Engineered Three-Dimensional Microenvironments with Starch Nanocrystals as Cell-Instructive Materials.

Naturally, cells reside in three-dimensional (3D) microenvironments composed of biopolymers that guide cellular behavior via topographical features as well as through mechanical and biochemical cues. However, most studies describing the influence of topography on cells' behavior are performed on rigid and synthetic two-dimensional substrates. To design systems that more closely resemble native microenvironments, herein we develop 3D nanocomposite hydrogels consisting of starch nanocrystals (SNCs) embedded in a gelatin matrix. The incorporation of different concentrations of SNCs (0.05, 0.2, and 0.5 wt %) results in an increase of compressive modulus when compared to hydrogels without SNCs, without affecting the swelling ratio, thus providing a tunable system. Confirming the cytocompatibility of the novel composites, the viability of encapsulated L929 fibroblasts is >90% in all hydrogels. The cellular metabolic activity and DNA content are similar for all formulations and increase over time, indicating that the fibroblasts proliferate within the hydrogels. After 4 d of culture, Live/Dead staining and F-actin/nuclei staining show that the encapsulated fibroblasts develop an elongated morphology in the hydrogels. On the other hand, encapsulated chondrogenic progenitor ATDC5 cells also maintain a viability around 90% but display a round morphology, especially in the hydrogels with SNCs, indicating a potential application of the materials for cartilage tissue engineering. We believe that topographical and mechanical cues within 3D microenvironments can be a powerful tool to instruct cells' behavior and that the developed gelatin/SNC nanocomposite warrants further study.

Synthesis of polycaprolactone: a review.

Polycaprolactone (PCL) is an important polymer due to its mechanical properties, miscibility with a large range of other polymers and biodegradability. Two main pathways to produce polycaprolactone have been described in the literature: the polycondensation of a hydroxycarboxylic acid: 6-hydroxyhexanoic acid, and the ring-opening polymerisation (ROP) of a lactone: epsilon-caprolactone (epsilon-CL). This critical review summarises the different conditions which have been described to synthesise PCL, and gives a broad overview of the different catalytic systems that were used (enzymatic, organic and metal catalyst systems). A surprising variety of catalytic systems have been studied, touching on virtually every section of the periodic table. A detailed list of reaction conditions and catalysts/initiators is given and reaction mechanisms are presented where known. Emphasis is put on the ROP pathway due to its prevalence in the literature and the superior polymer that is obtained. In addition, ineffective systems that have been tried to catalyse the production of PCL are included in the electronic supplementary information for completeness (141 references).

Polymer grafting onto starch nanocrystals.

Monocrystalline starch nanoparticles were successfully grafted with poly(tetrahydrofuran), poly(caprolactone), and poly(ethylene glycol) monobutyl ether chains using toluene 2,4-diisocyanate as a linking agent. Surface grafting was confirmed using Fourier transform infrared and X-ray photoelectron spectroscopies, differential scanning calorimetry, elemental analysis, and contact angle measurements. Transmission electron microscopy observations of modified starch nanocrystals showed either the individualization of nanoparticles or the formation of a film, depending on the polymer used. It was shown that grafting efficiency decreased with the length of the polymeric chains, as expected. The resulting modified nanoparticles can find applications in the field of co-continuous nanocomposite materials.