The Degradation Of α-CaSiO₃ And β-CaSiO₃ Bioactive Bioceramics In Vivo And In Vitro

Bone defects resulting from traumas, infections, tumors and other causes are common in the field of orthopedics. Large bone defects are still troublesome in clinical treatment. Common treatments include autograft and allograft of bone. However, both have restricted use. Alternative artificial bones with sound biocompatibility, safety and bone conductivity shall be taken into account. Recent research shows that calcium silicate is a kind of bioactive material with potential and promising applications. But, there are few reports on research of in vitro and in vivo degradability of bioceramics ofα-CS (α-CaSiO3) andβ-CS (β-CaSiO3). In particular, the report on comparison research of the two materials is still not available. Thus, their in vitro and in vivo degradability is of importance. This test is mainly intended to research on in vitro and in vivo degradable features of calcium silicate bioceramics and evaluate their degradability as artificial bones.1. In vitro study of macroporous calcium silicate bioceramics degradation Objective: The degradability of theα-CS andβ-CS bioactive macroporous bioceramic in vitro were comparatively studied, and the results were compared withβ-tricalcium phosphate (β-Ca3(PO4)2,β-TCP) macroporous bioceramics. Methods: The macroporousα-CS,β-CS andβ-TCP bioceramics were obtained after adding pore forming materials and sintering at high temperature. According to the methods as given in GB/T16886.14, prepare Tris-HCl buffer solution. Soak porousα-CS,β-CS andβ-TCP ceramics into the buffer solution separately on shaking table of 37℃for 1, 3 and 7 days. Replace the buffer solution every 24 hours. At every time point, take six samples for every material. Take out samples upon soaking them for certain time. Leach them with deionized water and acetone in sequence, dry them by baking and weigh them. Calculate the percentage of their weight in initial weight, which is represented as their degradable rate. Results: The in vitro experiment result showed that the degradable rates of the three materials are given as belowβ-CS>α-CS>β-TCP.. There is no significant difference in statistics betweenβ-CS andα-CS(p>0.05). There are significant difference betweenβ-TCP and the other two materials at every time point (p<0.05). The degraded percentage ofα-CS,β-CS andβ-TCP in 7 days amounts to 14.76%, 14.55% and 2.29% respectively.Conclusion: The in vitro degradability test shows that the degradability ofβ-CS andα-CS is significantly higher than that ofβ-TCP bioceramics.2. In vivo study of macroporous calcium silicate bioceramics degradationObjective: Research on the degradability ofα-CS andβ-CS ceramics in cancellous bone environment of living animals. Compare them withβ-TCP ceramics. Compare the ossification performance ofα-CS andβ-CS. Methods: 32 male New Zealand white rabbits of three months old are used in the test. Group them by random number table approach. Prepare cylindrical bone defects ofΦ5㎜×6㎜at condyles of femur. Implant materials in the defect. The specimens were harvested after 1, 4 , 8 and 12 weeks, respectively. Put them into formaldehyde buffer solution (pH=7.1) for 2 weeks. Embed with PMMA and slice it. Stain it by Van-Gieson. Conduct histological and histomorphometry observation, and calculate the area percentage of residue materials. Analyze their degradability in cancellous bone environment of live animals. Results: as time elapses, all three materials show degradation. The area percentage of residual materials ofβ-CS,α-CS andβ-TCP are respectively 50.87%, 51.12% and 52.3% in 12 weeks. It indicates that their degraded amount is given as below:β-CS>α-CS>β-TCP. However statistical analysis does not indicate significant statistical difference (p>0.05). The ossified amounts ofα-CS in 4, 8 and 12 weeks are all greater than that ofβ-TCP of the same period. Conclusion: At 12 weeks, there is not any significant difference between the degradability ofα-CS,β-CS andβ-TCP implanted in vivo. The ossification performance ofα-CS is better than that ofβ-TCP.The said study indicates: although statistical difference of degradability ofα-CS,β-CS andβ-TCP only occurs in vitro test and no significant difference is found in vivo histological observation, qualitative histological observation shows that the degradability ofβ-CS andα-CS is superior toβ-TCP. The whole research indicates that the degradability of porous and active bioceramics ofα-CS andβ-CS is superior to that ofβ-TCP. Bothα-CS andβ-CS are expected to be used for repair of sclerous tissues and as support materials for bone tissue in tissue engineering.