Tuning graft- and host-derived vascularization in modular tissue constructs: a potential role of HIF1 activation

Oxygen generating biomaterials at the forefront of regenerative medicine: advances in bone regeneration

Globally, an annual count of more than two million bone transplants is conducted, with conventional treatments, including metallic implants and bone grafts, exhibiting certain limitations. In recent years, there have been significant advancements in the field of bone regeneration. Oxygen tension regulates cellular behavior, which in turn affects tissue regeneration through metabolic programming. Biomaterials with oxygen release capabilities enhance therapeutic effectiveness and reduce tissue damage from hypoxia. However, precise control over oxygen release is a significant technical challenge, despite its potential to support cellular viability and differentiation. The matrices often used to repair large-size bone defects do not supply enough oxygen to the stem cells being used in the regeneration process. Hypoxia-induced necrosis primarily occurs in the central regions of large matrices due to inadequate provision of oxygen and nutrients by the surrounding vasculature of the host tissues. Oxygen generating biomaterials (OGBs) are becoming increasingly significant in enhancing our capacity to facilitate the bone regeneration, thereby addressing the challenges posed by hypoxia or inadequate vascularization. Herein, we discussed the key role of oxygen in bone regeneration, various oxygen source materials and their mechanism of oxygen release, the fabrication techniques employed for oxygen-releasing matrices, and novel emerging approaches for oxygen delivery that hold promise for their potential application in the field of bone regeneration.

Hypoxia-Inducible Factor Drives Vascularization of Modularly Assembled Engineered Tissue

IMPACT STATEMENT

Using two inhibitory methods, we demonstrated that hypoxia-inducible factor (HIF) plays an important role in vascularizing and oxygenating modularly-assembled engineered tissues. Each inhibitory technique elucidated a different mechanism by which this occurred. Whereas systemic inhibition negatively impacted early recruitment of host-derived cells, genetic inhibition in grafted endothelial cells was detrimental to their survival. Taken together, our study suggests that methods of HIF-mediated mechanisms could be harnessed to tune the extent and rate of vascularization in engineered tissue constructs.

An in vivo comparative study of the gelatin microtissue-based bottom-up strategy and top-down strategy in bone tissue engineering application

Tissue-engineered bone grafts (TEBGs) represent a promising treatment for bone defects. Nevertheless, drawbacks of the current construction strategy (top-down [TD] strategy) such as limited transmission of nutrients and nonuniform distribution of seeded cells, result in an unsatisfied therapeutic effect on large segmental bone defects. Theoretically, tissue-engineered microtissue (TEMT)-based bottom-up (BU) strategy is effective in preserving seed cells and vascularization, thus being regarded as a better alternative for TEBGs. Yet, there are few studies focusing on the comparison of the in vivo performance of TEBGs fabricated by TD or BU strategy. Here, we developed an ectopic bone formation rat model to compare the performance of these two construction strategies in vivo. TEBGs made from gelatin TEMT (BU strategy) and bulk tissue (BT; TD strategy) were seeded with equal number of rat bone marrow-derived mesenchymal stem cells and fabricated in 5 mm polydimethylsiloxane chambers. The grafts were implanted into subcutaneous pockets in the same rat. Four weeks after implantation, microcomputed tomography and hematoxylin and eosin staining results demonstrated that more bony tissue was formed in the microtissue (MT) group than in the BT group. CD31 staining further confirmed that there were more blood vessels in the MT group, indicating that the BU strategy was superior in inducing angiogenesis. This comparative study provides evidence that the BU construction strategy is more effective for in vivo application and bone defect treatment by bone tissue engineering. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 678-688, 2019.

Oxygen Delivering Biomaterials for Tissue Engineering

Tissue engineering (TE) has provided promising strategies for regenerating tissue defects, but few TE approaches have been translated for clinical applications. One major barrier in TE is providing adequate oxygen supply to implanted tissue scaffolds, since oxygen diffusion from surrounding vasculature in vivo is limited to the periphery of the scaffolds. Moreover, oxygen is also an important signaling molecule for controlling stem cell differentiation within TE scaffolds. Various technologies have been developed to increase oxygen delivery in vivo and enhance the effectiveness of TE strategies. Such technologies include hyperbaric oxygen therapy, perfluorocarbon- and hemoglobin-based oxygen carriers, and oxygen-generating, peroxide-based materials. Here, we provide an overview of the underlying mechanisms and how these technologies have been utilized for in vivo TE applications. Emerging technologies and future prospects for oxygen delivery in TE are also discussed to evaluate the progress of this field towards clinical translation.