Jet-based technologies are increasingly being explored as potential high-throughput and high-resolution methods for the manipulation of biological materials. Previously shown to be of use in generating scaffolds from biocompatible materials, we were interested to explore the possibility of using electrospinning technology for the generation of scaffolds comprised of living cells. For this, it was necessary to identify appropriate parameters under which viable threads containing living cells could be produced. Here, we describe a method of electrospinning that can be used to deposit active biological threads and scaffolds. This has been achieved by use of a coaxial needle arrangement where a concentrated living biosuspension flows through the inner needle and a medical-grade poly(dimethylsiloxane) (PDMS) medium with high viscosity (12,500 mPa s) and low electrical conductivity (10-15 S m-1) flows through the outer needle. Using this technique, we have identified the operational conditions under which the finest cell-bearing composite microthreads are formed. Collected cells that have been cultured, postelectrospinning, have been viable and show no evidence of having incurred any cellular damage during the bionanofabrication process. This study demonstrates the feasibility of using coaxial electrospinning technology for biological and biomedical applications requiring the deposition of living cells as composite microthreads for forming active biological scaffolds.

The electrohydrodynamic jet processing phenomenon is a unique and versatile jet-based technology, which has recently been explored for processing a wide range of advanced structural, functional, and bio-related materials. The exploitation of these jets as a processing route for generating droplets in the micrometer to nanometer size range is advancing, based on the capability of the jets for handling concentrated suspensions (> 20 vol %) with needles 100 mm in diameter-exceptional features that are possessed by no other jet-based processing technology in this category. We show here for the first time that this jet technology can be used to process and deposit living cells in suspension onto surfaces. The cells are intact and viable after jetting and they continue to divide normally.The physical process of applying a potential difference between a needle, having within it a flow of liquid medium, and a grounded electrode placed centrally below it gives rise to the phenomenon referred to as electrohydrodynamic jetting (EHDJ), also known as electrospraying (ES). [1] The charged medium exiting the needle enters a high-intensity electric field where it forms numerous liquid geometries from which a jet or jets evolve. The jets later undergo several nonlinear effects that promote fragmentation and initiate the formation of droplets. The size and distribution of these droplets can be controlled through the applied potential difference, the flow rate to the needle, and the liquid properties. [2] Inkjet printing (IJP), [3] also a jet-based technology, resides in the same category as EHDJ. This technology uses an ink reservoir with a series of miniature electrically heated chambers. Printing is achieved by pulsating a current through a heating element. A steam-type explosion in the reservoir generates a bubble and forces the formation of a droplet. However, current inkjets use piezoelectric crystals within needles. The crystal is flexed by applying a current, thereby promoting droplet generation. Such printing technology utilizes electrostatics or piezoelectricity to direct streams of ink droplets. Ultrasound-assisted means have also been employed for creating waves from which droplets can be generated.Despite rapid advances in inkjet printing employed for processing a variety of biological samples, [4] it has been difficult to explore the processing of concentrated suspensions (for example, those having a material loading of % 20 vol %) for producing droplets in the size range of tens of nanometers. This is due to the technology being predominantly driven by the size of the jetting needle, which leads to a droplet diameter approximately double that of the diameter of the internal orifice of the needle. If droplets in the size range of tens of micrometers are required from the processing of a concentrated suspension, reduction of the needle diameter to < 30 mm, for the production of droplets of % 60 mm, can promote serious needle blockage. In practice, after spreading of these generated droplet deposits, this technology...

Recent years have seen interest in approaches for directly generating fibers and scaffolds following a rising trend for their exploration in the health sciences. In this review the author wishes to briefly highlight the many approaches explored to date for generating such structures, while underlining their advantages and disadvantages, and their contribution in particular to the biomedical sciences. Such structures have been demonstrated as having implications in both the laboratory and the clinic, as they mimic the native extra cellular matrix. Interestingly the only materials investigated until very recently for generating fibrous architectures employed either natural or synthetic polymers with or without the addition of functional molecule(s). Arguably although such constructs have been demonstrated to have many applications, they lack the one unit most important for carrying out the ability to directly reconstruct a three-dimensional functional tissue, namely living cells. Therefore recent findings have demonstrated the ability to directly form cell-laden fibers and scaffolds in useful quantities from which functional three-dimensional living tissues can be conceived. These recent developments have far-reaching ramifications to many areas of research and development, a few of which range from tissue engineering and regenerative medicine, a novel approach to analyzing cell behavior and function in real time in three-dimensions, to the advanced controlled and targeted delivery of experimental and/or medical cells and/or genes for localized treatment. At present these developments have passed all in vitro and in vivo mouse model based challenge trials and are now spearheading their journey towards initiating human clinical trials.

Nano-sized, rod-like hydroxyapatite (nHA) crystals were produced and shown to be phasepure by X-ray diffraction analysis, as no secondary phases were observed. The nHA suspension was electrosprayed onto glass substrates using a novel processing routine to maintain nanocrystals of hydroxyapatite. The biocompatibility of nHAwas determined using human monocyte-derived macrophages and human osteoblast-like (HOB) cell models. The release of lactate dehydrogenase (LDH) from human monocyte-derived macrophages was measured as an indicator of cytotoxicity. The release of the inflammatory cytokine, tumour necrosis factor alpha (TNF-alpha) from cells in the presence of nHA crystallites was used as a measure of the inflammatory response. Although there was some evidence of LDH release from human monocyte-derived macrophages when in contact with high concentrations of nHA crystals, there was no significant release of TNF-alpha. Moreover, nHA-sprayed substrates were able to support the attachment and the growth of HOB cells. These results indicate that nHA crystals may be suitable for intraosseous implantation and offers the potential to formulate enhanced composites for biomedical applications.

Electrospraying, or electrohydrodynamic jetting, is one of several jet-based technologies being explored to process living biological organisms. One of the key advantages of electrospraying is its ability to deposit advanced materials with high resolution that cannot be obtained with other competing technologies, such as ink-jet printing. However, to generate a controlled droplet size distribution in the micrometre range necessary for precision drop and placement of materials requires jetting in stable cone-jet mode. In this paper, we describe the experimental set-up and conditions by which electrospray jetting in stable cone-jet is achieved and use this methodology to process a highly concentrated biological suspension having 10(7) cells ml(-1), the highest cellular loading processed to this day by a jetting approach in this jet based category. The areas of study to which this technology may be applied span the physical and the life sciences.