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Three-dimensional (3D) bioprinting is an emerging biofabrication technology, driving many innovations and opening new avenues in regenerative therapeutics. The aim of 3D bioprinting is to fabricate grafts in vitro, which can then be implanted in vivo. However, the tissue culture ex vivo carries safety risks and thereby complicated manufacturing equipment and practice are required for tissues to be implanted in the humans. The implantation of printed tissues also adds complexities due to the difficulty in maintaining the structural integrity of fabricated constructs. To tackle this challenge, the concept of in situ 3D bioprinting has been suggested in which tissues are directly printed at the site of injury or defect. Such approach could be combined with cells freshly isolated from patients to produce custom-made grafts that resemble target tissue and fit precisely to target defects. Moreover, the natural cellular microenvironment in the body can be harnessed for tissue maturation resulting in the tissue regeneration and repair. Here, we discuss literature reports on in situ 3D printing and we describe future directions and challenges for in situ 3D bioprinting. We expect that this novel technology would find great attention in different biomedical fields in near future.

To the extent possible, artificial organs should have characteristics that match those of the in vivo system. To this end, microfabrication techniques allow us to create microenvironments that can help maintain cell organization and functionality in in vitro cultures. We present three new microbioreactors, each of which allows cells to be cultured in a perfused microenvironment similar to that found in vivo. Our microbioreactors use new technology that permits integration onto the chip (35 mm × 20 mm) of an electrical sensor, in addition to one or more pumping systems and associated perfusion circuitry. The monitoring of Caco-2 cell cultures using electrical impedance spectroscopy (EIS) has allowed us to measure the effects of cell growth, cellular barrier formation and the presence of chemical compounds and/or toxins. Specifically, we have investigated the ability of the electrical sensor to maintain appropriate sensitivity and precision. Our results show that the sensor was very sensitive not only to the presence or the absence of the cells, but also to changes in cell state. Our perfused microbioreactors are highly efficient miniaturized tools that are easy to operate. We anticipate that they will offer promising new opportunities in many types of cell culture research, including drug screening and tissue engineering.

To improve primary adult rat hepatocyte cultures, two types of PDMS microbioreactors containing a membrane, used as a scaffold for the attachment of cells, were built: one with a commercially-available polyester membrane, the other with a PDMS membrane (5 x 5 microm hole sizes) made in our laboratory. In that way, the relative surface area between blood perfusion and hepatocytes seen in vivo was mimicked and as cells were bathed in both sides by the culture medium they expressed much higher functions. A new technique to build such PDMS membrane was created. With this technique we could build various PDMS membranes with down to 5 x 5 microm holes and with thickness even below 20 microm. During the fifteen days of perfusion in these microbioreactors, good cell attachment then cell reorganization was observed. Moreover compared to static cultures in tissue-culture-treated dishes and in cultures in inserts with the same polyester membranes, seven and two times increases in the albumin secretion by the cultured primary rat adult hepatocyte were demonstrated, respectively. Ammonium removal also increased 7 times in perfused cultures compared to static cultures. These new microbioreactors, which closely mimic the in vivo liver architecture, revealed themselves to be very promising tools towards future applications in drug screening or liver tissue engineering.

Engineered skeletal muscle tissues are ideal candidates for applications in drug screening systems, bio-actuators, and as implantable constructs in tissue engineering. Electrical field stimulation considerably improves the differentiation of muscle cells to muscle myofibers. Currently used electrical stimulators often use direct contact of electrodes with tissue constructs or their culture medium, which may cause hydrolysis of the culture medium, joule heating of the medium, contamination of the culture medium due to products of electrodes corrosion, and surface fouling of electrodes. Here, we used an interdigitated array of electrodes combined with an isolator coverslip as a contactless platform to electrically stimulate engineered muscle tissue, which eliminates the aforementioned problems. The effective stimulation of muscle myofibers using this device was demonstrated in terms of contractile activity and higher maturation as compared to muscle tissues without applying the electrical field. Due to the wide array of potential applications of electrical stimulation to two- and three-dimensional (2D and 3D) cell and tissue constructs, this device could be of great interest for a variety of biological applications as a tool to create noninvasive, safe, and highly reproducible electric fields.