Biodegradable elastomers based on POSS-Initiated poly(epsilon-caprolactone) for regulating smooth muscle cells

摘要

Biodegradable elastomers have attracted much attention as they can provide mechanical properties similar to soft tissues and manufacturing flexibility PH*1. Poly(e-caprolactone) (PCL) is a widely used semi-crystalline biodegradable polymer and various photc-crosslinkable polymers such as PCL diacrylates (PClDAs) and PCL triacrylates (PCLTAs) have been developed based on PCL for achieving biodegradable networks with controllable crystallinities in peripheral nerve and cardiovascular applications. Polyhedral oligomeric silsesquioxane (POSS) is a silicon-based nanocage-like molecule and has been used to prepare hybrid systems with biodegradable polymers for bone regeneration. As shown in Figure 1a, POSS-PCLs with hydroxyl end groups were synthesized via ring-opening polymerization of ε-caprolactone at 130°C for 12 h in the presence of Sn(Oct)_2 as the catalyst and 1,2-propanediol isobutyl POSS as the initiator. The molecular weight (M_n) was modulated using the monomer to initiator ratio, with 9670,6250,4620,3400 and 2530 g/mol corresponding to 10,20,30,40 and 50 wt% of POSS, respectively. Then acrylation of the POSS-PCLs was performed in the presence of K_2CO_3 as the proton scavenger. POSS-PCLDAs (Φ_(POSS) = 32,34,36 and 38%) were prepared by mixing POSS-PCLDAs (Φ_(POSS) = 30% and 40%) with mass ratio of 4:1,3:2,2:3 and 1:4, respectively. BAPO was used as the photo-initiator in crosslinking. POSS-PCLDA/BAPO/CH2Cl2 solution (1.5 g/15 mg/500 μL) was crosslinked under UV light for 20 min. Flat crosslinked PCLA substrates were soaked in acetone for two days to remove the sol fraction, dried in vacuum, and compressed between two glass plates to smoothen them. Because of the steric hindrance induced by the bulky POSS nanocages, photo-crosslinked POSS-PCLDA networks with significantly suppressed crystallinities demonstrated elastomeric characteristics, for example, a low elastic modulus (E) of 1.3 MPa and a reversible strain as high as 400%. These novel biodegradable elastomers were evaluated in terms of regulating primary rat aortic smooth muscle cells (SMCs). Primary rat aortic SMCs were cultured on the substrates for 4 days and characterized. The composition of POSS (Φ_(POSS)) in POSS-PCLDA was determined by the PCL molecular weight as there was only one POSS nanocage in the center of the chain. Thus a higher molecular weight corresponded to a lower Φ_(POSS). Similar to photo-crosslinked PCLDAs and PCLTAs,2-4 the stiffness of crosslinked POSS-PCLDA was efficiently controlled through the molecular weight because it determines both the crosslinking density and crystallinity simultaneously. When the molecular weight was high, the networks became semi-crystalline and thus stiffer than their amorphous counterparts resulted from lower molecular weights. The semi-crystalline POSS-PCLDA networks demonstrated necking phenomenon while the amorphous ones were elastomeric with high strains at break (ε_b). The E and ε_b values of photo-crosslinked POSS-PCLDA Φ_(POSS).= 32%) were 1.3 ± 0.4 MPa and 430 ± 50%, respectively. As shown in Figure 1c,d, semi-crystalline networks of POSS-PCLDA with higher stiffnesses were found to better support attachment and proliferation of SMCs. For the ones with much lower stiffnesses, the cell attachment and proliferation did not vary too much when E decreased from 50 to 1.3 MPa. Figure 1. (a) Synthesis of POSS-PCLDAs. (b) Stress-strain curves of photo-crosslinked POSS-PCLDAs with various Φ_(POSS) at 37°C. (c) SMC attachment and proliferation on crosslinked POSS-PCLDA substrates at days 1,2, and 4. ~*: p ＜ 0.05, #: p ＜ 0.05 relative to Φ_(POSS) =10%. (d) Images of SMCs on the substrates at day 1, stained with rhodamine-phalloidin. Conclusions: POSS-PCL with two hydroxyl end groups were synthesized with 1,2-propanediol isobutyl POSS as the initiator and further acrylated to photo-crosslinkable POSS-PCLDA. Both semi-crystalline stiff and amorphous elastomeric POSS-PCLDA networks were fabricated for supporting SMC attachment and proliferation.