Photobiomodulation and Vascularization in Conduit-Based Peripheral Nerve Repair: A Narrative Review

Background: Peripheral nerve injuries pose a significant clinical issue for patients, especially in the most severe cases wherein complete transection (neurotmesis) results in total loss of sensory/motor function. Nerve guidance conduits (NGCs) are a common treatment option that protects and guides regenerating axons during recovery. However, treatment outcomes remain limited and often fail to achieve full reinnervation, especially in critically sized defects (>3 cm) where a lack of vascularization leads to neural necrosis. Conclusions: A multitreatment approach is, therefore, necessary to improve the efficacy of NGCs. Stimulating angiogenesis within NGCs can help alleviate oxygen deficiency through rapid inosculation with the host vasculature, whereas photobiomodulation therapy (PBMT) has demonstrated beneficial therapeutic effects on regenerating nerve cells and neovascularization. In this review, we discuss the current trends of NGCs, vascularization, and PBMT as treatments for peripheral nerve neurotmesis and highlight the need for a combinatorial approach to improve functional and clinical outcomes.

Critical Considerations for Regeneration of Vascularized Composite Tissues

Effective vascularization is vital for survival and functionality of complex tissue-engineered organs. The formation of the microvasculature, composed of endothelial cells (ECs) alone, has been mostly used to restore the vascular networks in organs. However, recent heterocellular studies demonstrate that co-culturing is a more effective approach in revascularization of engineered organs. This review presents key considerations for manufacturing of artificial vascularized composite tissues. We summarize the importance of co-cultures and the multicellular interactions with ECs, as well as design and use of bioreactors, as critical considerations for tissue vascularization. In addition, as an emerging scaffolding technique, this review also highlights the current caveats and hurdles associated with three-dimensional bioprinting and discusses recent developments in bioprinting strategies such as four-dimensional bioprinting and its future outlook for manufacturing of vascularized tissue constructs. Finally, the review concludes with addressing the critical challenges in the regulatory pathway and clinical translation of artificial composite tissue grafts. Impact statement Regeneration of composite tissues is critical as biophysical and biochemical characteristics differ between various types of tissues. Engineering a vascularized composite tissue has remained unresolved and requires additional evaluations along with optimization of methodologies and standard operating procedures. To this end, the main hurdle is creating a viable vascular endothelium that remains functional for a longer duration postimplantation, and can be manufactured using clinically appropriate source of cell lines that are scalable in vitro for the fabrication of human-scale organs. This review presents key considerations for regeneration and manufacturing of vascularized composite tissues as the field advances.

Design, Development, and Validation of an Intra-Osseous Needle Placement Guide

Intra-osseous (IO) needles are an easy and reliable alternative to intravenous (IV) access in the prehospital and emergency settings for treating patients in shock. The advantage of utilizing an IO is that secure, noncollapsible peripheral venous access can be obtained rapidly in critically ill patients. Placement of IO needles in the proximal tibia, humerus, or sternum, however, requires knowledge of human anatomy and the requisite skill to position, align, and place the device. In the developing world, this is not always available, and in the chaos of an in-hospital code, prehospital trauma, or a mass-casualty incident, even trained providers can have trouble correctly placing IV or IO needles. The Tib-Finder is an intuitive drill guide that significantly improves efficiency with which IO can be placed in the proximal tibia. Here, we present the conceptualization, design, and creation of an alpha-prototype Tib-Finder drill guide in less than 90 days; initial validation was achieved through analysis of anthropometric measurements of human skeletons, and usability studies were performed using untrained volunteers and mannequins. The Tib-Finder is intended to provide first responders and medical personnel, in the first world and the developing world, a way to accurately and repeatably locate the proximal tibia and achieve safe, rapid intravascular access in critically ill patients. Further, it eliminates the need for direct contact between patients and caregivers and improves the ease-of-use of IO devices by first responders and healthcare providers.

Time course of peri-implant bone regeneration around loaded and unloaded implants in a rat model

The time-course of cancellous bone regeneration surrounding mechanically loaded implants affects implant fixation, and is relevant to determining optimal rehabilitation protocols following orthopaedic surgeries. We investigated the influence of controlled mechanical loading of titanium-coated polyether-ether ketone (PEEK) implants on osseointegration using time-lapsed, non-invasive, in vivo micro-computed tomography (micro-CT) scans. Implants were inserted into proximal tibial metaphyses of both limbs of eight female Sprague-Dawley rats. External cyclic loading (60 or 100 μm displacement, 1 Hz, 60 s) was applied every other day for 14 days to one implant in each rat, while implants in contralateral limbs served as the unloaded controls. Hind limbs were imaged with high-resolution micro-CT (12.5 μm voxel size) at 2, 5, 9, and 12 days post-surgery. Trabecular changes over time were detected by 3D image registration allowing for measurements of bone-formation rate (BFR) and bone-resorption rate (BRR). At day 9, mean %BV/TV for loaded and unloaded limbs were 35.5 ± 10.0% and 37.2 ± 10.0%, respectively, and demonstrated significant increases in bone volume compared to day 2. BRR increased significantly after day 9. No significant differences between bone volumes, BFR, and BRR were detected due to implant loading. Although not reaching significance (p = 0.16), an average 119% increase in pull-out strength was measured in the loaded implants. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:997-1006, 2017.

3D Printing of Personalized Artificial Bone Scaffolds

Additive manufacturing technologies, including three-dimensional printing (3DP), have unlocked new possibilities for bone tissue engineering. Long-term regeneration of normal anatomic structure, shape, and function is clinically important subsequent to bone trauma, tumor, infection, nonunion after fracture, or congenital abnormality. Due to the great complexity in structure and properties of bone across the population, along with variation in the type of injury or defect, currently available treatments for larger bone defects that support load often fail in replicating the anatomic shape and structure of the lost bone tissue. 3DP could provide the ability to print bone substitute materials with a controlled chemistry, shape, porosity, and topography, thus allowing printing of personalized bone grafts customized to the patient and the specific clinical condition. 3DP and related fabrication approaches of bone grafts may one day revolutionize the way clinicians currently treat bone defects. This article gives a brief overview of the current advances in 3DP and existing materials with an emphasis on ceramics used for 3DP of bone scaffolds. Furthermore, it addresses some of the current limitations of this technique and discusses potential future directions and strategies for improving fabrication of personalized artificial bone constructs.