Reinforcement On 3-D Chitosan Rod: Potential Utilization For Bone Fracture Internal Fixation

Three dimensional chitosan rod is one kind of biocompatible and biodegradablematerial, which could be used for internal fixation of bone fracture and could avoidsome defects of metallic material and PLA screws, such as second operation toremove the implant, stress-shielding phenomenon, aseptic inflammation caused byacid degradation products, and so on. To meet the demand for the clinical bonefracture internal fixation, several strategies have been used for reinforcing chitosanrods, and the reinforcement mechanisms also have been studied in this research.(1) Chitosan could be dissolved in acetic acid aqueous solution, but chitin fibercould not be dissolved, due to the different deacetylation degree, so chitin fiber couldbe suspended equably in the viscous chitosan solution. Chitin fiber/chitosan 3-Dcomposite rods with layer by layer structure were prepared by in-situ precipitation.Chitosan was continuous phase which could transfer stress, whereas chitin fibers asreinforcement element were randomly dispersed in chitosan matrix and could endureoutside stress so as to improve the mechanical properties of composite rods.The surface of filter paper fiber was accidented and the fiber reacted withchitosan to form small amount of Schiff-base, which could enhance the mechanicalcombining stress of the interface between fiber and matrix, so filter paper fiber couldreinforce chitosan rod effectively.Poly(4-aminophenylacetylene) macromolecular chains were thickly wrappedonto the outer surface of MWNTs byÏ€-Ï€electronic interaction and donor-acceptor(D-A) complexation, so water soluble MWNTs were uniformly dispersed in chitosanmatrix and could bear outside stress effectively. Alignment of MWNTs in chitosanmatrix has also been studied. MWNTs were coated byFe₃O₄/poly(4-aminophenylacetylene), so they became water soluble and could beoriented by magnetic field. TEM results indicated that MWNTs were uniformlydispersed and parallel aligned in chitosan matrix.(2) Sodium aiginate and N-carboxyl propionyl chitosan sodium were used for reinforcing chitosan rods. FTIR spectra confirmed that amino groups and acetamidogroups on chitosan have stronger electrostatic attraction with carboxylate salt groups.So layer-by-layer structure of composite rods became much tighter compared withpure chitosan rod, and mechanical properties improved.(3) Sodium polyphosphate/chitosan composite rods with bionic hollow structureand layer structure have been constructed successfully. Bionic structure formingmechanism has been explored, the layer structure could be explained by LiesegangRing and the hollow structure could be controlled by precipitation time. FTIR spectraconfirmed that there are electrostatic attractions between sodium polyphosphate andchitosan. So the improved mechanical properties of composite rods could beattributed to strong electrostatic attraction, layer structure similar to wood's annualring and hollow structure similar to bamboo.(4) Co60-γ-rays induces chitosan chain scission reaction, resulting in shortermolecular chains which are beneficial for segmental mobility due to lowerintermolecular attraction forces and less chain entanglement, so a higher level ofcrystallinity after irradiation could be observed. Enhanced crystallinity improves themechanical properties of rods, so Co60-γ-rays irradiation is an effective way toimprove the mechanical properties of 3-D biodegradable chitosan rods.Chitosan rods were self-crosslinked to form network structure throughcrosslinking reaction between amino groups caused by thermal effect of microwaveirradiation. The improvement of mechanical properties of chitosan rods treated bymicrowave could be attributed to thermal crosslinking reaction.(5) Chitosan rods and hydroxyapatite/chitosan nanocomposite rods werereinforced through covalently crosslinking to form network structure byglutaraldehyde. The size of hydroxyapatite particles became smaller after crosslinkingof chitosan matrix. Layer-by-layer structure became much tighter after crosslinkingand cracks in one layer turnned around when they reached another layer to absorbenergy, so the mechanical properties of 3-D chitosan rods enhanced.Mechanical properties of chitosan rods have been improved remarkably in thisresearch. Bending strength of bionic hollow sodium polyphosphate/chitosan composite rods, microwave treated rods and glutaraldehyde crosslinked rods arrivedat～180 MPa, which were approximately twice stronger than pure chitosan rods.Reinforced chitosan rods should be a novel internal fixation device for bone fracture.