Morphology and enzymatic degradation of oriented thin film of ultrahigh molecular weight poly[(R)-3-hydroxybutyrate]

Optimum processing conditions for the maximum crystallization rate of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)

The effect of thermal and shear histories on the crystallization rate of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) was studied. As with other crystalline polymers, the shear history greatly affected the crystallization rate when the shear rate was beyond a critical value, i.e., the inverse of the Rouse relaxation time. Even after the formation of extended chain crystals, spherulite texture was clearly discernable. It grew from certain points on the extended chain crystals. Consequently, a row of spherulites appeared along the flow direction. The resin temperature in the molten state was also significant. When the sample was heated to 170 °C, which is beyond the main melting peak in the differential scanning calorimetry curve, unmolten crystals did not affect the linear viscoelastic properties. They acted as effective nucleating agents for the rest of the polymer during cooling. Therefore, the shear history hardly affected the crystallization rate and the number of spherulites.

Crystallization of microbial polyhydroxyalkanoates: A review

Polyhydroxyalkanoates (PHAs), produced by the microbial fermentation, is a promising green polymer and has attracted much attention due to its excellent biocompatibility, complete biodegradability, and non-cytotoxicity. The physical properties of PHAs are closely related to their chemical and crystalline structure. Therefore, deep understanding and regulating the structure and crystallization of PHAs are the key factors to improve the performance of PHAs. This review first provides a brief overview of the development history, chemical structure, and basic properties of PHAs. Then, the crystal structure, crystal morphology, kinetics theories and crystallization behavior of nucleation-induced PHAs are systematically summarized to provide a theoretical foundation for improving PHAs crystallization rate and physical properties. In the end, the outlook on the crystallization and application prospects of PHAs is also addressed.

Biocomposite foams based on polyhydroxyalkanoate and nanocellulose: Morphological and thermo-mechanical characterization

The application of bio-based and biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is restricted by its high cost and brittleness. In the present work, these deficiencies were overcome by the manufacture of PHBV foams using thermally expandable microspheres (TES). Nanocellulose (Nc) and a crosslinking agent were added to PHBV-TES to control the foam structure and to improve the mechanical properties. Foams with almost perfect pores, well embedded in the polymer matrix, were obtained by a simple melt molding process. The closed-cell foams have a density 2.5-2.7 times lower than that of PHBV. The addition of Nc increased the expansion ratio, cell density and porosity and also led to a more uniform cell size distribution. The incorporation of the crosslinking agent, together with Nc and TES, increased the glass transition temperature with about 7 °C and strengthened the PHBV-Nc interactions. PHBV foams showed a 1.7-3 times higher deformation compared to PHBV and absorbed up to 15 times more energy. The fully biodegradable PHBV-Nc foams obtained in this work exhibit an advantageous porosity, good specific mechanical properties and high energy absorption, being promising alternatives for insulation, packaging or biomedical application.

Chitosan based bioactive materials in tissue engineering applications-A review

In recent years, there have been increasingly rapid advances of using bioactive materials in tissue engineering applications. Bioactive materials constitute many different structures based upon ceramic, metallic or polymeric materials, and can elicit specific tissue responses. However, most of them are relatively brittle, stiff, and difficult to form into complex shapes. Hence, there has been a growing demand for preparing materials with tailored physical, biological, and mechanical properties, as well as predictable degradation behavior. Chitosan-based materials have been shown to be ideal bioactive materials due to their outstanding properties such as formability into different structures, and fabricability with a wide range of bioactive materials, in addition to their biocompatibility and biodegradability. This review highlights scientific findings concerning the use of innovative chitosan-based bioactive materials in the fields of tissue engineering, with an outlook into their future applications. It also covers latest developments in terms of constituents, fabrication technologies, structural, and bioactive properties of these materials that may represent an effective solution for tissue engineering materials, making them a realistic clinical alternative in the near future.

Shish-kebab-structured poly(ε-caprolactone) nanofibers hierarchically decorated with chitosan-poly(ε-caprolactone) copolymers for bone tissue engineering

In this work, scaffolds with a shish-kebab (SK) structure formed by poly(ε-caprolactone) (PCL) nanofibers and chitosan-PCL (CS-PCL) copolymers were prepared via electrospinning and subsequent crystallization for bone tissue engineering applications. The aim of this study was to introduce nanosized topography and the high biocompatibility of chitosan onto PCL nanofibers to enhance cell affinity to PCL scaffolds. CS-PCL copolymers with various ratios were synthesized, and then spontaneously crystallized as kebabs onto the electrospun PCL fibers, which acted as shishes. Scanning electron microscopy (SEM) results demonstrated that the copolymer with PCL to chitosan ratio of 8.8 could hierarchically decorate the PCL nanofibers and formed well-shaped kebabs on the PCL nanofiber surface. Water contact angle tests and biomimetic activity experiments revealed that the shish-kebab scaffolds with CS-PCL kebabs (PCL-SK(CS-PCL(8.8))) showed enhanced hydrophilicity and mineralization ability compared with smooth PCL and PCL-SK(PCL) shish-kebab scaffolds. Osteoblast-like MG63 cells cultured on the PCL-SK(CS-PCL(8.8)) scaffolds showed optimizing cell attachment, cell viability, and metabolic activity, demonstrating that this kind of scaffold has potential applications in bone tissue engineering.

Enzymatic surface erosion of poly(trimethylene carbonate) films studied by atomic force microscopy

In this article, the surface erosion of spin-coated poly(trimethylene carbonate) (PTMC) films by lipase solutions from Thermomyces lanuginosus was studied using atomic force microscopy (AFM). PTMC films (23-48 nm thick) were stable in water at 37 degrees C for 16 h, while after immersion in lipase solutions at 37 degrees C for 30 s and 1 min, the average thickness of the film decreased in time at a rate of 11.0 +/- 3.7 nm/min. The initially smooth films became significantly rougher during the erosion process. When the immersion time of the films in the lipase solutions was limited to less than 5 s, degradation of the surface was minimal and individual lipase molecules adsorbed on PTMC films could be discerned. By microcontact printing of the PTMC surfaces using a patterned PDMS stamp and lipase solution for 30 s, a predefined micropattern consisting of parallel, 5-microm-wide lines lying 5-nm deep and separated at a distance of 2 microm was formed. Friction images showed differences in surface properties between the recessed and protruding lines in the pattern.