Biomedical Engineering Reference
In-Depth Information
Calcium phosphate (CaP) ceramics are generally known to be bioactive and osteocon-
ductive but not osteoinductive. Some CaP ceramics, such as some HA, coralline HA, BCP
(Kuboki et al., 1998; LeNihouannen et al., 2005; Ripamonti, 1996; Zhang et al., 1992), and
some experimental coatings (e.g., OCP) on Ti alloy implants (Barrere, 2003) have been
reported to form bone in nonosseous sites of different animals without the addition of
osteogenic factors, whereas other CaP ceramics of the same composition did not show
osteoinductive properties. Based on their studies, Habibovic and deGroot (2007) concluded
that the macrostructure (e.g., interconnecting macroporosity) and microstructure (micro-
porosity and microroughness) play important roles in “material-directed” osteoinduction.
The osteoinduction phenomenon exhibited by some CaP ceramics or coating, but not by
others, was attributed to a particular combination of interconnecting macro- and micropo-
rosities as well as structural concavities in the CaP ceramic particles or scaffolds that allow
the adsorption, entrapment, and concentration of circulating BMPs and/or osteogenic fac-
tors and osteoprogenitor cells (Reddi, 2006; Ripamonti et al., 1992) to impart osteoinductive
properties to these materials (LeGeros et al., 2008).
Engineered osteoinductive properties can be achieved by grafting growth factors or bio-
active peptides to the metal implants or to the calcium phosphate coating of the implant
(deBruyn et al., 2008; Liu et al., 2006; Waldeman et al., 2004). Some authors claim that the
nanonodular texturing of Ti may provide an osteoinductive surface (Ogawa et al., 2006).
SurfaceTreatmentsandCoatingswithAntibacterialProperties
The long-term failure rate of dental implants, reported to be between 5% and 10%, is asso-
ciated with presence of certain bacteria population (Esposito et al., 1998; Tabanella et al.,
2008). With regard to orthopedic implants, microbial infection caused by bacterial adhe-
sion and colonization is also a major concern (Darouche, 2003; Shi et al., 2008). Bacterial
adhesion and colonization is also a problem with orthodontic brackets (Park et al., 2005)
and guided tissue regeneration membranes (Chuo et al., 2007). Some of the recommended
strategies to inhibit bacterial growth and development include implantation of zinc ions
(Ansilmi et al., 2003; Petrini et al., 2006) or silver or copper (Wan et al., 2007), deposition of
zinc-calcium phosphate coatings on metal substrates or membranes (Park et al., 2005; Chou
et al., 2007), polypeptide nanocoatings incorporating antibiotics (Jiang and Li, 2009), TiO
2
(anatase form),
nanoparticle-chitosan incorporating antibiotic (heparin) or nanosilver (Yuan
et al., 2008), and calcium phosphate coatings incorporating antibiotics (Alt et al., 2006; Stigter
et al., 2002) or antibacterial agent, such as chlorhexidine (Campbell et al., 2002) and nitric
oxide-releasing sol-gel coatings (Nablo et al., 2005). Our current exploratory study showed
that surface-treated Ti alloy prevented bacterial colonization (Figure 7.16) (Holmes, 2010).
SummaryandConclusion
The ideal property of orthopedic or dental implants used to replace missing or diseased
bones or teeth is long-term stability. Strategies to accomplish this are based on (1) enhanc-
ing osseointegration (bone bonding) and (2) preventing microbial infection that could
