Effect Of Molecular Structure Of O-carboxymethylchitin On Properties Of Its 3D Porous Cross-linked Scaffold

In this paper, Series of O-carboxymethylchitin(CMC) were synthesisd by alkailized acid substitution method(α-chitin as raw material, chloroacetic acid as modifier) positioning carboxymethyl on the hydroxyl of α-chitin. The O-carboxymethylchitin was characterized by element analysis, potentiometric titration, fourier transform infrared spectroscopy(FITR), nuclear magnetic resonance(1HNMR), XRD, TG/DSC. 3-dimensional porous scaffolds were prepared by sol-gel freeze-drying method, in which N-(3-dimethylaminopropyl)-N￠-ethyl-carbodiimide hydrochloride(EDC) as dehydrating agent and N- hydroxysuccinimide(NHS) as catalyst, The surface morphology, pore distribution and pore size of the cross-linked scaffold were observed and characterized by scanning electron microscope(SEM). The porosity of the scaffold was measured by liquid discharge method. The swelling properties of the scaffold were investigated by soaking method in the phosphate buffer solution at p H 7.4. The cross-linked degree of the scaffold was calculated by hot soak weight loss method. The thermal stability and crystallinity of the scaffold were tested by TG/DSC and XRD respectively. The mechanical properties of the scaffold were characterized by the tensile machine test. The degradability of the scaffold in vitro was evaluated in lysozyme solution. The effects of deacetylation degree and substitution degree on the properties of scaffold were investigated. Hydroxyapatite(HAP) was added to the CMC to produce CMC-HAP cross-linked scaffold, and effects of HAP on the scaffold were studied.The results of the preparation and characterization of O-carboxymethylchitin revealed that, series of water soluble O-carboxymethylchitin with different DD(with similar DS) and DS(with similar DD) were prepared by changing the the mole ratio of reactant(repeating unit of O-carboxymethylchitin: chloroacetic acid: Na OH), reaction time and temperature. The mole ratio of the reactant(repeating unit of O-carboxymethylchitin: chloroacetic acid; Na OH) mainly affected the DS of O-carboxymethylchitin, the mass concentration of Na OH, react time, react temperature mainly affect the DD of O-carboxymethylchitin. The crystallinity of O-carboxymethylchitin was decreased as the DD and DS increased. The thermal stability of O-carboxymethylchitin was significantly decreased compared with chitin while the water-soluble and water absorption increased significantly compared with chitin.The results revealed that the pore size of O-carboxymethylchitin was decreased as the DD of O-carboxymethylcihtin increased and the DS of O-carboxymethylchitin decreased. The cross-linked degree and porosity of cross-linked O-carboxymethylchitin scaffold were increased as the DD of O-carboxymethylchitin increased and the DS of the O-carboxymethylchitin decreased. The swelling rate of the cross-linked scaffold was decreased as the DD of O-carboxymethylchitin increased and the DS of O-carboxymethylchitin increased. The tensile strength of cross-linked scaffold was increased as the DD of O-carboxymethylchitin increased and the DS of O-carboxymethylchitin decreased. The break elongation of the cross-linked scaffold was decreased as the DD of O-carboxymethylchitin increased and the DS of O-carboxymethylchitin decreased.The time of enzymatic degradation in vitro was increased as the DD of O-carboxymethylchitin increased and the DS of O-carboxymethylchitin decreased. The scaffold was prepared by sol-gel freeze-drying methold. DD was 0.53, DS was 0.61, the scaffold possessed high porosity(93.52±4.68%), swelling rate(1402±70%) and cross-linked degree(93.4±4.6%). The pore size of the scaffold was 100~200μm and the interconnected pore was uniformly distributed. The mechanical prperties tests showed that the tensile strength of the scaffold was up to 0.183±0.009 MPa and the break elongation was 18.7±0.9%.This cross-linked scaffold was decomposed to 10% after 17 days in 0.2mg/m L of lysozyme solution and met the requirement of degradation properties of soft tissue engineering scaffold.The cross-linked CMC-HAP scaffold was prepared by adding the same amount HAP to the O-carboxymethylchitin and the properties of the scaffold were tested. The properties of the scaffold revealed that HAP could reduce the porosity, swelling rate, cross-linked degree and tensile strength of the scaffold, meanwhile increase the degradation time of scaffold prepared by low DD.The cross-linked O-carboxymethylchitin and CMC-HAP scaffold were prepared by sol-gel freeze-drying method, in which the DD and DS was 0.53 and 0.61 respectively. The scaffold possessed interconnect pore, high porosity(>90%), good swelling rate(>1000%), good tensile strength and good biodegradability, basically met the requirements of the soft tissue engineering scaffolds and have the potential applications and value to be soft tissue engineering scaffold material.