Perfused Platforms to Mimic Bone Microenvironment at the Macro/Milli/Microscale: Pros and Cons

Abstract

As life expectancy increases, the population experiences progressive ageing. Ageing, in turn, is connected to an increase in bone-related diseases (i.e., osteoporosis and increased risk of fractures). Hence, the search for new approaches to study the occurrence of bone-related diseases and to develop new drugs for their prevention and treatment becomes more pressing. However, to date, a reliable in vitro model that can fully recapitulate the characteristics of bone tissue, either in physiological or altered conditions, is not available. Indeed, current methods for modelling normal and pathological bone are poor predictors of treatment outcomes in humans, as they fail to mimic the in vivo cellular microenvironment and tissue complexity. Bone, in fact, is a dynamic network including differently specialized cells and the extracellular matrix, constantly subjected to external and internal stimuli. To this regard, perfused vascularized models are a novel field of investigation that can offer a new technological approach to overcome the limitations of traditional cell culture methods. It allows the combination of perfusion, mechanical and biochemical stimuli, biological cues, biomaterials (mimicking the extracellular matrix of bone), and multiple cell types. This review will discuss macro, milli, and microscale perfused devices designed to model bone structure and microenvironment, focusing on the role of perfusion and encompassing different degrees of complexity. These devices are a very first, though promising, step for the development of 3D in vitro platforms for preclinical screening of novel anabolic or anti-catabolic therapeutic approaches to improve bone health.

Bone on-a-chip: a 3D dendritic network in a screening platform for osteocyte-targeted drugs

“…Furthermore, in vivo, under physiological conditions, Oc reside in interconnected microscopic spaces and are surrounded by a stiff ECM, whereas, in growing bone, osteoblasts are not surrounded by calcified bone matrix, but are located on the surface of soft osteoid in highly porous regions [75][76][77]. Therefore, it is likely that MLO-Y4 survive better than MLO-A5 in matrices with high stiffness, such as those obtained with the hydrogel blend [34]. We next studied Oc differentiation within the chip by analysing cell morphology and the expression of Oc markers as Cx43 and ALP.…”

“…Despite the inherent advantages of these solutions, recapitulation of the 3D dendritic morphology has been difficult to achieve, suggesting the need of developing matrices to be combined with 3D devices that allow a homogeneous cell distribution over the matrix, adequate perfusion, and compatibility with cellular structures and functionality. On this regard, the combined use of 3D matrices and inorganic phase, or the culture of Oc in a perfused microfluidic channel filled with a crosslinked matrix has never been considered, or neither proposed for the set-up of largescale microfluidic drug screening platforms [34]. In accordance with the European Union's regulation on the 3R rule (Replacement, Reduction, Refinement), the development of such a device would greatly reduce need for animal models that is currently the gold standard for the preclinical evaluation of new drugs [35,36].…”

A microphysiological system for studying human bone biology under simultaneous control of oxygen tension and mechanical loading

“…31 For this reason, it is necessary to develop an appropriate in vitro model covering both aspects, modulation of oxygen tension and mechanical loading as driving factors of bone formation. Up to now, only a few published MPS enable studies on bone biology, especially mechanobiology, 31 while none of them provide control over perfusion, oxygen tension and mechanical loading simultaneously. 8…”

“…14,[28][29][30] Current scientific literature indicates that, in humans, the simultaneous presence of biochemical factors such as nutrient and oxygen gradients in addition to variable mechanical loads is continuously fine-tuned to ensure bone homeostasis. 31 For this reason, it is necessary to develop an appropriate in vitro model covering both aspects, modulation of oxygen tension and mechanical loading as driving factors of bone formation. Up to now, only a few published MPS enable studies on bone biology, especially mechanobiology, 31 while none of them provide control over perfusion, oxygen tension and mechanical loading simultaneously.…”

“…31 For this reason, it is necessary to develop an appropriate in vitro model covering both aspects, modulation of oxygen tension and mechanical loading as driving factors of bone formation. Up to now, only a few published MPS enable studies on bone biology, especially mechanobiology, 31 while none of them provide control over perfusion, oxygen tension and mechanical loading simultaneously. 8 In this work, we present an MPS that allows studying the influence of perfusion, oxygen environment and defined longitudinal mechanical load on three-dimensional (3D) bone tissue constructs.…”