It
remains elusive about the modification selection of polymers
under coupled fields prevalent in actual polymer processing. In this
work, we investigated the effect of pressure, flow, and temperature
(the three most essential parameters in polymer processing) on the
polymorphic behavior of syndiotactic polystyrene (sPS) that is a representative
model polymer due to its complicated yet diverse modifications. Unlike
the β crystal usually observed under pressure or flow alone,
the α crystal was induced with the coupling of pressure and
flow. The critical shear rate for the formation of α crystals
showed a negative dependence on the imposed pressure. Such a promotion
became more pronounced at lower crystallization temperature. The phase
diagram for the formation of α/β crystals was drawn with
respect to three coupled variables for the first time. There was a
strong synergy between pressure and shear on the formation of α
crystals, where lowering the temperature intensified this effect.
The exclusive formation of α crystals was attributed to the
enhanced nucleation competitiveness under high pressure and at low T
c and the orientation of chains induced by flow,
where pressure and T
c played an essential
part by slowing down the orientation relaxation. Our current effort
provides a deep insight into polymorphism selection of sPS under melt
processing-related conditions by which the structure manipulation
can be directed.
Periodontitis is a worldwide bacterial infectious disease, resulting in the resorption of tooth-supporting structures. Biodegradable polymeric microspheres are emerging as an appealing local therapy candidate for periodontal defect regeneration but suffer from tedious procedures and low yields. Herein, we developed a facile yet scalable approach to prepare polylactide composite microspheres with outstanding drug-loading capability. It was realized by blending equimolar polylactide enantiomers at the temperature between the melting point of homocrystallites and stereocomplex (sc) crystallites, enabling the precipitation of sc crystallites in the form of microspheres. Meanwhile, epigallocatechin gallate (EGCG) and nano-hydroxyapatite were encapsulated in the microspheres in the designated amount. Such an assembly allowed the fast and sustained release of EGCG and Ca 2+ ions. The resultant hybrid composite microspheres not only exhibited strong antimicrobial activity against typical oral pathogens (Porphyromonas gingivalis and Enterococcus faecalis), but also directly promoted osteogenic differentiation of periodontal ligament stem cells with good cytocompatibility. These dual-functional composite microspheres offer a desired drug delivery platform to address the practical needs for periodontitis treatment.
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