Luca Gasperini

Natural polymers for the microencapsulation of cells

The encapsulation of living mammalian cells within a semi-permeable hydrogel matrix is an attractive procedure for many biomedical and biotechnological applications, such as xenotransplantation, maintenance of stem cell phenotype and bioprinting of three-dimensional scaffolds for tissue engineering and regenerative medicine. In this review, we focus on naturally derived polymers that can form hydrogels under mild conditions and that are thus capable of entrapping cells within controlled volumes. Our emphasis will be on polysaccharides and proteins, including agarose, alginate, carrageenan, chitosan, gellan gum, hyaluronic acid, collagen, elastin, gelatin, fibrin and silk fibroin. We also discuss the technologies commonly employed to encapsulate cells in these hydrogels, with particular attention on microencapsulation.

Microencapsulation of cells in alginate through an electrohydrodynamic process

The encapsulation of living cells within a semi-permeable matrix is an attractive process for transplanting nonautologous cells by limiting the interaction with the host immune system. The electrohydrodynamic process is a low-cost and high-throughput system to encapsulate cells by means of a static potential. We evaluated the use of this system for cell entrapment by assessing and then manufacturing capsules that had the best dimensions. The effect of different cell densities on the beads was determined to set up the basic parameters of the encapsulation system. The cell viability inside the beads and as a function of release time was observed for their biological response.

An electrohydrodynamic bioprinter for alginate hydrogels containing living cells.

In this work we present a bioprinting technique that exploits the electrohydrodynamic process to obtain a jet of liquid alginate beads containing cells. A printer is used to microfabricate hydrogels block by block following a bottom-up approach. Alginate beads constitute the building blocks of the microfabricated structures. The beads are placed at predefined position on a target substrate made of calcium-enriched gelatin, where they crosslink upon contact without the need of further postprocessing. The printed sample can be easily removed from the substrate at physiological temperature. Three-dimensional printing is accomplished by the deposition of multiple layers of hydrogel. We have investigated the parameters influencing the process, the compatibility of the printing procedure with cells, and their survival after printing.

Synthesis, mechanical and thermal rheological properties of new gellan gum derivatives

New derivatives of gellan gum (GG) were prepared by covalent attachment of octadecylamine (C18-NH2) to polysaccharide backbone via amide linkage by using bis(4-nitrophenyl) carbonate (4-NPBC) as a coupling agent. The effect of the alkyl chain grafted onto hydrophilic backbone of high molecular weight GG was investigated in terms of physicochemical properties and ability of new derivatives to form hydrogels. A series of hydrogels was obtained in solutions with different kind and concentration of ions and their stability and mechanical properties were evaluated. The obtained derivatives resulted soluble at temperature lower than starting GG and physicochemical properties of obtained hydrogels suggested their potential use in biomedical field.

3D Bioprinting Technology: Scientific Aspects and Ethical Issues

The scientific development of 3D bioprinting is rapidly advancing. This innovative technology involves many ethical and regulatory issues, including theoretical, source, transplantation and enhancement, animal welfare, economic, safety and information arguments. 3D bioprinting technology requires an adequate bioethical debate in order to develop regulations in the interest both of public health and the development of research. This paper aims to initiate and promote ethical debate. The authors examine scientific aspects of 3D bioprinting technology and explore related ethical issues, with special regard to the protection of individual rights and transparency of research. In common with all new biotechnologies, 3D bioprinting technology involves both opportunities and risks. Consequently, several scientific and ethical issues need to be addressed. A bioethical debate should be carefully increased through a multidisciplinary approach among experts and also among the public.

Control of osmotic pressure to improve cell viability in cell‐laden tissue engineering constructs

Design of tissue engineering strategies deals with the need to balance both biomaterials characteristics and techniques specificities, often resulting in cell‐compromising processing conditions. One important factor often disregarded is the osmotic pressure to which cells are exposed. An in‐house microfluidic system was used to prove that addition of an osmotic regulator significantly benefits the generation of viable cell‐laden hydrogels under harsh processing conditions. Human adipose‐derived stem cells were resuspended in 1.5% alginate and 1% gellan gum (GG; w/v) solutions containing different concentrations (0.12 m, 0.25 m and 1.5 m) of sucrose as osmotic regulator. GG (in water) and alginate (in water or phosphate‐buffered saline) solutions were used to vary the conditions under which cells were kept prior processing. Independently of the polymer, addition of sucrose did not affect the processing conditions or the viscosity of the solutions, except at 1.5 m. The obtained results clearly demonstrate that inclusion of 0.25 m sucrose during processing of the cell‐laden hydrogels allowed to keep cell viability around 80%, in opposition to the 20% observed in its absence, both for GG and alginate‐derived hydrogels prepared in water. Impressively, the level of cell viability observed with the inclusion of 0.25 m sucrose, 76% for GG and 86% for alginate, was similar to that obtained with the standard alginate solution prepared in phosphate‐buffered saline (82%). The beneficial effect of sucrose was observed within the first 5 min of processing and was maintained for prolonged experimental setups with viability values above 50%, even after a 2‐h time‐frame and independently of the material.