A simple and scalable 3D printing methodology for generating aligned and extended human and murine skeletal muscle tissues.

Preclinical biomedical and pharmaceutical research on disease causes, drug targets, and side effects increasingly relies onin vitromodels of human tissue. 3D printing offers unique opportunities for generating models of superior physiological accuracy, as well as for automating their fabrication. Towards these goals, we here describe a simple and scalable methodology for generating physiologically relevant models of skeletal muscle. Our approach relies on dual-material micro-extrusion of two types of gelatin hydrogel into patterned soft substrates with locally alternating stiffness. We identify minimally complex patterns capable of guiding the large-scale self-assembly of aligned, extended, and contractile human and murine skeletal myotubes. Interestingly, we find high-resolution patterning is not required, as even patterns with feature sizes of several hundred micrometers is sufficient. Consequently, the procedure is rapid and compatible with any low-cost extrusion-based 3D printer. The generated myotubes easily span several millimeters, and various myotube patterns can be generated in a predictable and reproducible manner. The compliant nature and adjustable thickness of the hydrogel substrates, serves to enable extended culture of contractile myotubes. The method is further readily compatible with standard cell-culturing platforms as well as commercially available electrodes for electrically induced exercise and monitoring of the myotubes.

Catch-up growth in infants born small for gestational age--a longitudinal study.

BACKGROUND: Epidemiological studies correlate low birth weight and the subsequent development of diabetes mellitus (DM). Early changes in insulin resistance in infants with catch-up growth (CUG) have not been evaluated in our population. AIM: To identify dietary and metabolic features associated with CUG in infants born small for gestational age (SGA) at 1 year old. METHODS: In a cohort study of 88 term infants (44 SGA and 44 appropriate for gestational age [AGA]), breastfeeding and weaning age were registered. Anthropometric measurements, glucose, insulin, and leptin concentrations were measured at birth and at 1 year old. RESULTS: A history of DM in a second-degree relative (p = 0.01) and complementary breastfeeding (p = 0.0003) were higher in SGA compared to AGA infants. Ten (13.6%) infants showed CUG in length and weight combined. They had lower weight, glucose, IR index, and leptin concentrations at birth than those without CUG. After logistic regression analysis for factors related to weight CUG, gender, weaning age, birth weight and leptin concentration at birth were included in the model (R2 = 0.31; p = 0.00004). CONCLUSIONS: Female gender, early weaning, lower birth weight, and lower leptin concentration at birth are related to weight CUG in Mexican infants.