Jan P. Stegemann

Background/Objectives: The timely evaluation of blood clot formation and breakdown is essential in the care of patients with severe bleeding or critical illness. Resonant acoustic rheometry is a novel, non-contact ultrasound method that measures changes in the viscoelastic properties of blood in a standard microplate format. Here, we present the first clinical description of whole blood coagulation and fibrinolysis assessed with resonant acoustic rheometry, with paired thromboelastography measurements for comparison. Methods: In this retrospective analysis, whole blood samples from three critically ill patients were divided and tested under four different conditions that included a control mixture, kaolin activation, tissue factor activation, and a tissue factor mixture supplemented with tissue plasminogen activator. The resonant acoustic rheometry system obtained real time measurements of resonant surface waves and displacements from the samples. Heat maps and spectrograms of the resonant surface waves were analyzed to determine the onset of clotting, the rate of viscoelastic stiffening, the time to maximum rigidity, and the onset as well as magnitude of fibrinolysis. These measurements were compared with thromboelastography reaction time, clot strength, fibrinogen contribution, and lysis values. Results: Resonant acoustic rheometry detected reproducible transitions from liquid to clot and from clot to lysis in all samples. Activator-dependent changes in clot initiation and propagation matched the expected hierarchy observed in thromboelastography. Significantly, samples exposed to tissue plasminogen activator demonstrated a clear fall in resonant frequency and a corresponding rise in surface displacement that reflected fibrinolysis. The technique also reproduced clinically meaningful patterns of hemostasis that aligned with each patient’s underlying disease. Conclusions: Whole blood clotting can be measured with resonant acoustic rheometry in a manner that aligns with established clinical assays. These results suggest strong potential for future use of resonant acoustic rheometry as a cost-effective, complementary platform for rapid, scalable, and clinically informative hemostatic assessment.

The University of Michigan has developed the Advanced Medical Product Engineering and Development (AMPED) program to increase the professional preparation of engineers for careers in the medical technology industries. Address this need. AMPED is a professional Master's degree (M.Eng.) that includes a design-build-test sequence in which student teams develop solutions to current clinical problems, as well as ancillary courses on quality systems, risk management, and regulatory structures. In addition, the program provides content on professional and leadership development to help students examine career options and prepare for their chosen path. AMPED participants also choose a set of technical electives that provide deeper understanding of current advanced concepts in medical product development. The program uses a variety of experiential and student-centered learning formats, including seminars, workshops, case studies, team reviews, expert lectures, and teamwork sessions. Graduates of the AMPED program move into a variety of careers in the medical technology industries at large global healthcare companies, as well as smaller companies, the U.S. government, and other enterprises. The program is growing and invites applications from engineers who seek to have impact in the medical technology industries.

Establishing a robust, functional microvascular network remains a critical challenge for both the revascularization of damaged or diseased tissues and the development of engineered biological materials. Vascularizing microgels may aid in efforts to develop complex, multiphasic tissues by providing discrete, vascularized tissue modules that can be distributed throughout engineered constructs to vascularize large volumes. Here, we fabricated poly(ethylene glycol)‐norbornene (PEGNB) microgels containing endothelial and stromal cells via flow‐focusing microfluidic droplet generation. When embedded in bulk fibrin hydrogels, these cell‐laden microgels initiated the formation and development of robust microvascular networks. Furthermore, extended preculture of cell‐laden PEGNB microgels enabled the formation of vessel‐like structures supported by basement membrane within the matrix without aggregation. Our findings highlight the suitability of PEG‐based matrices for the development of vascularizing microgels capable of forming well‐distributed, robust microvascular networks.

The development of perfusable and multiscale vascular networks remains one of the largest challenges in tissue engineering. As such, there is a need for the creation of customizable and facile methods to produce robustly vascularized constructs. In this study, secondarily crosslinkable (clickable) poly(ethylene glycol)-norbornene (PEGNB) microbeads were produced and evaluated for their ability to sequentially support suspension bioprinting and microvascular self-assembly towards the aim of engineering hierarchical vasculature. The clickable PEGNB microbead slurry exhibited mechanical behavior suitable for suspension bioprinting of sacrificial bioinks, could be UV crosslinked into a granular construct post-print, and withstood evacuation of the bioink and subsequent perfusion of the patterned void space. Endothelial and stromal cells co-embedded within jammed RGD-modified PEGNB microbead slurries assembled into capillary-scale vasculature after secondary crosslinking of the beads into granular constructs, with endothelial tubules forming within the interstitial space between microbeads and supported by the perivascular association of the stromal cells. Microvascular self-assembly was not impacted by printing sacrificial bioinks into the cell-laden microbead support bath before UV crosslinking. Collectively, these results demonstrate that clickable PEGNB microbeads are a versatile substrate for both suspension printing and microvascular culture and may be the foundation for a promising methodology to engineer hierarchical vasculature.

Insufficient vascularization is a main barrier to creating engineered bone grafts for treating large and ischemic defects. Modular tissue engineering approaches have promise in this application because of the ability to combine tissue types and to localize microenvironmental cues to drive desired cell function. In direct bone formation approaches, it is challenging to maintain sustained osteogenic activity, since vasculogenic cues can inhibit tissue mineralization. This study harnessed the physiological process of endochondral ossification to create multiphase tissues that allowed concomitant mineralization and vessel formation. Mesenchymal stromal cells in pellet culture were differentiated toward a cartilage phenotype, followed by induction to chondrocyte hypertrophy. Hypertrophic pellets exhibited increased alkaline phosphatase activity, calcium deposition, and osteogenic gene expression relative to chondrogenic pellets. In addition, hypertrophic pellets secreted and sequestered angiogenic factors, and supported new blood vessel formation by co-cultured endothelial cells and undifferentiated stromal cells. Multiphase constructs created by combining hypertrophic pellets and vascularizing microtissues and maintained in unsupplemented basal culture medium were shown to support robust vascularization and sustained tissue mineralization. These results demonstrate a new in vitro strategy to produce multiphase engineered constructs that concomitantly support the generation of mineralize and vascularized tissue in the absence of exogenous osteogenic or vasculogenic medium supplements. Graphical

There is a significant clinical need to develop effective vascularization strategies for tissue engineering and the treatment of ischemic pathologies. In patients afflicted with critical limb ischemia, comorbidities may limit common revascularization strategies. Cell‐encapsulating modular microbeads possess a variety of advantageous properties, including the ability to support prevascularization in vitro while retaining the ability to be injected in a minimally invasive manner in vivo. Here, fibrin microbeads containing human umbilical vein endothelial cells (HUVEC) and bone marrow‐derived mesenchymal stromal cells (MSC) were cultured in suspension for 3 days (D3 PC microbeads) before being implanted within intramuscular pockets in a SCID mouse model of hindlimb ischemia. By 14 days post‐surgery, animals treated with D3 PC microbeads showed increased macroscopic reperfusion of ischemic foot pads and improved limb salvage compared to the cellular controls. Delivery of HUVEC and MSC via microbeads led to the formation of extensive microvascular networks throughout the implants. Engineered vessels of human origins showed evidence of inosculation with host vasculature, as indicated by erythrocytes present in hCD31+ vessels. Over time, the total number of human‐derived vessels within the implant region decreased as networks remodeled and an increase in mature, pericyte‐supported vascular structures was observed. Our findings highlight the potential therapeutic benefit of developing modular, prevascularized microbeads as a minimally invasive therapeutic for treating ischemic tissues.