interface 70 . Composites that do not contain collagen can be produced via a
hot temperature method such as hot pressing. Recently, a biomimetic self-assem-
bly method that has been developed is said to be suitable for fabricating collagen-
containing composites because collagen degrades rapidly in environments higher
than the body temperature of 37 °C. In this method, illustrated in Figure 16.2 71 ,
Type I collagen was fi rst dissolved in acetic acid. Aqueous solutions of Ca 2+ and
PO − were added into the mixture for the initial nucleation of apatite. To adjust the
pH of the solution, drops of sodium hydroxide were carefully added until the pH
was approximately eight. At this time, calcium phosphates begin to co-precipitate
with the collagen. The precipitates were aged for two hours. Nano-HA can be
retrieved via centrifugation 72,73 .