Ushering in the era of regenerative surgery

Tissue loss, irrespective of etiology, often requires extensive reconstruction. In many instances, the need exceeds what current treatments and technologies modern medicine can offer. Tissue engineering has made immense strides within the past few decades due to advances in biologics, biomaterials, and manufacturing. The convergence of these three domains has created limitless potential for future surgical care. Unfortunately, there still exists a disconnect on how to best implant these 'replacement parts' and care for the patient. It is therefore vital to develop paradigms for the integration of advanced surgical and tissue engineering technologies. This paper explores the convergence between tissue engineering and reconstructive surgery. We will describe the clinical problem of tissue loss, discuss currently available solutions, address limitations, and propose processes for integrating surgery and tissue engineering, thereby ushering in the era of regenerative surgery.

Intraoperative bioprinting of human adipose-derived stem cells and extra-cellular matrix induces hair follicle-like downgrowths and adipose tissue formation during full-thickness craniomaxillofacial skin reconstruction

Craniomaxillofacial (CMF) reconstruction is a challenging clinical dilemma. It often necessitates skin replacement in the form of autologous graft or flap surgery, which differ from one another based on hypodermal/dermal content. Unfortunately, both approaches are plagued by scarring, poor cosmesis, inadequate restoration of native anatomy and hair, alopecia, donor site morbidity, and potential for failure. Therefore, new reconstructive approaches are warranted, and tissue engineered skin represents an exciting alternative. In this study, we demonstrated the reconstruction of CMF full-thickness skin defects using intraoperative bioprinting (IOB), which enabled the repair of defects via direct bioprinting of multiple layers of skin on immunodeficient rats in a surgical setting. Using a newly formulated patient-sourced allogenic bioink consisting of both human adipose-derived extracellular matrix (adECM) and stem cells (ADSCs), skin loss was reconstructed by precise deposition of the hypodermal and dermal components under three different sets of animal studies. adECM, even at a very low concentration such as 2 % or less, has shown to be bioprintable via droplet-based bioprinting and exhibited de novo adipogenic capabilities both in vitro and in vivo. Our findings demonstrate that the combinatorial delivery of adECM and ADSCs facilitated the reconstruction of three full-thickness skin defects, accomplishing near-complete wound closure within two weeks. More importantly, both hypodermal adipogenesis and downgrowth of hair follicle-like structures were achieved in this two-week time frame. Our approach illustrates the translational potential of using human-derived materials and IOB technologies for full-thickness skin loss.

Accelerating Patterned Vascularization Using Granular Hydrogel Scaffolds and Surgical Micropuncture

Bulk hydrogel scaffolds are common in reconstructive surgery. They allow for the staged repair of soft tissue loss by providing a base for revascularization. Unfortunately, they are limited by both slow and random vascularization, which may manifest as treatment failure or suboptimal repair. Rapidly inducing patterned vascularization within biomaterials has profound translational implications for current clinical treatment paradigms and the scaleup of regenerative engineering platforms. To address this long-standing challenge, a novel microsurgical approach and granular hydrogel scaffold (GHS) technology are co-developed to hasten and pattern microvascular network formation. In surgical micropuncture (MP), targeted recipient blood vessels are perforated using a microneedle to accelerate cell extravasation and angiogenic outgrowth. By combining MP with an adjacent GHS with precisely tailored void space architecture, microvascular pattern formation as assessed by density, diameter, length, and intercapillary distance is rapidly guided. This work opens new translational opportunities for microvascular engineering, advancing reconstructive surgery, and regenerative medicine.

Vascular persistence following precision micropuncture

OBJECTIVE

The success of engineered tissues continues to be limited by time to vascularization and perfusion. Recently, we described a simple microsurgical approach, termed micropuncture (MP), which could be used to rapidly vascularize an adjacently placed scaffold from the recipient macrovasculature. Here we studied the long-term persistence of the MP-induced microvasculature.

METHODS

Segmental 60 μm diameter MPs were created in the recipient rat femoral artery and vein followed by coverage with a simple Type 1 collagen scaffold. The recipient vasculature and scaffold were then wrapped en bloc with a silicone sheet to isolate intrinsic vascularization. Scaffolds were harvested at 28 days post-implantation for detailed analysis, including using a novel artificial intelligence (AI) approach.

RESULTS

MP scaffolds demonstrated a sustained increase of vascular density compared to internal non-MP control scaffolds (p < 0.05) secondary to increases in both vessel diameters (p < 0.05) and branch counts (p < 0.05). MP scaffolds also demonstrated statistically significant increases in red blood cell (RBC) perfused lumens.

CONCLUSIONS

This study further highlights that the intrinsic MP-induced vasculature continues to persist long-term. Its combination of rapid and stable angiogenesis represents a novel surgical platform for engineered scaffold and graft perfusion.

Intraoperative Bioprinting of Human Adipose-derived Stem cells and Extra-cellular Matrix Induces Hair Follicle-Like Downgrowths and Adipose Tissue Formation during Full-thickness Craniomaxillofacial Skin Reconstruction

Craniomaxillofacial (CMF) reconstruction is a challenging clinical dilemma. It often necessitates skin replacement in the form of autologous graft or flap surgery, which differ from one another based on hypodermal/dermal content. Unfortunately, both approaches are plagued by scarring, poor cosmesis, inadequate restoration of native anatomy and hair, alopecia, donor site morbidity, and potential for failure. Therefore, new reconstructive approaches are warranted, and tissue engineered skin represents an exciting alternative. In this study, we demonstrated the reconstruction of CMF full-thickness skin defects using intraoperative bioprinting (IOB), which enabled the repair of defects via direct bioprinting of multiple layers of skin on immunodeficient rats in a surgical setting. Using a newly formulated patient-sourced allogenic bioink consisting of both human adipose-derived extracellular matrix (adECM) and stem cells (ADSCs), skin loss was reconstructed by precise deposition of the hypodermal and dermal components under three different sets of animal studies. adECM, even at a very low concentration such as 2% or less, has shown to be bioprintable via droplet-based bioprinting and exhibited de novo adipogenic capabilities both in vitro and in vivo . Our findings demonstrate that the combinatorial delivery of adECM and ADSCs facilitated the reconstruction of three full-thickness skin defects, accomplishing near-complete wound closure within two weeks. More importantly, both hypodermal adipogenesis and downgrowth of hair follicle-like structures were achieved in this two-week time frame. Our approach illustrates the translational potential of using human-derived materials and IOB technologies for full-thickness skin loss.

Mesenchymal Stem Cell-Derived Extracellular Vesicles for Therapeutic Use and in Bioengineering Applications

Extracellular vesicles (EVs) are small lipid bilayer-delimited particles that are naturally released from cells into body fluids, and therefore can travel and convey regulatory functions in the distal parts of the body. EVs can transmit paracrine signaling by carrying over cytokines, chemokines, growth factors, interleukins (ILs), transcription factors, and nucleic acids such as DNA, mRNAs, microRNAs, piRNAs, lncRNAs, sn/snoRNAs, mtRNAs and circRNAs; these EVs travel to predecided destinations to perform their functions. While mesenchymal stem cells (MSCs) have been shown to improve healing and facilitate treatments of various diseases, the allogenic use of these cells is often accompanied by serious adverse effects after transplantation. MSC-produced EVs are less immunogenic and can serve as an alternative to cellular therapies by transmitting signaling or delivering biomaterials to diseased areas of the body. This review article is focused on understanding the properties of EVs derived from different types of MSCs and MSC-EV-based therapeutic options. The potential of modern technologies such as 3D bioprinting to advance EV-based therapies is also discussed.

Smooth Versus Textured Tissue Expander Breast Reconstruction: Complications and Efficacy

INTRODUCTION

Ongoing recognition of breast implant-associated anaplastic large cell lymphoma (BIA-ALCL) and its link with textured devices has brought a paradigm shift in prosthetic-based breast reconstruction. Many institutions no longer offer textured expansion devices for staged reconstruction. However, there is a paucity of data regarding the efficacy of smooth tissue expanders (TE). We hypothesized that the time to final reconstruction and complication profile between smooth and textured TEs would be similar in breast reconstruction patients.

METHODS

A retrospective chart review was performed of all patients who underwent TE breast reconstruction during a 6-year period at the Penn State Hershey Medical Center. Rates of complications treated nonoperatively and those requiring reoperation were assessed. Mechanical complications, including expander malposition and rupture, were evaluated. Time to final breast reconstruction was quantified. Mixed-effects logistic regression and linear regression models, as appropriate, were used to compare textured to smooth TEs. Patient characteristics and anatomic plane placement were adjusted for in all analyses of outcomes.

RESULTS

Data were collected on 389 patients, encompassing 140 smooth and 604 textured TEs. Textured devices had an increased incidence of complications treated nonsurgically (16.7% vs 10.7%; P = 0.14). However, smooth TEs had an increased incidence of reoperation (12.1% vs 7.6%; P = 0.06). Most noteworthy was that although smooth TEs had a 40-fold increase in malposition (13.6% vs 0.3%; P < 0.001), no reoperation for this complication was warranted. Further, the time to final reconstruction was comparable between the 2 devices (textured expanders: 221 days and smooth expanders: 234 days; P = 0.15).

CONCLUSIONS

Staged, implant-based reconstruction is the most common surgical approach to recreate the breast mound following mastectomy. Textured TEs were the cornerstone to this approach. Unfortunately, the association between textured devices and BIA-ALCL now mandates an alternative. We postulated that smooth expanders would compare favorably for breast reconstruction. Although our study suggests that smooth TEs suffer more malposition, this has a negligible impact on the reconstructive timeline. Thus, smooth TEs may prove beneficial when considering the risk of BIA-ALCL associated with textured devices.

Regenerative Engineering: Current Applications and Future Perspectives

Many pathologies, congenital defects, and traumatic injuries are untreatable by conventional pharmacologic or surgical interventions. Regenerative engineering represents an ever-growing interdisciplinary field aimed at creating biological replacements for injured tissues and dysfunctional organs. The need for bioengineered replacement parts is ubiquitous among all surgical disciplines. However, to date, clinical translation has been limited to thin, small, and/or acellular structures. Development of thicker tissues continues to be limited by vascularization and other impediments. Nevertheless, currently available materials, methods, and technologies serve as robust platforms for more complex tissue fabrication in the future. This review article highlights the current methodologies, clinical achievements, tenacious barriers, and future perspectives of regenerative engineering.

Navigating the Genomic Landscape of Human Adipose Stem Cell-Derived β-Cells

Diabetes is a pandemic manifested through glucose dysregulation mediated by inadequate insulin secretion by beta cells. A beta cell replacement strategy would transform the treatment paradigm from pharmacologic glucose modulation to a genuine cure. Stem cells have emerged as a potential source for beta cell (β-cell) engineering. The detailed generation of functional β-cells from both embryonic and induced pluripotent stem cells has recently been described. Adult stem cells, including adipose derived, may also offer a therapeutic approach, but remain ill defined. In our study, we performed an in-depth assessment of insulin-producing beta cells generated from human adipose, irrespective of donor patient age, gender, and health status. Cellular transformation was confirmed using flow cytometry and single-cell imaging. Insulin secretion was observed with glucose stimulation and abrogated following palmitate exposure, a common free fatty acid implicated in human beta cell dysfunction. We used next-generation sequencing to explore gene expression changes before and after differentiation of patient-matched samples, which revealed more than 5,000 genes enriched. Adipose-derived beta cells displayed comparable gene expression to native β-cells. Pathway analysis demonstrated relevance to stem cell differentiation and pancreatic developmental processes, which are vital to cellular function, structural development, and regulation. We conclude that the functions associated with adipose derived beta cells are mediated through relevant changes in the transcriptome, which resemble those seen in native β-cell morphogenesis and maturation. Therefore, they may represent a viable option for the clinical translation of stem cell-based therapies in diabetes.

Intra-Operative Bioprinting of Hard, Soft, and Hard/Soft Composite Tissues for Craniomaxillofacial Reconstruction

Reconstruction of complex craniomaxillofacial (CMF) defects is challenging due to the highly organized layering of multiple tissue types. Such compartmentalization necessitates the precise and effective use of cells and other biologics to recapitulate the native tissue anatomy. In this study, intra-operative bioprinting (IOB) of different CMF tissues, including bone, skin, and composite (hard/soft) tissues, is demonstrated directly on rats in a surgical setting. A novel extrudable osteogenic hard tissue ink is introduced, which induced substantial bone regeneration, with ≈80% bone coverage area of calvarial defects in 6 weeks. Using droplet-based bioprinting, the soft tissue ink accelerated the reconstruction of full-thickness skin defects and facilitated up to 60% wound closure in 6 days. Most importantly, the use of a hybrid IOB approach is unveiled to reconstitute hard/soft composite tissues in a stratified arrangement with controlled spatial bioink deposition conforming the shape of a new composite defect model, which resulted in ≈80% skin wound closure in 10 days and 50% bone coverage area at Week 6. The presented approach will be absolutely unique in the clinical realm of CMF defects and will have a significant impact on translating bioprinting technologies into the clinic in the future.

Hybrid adipose graft materials synthesized from chemically modified adipose extracellular matrix

Decellularized extracellular matrix (ECM) from tissues is a promising biomaterial that can provide a complex 3D microenvironment capable of modulating cell response and tissue regeneration. In this study, we have integrated the decellularized thiolated adipose-derived ECM, at different concentrations, with polyethylene glycol (PEG) using Michael addition between thiol and acrylate moieties. The potential for this material to support adipogenic differentiation of human adipose-derived stem cells was evaluated by encapsulating cells in hydrogels with increasing concentrations of chemically modified ECM (mECM). Our results demonstrated a positive correlation between the ECM content in the hydrogels and cell proliferation, adipogenic marker expression, and lipid formation and accumulation. Furthermore, we have shown host cell infiltration and enhanced adipogenesis in vivo after implantation. These findings support the graft as a potential alternative for adipose tissue regeneration.

Induction of scaffold angiogenesis by recipient vasculature precision micropuncture

The success of engineered tissues continues to be limited by time to vascularization and perfusion. Here, we studied the effects of precision injury to a recipient macrovasculature in promoting neovessel formation in an adjacently placed scaffold. Segmental 60 μm diameter micropunctures (MP) were created in the recipient rat femoral artery and vein followed by coverage with a simple collagen scaffold. Scaffolds were harvested at 24, 48, 72, and 96 h post-implantation for detailed analysis. Those placed on top of an MP segment showed an earlier and more robust cellular infiltration, including both endothelial cells (CD31) and macrophages (F4/80), compared to internal non-micropunctured control limbs (p < 0.05). At the 96-hour timepoint, MP scaffolds demonstrated an increase in physiologic perfusion (p < 0.003) and a 2.5-fold increase in capillary network formation (p < 0.001). These were attributed to an overall upsurge in small vessel quantity. Furthermore, MP positioned scaffolds demonstrated significant increases in many modulators of angiogenesis, including VEGFR2 and Tie-2 despite a decrease in HIF-1α at all timepoints. This study highlights a novel microsurgical approach that can be used to rapidly vascularize or inosculate contiguously placed scaffolds and grafts. Thereby, offering an easily translatable route towards the creation of thicker and more clinically relevant engineered tissues.

Computer-Aided Design and Manufacture of Intraoral Splints: A Potential Role in Cleft Care

BACKGROUND

Nasoalveolar molding is a nonsurgical modality for the treatment of cleft lip and palate that uses an intraoral splint to align the palatal shelves. Repeated impressions are needed for splint modification, each carrying risk of airway obstruction. Computer-aided design and manufacturing (CAD/CAM) has the ability to simplify the process. As a precursor to CAD/CAM splint fabrication, a proof-of-concept study was conducted to compare three-dimensional splints printed from alginate impressions versus digital scans. We hypothesized that intraoral digital scanning would compare favorably to alginate impressions for palate registration and subsequent splint manufacture, with decreased production times.

METHODS

Alginate and digital impressions were taken from 25 healthy teenage volunteers. Digital impressions were performed with a commercially available intraoral scanner. Plaster casts made from alginate impressions were converted to Standard Triangle Language files. Patient-specific matched scans were evaluated for total surface area with the concordance correlation coefficient. Acrylic palatal splints were three-dimensionally printed from inverse digital molds. Subjective appliance fit was assessed using a five-point scale.

RESULTS

A total of 23 participants were included. Most subjects preferred digital impression acquisition. Impression methods showed moderate agreement (concordance correlation coefficient 0.93). Subjects rated splints from digital impressions as having a more precise fit (4.4 versus 3.9). The digital approach decreased impression phase time by over 10-fold and overall production time by 28%.

CONCLUSIONS

CAD/CAM has evolved extensively over the past two decades and is now commonplace in medicine. However, its utility in cleft patients has not been fully realized. This pilot study demonstrated that CAD/CAM technologies may prove useful in patients requiring intraoral splints.

Hybrid Bioprinting of Zonally Stratified Human Articular Cartilage Using Scaffold-Free Tissue Strands as Building Blocks

The heterogeneous and anisotropic articular cartilage is generally studied as a layered structure of "zones" with unique composition and architecture, which is difficult to recapitulate using current approaches. A novel hybrid bioprinting strategy is presented here to generate zonally stratified cartilage. Scaffold-free tissue strands (TSs) are made of human adipose-derived stem cells (ADSCs) or predifferentiated ADSCs. Cartilage TSs with predifferentiated ADSCs exhibit improved mechanical properties and upregulated expression of cartilage-specific markers at both transcription and protein levels as compared to TSs with ADSCs being differentiated in the form of strands and TSs of nontransfected ADSCs. Using the novel hybrid approach integrating new aspiration-assisted and extrusion-based bioprinting techniques, the bioprinting of zonally stratified cartilage with vertically aligned TSs at the bottom zone and horizontally aligned TSs at the superficial zone is demonstrated, in which collagen fibers are aligned with designated orientation in each zone imitating the anatomical regions and matrix orientation of native articular cartilage. In addition, mechanical testing study reveals a compression modulus of ≈1.1 MPa, which is similar to that of human articular cartilage. The prominent findings highlight the potential of this novel bioprinting approach for building biologically, mechanically, and histologically relevant cartilage for tissue engineering purposes.

Intraoperative Bioprinting: Repairing Tissues and Organs in a Surgical Setting

3D bioprinting directly into injured sites in a surgical setting, intraoperative bioprinting (IOB), is an effective process, in which the defect information can be rapidly acquired and then repaired via bioprinting on a live subject. In patients needing tissue resection, debridement, traumatic reconstruction, or fracture repair, the ability to scan and bioprint immediately following surgical preparation of the defect site has great potential to improve the precision and efficiency of these procedures. In this opinion article, we provide the reader with current major limitations of IOB from engineering and clinical points of view, as well as possibilities of future translation of bioprinting technologies from bench to bedside, and expound our perspectives in the context of IOB of composite and vascularized tissues.

Differentiation of Adipose Tissue-Derived CD34+/CD31- Cells into Endothelial Cells In Vitro

In this study, CD34+/CD31- progenitor cells were isolated from the stromal vascular fraction (SVF) of adipose tissue using magnetic activated cell sorting. The endothelial differentiation capability of these cells in vitro was evaluated by culturing them in vascular endothelial growth factor (VEGF) induced medium for 14 days. Viability, proliferation, differentiation and tube formation of these cells were evaluated. Cell viability study revealed that both undifferentiated and endothelial differentiated cells remained healthy for 14 days. However, the proliferation rate was higher in undifferentiated cells compared to endothelial differentiated ones. Upregulation of endothelial characteristic genes (Von Willebrand Factor (vWF) and VE Cadherin) was observed in 2D culture. However, PECAM (CD31) was only found to be upregulated after the cells had formed tube-like structures in 3D Matrigel culture. These results indicate that adipose derived CD34+/CD31- cells when cultured in VEGF induced medium, are capable differentiation into endothelial-like lineages. Tube formation of the cells started 3h after seeding the cells on Matrigel and formed more stable and connected network 24 h post seeding in presence of VEGF.

Bioprinting functional tissues

Despite the numerous lives that have been saved since the first successful procedure in 1954, organ transplant has several shortcomings which prevent it from becoming a more comprehensive solution for medical care than it is today. There is a considerable shortage of organ donors, leading to patient death in many cases. In addition, patients require lifelong immunosuppression to prevent graft rejection postoperatively. With such issues in mind, recent research has focused on possible solutions for the lack of access to donor organs and rejections, with the possibility of using the patient's own cells and tissues for treatment showing enormous potential. Three-dimensional (3D) bioprinting is a rapidly emerging technology, which holds great promise for fabrication of functional tissues and organs. Bioprinting offers the means of utilizing a patient's cells to design and fabricate constructs for replacement of diseased tissues and organs. It enables the precise positioning of cells and biologics in an automated and high throughput manner. Several studies have shown the promise of 3D bioprinting. However, many problems must be overcome before the generation of functional tissues with biologically-relevant scale is possible. Specific focus on the functionality of bioprinted tissues is required prior to clinical translation. In this perspective, this paper discusses the challenges of functionalization of bioprinted tissue under eight dimensions: biomimicry, cell density, vascularization, innervation, heterogeneity, engraftment, mechanics, and tissue-specific function, and strives to inform the reader with directions in bioprinting complex and volumetric tissues. STATEMENT OF SIGNIFICANCE: With thousands of patients dying each year waiting for an organ transplant, bioprinted tissues and organs show the potential to eliminate this ever-increasing organ shortage crisis. However, this potential can only be realized by better understanding the functionality of the organ and developing the ability to translate this to the bioprinting methodologies. Considering the rate at which the field is currently expanding, it is reasonable to expect bioprinting to become an integral component of regenerative medicine. For this purpose, this paper discusses several factors that are critical for printing functional tissues including cell density, vascularization, innervation, heterogeneity, engraftment, mechanics, and tissue-specific function, and inform the reader with future directions in bioprinting complex and volumetric tissues.

Porous tissue strands: avascular building blocks for scalable tissue fabrication

The scalability of cell aggregates such as spheroids, strands, and rings has been restricted by diffusion of nutrient and oxygen into their core. In this study, we introduce a novel concept in generating tissue building blocks with micropores, which represents an alternative solution for vascularization. Sodium alginate porogens were mixed with human adipose-derived stem cells, and loaded into tubular alginate capsules, followed by de-crosslinking of the capsules. The resultant cellular structure exhibited a porous morphology and formed cell aggregates in the form of strands, called 'porous tissue strands (pTSs).' Three-dimensional reconstructions show that pTSs were able to maintain ∼25% porosity with a high pore interconnectivity (∼85%) for 3 weeks. Owing to the porous structure, pTSs showed up-regulated cell viability and proliferation rate as compared to solid counterparts throughout the culture period. pTSs also demonstrated self-assembly capability through tissue fusion yielding larger-scale patches. In this paper, chondrogenesis and osteogenesis of pTSs were also demonstrated, where the porous microstructure up-regulated both chondrogenic and osteogenic functionalities indicated by cartilage- and bone-specific immunostaining, quantitative biochemical assessment and gene expression. These findings indicated the functionality of pTSs, which possessed controllable porosity and self-assembly capability, and had great potential to be utilized as tissue building blocks in distinct applications such as cartilage and bone regeneration.

Hybrid Synthetic-Biological Hydrogel System for Adipose Tissue Regeneration

Hydrogels are promising scaffolds for adipose tissue regeneration. Currently, the incorporation of bioactive molecules in hydrogel system is used, which can increase the cell proliferation rate or improve adipogenic differentiation performance of stromal stem cells but often suffers from high expense or cytotoxicity because of light/thermal curing used for polymerization. In this study, decellularized adipose tissue is incorporated, at varying concentrations, with a thiol-acrylate fraction that is then polymerized to produce hydrogels via a Michael addition reaction. The results reveal that the major component of isolated adipose-derived extracellular matrix (ECM) is Collagen I. Mechanical properties of ECM polyethylene glycol (PEG) are not negatively affected by the incorporation of ECM. Additionally, human adipose-derived stem cells (hASCs) are encapsulated in ECM PEG hydrogel with ECM concentrations varying from 0% to 1%. The results indicate that hASCs maintained the highest viability and proliferation rate in 1% ECM PEG hydrogel with most lipids formation when cultured in adipogenic conditions. Furthermore, more adipose regeneration is observed in 1% ECM group with in vivo study by Day 14 compared to other ECM PEG hydrogels with lower ECM content. Taken together, these findings suggest the ECM PEG hydrogel is a promising substitute for adipose tissue regeneration applications.

Development of Citrate-based Dual-Imaging Enabled Biodegradable Electroactive Polymers

Increasing occurrences of degenerative diseases, defective tissues and severe cancers heighten the importance of advanced biomedical treatments, which in turn enhance the need for improved biomaterials with versatile theranostic functionalities yet using minimal design complexity. Leveraging the advantages of citrate chemistry, we developed a multifunctional citrate-based biomaterial platform with both imaging and therapeutic capabilities utilizing a facile and efficient one-pot synthesis. The resulting aniline tetramer doped biodegradable photoluminescent polymers (BPLPATs) not only possess programmable degradation profiles (<1 to >6 months) and mechanical strengths (~20 MPa to > 400 MPa), but also present a combination of intrinsic fluorescence, photoacoustic (PA) and electrical conductivity properties. BPLPAT nanoparticles are able to label cells for fluorescence imaging and perform deep tissue detection with PA imaging. Coupled with significant photothermal performance, BPLPAT nanoparticles demonstrate great potential for thermal treatment and in vivo real-time detection of cancers. Our results on BPLPAT scaffolds demonstrate three-dimensional (3D) high-spatial-resolution deep tissue PA imaging (23 mm), as well as promote growth and differentiation of PC-12 nerve cells. We envision that the biodegradable dual-imaging-enabled electroactive citrate-based biomaterial platform will expand the currently available theranostic material systems and open new avenues for diversified biomedical and biological applications via the demonstrated multi-functionality.

Non-coding RNAs in Various Stages of Liver Disease Leading to Hepatocellular Carcinoma: Differential Expression of miRNAs, piRNAs, lncRNAs, circRNAs, and sno/mt-RNAs

Hepatocellular carcinoma (HCC) was the fifth leading cause of cancer death in men and eighth leading cause of death in women in the United States in 2017. In our study, we sought to identify sncRNAs in various stages of development of HCC. We obtained publicly available small RNA-seq data derived from patients with cirrhosis (n = 14), low-grade dysplastic nodules (LGDN, n = 9), high grade dysplastic nodules (HGDN, n = 6), early hepatocellular carcinoma (eHCC, n = 6), and advanced hepatocellular carcinoma (HCC, n = 20), along with healthy liver tissue samples (n = 9). All samples were analyzed for various types of non-coding RNAs using PartekFlow software. We remapped small RNA-seq to miRBase to obtain differential expressions of miRNAs and found 87 in cirrhosis, 106 in LGDN, 59 in HGDN, 80 in eHCC, and 133 in HCC. Pathway analysis of miRNAs obtained from diseased samples compared to normal samples showed signaling pathways in the microRNA dependent EMT, CD44, and others. Additionally, we analyzed the data sets for piRNAs, lncRNAs, circRNAs, and sno/mt-RNAs. We validated the in silico data using human HCC samples with NanoString miRNA global expression. Our results suggest that publically available data is a valuable resource for sncRNA identification in HCC progression (FDR set to <0.05 for all samples) and that a data mining approach is useful for biomarker development.

Small Non-coding RNA Abundance in Adrenocortical Carcinoma: A Footprint of a Rare Cancer

BACKGROUND: Adrenocortical carcinoma (ACC) is a relatively rare, but aggressive type of cancer, which affects both children and adults. OBJECTIVE: Small non-coding RNAs (sncRNAs) play important roles and may serve as biomarkers for disease diagnosis, prognosis and treatment. METHODS: In our study, we sought to identify sncRNAs associated with malignant adrenal tumors. We obtained publicly available, small RNA sequencing data derived from 45 ACC and 30 benign tumors arising from the cortex of the adrenal gland, adrenocortical adenomas (ACA), and compared their sncRNA expression profiles. RESULTS: First, we remapped small RNA-seq to miRBase version 21 to check expression of miRNAs and found 147 miRNAs were aberrantly expressed (p<0.05) in ACC samples compared to ACA samples. Pathway analysis of differentially expressed miRNAs revealed p53 signaling pathways to be profoundly affected in ACC samples. Further examination for other types of small RNAs revealed 16 piRNAs, 48 lncRNAs and 19 sn/snoRNAs identified in ACC samples. Conclusions: Our data analysis suggests that publically available resources can be mined for biomarker development and improvements in-patient care; however, further research must be performed to correlate tumor grade with gene expression.

Concise Review: Bioprinting of Stem Cells for Transplantable Tissue Fabrication

Bioprinting is a quickly progressing technology, which holds the potential to generate replacement tissues and organs. Stem cells offer several advantages over differentiated cells for use as starting materials, including the potential for autologous tissue and differentiation into multiple cell lines. The three most commonly used stem cells are embryonic, induced pluripotent, and adult stem cells. Cells are combined with various natural and synthetic materials to form bioinks, which are used to fabricate scaffold‐based or scaffold‐free constructs. Computer aided design technology is combined with various bioprinting modalities including droplet‐, extrusion‐, or laser‐based bioprinting to create tissue constructs. Each bioink and modality has its own advantages and disadvantages. Various materials and techniques are combined to maximize the benefits. Researchers have been successful in bioprinting cartilage, bone, cardiac, nervous, liver, and vascular tissues. However, a major limitation to clinical translation is building large‐scale vascularized constructs. Many challenges must be overcome before this technology is used routinely in a clinical setting. Stem Cells Translational Medicine2017;6:1940–1948

Abstract 3490: Interrogation of small RNA-seq data for small noncoding RNA in human colon cancer

Genomic analysis of the human transcriptome has been made possible only in last decade by next generation sequencing (NGS). Recent advancements in NGS has further allowed us to look into small non-coding RNAs (sncRNAs) such as microRNAs (miRNAs), Piwi-interacting-RNAs (piRNAs), long non-coding RNAs (lncRNAs) & small nuclear/nucleolar RNAs (sn/snoRNAs). Recently, the roles of sncRNAs in biological processes have been implicated in biomarker development for diagnosis, prognosis &therapy. In the present study, 50 colon cancer patient’s small RNA sequencing raw data was downloaded from NIH bioproject (PRJNA266667; 7 TNM stage II & 43 TNM stage III) which contained 27 female & 23 male samples. 24 samples had metachronous metastasis (MM) & 26 non-metachronous metastasis (NMM). The small RNA-seq data was analyzed using PartekFlow. In depth analysis showed aberrant expression of 48 miRNAs (all upregulated) in TNM-III vs TNM-II specimens & 20 miRNAs (17 upregulated & 3 downregulated) in MM vs NMM. Further investigation of dysregulated miRNA through pathway analysis confirmed that the majority of the miRNAs were involved in cancer signaling pathways. Analysis of piRNA found unusual expression of 60 piRNAs (57 upregulated & 3 downregulated) in TNM-III vs TNM-II & 31 piRNAs (28 upregulated & 3 downregulated) in MM vs NMM. Further analysis of long non-coding RNAs, we found 77 lncRNAs were significantly expressed in TNM-III vs TNM-II &18 lncRNAs in MM vs NMM. We also, investigated small nuclear/nucleolar RNAs (sn/snoRNAs), miscRNAs & mtRNAs, we identified 37 snRNAs, 105 snoRNAs, 28 miscRNAs & 5 mtRNAs in TNM-III vs TNM-II whereas 2 snRNAs, 11 snoRNAs, 57 miscRNAs & 8 mtRNAs in MM vs NMM were identified. In summary, our comprehensive analysis on publicly available small RNA-seq data identified multiple small non-coding RNAs that need to be further explored for their use in the prognosis, diagnosis & therapy of colon cancer.

Citation Format: Srinivas V. Koduru, Angelique Nyinawabera, Dino J. Ravnic, Amit K. Tiwari. Interrogation of small RNA-seq data for small noncoding RNA in human colon cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3490. doi:10.1158/1538-7445.AM2017-3490

Abstract 3489: Noncoding RNA distribution in clear cell renal cell cancer: small RNA-seq data

Small noncoding RNAs (sncRNAs) play pivotal roles in biological processes and may prove to be a tool in cancer diagnosis, prognosis, and treatment. Noncoding RNAs such as microRNAs (miRNAs), piwi-interacting-RNAs (piRNAs), long noncoding RNA (lncRNAs) and small nuclear/nucleolar RNAs (sn/snoRNAs) have recently been investigated to identify their role in cancer. Approximately 62,700 new cases of kidney cancer are expected each year in the United States leading to 14,240 deaths, with rates rising over the past 20 years. Nearly 90% of all kidney cancers will be renal cell carcinoma, of which 70% will be a clear cell renal cell carcinoma (ccRCC) subtype. When detected early most cases can be treated effectively, however there is a lack of early detection tests. We sought to identify molecular markers for early detection and diagnosis. We downloaded publically available (NIH bioproject PRJNA162397) ccRCC small RNA sequence raw data for noncoding RNA analysis. 22 ccRCC and 11 non-tumor renal cortex patient samples were evaluated. Data was analyzed by PartekFlow software. sRNA-seq data was annotated to miRNAs with 69 miRNAs aberrantly expressed in ccRCC with 37 being upregulated (top five: miR-122, miR-210, miR155, miR-224 and miR-21) and 32 being downregulated (top five: miR-200c, miR-502, miR-20b, miR10a and miR-204). Utilizing MetaCore software for pathway analysis the majority of expressed miRNAs were involved in metabolism related signaling pathways. Examining data for piRNAs revealed 22 which were significantly expressed (8 upregulated and 14 downregulated). Investigation of lncRNAs revealed 15 to be downregulated and 27 upregulated. We also uncovered 2 mitochondrial rRNAs, 10 miscRNAs, 1 snRNA, 7 snoRNAs, and 5 rRNAs in ccRCC samples. Our comprehensive analysis of publically available small RNA-seq data identified numerous sncRNAs associated with ccRCC. Pending further validation, they may prove useful as early detection biomarkers in this common cancer.

Citation Format: Srinivas V. Koduru, Dino J. Ravnic. Noncoding RNA distribution in clear cell renal cell cancer: small RNA-seq data [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3489. doi:10.1158/1538-7445.AM2017-3489

Abstract 4447: Analysis of small RNA-seq data for differential expression of small noncoding RNAs in human colorectal cancer

Background: Cancer is a major cause of deaths worldwide, despite improved healthcare and technologies. Recent advancements in genome sequencing have led to the rapid study of the whole transcriptome and small RNAs with their biological functions. Non-coding RNAs (ncRNAs) play an important role in biological processes that greatly impact biomarker development for diagnosis, prognosis, and therapy. Non-coding RNAs such as microRNAs (miRNA), Piwi-interacting-RNAs (piRNAs), small nuclear/nucleolar RNAs (sn/snoRNAs) have recently been studied to understand their biology and pathology.

Results: In the present study, we used eight matched colorectal patient tissue samples (benign, tumor, and metastasis) small RNA sequencing data remapped for various small RNA annotation. We identified aberrant expression of 13 miRs in tumor and metastasis specimens [tumor vs benign group (19 miRs) and metastasis vs benign group (38 miRs)] of which five were upregulated, and eight were downregulated, during disease progression. We also investigated pathway analysis on abbarent expression of miRNAs, which showed majority of miRs involved in the colon other types of cancers. Further analysis of piRNAs revealed that six piRNAs in tumor vs benign and 24 in metastasis vs benign samples (commonly in both groups, only two piRNAs). Additionally, we examined other types of small RNAs [sn/snoRNAs, mt_rRNA, misc_RNA, nonsense mediated decay (NMD) and rRNA], we identified 15 in tumor vs benign and 104 metastasis vs benign and only four in commonly expressed.

Conclusion: In summary, our results identified multiple sncRNAs during colorectal cancer progression which needs to be further validated and can be used for prognosis, diagnosis, and therapeutic potentials.

Citation Format: Srinivas V. Koduru, Amit K. Tiwari, Sprague W. Hazard, Milind K. Mahajan, Dino J. Ravnic. Analysis of small RNA-seq data for differential expression of small noncoding RNAs in human colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4447. doi:10.1158/1538-7445.AM2017-4447

Abstract 3499: Differentially expressed small noncoding RNAs in triple-negative breast cancer

Cancer is the second leading cause of death in the United States and is a major public health concern worldwide. Basic, clinical and epidemiological research is leading to improved cancer detection, prevention, and outcomes. Recent technological advances have allowed unbiased and comprehensive screening of genome-wide gene expression. Small non-coding RNAs (sncRNAs) have been shown to play an important role in biological processes and could serve as a diagnostic, prognostic and therapeutic biomarker for specific diseases. Recent findings have begun to reveal and enhance our understanding of the complex architecture of sncRNA expression including miRNAs, piRNAs, sn/snoRNAs and their relationships with biological systems. We used publicly available small RNA sequencing data that was derived from 24 triple negative breast cancers (TNBC) and 14 adjacent normal tissue samples to remap various types of sncRNAs. We found a total of 55 miRNAs were aberrantly expressed (p&lt;0.005) in TNBC samples (8 miRNAs upregulated; 47 downregulated) compared to adjacent normal tissues whereas the original study reported only 25 novel miRs. In this study, we used pathway analysis of differentially expressed miRNAs which revealed TGF-beta signaling pathways to be profoundly affected in the TNBC samples. Furthermore, our comprehensive re-mapping strategy allowed us to discover a number of other differentially expressed sncRNAs including piRNAs, sn/snoRNAs, rRNAs, miscRNAs and nonsense-mediated decay RNAs. We believe that our sncRNA analysis workflow is extremely comprehensive and suitable for discovery of novel sncRNAs changes, which may lead to the development of innovative diagnostic and therapeutic tools for TNBC.

Citation Format: Srinivas V. Koduru, Amit K. Tiwari, Ashley Leberfinger, Sprague W. Hazard, Yuka Imamura Kawasawa, Milind Mahajan, Dino J. Ravnic. Differentially expressed small noncoding RNAs in triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3499. doi:10.1158/1538-7445.AM2017-3499

Exploration of small RNA-seq data for small non-coding RNAs in Human Colorectal Cancer

Background: Improved healthcare and recent breakthroughs in technology have substantially reduced cancer mortality rates worldwide. Recent advancements in next-generation sequencing (NGS) have allowed genomic analysis of the human transcriptome. Now, using NGS we can further look into small non-coding regions of RNAs (sncRNAs) such as microRNAs (miRNAs), Piwi-interacting-RNAs (piRNAs), long non-coding RNAs (lncRNAs), and small nuclear/nucleolar RNAs (sn/snoRNAs) among others. Recent studies looking at sncRNAs indicate their role in important biological processes such as cancer progression and predict their role as biomarkers for disease diagnosis, prognosis, and therapy. Results: In the present study, we data mined publically available small RNA sequencing data from colorectal tissue samples of eight matched patients (benign, tumor, and metastasis) and remapped the data for various small RNA annotations. We identified aberrant expression of 13 miRNAs in tumor and metastasis specimens [tumor vs benign group (19 miRNAs) and metastasis vs benign group (38 miRNAs)] of which five were upregulated, and eight were downregulated, during disease progression. Pathway analysis of aberrantly expressed miRNAs showed that the majority of miRNAs involved in colon cancer were also involved in other cancers. Analysis of piRNAs revealed six to be over-expressed in the tumor vs benign cohort and 24 in the metastasis vs benign group. Only two piRNAs were shared between the two cohorts. Examining other types of small RNAs [sn/snoRNAs, mt_rRNA, miscRNA, nonsense mediated decay (NMD), and rRNAs] identified 15 sncRNAs in the tumor vs benign group and 104 in the metastasis vs benign group, with only four others being commonly expressed. Conclusion: In summary, our comprehensive analysis on publicly available small RNA-seq data identified multiple differentially expressed sncRNAs during colorectal cancer progression at different stages compared to normal colon tissue. We speculate that deciphering and validating the roles of sncRNAs may prove useful in colorectal cancer prognosis, diagnosis, and therapy.

A Comprehensive NGS Data Analysis of Differentially Regulated miRNAs, piRNAs, lncRNAs and sn/snoRNAs in Triple Negative Breast Cancer

Cancer is the second leading cause of death in the United States and is a major public health concern worldwide. Basic, clinical and epidemiological research is leading to improved cancer detection, prevention, and outcomes. Recent technological advances have allowed unbiased and comprehensive screening of genome-wide gene expression. Small non-coding RNAs (sncRNAs) have been shown to play an important role in biological processes and could serve as a diagnostic, prognostic and therapeutic biomarker for specific diseases. Recent findings have begun to reveal and enhance our understanding of the complex architecture of sncRNA expression including miRNAs, piRNAs, lncRNAs, sn/snoRNAs and their relationships with biological systems. We used publicly available small RNA sequencing data that was derived from 24 triple negative breast cancers (TNBC) and 14 adjacent normal tissue samples to remap various types of sncRNAs. We found a total of 55 miRNAs were aberrantly expressed (p<0.005) in TNBC samples (8 miRNAs upregulated; 47 downregulated) compared to adjacent normal tissues whereas the original study reported only 25 novel miRs. In this study, we used pathway analysis of differentially expressed miRNAs which revealed TGF-beta signaling pathways to be profoundly affected in the TNBC samples. Furthermore, our comprehensive re-mapping strategy allowed us to discover a number of other differentially expressed sncRNAs including piRNAs, lncRNAs, sn/snoRNAs, rRNAs, miscRNAs and nonsense-mediated decay RNAs. We believe that our sncRNA analysis workflow is extremely comprehensive and suitable for discovery of novel sncRNAs changes, which may lead to the development of innovative diagnostic and therapeutic tools for TNBC.

Topical vanadate enhances the repair of median laparotomy incisions

BACKGROUND

There are over two million laparotomies performed in the United States each year with an incisional hernia rate between 2% and 11%. A total of 100,000 ventral hernia repairs are undertaken each year with recurrences as high as 50%.

MATERIALS AND METHODS

Full thickness midline fascia incisions from the xiphoid to the pubic symphysis were made in rats. The fascia and/or muscular layer was sutured closed and a gel with 300 μM of sodium orthovanadate or saline was placed over the suture line with the skin closed over it. On day 10, 1-cm strips from the superior, middle, and inferior regions of the abdominal wall were tested for breaking strength and processed for histology.

RESULTS

The mean wound breaking strength of vanadate-treated wounds was 18.6 ± 2.7 N compared with 9.4 ± 3.6 N for controls (P < 0.0001). Similar quantities of granulation tissue were deposited in treated and control wounds. Fine green birefringence patterns, characteristic of immature connective tissue, were seen in control samples viewed with polarized light. In contrast, vanadate-treated wounds showed thick yellow-orange birefringence patterns characteristics of more mature connective tissue. Using α-smooth muscle actin immunostaining, myofibroblasts were prominent in control incisions, but few were identified in vanadate-treated incisions.

CONCLUSIONS

In rat laparotomy wounds, a single application of vanadate increases wound breaking strength, through enhanced connective tissue organization. These combined data suggest topical application of vanadate immediately after fascial closure will increase wound strength, possibly reducing hernia recurrences in the repaired abdominal wall.

Inflammation-induced intussusceptive angiogenesis in murine colitis

Intussusceptive angiogenesis is a morphogenetic process that forms new blood vessels by the division of a single blood vessel into two lumens. Here, we show that this process of intraluminal division participates in the inflammation-induced neovascularization associated with chemically induced murine colitis. In studies of both acute (4-7 days) and chronic (28-31 days) colitis, intravital microscopy of intravascular tracers demonstrated a twofold reduction in blood flow velocity. In the acute colitis model, the decreased velocity was associated with marked dilatation of the mucosal plexus. In contrast, chronic inflammation was associated with normal caliber vessels and duplication (and triplication) of the quasi-polygonal mucosal plexus. Scanning electron microscopy (SEM) of intravascular corrosion casts suggested that pillar formation and septation, previously linked to the morphogenetic process of intussusceptive angiogenesis, were present within days of the onset of inflammation. Four weeks after the onset of inflammation, SEM of vascular corrosion casts demonstrated replication of the mucosal plexus without significant evidence of sprouting angiogenesis. These data suggest that mucosal capillaries have comparable aggregate cross-sectional area in acute and chronic colitis; however, there is a significant increase in functional capillary density in chronic colitis. We conclude that intussusceptive angiogenesis is a fundamental mechanism of microvascular adaptation to prolonged inflammation.

Bridging mucosal vessels associated with rhythmically oscillating blood flow in murine colitis

Oscillatory blood flow in the microcirculation is generally considered to be the result of cardiopulmonary influences or active vasomotion. In this report, we describe rhythmically oscillating blood flow in the bridging vessels of the mouse colon that appeared to be independent of known biological control mechanisms. Corrosion casting and scanning electron microscopy of the mouse colon demonstrated highly branched bridging vessels that connected the submucosal vessels with the mucosal plexus. Because of similar morphometric characteristics (19 +/- 11 microm vs. 28 +/- 16 microm), bridging arterioles and venules were distinguished by tracking fluorescent nanoparticles through the microcirculation using intravital fluorescence videomicroscopy. In control mice, the blood flow through the bridging vessels was typically continuous and unidirectional. In contrast, two models of chemically induced inflammation (trinitrobenzenesulfonic acid and dextran sodium sulfate) were associated with a twofold reduction in flow velocity and the prominence of rhythmically oscillating blood flow. The blood oscillation was characterized by tracking the bidirectional displacement of fluorescent nanoparticles. Space-time plots and particle tracking of the oscillating segments demonstrated an oscillation frequency between 0.2 and 5.1 cycles per second. Discrete Fourier transforms demonstrated a power spectrum composed of several base frequencies. These observations suggest that inflammation-inducible changes in blood flow patterns in the murine colon resulted in both reduced blood flow velocity and rhythmic oscillations within the bridging vessels of the mouse colon.

Inflammation-responsive focal constrictors in the mouse ear microcirculation

In many capillary exchange beds, blood flow is locally regulated by precapillary sphincter-like activity. In this study, we used intravascular tracers and scanning electron microscopy to investigate precapillary blood flow regulation in the mouse ear. Gelatin ink injections of the normal mouse ear demonstrated 6.8 +/- 2.3 axial vessels with a cutoff of detectable tracer in the early branches: 19 +/- 11 focal constrictions were observed along the 1st to 5th order branches of the axial vessels. A perfusion tracer consisting of biotinylated anti-endothelial lectins (Ricinus Communis Agglutin, Lycopersicon Esculentum and Griffonia Simplicifolia) was circulated for 30 min under physiological conditions. Subsequent enzyme histochemistry demonstrated no significant change in distal perfusion or in the number of focal constrictions (P > 0.05). Furthermore, the focal constrictions were unresponsive to vasodilators such as organic nitrates and prostaglandin E1. By contrast, the presence of oxazolone-induced inflammation resulted in significant and sustained vasodilatation for more than 96 h (P > 0.001). Scanning electron microscopy demonstrated discrete constricting bands morphologically distinct from known precapillary sphincters. These results suggest that these previously unappreciated inflammation-responsive precapillary constrictors regulate capillary recruitment in the mouse ear microcirculation.

Murine microvideo endoscopy of the colonic microcirculation

Natural orifice endoscopy in small animal models has been limited in the past by instrument size and optical performance. In this report, we investigate the feasibility of using a recently developed microvideo endoscopy system to evaluate the colon microcirculation. Using a murine model of acute colitis, microvideo endoscopy was useful in mapping the topography of inflammation as well as identifying relevant structures in the microcirculation. We conclude that natural orifice endoscopy is a useful method for the minimally invasive longitudinal assessment of the colonic mucosal microcirculation.

Structural adaptations in the murine colon microcirculation associated with hapten-induced inflammation

BACKGROUND

Blood flowing across the vascular endothelium creates wall shear stress, dependent on velocity of flow and vessel geometry, that tends to disrupt lymphocyte-endothelial cell adhesion.

OBJECTIVE

The microcirculation in a murine model of acute colitis was investigated to identify structural adaptations during acute colitis that may facilitate transmigration.

METHODS

In 2,4,6-trinitrobenzenesulphonic acid-induced acute colitis, the infiltrating cells and colonic microcirculation was investigated by cellular topographic mapping, corrosion casting and three-dimensional scanning electron microscopy (SEM). Colonic blood velocimetry was performed using intravital microscopy.

RESULTS

Clinical and histological parameters suggested a peak inflammatory response at 96 h (p<0.001). The infiltrating cells were spatially related to the mucosal capillary plexus by three-dimensional topographic mapping (p<0.001). In normal mice, corrosion casting and three-dimensional SEM showed a polygonal mucosal plexus supplied by ascending arteries and descending veins. After 2,4,6-trinitrobenzenesulphonic acid stimulation, three-dimensional SEM showed preserved branch angles (p = 0.52) and nominal vessel lengths (p = 0.93), but a significantly dilated mucosal capillary plexus (p<0.001). Intravital microscopy of the mucosal plexus showed a greater than twofold decrease in the velocity of flow (p<0.001).

CONCLUSIONS

The demonstrable slowing of the velocity of flow despite an increase in volumetric flow suggests that these microvascular adaptations create conditions suitable for leucocyte adhesion and transmigration.

The murine bronchopulmonary microcirculation in hapten-induced inflammation

OBJECTIVE

The clinical observation of central bronchial artery hypertrophy in chronic lung inflammation suggests the possibility that the bronchial circulation may also participate in adaptive responses in peripheral lung inflammation.

METHODS

To investigate the potential role of the bronchial microcirculation in peripheral lung inflammation, we developed a murine model of lung inflammation using the intratracheal instillation of the peptide-hapten trinitrophenol in presensitized mice.

RESULTS

Clinical parameters indicated a peak inflammatory response at 96 hours. Similarly, gross and microscopic evidence of inflammation was observed 96 hours after antigen instillation. Using a forced oscillation technique to probe peripheral lung mechanics at 96 hours, we detected no change in central airway resistance (P > .05), but a significant increase in peripheral tissue resistance (P < .05). The structure of the bronchial circulation was investigated by microsphere occlusion of the pulmonary circulation and corrosion casting of the bronchial circulation. SEM of the bronchial artery casts demonstrated (1) the presence of the peripheral bronchial circulation in mice, (2) interconnections of the two systems in the distal bronchial arteries and at the level of alveolar capillaries, and (3) functional evidence of increased bronchial perfusion of alveolar capillaries during mononuclear inflammation.

CONCLUSION

These results suggest an important adaptive role of the bronchial circulation in pulmonary inflammation.

Biological and Optical Properties of Fluorescent Nanoparticles Developed for Intravascular Imaging

Intravascular tracers in the blood circulation can provide a description of the flow field over time and space. To address the limitations of existing intravascular tracers, we have developed fluorescent nanoparticles capable of providing detailed information regarding the intravascular flow field. The nanoparticles were designed to maximize plasma half-life as well as minimize interactions with other blood components. The bioavailability of the particles in the blood circulation required nanoscale size and low surface charge density. Intravital imaging of nanoparticles in the microcirculation demonstrated that the fluorescence intensity of the nanoparticles was a major determinant of both temporal and spatial resolution of the flow field. We conclude that nanoparticles prepared with these physical and optical properties can provide an accurate description of the localized intravascular flow field.

Multiframe particle tracking in intravital imaging: defining Lagrangian coordinates in the microcirculation

The cellular composition of the microcirculation creates blood flow that can be unsteady and nonuniform. To obtain information about nonuniform cellular trajectories, we describe in vivo imaging techniques that provide both detailed tracking of individual particles as well as an approach to simultaneous multicolor particle tracking. Particularly relevant to biologic systems, Lagrangian methods provide information about the fate of individual particles and flow in the system.

Multi-image particle tracking velocimetry of the microcirculation using fluorescent nanoparticles

Particle tracking velocimetry provides a Lagrangian description of flow properties in the microcirculation. To determine the utility of fluorescent nanoparticles to provide Lagrangian coordinates, we tracked these particles both in vitro and in vivo. The particles had a neutral charge and fluorescence intensity greater than 1,000 times the PKH26-labeled red blood cells. At image acquisition rates of 60 frames per second, particles were tracked at velocities up to 4,000 microm/s. Morphometric changes reflecting streaking artifact were significant at velocities of 4,000 microm/s (P < 0.05), but not at lower velocities (P > 0.05). Intravital microscopy monitoring after intravenous injection of the particles demonstrated a circulation half-life that was inversely related to particle size: 500 nm nanoparticles demonstrated a smaller change in plasma concentration than larger particles. Regardless of the size of the particles, more than 50% of the recovered fluorescence was located in the liver. These results suggest that fluorescent nanoparticles provide a convenient and practical Lagrangian description of flow velocity in the microcirculation.

Structural mapping of immunoglobulin subclasses using multiplexed bead flow cytometry

Monoclonal hybridomas secrete immunoglobulin molecules with a single specificity and distinct class/subclass structure. The determination of immunoglobulin structure can be used to facilitate hybridoma colony management and predict monoclonality. In this report, we used multiplexed bead flow cytometry to define hybridoma class/subclass. The assay was sufficiently sensitive to detect 50 ng/mL of antibody. The multiplexed bead assay efficiently defined traditional class/subclass determinants as well as more subtle patterns of crossreactivity. Further, the assay was combined with Poisson statistics to provide a numerical estimate of hybridoma monoclonality. The sensitivity and flexibility of this approach suggests the utility of multiplexed bead flow cytometry in the early management of immunoglobulin-secreting hybridomas.

Melittin-induced membrane permeability: A nonosmotic mechanism of cell death

Derived from honeybees, melittin is a 26-amino acid, alpha-helical, membrane-attack protein that efficiently kills mammalian cells. To investigate the contribution of colloid-osmotic effects to the mechanism of cell death, we studied the effect of melittin on lymphocyte membrane permeability and cell volumes. Melittin concentrations of 0.5 to 2.0 microM induced release of membrane permeability markers without total disruption of the cell membrane. At these melittin concentrations, electrical-impedance cytometry demonstrated melittin-induced changes in red blood cell volumes (P<0.01), but no change in lymphocyte cell volumes (P>0.05). Streaming video microscopy, obtaining images of melittin-treated lymphocytes at 80-ms intervals, demonstrated a loss of optical density (P<0.001) suggesting a flattening of the cell but no significant increase in cell perimeter (P>0.05). Real-time multiparameter flow cytometry of melittin-treated lymphocytes confirmed simultaneous loss of the cytoplasmic marker, calcein, and uptake of the DNA dye, ethidium homodimer, but demonstrated no increase in forward light scatter. Transmission-electron microscopy of melittin-treated lymphocytes showed normal cell volumes but discontinuities in the cell membrane suggesting direct membrane toxicity. We conclude that melittin causes lymphocyte death by a "leaky patch" mechanism that is independent of colloid-osmotic effects.

Vessel painting of the microcirculation using fluorescent lipophilic tracers

Flexible approaches to defining microvessel morphometry are useful in the study of both acute and chronic structural changes of the microcirculation. In this report, we examined the utility of the intravascular infusion of lipophilic carbocyanine tracers in the structural assessment of the retina, skin, lung, and colon microcirculation. The microvessel labeling technique, here termed fluorescent vessel painting, involved the intravascular injection of sulfonated lipophilic carbocyanine tracers. The utility of vessel painting in morphometry was assessed using morphometric comparisons with corrosion casting and 2-dimensional and 3-dimensional scanning electron microscopy. The comparisons demonstrated that fluorescent vessel painting modestly overestimated the interbranch angles, interbranch distances, and vessel diameters of the 2D mucosal plexus of the colon. These differences were narrowed with the application of confocal microscopy. The advantages of fluorescence vessel painting included (1) the filling of all tissues including the relatively high resistance microvessels of the mouse skin, (2) the ability to use tissue counterstains such as DAPI, and (3) the prolonged stability of the lipophilic tracer after aldehyde fixation. These studies suggest the utility of fluorescent vessel painting as a complementary technique to corrosion casting in the morphometric study of the microcirculation.