Advances in Limb Preservation: From Replantation to Transplantation

Study on the preservation effects of the amputated forelimb by machine perfusion at physiological temperature

PURPOSE

Ischemia and hypoxia are the main factors limiting limb replantation and transplantation. Static cold storage (SCS), a common preservation method for tissues and organs, can only prolong limb ischemia time to 4 - 6 h. The normothermic machine perfusion (NMP) is a promising method for the preservation of tissues and organs, which can extend the preservation time in vitro by providing continuous oxygen and nutrients. This study aimed to evaluate the difference in the efficacy of the 2 limb preservation methods.

METHODS

The 6 forelimbs from beagle dogs were divided into 2 groups. In the SCS group (n = 3), the limbs were preserved in a sterile refrigerator at 4 °C for 24 h, and in the NMP group (n = 3), the perfusate prepared with autologous blood was used for the oxygenated machine perfusion at physiological temperature for 24 h, and the solution was changed every 6 h. The effects of limb storage were evaluated by weight gain, perfusate biochemical analysis, enzyme-linked immunosorbent assay, and histological analysis. All statistical analyses and graphs were performed using GraphPad Prism 9.0 one-way or two-way analysis of variance. The p value of less than 0.05 was considered to indicate statistical significance.

RESULTS

In the NMP group, the weight gained percentage was 11.72% ± 4.06%; the hypoxia-inducible factor-1α contents showed no significant changes; the shape of muscle fibers was normal; the gap between muscle fibers slightly increased, showing the intercellular distance of (30.19 ± 2.83) μm; and the vascular α-smooth muscle actin (α-SMA) contents were lower than those in the normal blood vessels. The creatine kinase level in the perfusate of the NMP group increased from the beginning of perfusion, decreased after each perfusate change, and remained stable at the end of perfusion showing a peak level of 4097.6 U/L. The lactate dehydrogenase level of the NMP group increased near the end of perfusion and reached the peak level of 374.4 U/L. In the SCS group, the percentage of weight gain was 0.18% ± 0.10%, and the contents of hypoxia-inducible factor-1α increased gradually and reached the maximum level of (164.85 ± 20.75) pg/mL at the end of the experiment. The muscle fibers lost their normal shape and the gap between muscle fibers increased, showing an intercellular distance of (41.66 ± 5.38) μm. The contents of vascular α-SMA were much lower in the SCS group as compared to normal blood vessels.

CONCLUSIONS

NMP caused lesser muscle damage and contained more vascular α-SMA as compared to SCS. This study demonstrated that NMP of the amputated limb with perfusate solution based on autologous blood could maintain the physiological activities of the limb for at least 24 h.

Current opinion: advances in machine perfusion and preservation of vascularized composite allografts - will time still matter?

PURPOSE OF REVIEW

A major hurdle hindering more widespread application of reconstructive transplantation is the very limited cold ischemia time (CIT) of vascularized composite allografts (VCAs). In this review, we discuss cutting edge machine perfusion protocols and preservation strategies to overcome this limitation.

RECENT FINDINGS

Several preclinical machine perfusion studies have demonstrated the multifactorial utility of this technology to extend preservation windows, assess graft viability prior to transplantation and salvage damaged tissue, yet there are currently no clinically approved machine perfusion protocols for reconstructive transplantation. Thus, machine perfusion remains an open challenge in VCA due to the complexity of the various tissue types. In addition, multiple other promising avenues to prolong preservation of composite allografts have emerged. These include cryopreservation, high subzero preservation, vitrification and nanowarming. Despite several studies demonstrating extended preservation windows, there are several limitations that must be overcome prior to clinical translation. As both machine perfusion and subzero preservation protocols have rapidly advanced in the past few years, special consideration should be given to their potential complementary utilization.

SUMMARY

Current and emerging machine perfusion and preservation technologies in VCA have great promise to transform the field of reconstructive transplantation, as every extra hour of CIT helps ease the complexities of the peri-transplant workflow. Amongst the many advantages, longer preservation windows may allow for elective procedures, improved matching, establishment of novel immunomodulatory protocols and global transport of grafts, ultimately enabling us the ability to offer this life changing procedure to more patients.

Bioinks for Space Missions: The Influence of Long-Term Storage of Alginate-Methylcellulose-Based Bioinks on Printability as well as Cell Viability and Function

Bioprinting is considered a key technology for future space missions and is currently being established on the International Space Station (ISS). With the aim to perform bioink production as a critical and resource-consuming preparatory step already on Earth and transport a bioink cartridge "ready to use" to the ISS, the storability of bioinks is investigated. Hydrogel blends based on alginate and methylcellulose are laden with either green microalgae of the species Chlorella vulgaris or with different human cell lines including immortilized human mesenchymal stem cells, SaOS-2 and HepG2, as well as with primary human dental pulp stem cells. The bioinks are filled into printing cartridges and stored at 4°C for up to four weeks. Printability of the bioinks is maintained after storage. Viability and function of the cells embedded in constructs bioprinted from the stored bioinks are investigated during subsequent cultivation: The microalgae survive the storage period very well and show no loss of growth and functionality, however a significant decrease is visible for human cells, varying between the different cell types. The study demonstrates that storage of bioinks is in principle possible and is a promising starting point for future research, making complex printing processes more effective and reproducible.

Improving the ischemia-reperfusion injury in vascularized composite allotransplantation: Clinical experience and experimental implications

Long-time ischemia worsening transplant outcomes in vascularized composite allotransplantation (VCA) is often neglected. Ischemia-reperfusion injury (IRI) is an inevitable event that follows reperfusion after a period of cold static storage. The pathophysiological mechanism activates local inflammation, which is a barrier to allograft long-term immune tolerance. The previous publications have not clearly described the relationship between the tissue damage and ischemia time, nor the rejection grade. In this review, we found that the rejection episodes and rejection grade are usually related to the ischemia time, both in clinical and experimental aspects. Moreover, we summarized the potential therapeutic measures to mitigate the ischemia-reperfusion injury. Compare to static preservation, machine perfusion is a promising method that can keep VCA tissue viability and extend preservation time, which is especially beneficial for the expansion of the donor pool and better MHC-matching.

Proof of Concept Study for a Closed Ex-Vivo Limb Perfusion System for 24-hour Subnormothermic Preservation Using Acellular Perfusate

BACKGROUND

The two approaches to vascularized tissue machine perfusion utilize either the open (non-pressurized) or closed (pressurized) perfusion system. Most studies describing isolated limb perfusion preservation rely on open perfusion systems and report tissue edema exceeding 40% after 12-14 hours of preservation.A variant of machine perfusion places the limb and perfusate into a reservoir closed to atmosphere. It is hypothesized that the reservoir pressure, acting as a transmural pressure, has the advantage of reducing edema formation by counteracting the hydrostatic pressure gradient from the perfusion pressure.This proof-of-concept study aim was to demonstrate feasibility of the ULiSSESTM device (closed, vertical perfusion system) to preserve forelimbs of Sus Scrofa swine for 24 hours of subnormothermic perfusion compared to an open, horizontal perfusion system. The ULiSSES™ is a compact, practical device that applies pulsatile, pressurized perfusion through the novel use of a diaphragm pump powered by compressed oxygen.

METHODS

Forelimbs from swine were preserved in ULiSSES™ device (closed perfusion system) (n = 9) and in an open perfusion system (n = 4) using sub-normothermic modified Krebs-Henseleit Solution. Physiological parameters were measured at the start and every 3 hours for 24 hours. Limbs were weighed prior to and post perfusion to compare weight gain. Edema and cellular integrity were evaluated using histopathology pre and post perfusion.

RESULTS

Closed perfusion system showed superiority compared to the open perfusion system in terms of oxygen consumption, reduction in vascular resistance, and overall tissue integrity. The closed perfusion system demonstrated a 21% reduction in weight gain compared to the open perfusion system and significantly reduced intracellular edema.

CONCLUSION

The ULiSSES™ closed, pressurized perfusion technology has translatable military applications with the potential to preserve porcine limbs for 24 hours with improved results compared to an open perfusion system.

LEVEL OF EVIDENCE

N/A.

Structured evaluation of a comprehensive microsurgical training program

OBJECTIVES

This study proposed a structured microsurgical training program and evaluated it with the assistance of a large sample of surgeons.

METHODS

The practical course comprised 16 sessions of approximately 4 hours each. This included two sessions for suturing rubber gloves and two sessions for suturing arteries, veins, and nerves in chicken thighs. The other sessions were performed on the femoral vessels of rats: 5 sessions for end-to-end arterial anastomosis, 5 for end-to-end venous anastomosis, 1 for arterial grafting, and 1 for end-to-side anastomosis. We conducted a structured assessment of the microsurgical skills in each training session.

RESULTS

In this study, 89 surgeons were evaluated. The mean scores for the different procedures were as follows: glove suturing, 33.3±0.59; chicken nerve end-to-end anastomosis, 40.3±0.49; chicken artery suturing, 40.9±0.36; chicken vein suturing, 42.3±0.36; graft interposition, 44.8±0.7; and end-to-side anastomosis, 43.7±0.63 (p<0.05 for all). The chicken thigh suturing scores were significantly higher than the rubber gloves suturing scores (p<0.01). There were no differences between scores of the rat artery and chicken thigh suturing procedures (p=0.24). The rat venous anastomosis scores were higher than the rat arterial anastomosis scores (p=0.02), as were graft interposition scores when compared with end-to-end venous anastomosis scores. The end-to-side anastomosis scores did not differ significantly from the grafting scores (p=0.85). The most common errors were inadequate knotting technique and suture rupture due to inadequate technique (both n=88 [98.9%]).

CONCLUSION

We propose a 16-step, progressive microsurgical training program to learn the basic microsurgical techniques comprehensively and reliably. The program was evaluated in a large sample of trainees, and it demonstrated the adequacy of the training sequence and results.