A magnetic target drug delivery system consisting of biodegradable polymeric microspheres (poly D, L-lactic acid) loaded with magnetite nanoparticles (10-100 nm) and anticancer drug (paclitaxel) was studied. The magnetite nanoparticles were synthesized by chemical precipitation. The as-synthesized magnetite nanoparticles were subsequently introduced into a mixture of polymer magnetic polymeric composite particles were investigated and further correlated with the reaction parameters. It was found that the size and characteristics of the polymeric composite particles depended on the viscosity of the polymer solution. Preliminary drug release experiments showed that the loaded drug was released with the degradation of the polymer. The release rates could be enhanced by an oscillating external magnetic field. / Singapore-MIT Alliance (SMA)

Co-delivery of the embedded growth factor-loaded microspheres and adult stem cells in a hydrogel matrix was studied for its potential as a cell-based therapeutic strategy for cartilage regeneration in partial thickness chondral defects. A photopolymerizable N-methacrylate glycol chitosan (MGC) was employed to form an in situ gel that was embedded with two formulations of growth factor-loaded microspheres and human adipose-derived stem cells (ASC). The polymeric microspheres were used as a delivery vehicle for the controlled release of growth factors to stimulate differentiation of the ASC towards the chondrocyte lineage. The microspheres were made of amphiphilic low molecular weight (Mn < 10,000 Da) poly(1,3-trimethylene carbonate-co--caprolactone)-b-poly(ethylene glycol)-b-poly(1,3-trimethylene carbonate-co--caprolactone) (P(TMC-CL)2-PEG)). This triblock copolymer is solid below 100C, but liquid with a low degree of crystallinity at physiological temperature and degrades slowly, and so acidic degradation products do not accumulate locally. Bone morphogenetic protein-6 (BMP-6) and transforming growth factor-3 (TGF-3) were delivered at 5 ng/day with initial bursts of 14.3 and 23.6%, respectively. Both growth factors were highly bioactive when released, retaining greater than 95% bioactivity for 33 days as measured by cell-based assays. To improve ASC viability within the MGC vehicle, an RGD-containing ligand was grafted to the MGC backbone. Prior to chondrogenic induction within the MGC gel, ASC viability was assessed and greater than 90% of ASC were viable in the gel grafted with cell-adhesive RGD peptides as compared to that in non-RGD grafted gels. For ASC chondrogenesis induced by the sustained release of BMP-6 and TGF-3 in MGC gels, the ASC cellularity and glycosaminosglycan production were similar for 28 days. The ratio of collagen type II to I per cell (normalized to deoxyribonucleic acid content) in the microsphere delivery group was significantly higher than that of non-induced ASC or with soluble growth factor administration in the culture media, and increased with time. Thus, the co-delivery of growth factor-loaded microspheres and ASC in MGC gels successfully induced ASC chondrogenesis and is a promising strategy for cartilage repair. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2011-06-07 19:32:50.94

<p dir="ltr">Air-entraining agents (AEA) were introduced in the 1930s to improve concrete's resistance to cyclic freezing-thawing exposure. Over the past 90 years, there has been extensive discussion about how traditional AEAs contribute to durability improvements. However, the issue of strength loss associated with conventional AEA use remains unresolved unless the cement is overdosed. Moreover, the effectiveness of traditional AEAs in entraining air voids has proven inconsistent, as it is influenced by various factors. As a result, the increased costs and carbon footprint associated with AEA use continue to be ongoing concerns for the industry.</p><p dir="ltr">Hollow polymeric microspheres have emerged as a promising solution for enhancing concrete's cyclic freezing-thawing resistance by providing encapsulated air without compromising mechanical performance or durability. In this study, the hydration, fresh properties, hardening performance, and freezing-thawing resistance of air-entrained cement mortar and concrete were investigated using the novel hollow polymeric microspheres and a traditional aqueous AEA, respectively. Additionally, the dynamic modulus of elasticity change and surface spalling damage of concrete beams following cyclic freezing-thawing exposure were evaluated. The air-void system and capillary pore structure of cement mortar and concrete, air-entrained with the traditional AEA and microspheres, respectively, were examined through various characterization methods, including optical microscopy (OM), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and 3D X-ray microscopy (micro-CT, or XCT). The properties of mortar and concrete with varying dosages of AEA and microspheres were assessed, and the mechanisms behind the enhanced freezing-thawing resistance were explored.</p><p dir="ltr">The microspheres used in this study were found to have a 'curing' effect, enhancing the hydration, workability, and mechanical strength of the mortar compared to both plain mortar without air entrainment and mortar air-entrained with the traditional aqueous AEA. Evaluating the mechanical strength changes and mass loss of mortar specimens demonstrated that the freezing-thawing resistance of mortar air-entrained with microspheres was superior to that achieved with aqueous AEA. The small size and compressibility of the microspheres resulted in a fine and well-distributed air void system, offering improved freezing-thawing resistance in the mortar specimens.</p><p dir="ltr">Additionally, due to the potential 'curing' and nucleation effects of the microspheres, the strength of air-entrained concrete with microspheres was slightly higher than that of plain concrete without air entrainment. In contrast, the traditional air-entraining method led to a 7.0% to 8.4% strength loss in concrete with 1% entrained air. Furthermore, concrete air-entrained with microspheres exhibited significantly less surface spalling damage compared to plain concrete, thanks to its well-distributed air void system and enhanced strength. On the other hand, although traditionally air-entrained concrete maintained its dynamic modulus throughout the 300 cycles of freezing-thawing exposure, it still suffered severe surface spalling damage, likely due to its reduced strength.</p><p dir="ltr">This study provides valuable insights into the practical application of polymeric microspheres for enhancing the freezing-thawing resistance of concrete.</p>