3D Printed Hydrogel Sensor for Rapid Colorimetric Detection of Salivary pH.

Salivary pH is one of the crucial biomarkers used for non-invasive diagnosis of intraoral diseases, as well as general health conditions. However, standard pH sensors are usually too bulky, expensive, and impractical for routine use outside laboratory settings. Herein, a miniature hydrogel sensor, which enables quick and simple colorimetric detection of pH level, is shown. The sensor structure was manufactured from non-toxic hydrogel ink and patterned in the form of a matrix with 5 mm × 5 mm × 1 mm individual sensing pads using a 3D printing technique (bioplotting). The authors' ink composition, which contains sodium alginate, polyvinylpyrrolidone, and bromothymol blue indicator, enables repeatable and stable color response to different pH levels. The developed analysis software with an easy-to-use graphical user interface extracts the R(ed), G(reen), and B(lue) components of the color image of the hydrogel pads, and evaluates the pH value in a second. A calibration curve used for the analysis was obtained in a pH range of 3.5 to 9.0 using a laboratory pH meter as a reference. Validation of the sensor was performed on samples of artificial saliva for medical use and its mixtures with beverages of different pH values (lemon juice, coffee, black and green tea, bottled and tap water), and correct responses to acidic and alkaline solutions were observed. The matrix of square sensing pads used in this study provided multiple parallel responses for parametric tests, but the applied 3D printing method and ink composition enable easy adjustment of the shape of the sensing layer to other desired patterns and sizes. Additional mechanical tests of the hydrogel layers confirmed the relatively high quality and durability of the sensor structure. The solution presented here, comprising 3D printed hydrogel sensor pads, simple colorimetric detection, and graphical software for signal processing, opens the way to development of miniature and biocompatible diagnostic devices in the form of flexible, wearable, or intraoral sensors for prospective application in personalized medicine and point-of-care diagnosis.

Lab-on-chip technologies for space research - current trends and prospects.

The in-depth analysis concerning application of microfluidic instruments for space biology research is presented. The article focuses on recently investigated key scientific fields, i.e., lab-on-chips applied to the biomedical studies performed in the (1) International Space Station and (2) CubeSat nanosatellites. The paper presents also the lab-on-chip devices that were fabricated with a view to future space biology research and to those that to date have been solely been tested under Earth laboratory conditions and/or simulated microgravity environments. NASA and ESA conceptual mission plans for future are also mentioned, concerning for instance "tissue chips" and the ESA-SPHEROIDS campaign. The paper ends with final conclusions and future perspectives regarding lab-on-chip application in the space biology sector and its impact on novel biomedical and pharmaceutical strategies.

3D bio-printed hydrogel inks promoting lung cancer cell growth in a lab-on-chip culturing platform.

The results of a lab-on-chip (LOC) platform fabrication equipped with a hydrogel matrix is reported. A 3D printing technique was used to provide a hybrid, "sandwiched" type structure, including two microfluidic substrates of different origins. Special attention was paid to achieving uniformly bio-printed microfluidic hydrogel layers of a unique composition. Six different hydrogel inks were proposed containing sodium alginate, agar, chitosan, gelatin, methylcellulose, deionized water, or 0.9% NaCl, varying in proportions. All of them exhibited appropriate mechanical properties showing, e.g., the value of elasticity modulus as similar to that of biological tissues, such as skin. Utilizing our biocompatible, entirely 3D bio-printed structure, for the first time, a multi-drug-resistant lung cancer cell line (H69AR) was cultured on-chip. Biological validation of the device was performed qualitatively and quantitatively utilizing LIVE/DEAD assays and Presto blue staining. Although all bio-inks exhibited acceptable cell viability, the best results were obtained for the hydrogel composition including 3% sodium alginate + 7% gelatin + 90% NaCl (0.9%), reaching approximately 127.2% after 24 h and 105.4% after 48 h compared to the control group (100%). Further research in this area will focus on the microfluidic culture of the chosen cancer cell line (H69AR) and the development of novel drug delivery strategies towards appropriate in vivo models for chemotherapy and polychemotherapy treatment.