Biofabricating the vascular tree in engineered bone tissue

The development of tissue engineering strategies for treatment of large bone defects has become increasingly relevant, given the growing demand for bone substitutes. Native bone is composed of a dense vascular network necessary for the regulation of bone development, regeneration and homeostasis. A major obstacle in fabricating living, clinically relevant-sized bone mimics (1-10 cm3) is the limited supply of nutrients, including oxygen to the core of the construct. Therefore, strategies to support vascularization are pivotal for the development of tissue engineered bone constructs. Creating a functional bone construct integrated with a vascular network, capable of delivering the necessary nutrients for optimal tissue development is imperative for translation into the clinics. The vascular system is composed of a complex network that runs throughout the body in a tree-like hierarchical branching fashion. A significant challenge for tissue engineering approaches lies in mimicking the intricate, multi-scale structures consisting of larger vessels (macro-vessels) which interconnect with multiple sprouting vessels (microvessels) in a closed network. The advent of biofabrication has enabled complex, out of plane channels to be generated and has laid the groundwork for the creation of multi-scale vasculature in recent years. This review highlights the key state-of-the-art achievements for the development of vascular networks of varying scales in the field of biofabrication with a particular focus for its application in developing a functional tissue engineered bone construct. STATEMENT OF SIGNIFICANCE: There is a growing need for bone substitutes to overcome the limited supply of patient-derived bone. Bone tissue engineering aims to overcome this by combining stem cells with scaffolds to restore missing bone. The current bottleneck in upscaling is the lack of an integrated vascular network, required for the delivery of nutrients to cells. 3D bioprinting techniques has enabled the creation of complex hollow structures of varying dimensions that resemble native blood vessels. The convergence of multiple materials, cell types and fabrication approaches, opens the possibility of developing clinically-relevant sized vascularized bone constructs. This review provides an up-to-date insight of the technologies currently available for the generation of complex vascular networks, with a focus on their application in bone tissue engineering

The priming effect of diesel exhaust on native pollen exposure at the air-liquid interface.

Pollen related allergic diseases have been increasing for decades. The reasons for this increase are unknown, but environmental pollution like diesel exhaust seem to play a role. While previous studies explored the effects of pollen extracts, we studied here for the first time priming effects of diesel exhaust on native pollen exposure using a novel experimental setup. Methods: Human bronchial epithelial BEAS-2B cells were exposed to native birch pollen (real life intact pollen, not pollen extracts) at the air-liquid interface (pollen-ALI). BEAS-2B cells were also pre-exposed in a diesel-ALI to diesel CAST for 2 h (a model for diesel exhaust) and then to pollen in the pollen-ALI 24 h later. Effects were analysed by genome wide transcriptome analysis after 2 h 25 min, 6 h 50 min and 24 h. Selected genes were confirmed by qRT-PCR. Results: Bronchial epithelial cells exposed to native pollen showed the highest transcriptomic changes after about 24 h. About 3157 genes were significantly up- or down-regulated for all time points combined. After pre-exposure to diesel exhaust the maximum reaction to pollen had shifted to about 2.5 h after exposure, plus the reaction to pollen was desensitised as only 560 genes were differentially regulated. Only 97 genes were affected synergistically. Of these, enrichment analysis showed that genes involved in immune and inflammatory response were involved. Conclusion: Diesel exhaust seems to prime cells to react more rapidly to native pollen exposure, especially inflammation related genes, a factor known to facilitate the development of allergic sensitization. The marker genes here detected could guide studies in humans when investigating whether modern and outdoor diesel exhaust exposure is still detrimental for the development of allergic disease

Numerical analysis of ischemia- and compression-induced injury in tissue-engineered skeletal muscle constructs

Pressure-related deep tissue injury may develop in skeletal muscle tissue which is subjected to prolonged compression. For early detection, it is important to understand the underlying damage processes. Gawlitta et al. [Gawlitta, D., C. W. J. Oomens, D. L. Bader, F. P. T. Baaijens, and C. V. C. Bouten. Temporal differences in the influence of ischemic factors and deformation on the metabolism of engineered skeletal muscle. J. Appl. Physiol. 103(2):464–473, 2007b] subjected tissue-engineered muscle constructs to ischemia and deformation to study their effects on viability. Contrary to previous findings, no decrease in viability was found due to compression. However, the nature of their measurement method complicated interpretation of the results, particularly when deformation was involved. Changes in the constructs were assessed by measurements in the surrounding medium. The theoretical model developed in the present study describes metabolism, diffusion, and cell death in the experiments, and accounts for reduced diffusion due to compression. It was demonstrated that the lack of effect of compression on tissue viability, as measured in the experiments, could be explained by the compression-induced decrease in diffusivity. Compression did lead to considerable cell death but this could not be measured by Gawlitta et al. [Gawlitta, D., C. W. J. Oomens, D. L. Bader, F. P. T. Baaijens, and C. V. C. Bouten. Temporal differences in the influence of ischemic factors and deformation on the metabolism of engineered skeletal muscle. J. Appl. Physiol. 103(2):464–473, 2007b] because diffusion of the cell death marker to the medium was limited. This study shows that a proper description of transport processes is essential for a correct interpretation of experiments in which indirect measurement methods are used

Impact of volatile and semi-volatile organic compounds from farming environments on allergy-related cellular processes.

Allergic diseases are an increasing global burden. Epidemiological and in vivo studies showed that farming environments could protect from allergic asthma. Studies explaining this protective effect mainly focused on the influence of chemical compounds in the molecular size range of proteins and endotoxins. Our study aimed at deciphering the possible role of small-sized semi-volatile organic compounds (SVOCs) of farming aerosols in immunomodulation processes. Bronchial epithelial BEAS-2B cells were exposed to aerosol extracts of particulate matter (PM2.5) from farming environments. These cell exposures revealed a decisive effect of the smaller sized fraction (< 3 kDa) compared to extracts including the larger sized fraction. We demonstrated that smaller compounds can induce regulations of inflammatory and allergy-related genes including interleukin-8, xanthine dehydrogenase and toll-like receptor 2 (TLR2). Additionally, we performed a comprehensive chemical investigation of two typical farming aerosols (cow vs. sheep) by applying comprehensive gas chromatography coupled to time-of-flight mass spectrometry. We were able to identify several SVOCs characteristic for the protective cow sheds environment including four key components. Cell exposure with the two farming extracts showed a distinct regulation of the E3 ubiquitin ligase PELI2 gene and TLR2 by cow shed extracts. Finally, the regulation of TLR2 corresponded to the regulation that was observed after exposing cells to an artificial mixture of the four key components identified in the cow sheds. In summary, we were able to demonstrate the importance of smaller particle-bound SVOCs found in farming environments concerning their possible contribution to a protective farm effect

A study on the chemical profile and the derived health effects of heavy-duty machinery aerosol with a focus on the impact of alternative fuels.

The combustion of petroleum-based fossil fuels is associated with a high environmental burden. Several alternative fuels, including synthetic fuels (e.g., gas-to-liquid, GTL) and biofuels (e.g., rapeseed methyl ester, RME) have been studied in the last few years. While the advantages for the environment (sustainability of biofuels) are well known, research on the resulting health effects from combustion aerosols of these alternative fuels is still scarce. Consequently, we investigated the chemical combustion profile from three distinct fuel types, including a petroleum-based fossil fuel (B0) and two alternative fuels (GTL, RME) under real exposure conditions. We sampled particulate matter (PM2.5, PM0.25) and the gas phase from heavy-duty machinery and evaluated the general pattern of volatile and semi-volatile organic compounds, elemental and organic carbon as well as a range of transition metals in the size segregated PM and/or gas phase. The use of comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry enabled us to classify distinct methylated PAHs in the PM samples and its high abundance, especially in the fine fraction of PM. We found that (methylated) PAHs were highly abundant in the PM of B0 compared to GTL and RME. Highest concentrations of targeted aromatic species in the gas phase were released from B0. In summary, we demonstrated that GTL and RME combustion released lower amounts of chemical compounds related to adverse health effects, thus, the substitution of petroleum-based fuels could improve air quality for human and the environment

A unique data analysis framework and open source benchmark data set for the analysis of comprehensive two-dimensional gas chromatography software.

Comprehensive two-dimensional gas chromatography (GC × GC) is amongst the most powerful separation technologies currently existing. Since its advent in early 1990, it has become an established method which is readily available. However, one of its most challenging aspects, especially in hyphenation with mass spectrometry is the high amount of chemical information it provides for each measurement. The GC × GC community agrees that there, the highest demand for action is found. In response, the number of software packages allowing for in-depth data processing of GC × GC data has risen over the last couple of years. These packages provide sophisticated tools and algorithms allowing for more streamlined data evaluation. However, these tools/algorithms and their respective specific functionalities differ drastically within the available software packages and might result in various levels of findings if not appropriately implemented by the end users. This study focuses on two main objectives. First, to propose a data analysis framework and second to propose an open-source dataset for benchmarking software options and their specificities. Thus, allowing for an unanimous and comprehensive evaluation of GC × GC software. Thereby, the benchmark data includes a set of standard compound measurements and a set of chocolate aroma profiles. On this foundation, eight readily available GC × GC software packages were anonymously investigated for fundamental and advanced functionalities such as retention and detection device derived parameters, revealing differences in the determination of e.g. retention times and mass spectra