本文選題：微孔發(fā)泡注射成型 + 骨組織工程支架�。� 參考：《華南理工大學(xué)》2013年博士論文

【摘要】：微孔發(fā)泡注射成型采用超臨界CO_2/N_2做為物理發(fā)泡劑，具有可顯著減輕制品重量、縮短成型周期和極大改善制品翹曲變形和尺寸穩(wěn)定性等特點，將微孔發(fā)泡注射成型技術(shù)應(yīng)用于制備三維多孔連通結(jié)構(gòu)的生物可降解骨組織工程支架，不涉及任何有機(jī)溶劑且批量生產(chǎn)顯著降低成本，對人類骨組織重建和再生醫(yī)學(xué)的發(fā)展具有重要的現(xiàn)實意義和科學(xué)研究價值。 聚乳酸強(qiáng)度高、成本低廉、生物相容性好且可降解，，目前在組織工程領(lǐng)域已得到廣泛應(yīng)用。然而將聚乳酸這種半結(jié)晶性聚合物應(yīng)用微孔發(fā)泡注射成型制備真三維連通結(jié)構(gòu)且具有高孔隙率的支架仍存在較多加工難題，因此研究聚乳酸的微孔發(fā)泡注射成型成核機(jī)理和加工特性，對于制備理想結(jié)構(gòu)的生物骨組織工程支架具有重要的指導(dǎo)意義。據(jù)此，本文從結(jié)晶、流變特性和異相成核等角度著手，做了以下幾方面的工作： 首先，介紹了微孔發(fā)泡注射成型過程泡孔成核和長大的機(jī)理，研究了超臨界流體作用下結(jié)晶對聚合物流變特性和發(fā)泡形態(tài)結(jié)構(gòu)的影響。針對半結(jié)晶型聚合物氣體溶解和擴(kuò)散相對困難、溶解度低，發(fā)泡溫度窗口窄，熔體強(qiáng)度對溫度敏感等特點，以及超臨界流體注入會降低聚合物熔體粘度的客觀實際情況，研究了結(jié)晶對半結(jié)晶型聚合物泡孔成核和長大的影響機(jī)理。研究發(fā)現(xiàn)，結(jié)晶有助于提高聚合物熔體的儲能模量和熔體彈性，對制備良好形態(tài)結(jié)構(gòu)的發(fā)泡制品具有積極作用。結(jié)晶不僅可以增加成核點數(shù)目，而且作為一種異相成核劑存在能夠促進(jìn)泡孔成核使得泡孔密度增大，同時還可以有效阻止泡孔長大從而減小泡孔的平均尺寸。 其次，為了克服氣熔混合不足和納米粒子在復(fù)合材料中分散不均帶來的制品“皮芯”結(jié)構(gòu)和力學(xué)性能下降的問題，將預(yù)發(fā)泡技術(shù)引入微孔發(fā)泡注射成型工藝中，開發(fā)了一種氣熔混合效果好、可有效改善發(fā)泡結(jié)構(gòu)和性能的方法。采用擠出發(fā)泡制備的含氣發(fā)泡粒料，使得納米復(fù)合材料在進(jìn)入微孔發(fā)泡注射成型機(jī)之前已經(jīng)基本充分形成了分散均勻的微納結(jié)構(gòu)，而且提高了超臨界流體與聚合物熔體的配混效果。實驗結(jié)果表明，采用預(yù)發(fā)泡顆粒制備的微孔注射成型納米復(fù)合材料，皮芯層的均勻度明顯改善，泡孔平均尺寸減小，泡孔密度增大，提高了發(fā)泡制品的力學(xué)性能。 然后，根據(jù)理想骨組織工程支架的結(jié)構(gòu)特征，利用共混法調(diào)控了聚乳酸共混體系的降解速率和力學(xué)性能，研究了它們的熱性能、動態(tài)熱機(jī)械性能和發(fā)泡形態(tài)結(jié)構(gòu)。通過調(diào)整加工工藝參數(shù)，制備了具有雙尺度模式泡孔結(jié)構(gòu)的高孔隙率發(fā)泡制品。人類骨髓間質(zhì)干細(xì)胞的培養(yǎng)實驗結(jié)果表明，所制備的支架酸堿度適當(dāng)，無毒性，細(xì)胞附著和生長繁殖良好，在PLA/PHBV(55:45)支架上培育14天的細(xì)胞呈現(xiàn)骨髓前體細(xì)胞典型樹突結(jié)構(gòu)。MTS分析測定結(jié)果表明，細(xì)胞在所制備的支架上繁殖速度較快，數(shù)目多，其中PLA/PHBV(55:45)試樣尤為突出，驗證了該種配方和工藝條件下制備的雙尺度連通發(fā)泡結(jié)構(gòu)的支架適合細(xì)胞培養(yǎng)，具有良好的載體作用。 最后，從熔體粘彈特性、結(jié)晶和異相成核機(jī)理等三重角度研究了納米粒子改善發(fā)泡制品泡孔形態(tài)結(jié)構(gòu)的機(jī)理和方法，討論了納米粒子對泡孔成核和結(jié)晶成核的雙重作用，分析了納米粒子增強(qiáng)復(fù)合材料的流變特性的響應(yīng)規(guī)律。對制備真三維多孔連通、可調(diào)控的力學(xué)性能和降解速率的納米填充復(fù)合高分子骨組織工程支架具有重要的研究價值。實驗結(jié)果表明：聚乳酸納米復(fù)合材料在整個頻率掃描范圍內(nèi)呈現(xiàn)非常明顯的剪切變稀現(xiàn)象，這種pseudo solid like行為充分說明了納米粘土與高分子之間形成很強(qiáng)的界面作用，這種類似于物理交聯(lián)點的作用限制了高分子鏈的松弛和滑移，增強(qiáng)了熔體粘度。
[Abstract]:Microcellular foaming injection molding using supercritical CO_2/N_2 as a physical foaming agent, which can significantly reduce the weight of products, shorten the molding cycle and greatly improve the warpage and dimensional stability of products. Microporous foam injection molding technology is applied to the biodegradable scaffold for the preparation of three-dimensional porous connected structure. It is of great practical significance and scientific research value for human bone tissue reconstruction and the development of regenerative medicine that any organic solvent is involved and the cost of mass production is significantly reduced.
Polylactic acid has high strength, low cost, good biocompatibility and degradability. It has been widely used in the field of tissue engineering. However, there are still many difficult problems in preparing the semi crystalline polymer of polylactic acid by microporous foam injection molding for the preparation of a truly three-dimensional connected structure with high porosity. The nucleation mechanism and processing characteristics of the injection molding of the orifice are of great guiding significance for the preparation of the scaffold for the ideal structure of biological bone tissue engineering. Accordingly, the following work has been done from the angles of crystallization, rheological properties and heterogenous nucleation.
Firstly, the mechanism of nucleation and growth of foam holes in microcellular foaming injection molding was introduced. The influence of crystallization on the rheological properties and foam morphology of polymer under the action of supercritical fluid was studied. The solubility and diffusion of the semi crystalline polymer gas were relatively difficult, the solubility was low, the foaming temperature window was narrow, and the melt strength was sensitive to temperature. Characteristics, as well as the objective reality of reducing the viscosity of polymer melt by supercritical fluid injection, the influence mechanism of crystallization on the nucleation and growth of semi crystalline polymer bubble holes is studied. It is found that crystallization helps to improve the energy storage modulus and melt elasticity of the polymer melts, and has a positive effect on the foaming products with good morphology and structure. It is used not only to increase the number of nucleation points, but also as an hetero nucleating agent, which can promote the nucleation of the bubble hole to increase the pore density, and can also effectively prevent the bubble hole growth and reduce the average size of the bubble hole.
Secondly, in order to overcome the problem of the "skin core" structure and the mechanical properties of the products caused by uneven gas melting and the uneven dispersion of nanoparticles in the composite materials, the pre foaming technology is introduced into the microcellular foaming injection molding process, and a method for improving the mixing effect of gas melt and improving the foaming structure and properties is developed. The foaming granular materials prepared by foaming make the nano composite basically fully formed the dispersed homogeneous microstructure before entering the microcellular foam injection molding machine, and improve the mixing effect of the supercritical fluid and the polymer melt. The experimental results show that the microporous injection molding nanocomposite prepared by the pre foaming particles has been shown. The uniformity of the core layer is obviously improved, the average size of the foams is reduced, and the density of the foams increases, which improves the mechanical properties of the foaming products.
Then, according to the structural characteristics of the ideal bone tissue engineering scaffold, the degradation rate and mechanical properties of the polylactic acid blends were controlled by blending, and their thermal properties, dynamic thermal mechanical properties and foam morphology were studied. By adjusting the processing parameters, the high porosity foaming with a double scale mode bubble structure was prepared. The results of cultured human bone marrow mesenchymal stem cells showed that the prepared scaffolds were properly acidity, non-toxic, cell adhesion and growth were good. The.MTS analysis of the typical dendritic structure of bone marrow precursor cells for 14 days on the PLA/PHBV (55:45) scaffold showed that the cells were propagated on the prepared stents. The PLA/PHBV (55:45) sample is particularly prominent, which proves that the scaffold of double scale connected foaming structure prepared under the formula and process conditions is suitable for cell culture and has good carrier effect.
Finally, the mechanism and methods of nano particles to improve the morphology and structure of foam holes in foaming products were studied from the three angles of viscoelastic properties, crystallization and heterogeneous nucleation mechanism. The double effects of nanoparticles on the nucleation and nucleation of the bubbles were discussed, and the response laws of the rheological properties of the nano particles reinforced composites were analyzed. The preparation of the true three was true. The experimental results show that the pseudo solid like behavior shows a very obvious shear thinning phenomenon in the range of frequency scanning, and the behavior of this kind of nanocomposites is fully explained. There is a strong interfacial interaction between the clay and the polymer. This action, similar to the physical crosslinking point, restricts the relaxation and slip of the polymer chain and enhances the viscosity of the melt.
【學(xué)位授予單位】：華南理工大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2013
【分類號】：R318.08

【引證文獻(xiàn)】

相關(guān)期刊論文 前1條

1 李金偉;何繼敏;李珊珊;顏克福;邵翠映;;聚乳酸注塑發(fā)泡技術(shù)研究進(jìn)展[J];塑料科技;2015年10期

本文編號：2052014