Biocompatible Organic-inorganic Nanocomposite Porous Scaffolds Fabricated By Pickering Emulsion Template Method

Biocompatible organic-inorganic nanocomposite(NC) porous scaffolds have gained much interest in tissue engineering, drug delivery and other biomedical applications, due to their special structures and properties. And the controlled fabrication of these scaffold materials has become a hot topic of research in the biomedical field. In this dissertation, we described the preparation of organic-inorganic NC porous scaffolds with open-porous structure or containing microspheres based on the Pickering emulsion templates. The external phase of emulsion template was solidified by solvent evaporation or physical gelation. The effects of preparation conditions on the structures and properties of NC porous scaffolds were investigated. The new strategies for the preparation of different structures and properties of NC porous scaffolds were developed. Furthermore, the applications of the NC porous scaffolds in drug delivery and tissue engineering were also explored. The main research contents and results of this dissertation are as follows:1. Hydroxyapatite(HAp)/poly(L-lactic acid)(PLLA) NC porous scaffolds were fabricated by solvent evaporation from Pickering emulsions. The HAp nanoparticles modified with PLLA(g-HAp) were used as effective particulate emulsifiers to produce stable W/O Pickering emulsions containing PLLA in oil phase. Evaporation of the W/O Pickering emulsions directly led to the NC scaffolds. The effect of preparation conditions on the pore structures of the NC scaffolds was discussed in detail. Furthermore, the physical properties, bioactivity, drug delivery and release behavior of NC scaffolds were also investigated. The results showed that the NC scaffolds possessed interconnected pore structures, which could be modulated by varying the g-HAp concentration, PLLA concentration, ratio of oil to water and PLLA molecular weight. With increasing g-HAp nanoparticle concentration, the thermal stability, surface hydrophilicity, mechanical property and density of NC scaffolds enhanced, while the porosity decreased. After being soaked in simulated body fluid(SBF), the calcium-sufficient, carbonated apatite particles were formed on the NC scaffolds, and their number and average size increased with increasing incubation time. With higher g-HAp nanoparticle concentration, more apatite particles grew on the NC scaffolds. Furthermore, the release behavior of the NC scaffolds using IBU as the model drug showed that the NC scaffolds exhibited a sustained release of IBU, which increased with higher g-HAp nanoparticle concentration and p H value of release medium. The release profiles could be well fitted by Higuchi model, and the release kinetic followed Fickian diffusion.2. The well-defined g-HAp/poly(lactide-co-glycolide)(PLGA) NC porous scaffolds were facilely fabricated by solvent evaporation of g-HAp-stabilized W/O Pickering high internal phase emulsion(HIPE) templates containing PLGA in oil phase. The effects of g-HAp concentration and internal phase volume fraction(IPVF) on the emulsion morphology, pore structure and mechanical properties of the NC scaffolds were discussed in detail. Furthermore, the bioactivity, anti-inflammatory drug release behavior and biocompatibility of NC scaffolds were also investigated. The results showed that the NC scaffolds exhibited an open and rough pore structure. The pore structure and mechanical properties of the scaffolds could be tuned readily by varying the g-HAp concentration and IPVF of the emulsion templates. With increasing the g-HAp concentration or decreasing the IPVF, the pore size and the porosity decreased, while the mechanical property enhanced. Moreover, the in vitro mineralization tests showed that the bone-like apatite particles were deposited on the pore wall surface of NC scaffolds, and the bioactivity of NC scaffolds increased with increasing the g-HAp concentration. Furthermore, the anti-inflammatory drug IBU was efficiently loaded into the scaffolds, and the drug release studies indicated that the loaded-IBU exhibited a sustained release profile. In vitro cell culture assays proved that the scaffolds were biocompatible because of supporting adhesion, spreading, and proliferation of mouse bone mesenchymal stem cells(BMSCs). All the results indicated that the solvent evaporation based on Pickering HIPE templates was a promising alternative method to fabricate NC porous scaffolds for potential drug delivery and bone tissue engineering applications.3. To further illustrate that the solvent evaporation based on Pickering HIPE templates had important potential applications in the fabrication of NC porous scaffolds, we used the g-HAp nanoparticles to stabilize W/O HIPEs, subsequently solvent evaporation to prepare g-HAp/PCL NC porous scaffolds. The influences of preparation parameters on the pore structures of porous scaffolds were investigated. Next, the mechanical property, biomineralization activity, anti-inflammatory drug IBU release profile and biocompatibility of the porous scaffolds were further evaluated. The results showed that the NC scaffolds demonstrated interconnected pore structures, which could be adjusted readily by varying g-HAp concentration, PCL concentration and IPVF. Increasing the g-HAp concentration significantly enhanced the mechanical property and apatite particle forming activity of the NC scaffolds. In addition, IBU was efficiently loaded into the scaffolds, and displayed a sustained release profile. In vitro cell culture assays confirmed that BMSCs could adhere, spread and proliferate on the NC scaffolds, indicating that the NC scaffolds were biocompatible. All these results suggested that the fabricated g-HAp/PCL NC scaffolds have a promising potential for bone tissue engineering application. And they indicated that solvent evaporation basing on Pickering HIPE templates was a simple and effective method for preparing biocompatible organic/inorganic NC scaffolds with open porous structures.4. The calcium alginate(ALG-Ca)/HAp NC porous scaffolds containing PLLA microspheres were prepared by physical gelation and freeze-drying basing on the O/W Pickering emulsion templates. The HAp nanoparticles were used to stabilize emulsions containing alginate in the aqueous phase and PLLA in oil phase. And the emulsion aqueous phase was solidified by in situ gelation of alginate with Ca2+ released from HAp by decreasing p H with hydrolysis of glucolactone(GDL). The effects of emulsion preparation conditions on the structure of porous scaffolds were studied. And the researches on the mechanical strength, swelling property, drug release and cell compatibility of porous scaffolds were performed to explore the application of scaffolds in drug delivery. The results showed that the PLLA microspheres were dispersedly existed in the pores or embedded in the pore walls of porous scaffolds. The structures of porous scaffolds and particle sizes of the microspheres could be adjusted by varying the preparation conditions. Increasing the concentrations of alginate, HAp, GDL and PLLA were beneficial to improve the mechanical properties of the porous scaffolds, while the excessive HAp could lead to the decrease in mechanical strength of the porous scaffolds. And the increase in HAp and GDL concentrations could reduce the swelling properties and enhance the stability of porous scaffolds. BMSCs could proliferate well on the scaffolds, indicating that the scaffolds possessed a good biocompatibility. In order to obtain the dual drug-loaded scaffold materials, the hydrophilic bovine serum albumin(BSA) and hydrophobic IBU were suspended into aqueous phase and oil phase, respectively. The in vitro drug release results indicated BSA had a short-term release while IBU had a long-term and sustained release in the dual drug delivery systems, and the release of both two drugs could be decreased by increasing the HAp and GDL concentrations.5. The PCL/BSA/ALG-Ca/HAp NC porous scaffolds were prepared by physical gelation and freeze-drying basing on the Pickering HIPE templates. The emulsions were stabilized by BSA. The aqueous dispersion containing BSA, alginate and HAp nanoparticles was homogenized with CH2Cl2 solution of PCL to form O/W Pickering HIPEs. The influence of PCL concentration on the structures and properties of porous scaffolds was investigated. The results showed that the scaffolds possessed an open-porous structure. With the increase in the PCL concentration, the thickness of pore wall increased, while the porosity decreased. Increasing PCL concentration assisted to improve the mechanical strength of porous scaffolds, reduce swelling rate of porous scaffolds. IBU could be loaded effectively in the scaffolds, and the in vitro drug release studies showed that increasing PCL concentration reduced the IBU release rate. In vitro cell culture experiments showed that BMSCs could grow and proliferate on the scaffolds, and the high PCL concentration could result in the decrease in the activity of BMSCs. Therefore, it should be considering the combination properties of the porous scaffolds in the practical applications.