Research On Nano-hydroxyapatite/PA66/Chitosan Composite For Bone Tissue Repair

Bone is one of the most complicated composite in the nature. Bone, not only provides mechanical support but also elegantly serves as a reservoir for minerals, particularly calcium and phosphate. It is a good example of a dynamic tissue, since it has a unique capability of self-regenerating or self-remodeling to a certain extent throughout the life. However, many circumstances call for bone grafting owing to bone defects either from traumatic or from non-traumatic destruction. In the case of severe defects and loss of volume, bone cann't heal by itself and grafting is required to restore function without damaging living tissues. There are multiple methods available for the treatment of bone defects, which include the traditional methods of autografting , allografting and synthetic bone. Although autografting and allografting are clinically considered as good therapies, they have limitations. For example, supply of autograft is limited and there is a possibility of pathogen transfer from allograft. Accordingly, there is a great need for the use of synthetic bone grafts. Nowadays, numerous synthetic bone graft materials, both single- and multi-phases, are available which are capable of alleviating some of the practical complications associated with the autogenous or allogeneic bones.The bone mineral is mainly composed of hydroxyapatite(HA) and the bone protein is mainly composed of collagen. Ideal bone-repair materials should be of good biocompatibility and high bioactivity. Besides, their mechanical properties should be equivalent to natural bone.HA is the main inorganic composition of bone tissue and is of good biocompatibility and high bioactivity, which makes it be able to chemically bond to bone tissue. However, the brittleness and hard machining limit its extensive clinical use. Chitosan(CS) is a natural biodegradable polymer. Its degradation product is alkalescent and is not harm and toxic to human body or tissue. Compounding chitosan with nano hydroxyapatite(n-HA) could overcome the brittleness of HA ceramics, and that the degradation of chitosan also makes space for the ingrowth of cells and tissuesPolyamide66 is used as matrix and can provide a good mechanical and biocompatible property. It is well known that polymers have better toughness, but it lacks of bioactivity. So, if combining the properties of the three materials to carry their good properties forward and get rid of their shortcomings, it will be hopeful to obtain a good bone substitute material. Here, PA66 acts as a structural framework in which tiny crystals of n-HA are embedded to strengthen the bone.In this paper, n-HA/PA66/CS composite is prepared with co-solution method. The testing results show that HA in the composite is poorly crystalline carbonated nano-crystals and dispersed uniformly in the CS/PA66organic phase. The three phases in n-HA/PA66/CS composite have an excellent miscibility and no phase-separation occurs in the blend. Stronger interactions exists among the three phases of n-HA, PA66 and CS, which endows the materials with excellent mechanical strength. When the weight content of n-HA/PA66/CS is 40/45/15 (wt%), the compressive strength of the composite is best, reaching to 70 MPa. In vitro test shows that bone-like apatite deposits onto the surface of the composite, indicating that the composite has good bioactivity.We use polyamide66 as scaffold, blend with n-HA and chitosan by porogen-leaching method in the paper, hoping to acquire a scaffold with good pore size, porosity and mechanical property. Results show that macro-pores and micro-pores coexist in the scaffold, and abundant micro-pores also exist on the wall of macro-pores, and these pores are highly interconnected. When the average pore size is 60.8%, the compressive strength of the scaffold can still reach 7.2 MPa, and can satisfy the demand of tissue engineering when as a cell scaffold.The biological and in vivo tests for n-HA/PA66/CS compostie indicated that, there were no toxic sysptoms showing up after the extract liquid of the composite was injected into the body of mice ; no irritative reactions were found in undermic stimulation test and also no derma allergy was observed. Intramuscular implantation showed that , inflammation reaction was observed in the early period but later a thin fibrin membrane still existed amound the implant and the inflammation reaction disappeared. When compostie was implanted in the bone , the compostie boned to bone tightly and no fibrin tissues were presented between material ans bone tissue, demomstrating cxcellent tissue compatibility and bone-bonding property. Therefore, n-HA/PA66 /CS composite can be figured to be biocompatible and has a potential to be used for new bone repair and substitute materials.