homogeneous network formation, is desirable because it maximizes the glass
transition temperature of the matrix; thereby rendering it less susceptible to the
softening effects of the aqueous oral environment. Several researchers have
investigated the degree of vinyl conversion and volumetric contraction of different
types of resin composites formulated with three types of ACP. They observed that
the conversion of methacrylate functional groups in the resin matrix of the various
types of composites is independent of the type of filler phase, but dependent on the
monomer and the compositional factors of the resin matrix. It was also observed
that volumetric contraction of these experimental composites appeared to depend
not only on the type of resin, but also on the type of ACP. Kim and coworkers [105]
proposed bioactive bone cement (BBC), composed of natural bone powder (HAp),
chitosan, and commercially available PMMA-based bone cement. The
investigators obtained three types of BBCs with different composition ratios:
BBC I, BBC II, and BBC III with 10 wt% of chitosan and 40, 50, and 60 wt% of
HAp, respectively. Observation of the interfacial area between the host bone and
the bone cement indicated that the BBC II composite has numerous pores that could
be expected to afford space for bone ingrowth. However, after 4 weeks, the gaps
between the host bone and the BBC II became narrower and PMMA exhibited
undesirable cleavage at the interfacial area; simultaneously, histological
examinations of the interfaces at 4 weeks post-implantation demonstrated more
new bone formations in the BBC II implant than in pure PMMA. In addition, the
exothermic effects in the BBCs were considerably lower than for pure PMMA.
6.2 Degradable Polymer/HAp Nanocomposites
For the last 40 years, the need for so-called “biodegradable” therapeutic material
systems has received much attention in order to replace the use of biostable (or
long-lasting) materials. This evolution is aimed at helping injured or diseased tissue
to self-repair because living systems have outstanding healing ability. Among these
domains, one can distinguish surgery with sutures, osteosynthesis devices (screws,
plates, staples, etc.), pharmacology with drug delivery systems, and tissue engineering [106]. Both synthetic and naturally derived biodegradable polymeric
materials have been investigated extensively as biomaterials for bone tissue regeneration and reconstruction. An overview of degradable polymeric materials (both
synthetic and natural) that are used as polymer matrices for HAp is presented in
Table 2.
6.2.1 Synthetic Biodegradable Polymers
Synthetic biodegradable polymers have attracted much interest for short-term
medical applications like sutures, drug delivery devices, orthopedic fixation
devices, wound dressings, temporary vascular grafts, stents, different types of tissue
Hydroxyapatite-Packed Chitosan-PMMA Nanocomposite: A Promising Material for. . .
155
transition temperature of the matrix; thereby rendering it less susceptible to the
softening effects of the aqueous oral environment. Several researchers have
investigated the degree of vinyl conversion and volumetric contraction of different
types of resin composites formulated with three types of ACP. They observed that
the conversion of methacrylate functional groups in the resin matrix of the various
types of composites is independent of the type of filler phase, but dependent on the
monomer and the compositional factors of the resin matrix. It was also observed
that volumetric contraction of these experimental composites appeared to depend
not only on the type of resin, but also on the type of ACP. Kim and coworkers [105]
proposed bioactive bone cement (BBC), composed of natural bone powder (HAp),
chitosan, and commercially available PMMA-based bone cement. The
investigators obtained three types of BBCs with different composition ratios:
BBC I, BBC II, and BBC III with 10 wt% of chitosan and 40, 50, and 60 wt% of
HAp, respectively. Observation of the interfacial area between the host bone and
the bone cement indicated that the BBC II composite has numerous pores that could
be expected to afford space for bone ingrowth. However, after 4 weeks, the gaps
between the host bone and the BBC II became narrower and PMMA exhibited
undesirable cleavage at the interfacial area; simultaneously, histological
examinations of the interfaces at 4 weeks post-implantation demonstrated more
new bone formations in the BBC II implant than in pure PMMA. In addition, the
exothermic effects in the BBCs were considerably lower than for pure PMMA.
6.2 Degradable Polymer/HAp Nanocomposites
For the last 40 years, the need for so-called “biodegradable” therapeutic material
systems has received much attention in order to replace the use of biostable (or
long-lasting) materials. This evolution is aimed at helping injured or diseased tissue
to self-repair because living systems have outstanding healing ability. Among these
domains, one can distinguish surgery with sutures, osteosynthesis devices (screws,
plates, staples, etc.), pharmacology with drug delivery systems, and tissue engineering [106]. Both synthetic and naturally derived biodegradable polymeric
materials have been investigated extensively as biomaterials for bone tissue regeneration and reconstruction. An overview of degradable polymeric materials (both
synthetic and natural) that are used as polymer matrices for HAp is presented in
Table 2.
6.2.1 Synthetic Biodegradable Polymers
Synthetic biodegradable polymers have attracted much interest for short-term
medical applications like sutures, drug delivery devices, orthopedic fixation
devices, wound dressings, temporary vascular grafts, stents, different types of tissue
Hydroxyapatite-Packed Chitosan-PMMA Nanocomposite: A Promising Material for. . .
155