The effects of cell adhesion on the growth and protein productivity of animal cells

Acoustic streaming induced by MHz-frequency ultrasound extends the volume limit of cell suspension culture

Large-scale cell suspension culture technology opens up opportunities for numerous medical and bioengineering applications. For these purposes, scale-up of the culture system is paramount. For initial small-scale culture, a simple static suspension culture (SSC) is generally employed. However, cell sedimentation due to the lack of agitation limits the culture volume feasible for SSC. Thus, when scaling up, cell suspensions must be manually transferred from the culture flask to another vessel suitable for agitation, which increases the risk of contamination and human error. Ideally, the number of culture transfer steps should be kept to a minimum. The present study describes the fabrication of an ultrasonic suspension culture system that stirs cell suspensions with the use of acoustic streaming generated by ultrasound irradiation at a MHz frequency. This system was applied to 100-mL suspension cultures of Chinese hamster ovary cells-a volume ten-fold larger than that generally used. The cell proliferation rate in this system was 1.88/day when applying an input voltage of 40 V to the ultrasonic transducer, while that of the SSC was 1.14/day. Hence, the proposed method can extend the volume limit of static cell suspension cultures, thereby reducing the number of cell culture transfer steps.

3D aggregation of cells in packed microgel media

In both natural and applied contexts, investigating cell self-assembly and aggregation within controlled 3D environments leads to improved understanding of how structured cell assemblies emerge, what determines their shapes and sizes, and whether their structural features are stable. However, the inherent limits of using solid scaffolding or liquid spheroid culture for this purpose restrict experimental freedom in studies of cell self-assembly. Here we investigate multi-cellular self-assembly using a 3D culture medium made from packed microgels as a bridge between the extremes of solid scaffolds and liquid culture. We find that cells dispersed at different volume fractions in this microgel-based 3D culture media aggregate into clusters of different sizes and shapes, forming large system-spanning networks at the highest cell densities. We find that the transitions between different states of assembly can be controlled by the level of cell-cell cohesion and by the yield stress of the packed microgel environment. Measurements of aggregate fractal dimension show that those with increased cell-cell cohesion are less sphere-like and more irregularly shaped, indicating that cell stickiness inhibits rearrangements in aggregates, in analogy to the assembly of colloids with strong cohesive bonds. Thus, the effective surface tension often expected to emerge from increased cell cohesion is suppressed in this type of cell self-assembly.

Micro-Nanofibrillar Polycaprolactone Scaffolds as Translatable Osteoconductive Grafts for the Treatment of Musculoskeletal Defects without Infection

The treatment of musculoskeletal defects is currently limited by the tissue-regenerative materials available to orthopedic surgeons: autologous bone grafts only have a finite amount of harvestable material within a given patient, while allografts are prone to severe immunological complications and host rejection. With this motivation, the production of poly(ε-caprolactone) (PCL) scaffolds as synthetic, biomimetic biomaterials was investigated, with a specific focus on potential orthopedic translation. PCL scaffolds were produced through three different fabrication techniques: electrospinning (ES), rotary jet spinning (RJS), and airbrush (AB). ES and RJS were observed to produce microfibrillar scaffolds, while all AB products were nanofibrous. Osteoblast viability, within the PCL scaffolds, and the osteogenic phenotype were assessed in vitro through a combination of adherence, metabolic activity, proliferation, gene expression, alkaline phosphatase bioactivity, and calcium deposition assays. While the polymeric scaffolds induced slight reductions in initial osteoblast adhesion and metabolic activity, seeded cells were able to proliferate and demonstrate the bone formation phenotype. AB products demonstrated reduced bacterial surface colonization when inoculated with both Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa) bacterial strains, in comparison to the microfibrous ES and RJS products, without any small-molecule antibiotics, antimicrobial peptides, or reactive nanomaterials included during scaffold synthesis.

Plant protein hydrolysates support CHO-320 cells proliferation and recombinant IFN-gamma production in suspension and inside microcarriers in protein-free media

We have recently developed a protein-free medium (PFS) able to support the growth of Chinese hamster ovary (CHO) cells in suspension. Upon further supplementation with some plant protein hydrolysates, medium performances reached what could be observed in serum-containing media [Burteau et al. In Vitro Cell. Dev. Biol.-Anim. 39 (2003) 291]. Now, we describe the use of rice and wheat protein hydrolysates, as non-nutritional additives to the culture medium to support productivity and cell growth in suspension or in microcarriers. When CHO-320 cells secreting recombinant interferon-gamma (IFN-gamma) were cultivated in suspension in a bioreactor with our PFS supplemented with wheat hydrolysates, the maximum cell density increased by 25% and the IFN-gamma secretion by 60% compared to the control PFS. A small-scale perfusion system consisting of CHO-320 cells growing on and inside fibrous microcarriers under discontinuous operation was first developed. Under these conditions, rice protein hydrolysates stimulated recombinant IFN-gamma secretion by 30% compared to the control PFS. At the bioreactorscale, similar results were obtained but when compared to shake-flasks studies, nutrients, oxygen or toxic by-products gradients inside the microcarriers seemed to be the main limitation of the system. An increase of the perfusion rate to maintain glucose concentration over 5.5 mM and dissolved oxygen (DO) at 60% was able to stimulate the production of IFN-gamma to a level of 6.6 mug h(-1) g(-1) of microcarriers after 160 h when a cellular density of about 4 x 10(8) cell g(-1) of carriers was reached.