Investigation of Low-Cost FDM-Printed Polymers for Elevated-Temperature Applications.

While fused deposition modeling (FDM) and other relatively inexpensive 3D printing methods are nowadays used in many applications, the possible areas of using FDM-printed objects are still limited due to mechanical and thermal constraints. Applications for space, e.g., for microsatellites, are restricted by the usually insufficient heat resistance of the typical FDM printing materials. Printing high-temperature polymers, on the other hand, necessitates special FDM printers, which are not always available. Here, we show investigations of common polymers, processible on low-cost FDM printers, under elevated temperatures of up to 160 °C for single treatments. The polymers with the highest dimensional stability and mechanical properties after different temperature treatments were periodically heat-treated between -40 °C and +80 °C in cycles of 90 min, similar to the temperature cycles a microsatellite in the low Earth orbit (LEO) experiences. While none of the materials under investigation fully maintains its dimensions and mechanical properties, filled poly(lactic acid) (PLA) filaments were found most suitable for applications under these thermal conditions.

Silica Hydrogels as Entrapment Material for Microalgae.

Despite being a promising feedstock for food, feed, chemicals, and biofuels, microalgal production processes are still uneconomical due to slow growth rates, costly media, problematic downstreaming processes, and rather low cell densities. Immobilization via entrapment constitutes a promising tool to overcome these drawbacks of microalgal production and enables continuous processes with protection against shear forces and contaminations. In contrast to biopolymer gels, inorganic silica hydrogels are highly transparent and chemically, mechanically, thermally, and biologically stable. Since the first report on entrapment of living cells in silica hydrogels in 1989, efforts were made to increase the biocompatibility by omitting organic solvents during hydrolysis, removing toxic by-products, and replacing detrimental mineral acids or bases for pH adjustment. Furthermore, methods were developed to decrease the stiffness in order to enable proliferation of entrapped cells. This review aims to provide an overview of studied entrapment methods in silica hydrogels, specifically for rather sensitive microalgae.

Atomic Force Microscopy (AFM) on Biopolymers and Hydrogels for Biotechnological Applications-Possibilities and Limits.

Atomic force microscopy (AFM) is one of the microscopic techniques with the highest lateral resolution. It can usually be applied in air or even in liquids, enabling the investigation of a broader range of samples than scanning electron microscopy (SEM), which is mostly performed in vacuum. Since it works by following the sample surface based on the force between the scanning tip and the sample, interactions have to be taken into account, making the AFM of irregular samples complicated, but on the other hand it allows measurements of more physical parameters than pure topography. This is especially important for biopolymers and hydrogels used in tissue engineering and other biotechnological applications, where elastic properties, surface charges and other parameters influence mammalian cell adhesion and growth as well as many other effects. This review gives an overview of AFM modes relevant for the investigations of biopolymers and hydrogels and shows several examples of recent applications, focusing on the polysaccharides chitosan, alginate, carrageenan and different hydrogels, but depicting also a broader spectrum of materials on which different AFM measurements are reported in the literature.

Measuring Biosignals with Single Circuit Boards.

To measure biosignals constantly, using textile-integrated or even textile-based electrodes and miniaturized electronics, is ideal to provide maximum comfort for patients or athletes during monitoring. While in former times, this was usually solved by integrating specialized electronics into garments, either connected to a handheld computer or including a wireless data transfer option, nowadays increasingly smaller single circuit boards are available, e.g., single-board computers such as Raspberry Pi or microcontrollers such as Arduino, in various shapes and dimensions. This review gives an overview of studies found in the recent scientific literature, reporting measurements of biosignals such as ECG, EMG, sweat and other health-related parameters by single circuit boards, showing new possibilities offered by Arduino, Raspberry Pi etc. in the mobile long-term acquisition of biosignals. The review concentrates on the electronics, not on textile electrodes about which several review papers are available.

Growth and photosynthetic activity of Chlamydomonas reinhardtii entrapped in lens-shaped silica hydrogels.

Entrapment of microalgae in silica hydrogels enables the application as biocatalysts in continuous production of secreted products. Despite a mitigation of substrate and product diffusion limitations by lens-shaped particles, there are no reports on light supply and limitation. This study investigated the impact of hydrogel structure, particle size and biomass loading on the behaviour of the microalga Chlamydomonas reinhardtii entrapped in lens-shaped silica particles. Entrapment in tetraethyl orthosilicate and tetra(n-propylamino)silane based hydrogels reduced the growth rate by 30% and 23%, respectively. In contrast, cells entrapped in sodium silicate based hydrogels displayed a growth rate similar to free cells and cells entrapped in calcium alginate (1.13 d-1), indicating a suitable biocompatibility. Reduction of lens height by 26% maintained the growth rate in silica hydrogel. A fourfold increase in biomass loading reduced the growth rate by 20% and elevated the yield coefficient by 211%, indicating the impact of biomass loading on light and nutrient supply on photosynthetic growth. Finally, hydrogen production was observed by entrapped cells. The results of this work will pave the way for robust biocatalytic processes where photosynthetically active cells are protected against harmful mechanical and biological influences.

Entrapment and growth of Chlamydomonas reinhardtii in biocompatible silica hydrogels.

In this work, we aimed at improved viability and growth of the microalga Chlamydomonas reinhardtii in transparent silica hydrogels based on low-ethanol, low-sodium and low-propylamine synthesis. Investigation into replacement of conventional base KOH by buffers dipotassium phosphate and tris(hydroxymethyl)aminomethane along with increased precursor concentrations yielded an aqueous synthesis route which provided a gelation within 10 min, absorptions below 0.1 and elastic moduli of 0.04-4.23 kPa. The abrasion resistance enhanced by 41% compared to calcium alginate hydrogels and increased to 70-85% residual material on addition of chitosan. Entrapment of microalgae in low-sodium and low-propylamine silica hydrogels maintained the PSII quantum yield above 0.3 and growth rates of 0.23 ± 0.01 d-1, similarly to cells entrapped in calcium alginate. These promising results pave the way for the entrapment of sensitive, photosynthetically active and growing cells for in robust biotechnological applications.