Biodegradable polymersomes that can potentially be employed in drug delivery systems were fabricated by blending poly(l-lactide)-b-poly(ethylene glycol)-b-poly(l-lactide) (PLLA-PEG-PLLA) and poly(d-lactide)-b-poly(ethylene glycol)-b-poly(d-lactide) (PDLA-PEG-PDLA) block copolymers in a weight ratio of 1:1 in an aqueous solution. A series of amphiphilic PLLA-PEG-PLLA and PDLA-PEG-PDLA triblock copolymers were synthesized with different hydrophobic chain lengths through ring-opening polymerization. The self-assembly of pure PLLA-PEG-PLLA and an equimolar mixture of enantiomers of PLLA-PEG-PLLA and PDLA-PEG-PDLA was investigated by transmission electron microscopy, X-ray diffraction, and dynamic light scattering. Various nanostructures including spherical micelles, worm-like micelles, and vesicles were obtained by controlling the hydrophobic chain length and the incubation temperature. In the pure PLLA-PEG-PLLA systems, the hydrophobic–hydrophilic balance dominated the self-assembled morphologies. In equimolar enantiomer mixtures, self-assembled morphologies were greatly affected by the formation of the PLLA-PDLA stereocomplex (SC). There was an inverse correlation between the SC crystallinity and the curvature of the self-assembled structures─the higher the SC content, the smaller the curvature. This rule was not applicable when the SC content was too high (≳50%), which produced spherical micelles as the main nanostructures. Since the SC-induced self-assembly could be controlled by changing the incubation temperature, the polymersomes can potentially be used in many applications, such as nanoreactors and nanovehicles.
There are intensive needs for scaffolds with new designs to meet the diverse requirements of bone repairing. Biodegradable microspheres are highlighted as injectable micro-scaffolds thanks to their advantages in filling irregular defects via a minimally invasive surgery. In this study, microspheres with surface micropores were made via the W1/O/W2 double emulsion method using amphiphilic triblock copolymers (PLLA-PEG-PLLA) composed of poly(L-lactide) (PLLA) and poly(ethylene glycol) (PEG) segments. When the PEG fraction was controlled as 10 wt.%, the microspheres demonstrated higher cell affinity than the smooth-surfaced PLLA microspheres. After being further functionalized with polydopamine coating and apatite deposition, the PLLA-PEG-PLLA microspheres could up-regulate the osteogenic differentiation of bone marrow mesenchymal stromal cells (BMSCs) significantly. Before subcutaneous implantation, bone morphogenetic protein-2 (BMP-2) was adsorbed onto the biomineralized microspheres by taking advantages of the strong affinity of apatite to BMP-2. The resulted microspheres induced ectopic osteogenesis efficiently without causing biocompatibility problems. In summary, this study provided a simple strategy to prepare functionalized microspheres with osteoconductivity and osteoinductivity, which showed great potential in promoting bone regeneration as injectable micro-scaffolds.
In an attempt to attain synergistic therapeutic benefits and address various intrinsic limitations of the highly efficient black phosphorus quantum dots (BPQDs), we fabricated poly( L -lactide)-poly(ethylene glycol)-poly( L -lactide) triblock copolymer (PLLA-PEG-PLLA)-based nanocomposites co-loaded with BPQDs and gambogic acid (GA) using the supercritical carbon dioxide (SC-CO 2 ) technology to achieve photoacoustic (PA) imaging-guided synergistic chemo-photothermal therapy. On the one hand, BPQDs displayed near-infrared (NIR)-induced hyperthermia through the high photothermal conversion efficiency. On the other hand, the NIR-responsive release of GA facilitated early apoptosis through specific binding to stress-induced overexpression of heat shock protein (HSP)-90 for combating thermoresistant tumor cells. GA significantly promoted the photothermal therapy (PTT) efficiency by enhancing both early and late apoptosis of BPQDs. Moreover, the encapsulation of BPQDs in the polymer significantly improved their chemical as well as photothermal stabilities. Our findings suggested that these nanocomposites fabricated using the eco-friendly supercritical fluid (SCF) technology provided good protection to the biodegradable BPQDs, offering a great potential towards cancer ablation through augmented synergistic effects.
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