The Study On Preparation And Properties Of α-TCP/α-CSH Bone Cement Modified By Micro-nano Silk Fibroin

Bone defect refers to a shortage of bone matrix caused by trauma or surgery,often resulting in bone nonunion,delayed or nonunion,and local body dysfunction."Critical size"bone defects are those that can not heal spontaneously and require further surgical intervention.Therefore,it is very important to find a kind of bone replacement material with good properties for repairing bone defects over the critical size.α-tricalcium phosphate bone cement（α-TCP）since 1978,and received extensive attention of the researchers after it was put forward,its good biocompatibility and degradation product non-toxic,can generate high thermal stability after hydration is similar to human bone inorganic material of hydroxyapatite（HA）.But it can only be applied to bone tissue repair in non-load-bearing area because of its in the body of the degradation speed is slow,and poor mechanical properties,which limits its clinical application.In order to improve its slow degradation rate and poor mechanical properties,α-hemihydrate calcium sulfate（α-CSH）in calcium sulfate cement was used to adjust the degradation properties of the material.α-CSH reacts with water to produce calcium sulfate dihydrate,which is extremely unstable in aqueous solution and prone to flake collapse.Pureα-CSH bone cement degrades quickly,so it is combined withα-TCP bone cement to accelerate the degradation rate ofα-TCP bone cement.In order to improve the poor mechanical properties ofα-TCP,3wt.%mineralized silk fibroin（HA-SF）was added as interface coupling agent between inorganic materials,and nano-silk fibroin fiber solution（SFFs）was used as curing solution to improve the maximum compressive strength of bone cement.The results are as follows:（1）Afterα-CSH composite,the setting time ofα-TCP/α-CSH composite bone cement was reduced to less than 10min,indicating that the CSD produced byα-CSH reaction with water can be used as a coagulator to accelerate the setting speed;The compressive strength of composite cement can be increased up to 2.7 Mpa,which meets the requirement of compressive strength of cancellous bone.In the degradation process,the degradation of the composite material will increase the weight,which is caused by the mineralization of calcium phosphate and degradation of calcium sulfate.α-TCP is degraded and mineralized layer by layer from the outside to the inside based onα-CSH.α-CSH can also provide Ca²⁺,causingα-TCP to form flake crystal HA.（2）After the compound HA-SF,due to the presence of C=O and N-H in the HA-SF,it can grab water molecules withα-CSH to form hydrogen bonds and delay the solidification reaction;The compressive strength of the material has no obvious increase when theα-CSH ratio is 0,5%,10%,15%,and the average maximum compressive strength can reach 5.41Mpa when theα-CSH ratio is 20%.It can be seen in the electron microscope that the surface morphology of the material becomes compact after the addition of HA-SF,indicating that HA-SF can indeed be used as an interface coupling agent,and can bind with Ca²⁺through C=O and N-H to increase the connection between inorganic materials.The degradation process of HA-SF bone cement is also different from that ofα-CSH composite,which increases the weight gain rate of the material.With the increase ofα-CSH in the composite bone cement,the weight loss rate gradually increases,indicating thatα-CSH can reduce the interface coupling effect of HA-SF to some extent.（3）Due to the combination of C=O and N-H with Ca²⁺and the hydrophilicity of SFFs,water can be as much as possible around the fiber,which can not react withα-CSH to form CSD rapidly,thus slowing down the curing reaction.Compared with the other two groups,the composite showed higher mechanical strength,with an average maximum compressive strength of 9.44 Mpa,but it was still within the required compressive strength range of cancellous bone,and could not be used for the repair of bone bearing area.Compared with Na₂HPO₄solution as the curing solution,the degradation rate of the composite was accelerated,but it showed a stronger ability to induce mineralization,so that the cells could still have a high alkaline phosphatase activity after two weeks.In conclusion,α-CSH can accelerate the degradation rate ofα-TCP and provide Ca²⁺for its mineralization.HA-SF can be used as an interface coupling agent to densify the material and increase the compressive strength to a certain extent.When SFFs as the curing solution,the compressive strength of the material can be improved and the degradation of the material can be accelerated.At the same time,the induced material was mineralized when the Ca/P ratio was close to 1.67.In the cell ALP experiment,compared with Na₂HPO₄as the curing solution,the material still showed a high level of ALP expression on 14th day.