| In bone tissue engineering, the architectural characteristics of porous scaffold are critical to cell behavior, angiogenesis and osteogenesis. The scaffold not only serves as template supports for cell growth and migration but also provide sufficient space to induce angiogenesis and osteogenesis. To optimize the architectural characteristics of scaffold would be improve the bone tissue formation, but the efficiency of bone tissue regeneration regulated merely by a single scaffold is still limited. Some studies concluded that the bone tissue regeneration would be enhanced by inducing exogenous growth factors and drugs.Hence, the porous scaffold combined with bio-factors and drugs have been gained considerable attention as bone substitutes to synergistically regulate angiogenesis and ectopic osteogenesis. In this study, the relationship between architectural characteristics and bone formation were investigated by controlling the architectural parameter (e.g.macro-pore size, inerconnectivity, pore distribution and surface topography) of porous Hydroxyapatite (HA) scaffold, and optimized the porous architectural of HA scaffold.Moreover, a drug-loaded polymer microsphere homogeneously immobilized on the surface of HA scaffold coated by alginate as a drug release system of porous scaffold was developed to improve angiogenesis and osteogenesis.Three kinds of porous HA scaffolds with controllable architectural characteristics were developed by sugar spheres-leaching. The macro-pore size and interconnecting window diameter was accurately tailored by chose the size of sugar spheres and adjusting the heat treat time on sugar sphere templates. In this paper, the HA scaffolds with different macro-pore sizes (500-650, 700-950 and 1100-1250 μm ) represented similar interconnecting structure which determined by the almost 0.26 d/s ratio (the ratio of interconnecting window diameter to macro-pore size) via heat treatment technique. All kinds of scaffolds with the same d/s ratio maintained similar interconnecting structure,which would be beneficial to accurately investigate the effects of macro-pore sizes on osteogenesis and ectopic angiogenesis. The in vivo results indicated that the macro-pore sizes of HA scaffolds impacted not only the speed of osteogenesis and angiogenesis but also the space distribution of newly formed bone. The scaffold with macro-pore sizes of 750-900 μm exhibited much faster angiogenesis and osteogenesis, and much more uniformly distribution of new bone than those with other macro-pore sizes.Three interconnecting windows size (87、228 and 367μm) in porous HA scaffold with pore sizes of 700-950μm (d/s ratio were 0.09、0.26 and 0.45, respectively.)were developed by sugar spheres-leaching and heat treatment technique and were investigated the effect of d/s ratio on ectopic angiogenesis and osteogenesis. The in vivo implantation results revealed that the d/s ratio of porous scaffold impacted not only angiogenesis and but also the osteogenesis. The mean diameter of blood vessels formed was increased with the increase of interconnecting windows size after 4 weeks of implantation, but the compressive strengths of scaffold with 0.49 d/s ratio was too low to brittle facture while it was implanted in dorsal muscles, which result in new bone formed nouniformly after 12 weeks of implantation. The scaffold with 0.09 d/s ratio limited the mean diameter and number of blood vessels formed result in the capacity of osteogenesis reduced. The scaffold with 0.26 d/s ratio exhibited better and uniformly angiogenesis.Two kinds of graded porous scaffolds were developed by graded sugar templates-leaching techniques: (1) the other with small pores of 500-650μm in the center and large pores of 1100-1250μm at the periphery (HASL), (2) one with large pores of 1100-1250μm in the center and small pores of 500-650μm at the periphery (HALS). In vivo experiment results showed that HASL displayed obviously larger diameter of blood vessels formed at the periphery than those in the center after 1 month of implantation,although the number of blood vessels formed at the periphery and in the center was almost the same. The diameter of blood vessels formed at the periphery and in the center was almost the same in HALS but the number of blood vessels formed at the periphery was obvious more than those in the center. The total mean diameter and number of blood vessels formed in HALS was smaller than those in HASL. After 3 months of implantation,the HASL displayed homogeneous osteogenesis in whole scaffold but the HALS displayed osteogenesis only at the periphery of scaffolds, and the total area percentage of newly formed bone in HASL was better than that in HALS. Hence the pore size distribution in graded porous HA scaffold affected not only the extent of vascularization but also the distribution of newly formed bone.The architecture of larger pore at the periphery would avail the new bone tissue growth in whole scaffold.A novel method for integration stripe patterns into pore walls of porous hydroxyapatite (HA) scaffolds was developed using sugar spheres templates treated by wet treatment technique. The results revealed that the quantity of moisture on sugar spheres templates was controlled by wet treatment technique, and the width of tripe patterns was regulated by the quantity of moisture. The cell experiment resulted showed that cells were oriented along the groove direction. The gene expression showed that stripe patterns on the pore wall was beneficial to osteogenesis.An novel method was developed to homogeneously immobilize Salvianolic acid B(Sal B)-loaded chitosan (CS) microspheres on the surface of HA scaffolds pre-coated with alginate to build drug release system of porous scaffold. To improve the adhesion between microspheres and HA scaffolds, alginate was used to pre-coat the porous surface of HA scaffolds. The results showed that the microspheres were solidly immobilized on the porous surface of HA scaffolds pre-coated with alginate via electrostatic interactions.During the adhering process, HA scaffolds coated were immersed in aqueous solution containing Sal B/CMs, followed by standing or shaking at 37℃ for a certain time. To be compared with static condition, the distribution of Sal B/CMs on the porous surface of pre-coated HA scaffolds were more homogeneous and almost non-aggregated in shaky condition. The various concentrations of alginate were used to optimize the adhesion of Sal B-loaded CS microspheres (Sal B/CMs) on the surface of scaffold. The optimal coating concentration of alginate was 1% in that the microspheres homogeneously immobilize on the surface of HA scaffolds and the microstructures of porous surfaces of HA scaffolds kept almost unchanged. The result of cell culture in vitro found that 1% alginate-coated scaffolds with Sal B-loaded CS microspheres (HAS/CS/Sal B) obviously promoted cell proliferation after 3 and 7 days cell culture, and cells were attached and uniformly distributed on the porous surface of scaffolds. |
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