Scaffold-based bone tissue engineering in microgravity: potential, concerns and implications

One of humanity's greatest challenges is space exploration, which requires an in-depth analysis of the data continuously collected as a necessary input to fill technological gaps and move forward in several research sectors. Focusing on space crew healthcare, a critical issue to be addressed is tissue regeneration in extreme conditions. In general, it represents one of the hottest and most compelling goals of the scientific community and the development of suitable therapeutic strategies for the space environment is an urgent need for the safe planning of future long-term manned space missions. Osteopenia is a commonly diagnosed disease in astronauts due to the physiological adaptation to altered gravity conditions. In order to find specific solutions to bone damage in a reduced gravity environment, bone tissue engineering is gaining a growing interest. With the aim to critically investigate this topic, the here presented review reports and discusses bone tissue engineering scenarios in microgravity, from scaffolding to bioreactors. The literature analysis allowed to underline several key points, such as the need for (i) biomimetic composite scaffolds to better mimic the natural microarchitecture of bone tissue, (ii) uniform simulated microgravity levels for standardized experimental protocols to expose biological materials to the same testing conditions, and (iii) improved access to real microgravity for scientific research projects, supported by the so-called democratization of space.

Population analysis of space travelers

Although many space missions have been completed in the last 60 years, space exploration is still technologically and medically challenging. While large-scale medical studies are impossible in space travelers, meta-analysis allows combining data from small crews that participated in space missions over several decades. Our primary objective was to examine space-travelers' sociodemographic characteristics and spaceflight activities, and their changes with time from the first spaceflight. Our secondary objective was to evaluate the publication practices to assess data availability for health-related meta-analytic studies. Based on state-funded space agencies used as primary sources, and third-party websites used as secondary sources, 565 humans (501 males/64 females) have currently completed spaceflight. The average age of space-travelers increased from 34±4 in the 1960s to 45±4 in the 2010s. While the duration of space missions has increased consistently, the number of missions per year varied in correlation with technological events. Using papers identified in the systematic review of bone health in astronauts, we examined the changes in reporting practices with time. The reported sample size varied from 1 to 58 people, in total providing data for 148 individuals. Data confidentiality significantly improved with time; however, the corresponding decrease in the availability of individual parameters did not allow stratification even by age, sex, and mission duration. Thus, space travelers represent a diverse population suitable for comparative studies, however, it is important to develop reporting practices that ensure consistent, transparent, and ethical presentation of outcomes to support meta-analyses that are critical for understanding the scope of spaceflight-induced health issues.

A human mission to Mars: Predicting the bone mineral density loss of astronauts

A round-trip human mission to Mars is anticipated to last roughly three years. Spaceflight conditions are known to cause loss of bone mineral density (BMD) in astronauts, increasing bone fracture risk. There is an urgent need to understand BMD progression as a function of spaceflight time to minimize associated health implications and ensure mission success. Here we introduce a nonlinear mathematical model of BMD loss for candidate human missions to Mars: (i) Opposition class trajectory (400-600 days), and (ii) Conjunction class trajectory (1000-1200 days). Using femoral neck BMD data (N = 69) from astronauts after 132-day and 228-day spaceflight and the World Health Organization's fracture risk recommendation, we predicted post-mission risk and associated osteopathology. Our model predicts 62% opposition class astronauts and 100% conjunction class astronauts will develop osteopenia, with 33% being at risk for osteoporosis. This model can help in implementing countermeasure strategies and inform space agencies' choice of crew candidates.

Simulated microgravity modulates the mesenchymal stromal cell response to inflammatory stimulation

The duration and distance of manned space flights emphasizes the importance of advanced elucidation of space flight factors and their effects on human beings. The exposure to inflammatory mediators under microgravity may contribute to the activity of different cells, perivascular stromal cells (MSCs) in particular. Inflammatory activation is now considered as a principal cue of MSC engagement in reparative remodeling. In the present paper, the effect of simulated microgravity (sµg) on TNFα-mediated priming of adipose tissue-derived MSC (ASCs) was examined. Sµg per se did not induce inflammatory-related changes, such as elevation of ICAM-1 and HLA-ABC expression, soluble mediator production, or shifting of the transcription profile in ASCs. Moreover, the attenuated ASC response to TNFα priming under sµg was manifested in decreased production of TNFα-dependent pleiotropic cytokines (IL-8 and MCP-1), matrix remodeling proteases, and downregulation of some genes encoding growth factors and cytokines. Time-dependent analysis detected the first signs of priming attenuation after 48 hours of 3D-clinorotation. A reduced response of MSCs to priming under sµg can be a negative factor in terms of MSC involvement in tissue remodeling processes.