The impact of fabrication parameters and substrate stiffness in direct writing of living constructs

Biomolecules and living cells can be printed in high‐resolution patterns to fabricate living constructs for tissue engineering. To evaluate the impact of processing cells with rapid prototyping (RP) methods, we modeled the printing phase of two RP systems that use biomaterial inks containing living cells: a high‐resolution inkjet system (BioJet) and a lower‐resolution nozzle‐based contact printing system (PAM²). In the first fabrication method, we reasoned that cell damage occurs principally during drop collision on the printing surface, in the second we hypothesize that shear stresses act on cells during extrusion (within the printing nozzle). The two cases were modeled changing the printing conditions: biomaterial substrate stiffness and volumetric flow rate, respectively, in BioJet and PAM². Results show that during inkjet printing impact energies of about 10^?8 J are transmitted to cells, whereas extrusion energies of the order of 10^?11 J are exerted in direct printing. Viability tests of printed cells can be related to those numerical simulations, suggesting a threshold energy of 10^?9 J to avoid permanent cell damage. To obtain well‐defined living constructs, a combination of these methods is proposed for the fabrication of scaffolds with controlled 3D architecture and spatial distribution of biomolecules and cells. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 2012     

A Novel Method to Produce Immobilised Biomolecular Concentration Gradients to Study Cell Activities: Design and Modelling

It is well known that many cell functions are activated by chemical signals with a time and space-dependent profile. To mimic these profiles in vitro, it is necessary to develop a system that is able to generate concentration gradients with a resolution similar to that perceived by cells, which is around nanomolar with a spatial resolution of a few tens of microns. Many devices capable of generating steady-state concentration gradients have been developed using continuous flow micro-fluidic techniques. However, these systems cannot reproduce the immobilised concentration gradients that are present in the extracellular matrix. For this reason, we have developed a new gradient generator to enable precise and reproducible studies on the effects of immobilised concentration gradients on cell behaviour. A well-known gradient of a desired molecule was generated on the bottom surface of a hydrogel, which was then used as a stamp to immobilise the molecule on a functionalised substrate. A concentration gradient was thus obtained using a simple silane-based chemical reaction. To validate the method, image analysis was performed on glass slides printed with fluorescein isothiocyanate (FITC)- collagen and FITC-poly-lysine concentration gradients. Preliminary cell adhesion tests were also carried out by seeding NIH-3T3 and mesencephalic cells on lab-glass slides printed with concentration profiles of collagen and poly-lysine, respectively.     

An in vitro model of glucose and lipid metabolism in a multicompartmental bioreactor

The energy balance in vivo is maintained through inter-organ cross-talk involving several different tissues. As a first step towards recapitulating the metabolic circuitry, hepatocytes, endothelial cells and adipose tissue were connected in a multicompartmental modular bioreactor to reproduce salient aspects of glucose and lipid metabolism in vitro. We first examined how the two-way cellular interplay between adipose tissue and endothelial cells affects glucose and lipid metabolism. The hepatocyte cell line HepG2 was then added to the system, creating a three-way connected culture, to determine whether circulating metabolite concentrations were normalized, or whether metabolic shifts, which may arise when endothelial cells and adipose tissue are placed in connection, were corrected. The addition of hepatocytes to the system prevented the drop in the concentrations of glucose, L-alanine and lactate, and the rise in that of free fatty acids. There was no significant change in glycerol levels in either of the connected cultures. The results show that connected cultures recapitulate complex physiological systemic processes, such as glucose and lipid metabolism, and that the HepG2 hepatocytes normalize circulating metabolites in this in vitro environment in the presence of other cell types.     

Evaluation of microalgal consortia for treatment of primary treated sewage effluent and biomass production

The present investigation was aimed towards analyzing the potential of consortia of native filamentous microalgal strains (MC2), native unicellular microalgal strains (MC3), and selected microalgae from germplasm (MC1) in terms of nutrient removal, water quality improvement, and biomass production using primary treated sewage water. Highest NO₃-N (90 %) and PO₄-P (97.8 %) removal was obtained with MC2-inoculated sewage water. Highest decrease in total dissolved solids to 806 from 1,120 mg L^?1 and highest increase in dissolved oxygen of 9.0 from 0.4 mg L^?1 were obtained using MC2-inoculated sewage water on the sixth day. The biomass production was also highest in MC2 (1.07 g L^?1) followed by MC1 and MC3 (0.90 and 0.94 g L^?1, respectively) on the sixth day. The consortium of filamentous strains from native environment not only proved promising in nutrient removal efficiency but also led to enhanced biomass. The present study highlighted the utility of such a consortium for sewage wastewater treatment and the promise of sewage water as a growth medium for biomass production.     

Effect of calcium chloride on the conformation of proteins. Thermodynamic studies of some model compounds

Partial molar heat capacities (CP2 degrees) and volumes (V2 degrees) for some amino acids and peptides were measured in 1 M aqueous calcium chloride solutions at 298.15 degrees K using a Picker flow microcalorimeter and an oscillating-tube digital density meter. Using the data for these amino acids and peptides in water, the corresponding partial molar heat capacities of transfer (CP2,tr degree) and volumes (V2,tr degree) from water to 1 M aqueous calcium chloride were deduced. These thermodynamic parameters are significantly positive, indicating that strong interactions occur between the ions of calcium chloride and the charged centres of these amino acids and peptides. A comparison has been made with a similar transfer of these compounds to sodium chloride solutions. The thermodynamic parameters of the transfer of peptide group (-CONH) are much more positive in calcium chloride than in sodium chloride solutions. The implication of this result for the ability of calcium chloride to act as a stronger destabilizer of protein conformation is discussed.     

Development of a Culturally Relevant Body Image Instrument among Urban African Americans

Objective: To validate a culturally relevant body image instrument among urban African Americans through three distinct studies. Research Methods and Procedures: In Study 1, 38 medical practitioners performed content validity tests on the instrument. In Study 2, three research staff rated the body image of 283 African‐American public housing residents (75% women, mean age = 44 years), with the residents completing body image, BMI, and percentage body fat measures. In Study 3, 35 African Americans (57% men, mean age = 42) completed body image measures and evaluated their cultural relevance. Results: In Study 1, 97% to 100% of practitioners sorted the jumbled figures into the correct ascending order. The correlation between the body image figures and the practitioners’ weight classifications of the figures was high (r = 0.91). In Study 2, observers arrived at similar ratings of body size with excellent consistency (α = 0.95). Ratings of body image were strongly correlated with participant BMI (r = 0.89 to 0.93 across observers and 0.81 for all participants) and percentage of body fat (r = 0.77 to 0.89 across observers and 0.76 for all participants). In Study 3, body image ratings with the new scale were positively correlated with other validated figural scales. The majority of participants reported that figures in the new body image scale looked most like themselves and other African Americans and were easiest to identify themselves with. Discussion: The instrument displayed strong psychometric performance and cultural relevance, suggesting that the scale is a promising tool for examining body image and obesity among African Americans.