A Comparative Study of the Adsorptive Characteristics of Mucin to Calcium Hydroxyapatite and Titanium Implants

Aims: The study is aimed to examine the adsorptive characteristics of the main salivary protein, mucin onto Ti surfaces and compare the scientific data with that onto CaHap; towards elucidating the biocompatibility of these two candidates in biomedical applications.
Place and Duration of Study: Department of Chemistry, Ahmadu Bello University, Zaria, Nigeria. Study was carried out between January and April, 2004.
Methodology: To 50 mg, 100 mg, 150 mg and 300 mg of Ti or CaHap powder, 10 mL of (1% or 5%) mucin solution already incubated at 37°C was added at a contact time of 45 minutes in an incubator. After discarding the supernatant, a 10 mL volume of doubly distilled water was added to each residue and rinsed to remove the unadsorbed mucin. The adsorbent particles with the adsorbed mucin of an experimental group was then heated to 60°C for five hours in an oven and then weighed. The samples were then placed in a muffle-furnace at 600°C for 30 minutes to remove the mucin by burning, so as to obtain the weight of adsorbed mucin.
For the experiment on the adsorptive strength, to seven sets of 500 mg Ti or CaHap powder 10 mL of 1% mucin solution was added in an incubator. After centrifugation, the supernatant solution above the titanium particles was removed from the precipitates, and 8 mL of distilled water incubated at 37°C added; after shaking, the supernatant was again removed by the same method. The same rinsing procedure as described above was repeated 0, 1, 2, 4, 8, 10 and 12 times in different experimental groups. The Ti or CaHap particles were heated to 60°C for 5 hours in an oven and weighed. The adsorptive strength was evaluated by comparing the weight change between the no rinse and multiple rinse samples.
One gramme of Ti or CaHap powder placed in test tubes was suspended in 1.0 mL of solutions containing 0.2 – 1.8 mg/mL mucin solution. Following constant shaking for 24 hours at 37°C, the suspensions were allowed to settle and the supernatants collected to determine the adsorption isotherms. Bradford assay was performed on 0.1 mL supernatant samples to obtain Langmuir adsorption isotherm for the materials.
Results: The amount of mucin adsorbed to CaHap was 1.79 ± 0.65 times higher than that to Ti. At the eighth rinse mucin particles remain adsorbed to CaHap but none on the Ti surfaces. The adsorption isotherms of mucin onto both materials exhibited the Langmuir adsorption isotherm, with a maximum of 0.14 mg mucin adsorbed/ 1.0 g CaHap powder compared to a maximum of 0.11 mg mucin/ 1.0 g Ti powder reported by Lori and Nok, (2004).
Conclusion: Mucin can be completely rinsed from the surfaces of artificial titanium tooth and braces deployed in the mouth, thereby prolonging the lifespan. Adsorption of mucin onto these two biomaterial surfaces exhibited the Langmuir type with similarity, so bio-engineered Ti-Hap composite has excellent biocompatibility. The results of these in vitro experiments were consistent with the proposal that ceramics have a higher adsorptive ability than do metals.