Longitudinal monitoring of cells is required in order to understand the role of delivered stem cells in therapeutic neovascularization. However, there is not an imaging technique that is capable of quantitative, longitudinal assessment of stem cell behaviors with high spatial resolution and sufficient penetration depth. In this study, in vivo and in vitro experiments were performed to demonstrate the efficacy of ultrasound-guided photoacoustic (US/PA) imaging to monitor mesenchymal stem cells (MSCs) labeled with gold nanotracers (Au NTs). The Au NT labeled MSCs, injected intramuscularly in the lower limb of the Lewis rat, were detected and spatially resolved. Furthermore, our quantitative in vitro cell studies indicate that US/PA imaging is capable of high detection sensitivity (1×104 cells/mL) of the Au NT labeled MSCs. Finally, Au NT labeled MSCs captured in the PEGylated fibrin gel system were imaged in vivo, as well as in vitro, over a one week time period, suggesting that longitudinal cell tracking using US/PA imaging is possible. Overall, Au NT labeling of MSCs and US/PA imaging can be an alternative approach in stem cell imaging capable of noninvasive, sensitive, quantitative, longitudinal assessment of stem cell behaviors with high spatial and temporal resolutions at sufficient depths.

Additive manufacturing/3D printing of medical devices is becoming more commonplace, a 3D printed drug is now commercially available, and bioprinting is poised to transition from laboratory to market. Despite the variety of technologies enabling these products, the US Food and Drug Administration (FDA) is charged with protecting and promoting the public health by ensuring these products are safe and effective. To that end, we are presenting the FDA’s current perspective on additive manufacturing/3D printing of medical products ranging from those regulated by the Center for Devices and Radiological Health (CDRH), the Center for Drug Evaluation and Research (CDER), and the Center for Biologics Evaluation and Research (CBER). Each Center presents an overview of the additively manufactured products in their area and the specific concerns and thoughts on using this technology in those product spaces.

Background: Stem cells can differentiate into multiple cell types, and therefore can be used for cellular therapies, including tissue repair. However, the participation of stem cells in tissue repair and neovascularization is not well understood. Therefore, implementing a noninvasive, long-term imaging technique to track stem cells in vivo is needed to obtain a better understanding of the wound healing response. Generally, we are interested in developing an imaging approach to track mesenchymal stem cells (MSCs) in vivo after delivery via a polyethylene glycol modified fibrin matrix (PEGylated fibrin matrix) using MSCs loaded with gold nanoparticles as nanotracers. The objective of the current study was to assess the effects of loading MSCs with gold nanoparticles on cellular function. Methods: In this study, we utilized various gold nanoparticle formulations by varying size and surface coatings and assessed the efficiency of cell labeling using darkfield microscopy. We hypothesized that loading cells with gold nanotracers would not significantly alter cell function due to the inert and biocompatible characteristics of gold. The effect of nanoparticle loading on cell viability and cytotoxicity was analyzed using a LIVE/DEAD stain and an MTT assay. The ability of MSCs to differentiate into adipocytes and osteocytes after nanoparticle loading was also examined. In addition, nanoparticle loading and retention over time was assessed using inductively coupled plasma mass spectrometry (ICP-MS). Conclusion: Our results demonstrate that loading MSCs with gold nanotracers does not alter cell function and, based on the ICP-MS results, long-term imaging and tracking of MSCs is feasible. These findings strengthen the possibility of imaging MSCs in vivo, such as with optical or photoacoustic imaging, to understand better the participation and role of MSCs in neovascularization.

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Additive manufacturing [also known as three-dimensional (3D) printing] is the layer-wise deposition of material to produce a 3D object. This rapidly emerging technology has the potential to produce new medical products with unprecedented structural and functional designs. Here, we describe the U.S. regulatory landscape of additive manufactured (3D-printed) medical devices and biologics and highlight key challenges and considerations.

Nonlinear photoacoustic effects, rarely seen in biomedical photoacoustic imaging of tissues, can manifest themselves strongly when plasmonic nanoparticles are used as imaging contrast agents. Specifically, nonlinear behavior of photoacoustic signal with modest laser fluences can occur when nanoparticles undergo cellular endocytosis and aggregation leading to thermal coupling and subsequent localized temperature enhancement. Our study demonstrated this effect using in vitro tissue models containing cells. While the photoacoustic signal amplitude was linearly proportional to the cell/nanoparticle concentration, the photoacoustic signal increased nonlinearly as the laser fluence increased. Our results, therefore, suggest that the nonlinear effects can be exploited in molecular/cellular photoacoustic imaging.

Stem cell-based therapies have demonstrated improved outcomes in preclinical and clinical trials for treating cardiovascular ischemic diseases. However, the contribution of stem cells to vascular repair is poorly understood. To elucidate these mechanisms, many have attempted to monitor stem cells following their delivery in vivo, but these studies have been limited by the fact that many contrast agents, including nanoparticles, are commonly passed on to non-stem cells in vivo. Specifically, cells of the reticuloendothelial system, such as macrophages, frequently endocytose free contrast agents, resulting in the monitoring of macrophages instead of the stem cell therapy. Here we demonstrate a dual gold nanoparticle system which is capable of monitoring both delivered stem cells and infiltrating macrophages using photoacoustic imaging. In vitro analysis confirmed preferential labeling of the two cell types with their respective nanoparticles and the maintenance of cell function following nanoparticle labeling. In addition, delivery of the system within a rat hind limb ischemia model demonstrated the ability to monitor stem cells and distinguish and quantify macrophage infiltration. These findings were confirmed by histology and mass spectrometry analysis. This work has important implications for cell tracking and monitoring cell-based therapies.

Dailey HL, Ricles LM, Yalcin HC, Ghadiali SN. Image-based finite element modeling of alveolar epithelial cell injury during airway reopening. J Appl Physiol 106: 221-232, 2009. First published November 13, 2008 doi:10.1152/japplphysiol.90688.2008.-The acute respiratory distress syndrome (ARDS) is characterized by fluid accumulation in small pulmonary airways. The reopening of these fluidfilled airways involves the propagation of an air-liquid interface that exerts injurious hydrodynamic stresses on the epithelial cells (EpC) lining the airway walls. Previous experimental studies have demonstrated that these hydrodynamic stresses may cause rupture of the plasma membrane (i.e., cell necrosis) and have postulated that cell morphology plays a role in cell death. However, direct experimental measurement of stress and strain within the cell is intractable, and limited data are available on the mechanical response (i.e., deformation) of the epithelium during airway reopening. The goal of this study is to use image-based finite element models of cell deformation during airway reopening to investigate how cell morphology and mechanics influence the risk of cell injury/necrosis. Confocal microscopy images of EpC in subconfluent and confluent monolayers were used to generate morphologically accurate three-dimensional finite element models. Hydrodynamic stresses on the cells were calculated from boundary element solutions of bubble propagation in a fluid-filled parallel-plate flow channel. Results indicate that for equivalent cell mechanical properties and hydrodynamic load conditions, subconfluent cells develop higher membrane strains than confluent cells. Strain magnitudes were also found to decrease with increasing stiffness of the cell and membrane/cortex region but were most sensitive to changes in the cell's interior stiffness. These models may be useful in identifying pharmacological treatments that mitigate cell injury during airway reopening by altering specific biomechanical properties of the EpC. flow-induced cell injury; epithelial cell mechanics; orthotropic membrane; ADINA CERTAIN PATHOLOGICAL CONDITIONS such as pneumonia and sepsis can lead to the development of the acute respiratory distress syndrome (ARDS), which is the most severe manifestation of acute lung injury (ALI). This condition is characterized by increased permeability of the alveolar-capillary barrier leading to fluid accumulation in the distal airways (43). In many cases, mechanical ventilation is necessary to stabilize patients with ARDS. However, ventilators can generate injurious mechanical forces that exacerbate the existing lung trauma. These mechanical forces, which are typically applied to lung epithelial cells (EpC), can cause cell necrosis (6, 46), further barrier disruption (9, 10, 46), and upregulation of inflammatory pathways (36). These mechanical and biological responses lead to additional lung injury known as ventilator-associated lung injury (VALI) (12). Although recent advances in ventilation protocols, including low tidal volu...