No abstract

Despite their increasing uses for cardiovascular and cerebrovascular tissue engineering, synthetic polymeric conduits still have their limitations in clinical applications, particularly in small vessels, mainly due to the thrombus formation. Seeding the synthetic scaffolds with endothelial cells (ECs) will potentially solve this problem, but this endothelialization approach demands synthetic materials with better hemacompatibility and cell affinity. To improve the currently used materials and screen for better surface properties, we synthesized copolymer of poly(lactide-co-beta-malic acid) (PLMA), and its derivatives with pendant hydroxyl arms (PLMAHE) or extended carboxyl arms (PLMA-ECA). We analyzed their physical and chemical properties, their hydrophilicity, and their degradation in physiological conditions. More importantly, their blood compatibility was investigated by the measurements of prothrombin time, activated partial thromboplastin time, and interaction with platelets; their cell affinity and cell growth potentials were observed using the human umbilical vein EC cultures. Results from these experiments showed that the copolymer with the carboxyl arms attracted little platelets, and exhibited better cell affinity and supported the cell proliferation, thus demonstrating the potential usefulness of PLMA-ECA for tissue engineering. We speculate that this novel material will offer new opportunities for the design of better vascular-engineered scaffolds owing to its improved biological and chemical properties.

No abstract

l-Tyrosine, which is widely used in the medical field and the food and chemical industries, is a high-value-added compound. In this research, we explored the ability to synthesize l-tyrosine from pyruvate using a Pichia pastoris whole-cell biocatalyst with Symbiobacterium toebii tyrosine phenol lyase (TPL) displayed on the surface. The optimal enzymatic reaction conditions consisted of 1 M ammonium chloride, 125 mM phenol, 200 mM HEPES, pH 8.0, and 60 °C. Under optimal conditions, the conversion rate was 76.7% at 5 h and the maximum conversion rate was >80% at 8 h. We then analyzed the reuse of our biocatalyst in three batches. In a 10 mL reaction system, the conversion rate at 5 h was 79.1% for the first batch, 67.9% for the second batch, and 58.6% for the third batch. In conclusion, our biocatalyst can synthesize high-value-added l-tyrosine at high temperatures within a short period of time and can be easily reused several times.

The modification of intracellular metabolic pathways by metabolic engineering has generated many engineered strains with relatively high yields of various target products in the past few decades. However, the unpredictable accumulation of toxic products, the cell membrane barrier, and competition between the carbon flux of cell growth and product synthesis have severely retarded progress toward the industrial-scale production of many essential chemicals. On the basis of an in-depth understanding of intracellular metabolic pathways, scientists intend to explore more sustainable methods and construct a cell-free biosynthesis system in vitro. In this review, the synthesis and application of pyruvate as a platform compound is used as an example to introduce cell-free biosynthesis systems. We systematically summarize a proposed methodology workflow of cell-free biosynthesis systems, including pathway design, enzyme mining, enzyme modification, multienzyme assembly, and pathway optimization. Some new methods, such as machine learning, are also mentioned in this review.