Preparation Of Mesoporous Silica Nanoparticles-Based Drug Delivery Systems And Application For Bone Tissue Repair

Nowadays, the injuries of bone tissue resulting from sports, traumas and tumors have become one of the important factors seriously damaging human being's health. Researches and developments of novel carriers for drugs/growth factors delivery and bone repair materials with excellent osteoinductive activity are the center part of repairing and remodeling of bone tissue damage.Mesoporous silica nanoparticles (MSNs), with uniform and tunable pore structure, high surface area, versatility in surface functionalization, membrane-permeable and endosomal escape capacity, have been designed and developed as the carrier of dexamethasone (Dex) and rhBMP-2. The law and mechanism of the synergistic induction of osteogenesis with Dex and rhBMP-2were investigated in the cellular and molecular levels. On this basis, high-bioactive bone repair materials were explored with these unique biomaterials.Preparation and biological properties of mesoporous silica nanoparticles with various size.The well-ordered MSNs in the range from55-nm,100-nm,200-nm to440-nm with similar pore texture and surface charge were first prepared by modified base-catalyzed sol-gel method. Then, we endeavored to address the size effect of MSNs on the cellular uptake, endosomal escape and controlled release, the key steps for the intracellular delivery. With MC3T3-E1model cell line, the in vitro results indicated that after12h cultivation, MSNs within55-440nm could all be internalized into the cells, and further escaped out of the endosomal compartment. The efficiency of the cellular uptake and endosomal escape strongly depended on the particle size, with the best efficiencies from100-nm MSNs. Furthermore, the MTT results indicated that these MSNs materials were all biocompatible. The controlled release experiments with Dex, vitamin C, BSA as models showed that for the small-molecular drugs, including hydrophobic Dex and hydrophilic vitamin C, the loading amount mainly determined by the surface area of the MSNs, and the subsequently release of the drug dramatically decreased with the increasing of the particle size. In the case of the macromolecular proteins (BSA), the loading amount had no significant correlation with particle size, but the release greatly depended on the particle size of MSNs. These findings presented here could provide new means to tailor the size of MSNs and thus to guide the design of MSNs-based intracellular delivery system.A magnetic, reversible pH-responsive nanogated ensemble based on Fe3O4nanoparticles-capped mesoporous silica. A magnetic and reversible pH-responsive, MSNs-based nanogated ensemble was fabricated by anchoring superparamagnetic Fe3O4nanoparticles on the pore outlet of MSNs via a reversible boronate esters linker. The successful incorporation of Fe3O4nanoparticles onto the MSNs was confirmed by the results of XRD, TEM, XPS and N2adsorption-desorption method. The pH-driven "gate-like" effect was studied by in vitro release of an entrapped model Dex from the pore voids into the bulk solution at different pH values. The results indicated that at pH5.0-8.0, the pores of the MSNs were effectively capped with Fe3O4nanoparticles and the drug release was strongly inhibited. While at pH2.0-4.0, the hydrolysis of the boroester bond took place and thus resulted in a rapid release of the entrapped drug. And by alternately changing the pH from3.0to7.0, these Fe3O4cap gate could be switched "on" and "of" and thereby released the entrapped drug in a pulsinate manner (in small portions). Additionally, this nanogated release system exhibited good magnetic property, high cell biocompatibility and cellular uptake for MC3T3-E1cells.A pH-sensitive silica ensemble with reversible acid-labile triazaadamantanes linker and magnetic nanoparticles caps. Furthermore, a pH-sensitive MSNs ensemble (i.e., MSN-TAA-Fe3O4) with magnetic nanoparticles caps was developed by anchoring superparamagnetic Fe3O4nanoparticles on the pore openings with a reversible acid-labile substituted1,3,5-triazaadamantane (TAA) group. The functionalized Fe3O4nanoparticles serve as nanogate to regulate the release pattern and/or dosage of payload. The in vitro release experiment with model Dex showed that the MCM-TAA-Fe3O4ensembles exhibited a precisely controlled release at pH5.0-6.0and zero release at physiological environment (pH=7.4). The nanogates could also be conveniently switched on/off by alternately changing the pH value between5.0and7.4. The release of model BSA proteins from SBA-TAA-Fe3O4showed the same results. Demonstrated with MC3T3-E1model cell line, MCM-TAA-Fe3O4materials could successfully be endocytosed and the encapsulated exogenous cargos were released into cytoplasma. The new pH-sensitive Fe3O4-capped-MSNs could serve as efficient carriers to deliver therapeutic agents to tissues with low pH environment and in clinic therapy for chronic and hard-to-cure diseases.Dexamethasone and bone morphogenetic protein-2synergistically induce osteoblastic differentiation in pluripotent mesenchymal precursor C2C12cells. In the present research, Dex was used to enhance the transdifferentiation bioactivity of BMP-2in the C2C12model cell line. The results indicated that Dex could dramatically enhance rhBMP-2-induced ALP expression and mineralization in C2C12. It showed typical synergistical induced effects, dose-and time-dependent effects. Also, we found that Dex had no obvious effect on the BMP-2-induced Smad signaling and the STAT3-dependent pathway in C2C12by western blotting and realtime RT-PCR. But Runx2-dependent mechanism was involved in the Dex-induced stimulation of osteoblastic differentiation.Osteogenic evaluation of chitosan/mesoporous silica scaffold with incorporation of dexamethasone and rhBMP-2.With organic/inorganic composite methods, a pH-responsive chitosan/mesoporous silica nanoparticles hybrid material (chi-MSNs) was fabricated. It could pH-sensitive release of small molecular drugs and simultaneously controlled release of rhBMP-2proteins. The successful incorporation of chitosan onto the MSNs was confirmed by the results of XRD, TEM, SEM, particle size and ζ-potentials measurement and N2adsorption-desorption method. These systems exhibited a precisely controlled release at pH6.0and zero release at physiological environment. The nanogates could also be conveniently switched on/off by alternately changing the pH value between6.0and7.4. The loading amount of rhBMP-2with chi-MSNs is32.4%and these carriers show good rhBMP-2release profiles. Additionally, these chi-MSNs materials exhibited high cell biocompatibility and good ability for inducing cell differentiation. The chi-MSNs hybrid systems carrying Dex and rhBMP-2had effective capability to induce osteoblastic differentiation of C2C12cells and induce ectopic bone formation in vivo.