Bone tissue-bonding mechanism

The tight bonding of mineralized cartilage to bone suggests a mechanical role for the interface of the two elastically different tissues, bone and cartilage. 

In our laboratory, we have studied the effects of various surface-modified alumoxane nanoparticles on the mechanical properties of a biodegradable polymer for load-bearing bone tissue applications [4j. Alumoxane nanoparticles with three different surface modifications were tested — activated alumoxanes possessing two reactive double bonds available for interaction with the cross-link network of the polymer surfactant alumoxanes modified with long fatty acid chains to aid in dispersion within the hydrophobic polymer and hybrid alumoxanes modified with a surfactant chain and a reactive double bond within the same substituent (Figure 40.2). These nanoparticles were incorporated into a biodegradable poly(propylene fumarate)-based (PPF) system and the nanocomposites were tested for flexural and compressive mechanical properties. 

In a parallel study, the influence of bioactive additives, such as short carbon fibres (CF), HAp nanoparticles and bioglass, on the thermal and mechanical properties of PLGA was examined under in vitro conditions. The presence of bioactive particles affects the process of apatite growth on composite surface, in which a chemical bond between the implant and the bone tissue is formed. Despite the deterioration of mechanical properties after incubation under in vitro conditions, the PLGA/HAp composites still showed advantageous biological behaviour [156]. 

Materials that are bioactive develop an adherent interface with tissue that resist substantial mechanical forces. In many cases, the interfacial strength of adhesion is equivalent to or greater than the cohesive strength of the implant material or the tissue bonded to the bioactive implant. Generally, the break takes place in the implant or in the bone but almost never in the interface. 

In addition to HA, silica has been used to improve PCL mechanical properties without compromising biocompatibility (CalandreUi et al., 2010). In this study, PCL and silica surfaces were modified to chanicaUy bond to each other, which reflects the criterion that nanocomposites should have a strong combination between components. Another study (Wei et al., 2009) observed the formation of apatite and the promoted cell proliferation on a calcium-silica-reinforced PCL, which further justifies the use of silica-polymer composite for bone-tissue engineering. 

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