Biodegradable Elastomers Enabling Thermoprocessing Below 100 °C.

Biodegradable and biocompatible elastomers are highly desirable for many biomedical applications. Here, we report synthesis and characterization of poly(ε-caprolactone)-co-poly(ß-methyl-δ-valerolactone)-co-poly(ε-caprolactone) (PCL-PßMδVL-PCL) elastomers. These materials have strain to failure values greater than 1000%. Tensile set measurements according to an ASTM standard revealed a 98.24% strain recovery 10 min after the force was removed and complete strain recovery 40 min after the force was removed. The PßMδVL midblock is amorphous with a glass-transition temperature of -51 °C, and PCL end blocks are semicrystalline and have a melting temperature in the range of 52-55 °C. Due to their thermoplastic nature and the low melting temperature, these elastomers can be readily processed by printing, extrusion, or hot-pressing at 60 °C. Lysozyme, a model bioactive agent, was incorporated into a PCL-PßMδVL-PCL elastomer through melt blending in an extruder, and the blend was further hot-pressed into films; both processing steps were performed at 60 °C. No loss of lysozyme bioactivity was observed. PCL-PßMδVL-PCL elastomers are as cytocompatible as tissue culture polystyrene in supporting cell viability and cell growth, and they are degradable in aqueous environments through hydrolysis. The degradable, cytocompatible, elastomeric, and thermoplastic properties of PCL-PßMδVL-PCL polymers collectively render them potentially valuable for many applications in the biomedical field, such as medical devices and tissue engineering scaffolds.

Implantable and Degradable Thermoplastic Elastomer.

Biodegradable and implantable materials having elastomeric properties are highly desirable for many biomedical applications. Here, we report that poly(lactide)-co-poly(ß-methyl-δ-valerolactone)-co-poly(lactide) (PLA-PßMδVL-PLA), a thermoplastic triblock poly(α-ester), has combined favorable properties of elasticity, biodegradability, and biocompatibility. This material exhibits excellent elastomeric properties in both dry and aqueous environments. The elongation at break is approximately 1000%, and stretched specimens completely recover to their original shape after force is removed. The material is degradable both in vitro and in vivo; it degrades more slowly than poly(glycerol sebacate) and more rapidly than poly(caprolactone) in vivo. Both the polymer and its degradation product show high cytocompatibility in vitro. The histopathological analysis of PLA-PßMδVL-PLA specimens implanted in the gluteal muscle of rats for 1, 4, and 8 weeks revealed similar tissue responses as compared with poly(glycerol sebacate) and poly(caprolactone) controls, two widely accepted implantable polymers, suggesting that PLA-PßMδVL-PLA can potentially be used as an implantable material with favorable in vivo biocompatibility. The thermoplastic nature allows this elastomer to be readily processed, as demonstrated by the facile fabrication of the substrates with topographical cues to enhance muscle cell alignment. These properties collectively make this polymer potentially highly valuable for applications such as medical devices and tissue engineering scaffolds.

Cellulose nanocrystal effect on crystallization kinetics and biological properties of electrospun polycaprolactone.

Mechanical properties of tissue engineering nanofibrous scaffolds are of importance because they not only determine their ease of application, but also influence the environment for cell growth and proliferation. Cellulose nanocrystals (CNCs) are natural renewable nanoparticles that have been widely used for manipulating nanofibers' mechanical properties. In this article, cellulose nanoparticles were incorporated into poly(caprolactone) (PCL) solution, and composite nanofibers were produced. Ozawa-Flynn-Wall (OFW) methodology and X-ray diffraction were used to investigate the effect of CNC incorporation on PCL crystalline structure and its biological properties. Results showed that CNC incorporation up to 1% increases the crystallization activation energy and reduces the crystal volume, while these factors remain constant above this critical concentration. MTT assay and microscopic images of seeded cells on the nanofiber scaffolds indicated increased cell growth on the samples containing CNC. This behavior could be attributed to their greater hydrophilicity, which was confirmed using parallel exponential kinetics (PEK) model fitting to results obtained from dynamic vapor sorption (DVS) studies. Superior performance of CNC containing samples was also confirmed by in vivo implantation on full-thickness wounds. The wound area faded away more rapidly in these samples. H&E and Masson's trichrome staining showed better regeneration and more developed tissues in wounds treated with PCL-CNC1% nanofibers.

Functional skeletal muscle constructs from transdifferentiated human fibroblasts.

Transdifferentiation of human non-muscle cells directly into myogenic cells by forced expression of MyoD represents one route to obtain highly desirable human myogenic cells. However, functional properties of the tissue constructs derived from these transdifferentiated cells have been rarely studied. Here, we report that three-dimensional (3D) tissue constructs engineered with iMyoD-hTERT-NHDFs, normal human dermal fibroblasts transduced with genes encoding human telomerase reverse transcriptase and doxycycline-inducible MyoD, generate detectable contractile forces in response to electrical stimuli upon MyoD expression. Withdrawal of doxycycline in the middle of 3D culture results in 3.05 and 2.28 times increases in twitch and tetanic forces, respectively, suggesting that temporally-controlled MyoD expression benefits functional myogenic differentiation of transdifferentiated myoblast-like cells. Treatment with CHIR99021, a Wnt activator, and DAPT, a Notch inhibitor, leads to further enhanced contractile forces. The ability of these abundant and potentially patient-specific and disease-specific cells to develop into functional skeletal muscle constructs makes them highly valuable for many applications, such as disease modeling.

Colloidal stability versus self-assembly of nanoparticles controlled by coiled-coil protein interactions.

Orientational discrimination of biomolecular recognition is exploited here as a molecular engineering tool to regulate nanoparticle self-assembly or stability. Nanoparticles are conjugated with the heterodimerizing coiled-coils, A and B, which associate in parallel orientation. Simply flipping the orientation of one coiled-coil results in either self-assembling or colloidally stable nanoparticles.

Efficient release of immunocaptured cells using coiled-coils in a microfluidic device.

Label-free and affinity-based cell separation allows highly specific cell capture through simple procedures, but it remains a major challenge to efficiently release the captured cells without changing their structure, phenotype, and function. We report a microfluidic platform for label-free immunocapture of target cells and efficient release of the cells with minimal biochemical and biophysical perturbations. The method capitalizes on self-assembly of a pair of heterodimerizing coiled-coils, A and B. Target cells are captured in microchannels functionalized with an antibody and A and efficiently released by a liquid flow containing B-PEG (a conjugate of B and polyethylene glycol) at a controlled, low shear stress. The released cells have no antibodies attached or endogenous surface molecules cleaved. In a model system, human umbilical vein endothelial cells (HUVECs) were isolated from a mixture of HUVECs and human ovarian carcinoma cells. The capture selectivity, capture capacity, and release efficiency were 96.3% ± 1.8%, 10 735 ± 1897 cells per cm2, and 92.5% ± 3.8%, respectively, when the flow was operated at a shear stress of 1 dyn cm-2. The method can be readily adapted for isolation of any cells that are recognizable by a commercially available antibody, and B-PEG is a universal cell-releasing trigger.