Multifunctional fibrous scaffolds, which combine the capabilities of biomimicry to the native tissue architecture and shape memory effect (SME), are highly promising for the realization of functional tissue-engineered products with minimally invasive surgical implantation possibility. In this study, fibrous scaffolds of biodegradable poly(d,l-lactide-co-trimethylene carbonate) (denoted as PDLLA-co-TMC, or PLMC) with shape memory properties were fabricated by electrospinning. Morphology, thermal and mechanical properties as well as SME of the resultant fibrous structure were characterized using different techniques. And rat calvarial osteoblasts were cultured on the fibrous PLMC scaffolds to assess their suitability for bone tissue engineering. It is found that by varying the monomer ratio of DLLA:TMC from 5:5 to 9:1, fineness of the resultant PLMC fibers was attenuated from ca. 1500 down to 680 nm. This also allowed for readily modulating the glass transition temperature Tg (i.e., the switching temperature for actuating shape recovery) of the fibrous PLMC to fall between 19.2 and 44.2 °C, a temperature range relevant for biomedical applications in the human body. The PLMC fibers exhibited excellent shape memory properties with shape recovery ratios of Rr > 94% and shape fixity ratios of Rf > 98%, and macroscopically demonstrated a fast shape recovery (∼10 s at 39 °C) in the pre-deformed configurations. Biological assay results corroborated that the fibrous PLMC scaffolds were cytocompatible by supporting osteoblast adhesion and proliferation, and functionally promoted biomineralization-relevant alkaline phosphatase expression and mineral deposition. We envision the wide applicability of using the SME-capable biomimetic scaffolds for achieving enhanced efficacy in repairing various bone defects (e.g., as implants for healing bone screw holes or as barrier membranes for guided bone regeneration).

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In tissue engineering research, there has recently been considerable interest in using electrospun biomimetic nanofibers of hybrids, in particular, from natural and synthetic polymers for engineering different tissues. However, phase separation between a pair of much dissimilar polymers might give rise to detrimental influences on both the electrospinning process and the resultant fiber performance. A representative natural-synthetic hybrid of gelatin (GT) and polycaprolactone (PCL) (50:50) was employed to study the phase separation behavior in electrospinning of the GT/PCL composite fibers. Using trifluoroethanol (TFE) as the cosolvent of the two polymers, observation of visible sedimentation and flocculation from dynamic light scattering analysis of the GT/PCL/TFE mixture both showed that phase separation does occur in just a few hours. This consequently led to gradually deteriorated fiber morphologies (e.g., splash, fiber bonding, and varied fiber size) over time during electrospinning GT/PCL. Quantitative analysis also indicated that the ratio of GT to PCL in the resultant GT/PCL fibers was altered over time. To address the phase separation related issues, a tiny amount (<0.3%) of acetic acid was introduced to improve the miscibility, which enabled the originally turbid solution to become clear immediately and to be single-phase stable for more than 1 week. Nanofibers thus obtained also appeared to be thinner, smooth, and homogeneous with enhanced performance in wettability and mechanical properties. Given the versatility and widely uses of the electrospun GT/PCL and other similar natural-synthetic hybrid systems in constructing tissue-engineered scaffolds, this work may offer a facile and effective approach to achieve finer and compositionally homogeneous hybrid nanofibers for effective applications.

In tissue engineering research, aligned electrospun ultrafine fibers have been shown to regulate cellular alignment and relevant functional expression, but the imposed effect of individual fiber surface nanotopography on cell behaviour has not been examined closely. This work investigates the impact of superimposing a nano-pore feature atop individual fiber surfaces on the responsive behaviour of human vascular smooth muscle cells (vSMCs) for blood vessel tissue engineering. Well-aligned ultrafine poly(L-lactic acid) (PLLA) microfibers with an average fiber diameter of ca. 1.6 mm were fabricated by using a novel stable jet electrospinning (SJES) method. Ellipse-shaped nano-pores with varied aspect ratios (defined as longto-short axis ratio) of 2.7-3.9, corresponding to a surface nano-roughness in the range of 54.8-110.0 nm, were in situ generated onto individual fiber surfaces by varying ambient humidity from 45% to 75% during the SJES process. The presence of elliptical nano-pores on fiber surfaces affected the characteristic anisotropic wettability of the aligned PLLA fibers and contributed to greater protein adsorption (up to 17.59 mg mg À1 ). A 7 day in vitro assessment of human umbilical arterial SMCs cultured on these aligned nano-porous fiber substrates indicated that cellular responses were in close correlation with the elliptical nano-pore feature. A pronounced fiber surface nanotopography was superior in soliciting favorable cellular responses, leading to enhanced cell attachment, proliferation, alignment, expression of the vascular matrix proteins and maintenance of a contractile phenotype. This study thus suggests that introduction of an elliptical nano-pore feature to the aligned microfiber surfaces could provide additional dimensionality of topographical cues to modulate the vSMC responses when using the aligned electrospun ultrafine fibers for engineering vascular constructs.

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