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ABSTRACT Purpose: Research in high-income countries has extensively documented the non-operative management of spleen injuries in children, resulting in low splenectomy rates (5%). However, there is a lack of literature on this topic in low- and-middle-income countries (LMICs), including Brazil. This scoping review analyzed pediatric spleen trauma research trends in Brazil and the United States of America (USA). Methods: Search strategy was conducted across five databases, considering articles published in English or Portuguese from January 1968 to 2023 that reported spleen injury in patients younger than 18 years old in Brazil or the USA. Two pairs of independent reviewers screened the title and the abstract, followed by a full-text review. Results: The total of 7,150 studies was identified, of which 295 were eligible for data extraction. Most papers (98.64%, 301) originated from the USA, while only 1.36% (4) were from Brazil. In addition, 46.44% (137) articles reported intrabdominal injury, including splenic trauma, 16.27% (48) liver and spleen injury, and 37.29% (110) reported isolated spleen injury. The operative rate for spleen injury was 11.33% in American studies (40,812/359,926) compared to 98.57% (137/139) in Brazilian studies. Conclusions: Brazil contributed only with four studies on pediatric splenic trauma over two decades. Future studies should explore the incidence and management of splenic trauma in LMICs.

Introduction: Pilonidal disease is a common condition in adolescents and young adults that is managed with medications, local wound care and surgery. Immunosuppression is not a standard therapy utilized in this disease but is routinely prescribed in hidradenitis, a folliculitis in the axillae and groin rather than in the gluteal cleft. Case presentation: We present the case of a patient with severe pilonidal disease, with multiple collections in and above the gluteal cleft. Prior to presentation to our clinic, they had failed a standard treatment regimen for three years which included local wound care, multiple courses of antibiotics and incision and drainage procedures. They started on a treatment plan focused on hygiene and hair removal after being evaluated in our clinic. During this time, a concomitant diagnosis of leukemia was made and they were treated with induction chemotherapy and subsequent bone marrow transplant. Their pilonidal disease fully resolved after immunosuppression. Conclusion: This patient's severe pilonidal disease resolved with immunosuppression, supporting an inflammatory basis of the condition.

Summary: Background: Non-operative management for pediatric blunt splenic injury is well established in high-income countries, leading to a low splenectomy rate in hemodynamically stable children. Splenectomy rate became a quality indicator for Trauma Center verification utilized by the American College of Surgeons Committee on Trauma. However, data on splenectomy rate in children from countries with different income levels, such as Brazil, remain limited. This study aimed to assess the post-traumatic splenectomy rate among Brazilian children over the past decade and the relation with local resources. Methods: Data on pediatric splenic injuries and splenectomies from 2008 to 2019, including patient age and admitting service (adult or pediatric), were obtained from FioCruz database, a public, free, cloud-based platform that offers extensive national health data. The regional numbers of pediatric surgeons, pediatric intensive care unit (PICU) beds, and computed tomography scanners were obtained from Brazilian national databases. A national analysis of splenectomy rate by year and service of admission and an analysis of splenectomy rate by the level of regional resources, the number of pediatric surgeons, PICU beds, and computed tomography scanners was performed. Findings: 4061 children were hospitalized with a splenic injury, and 2287 (51.8%) of them underwent splenectomy, unchanged over time. 76.8% were male and 23.1% female patients with splenic injury. Mean age was 11.61 years old. The odds of splenectomy was 14.77 times higher for pediatric patients admitted under adult surgical service compared to pediatric service (OR = 14.77, 95% CI 11.75–18.56, p

Background: The impact of public health policy to reduce the spread of COVID-19 on access to surgical care is poorly defined. We aim to quantify the surgical backlog during the COVID-19 pandemic in the Brazilian public health system and determine the relationship between state-level policy response and the degree of state-level delays in public surgical care. Methods: Monthly estimates of surgical procedures performed per state from January 2016 to December 2020 were obtained from Brazil's Unified Health System Informatics Department. Forecasting models using historical surgical volume data before March 2020 (first reported COVID-19 case) were constructed to predict expected monthly operations from March through December 2020. Total, emergency, and elective surgical monthly backlogs were calculated by comparing reported volume to forecasted volume. Linear mixed effects models were used to model the relationship between public surgical delivery and two measures of health policy response: the COVID-19 Stringency Index (SI) and the Containment & Health Index (CHI) by state. Findings: Between March and December 2020, the total surgical backlog included 1,119,433 (95% Confidence Interval 762,663–1,523,995) total operations, 161,321 (95%CI 37,468–395,478) emergent operations, and 928,758 (95%CI 675,202–1,208,769) elective operations. Increased SI and CHI scores were associated with reductions in emergent surgical delays but increases in elective surgical backlogs. The maximum government stringency (score = 100) reduced emergency delays to nearly zero but tripled the elective surgical backlog. Interpretation: Strong health policy efforts to contain COVID-19 ensure minimal reductions in delivery of emergent surgery, but dramatically increase elective backlogs. Additional coordinated government efforts will be necessary to specifically address the increased elective backlogs that accompany stringent responses.

When a patient suffers a blunt intestinal injury after a low-energy mechanism, be prepared to find a pathologic area in the bowel. We present the case of a previously healthy 13-year-old female who presented complaining of abdominal pain hours after impact with the safety bar of an amusement park ride. Upon operative exploration, she was found to have extensive inflammation of the distal ileum including the ileocecal valve with creeping mesenteric fat and a full-thickness perforation of the inflamed segment. An ileocecectomy and primary anastomosis were performed. Pathology confirmed the presence of Crohn's disease. This case is the first reported incidence of a traumatic perforation leading to a diagnosis of pediatric Crohn's disease. Blunt perforation of the bowel following a low-impact mechanism should heighten the suspicion of an underlying disease process.

Transforming growth factor-ß (TGF-ß) signaling plays an important role in regulating crucial biological processes such as cell proliferation, differentiation, apoptosis, and extracellular matrix remodeling. Many of these processes are also an integral part of amelogenesis. In order to delineate a precise role of TGF-ß signaling during amelogenesis, we developed a transgenic mouse line that harbors bovine amelogenin promoter-driven Cre recombinase, and bred this line with TGF-ß receptor II floxed mice to generate ameloblast-specific TGF-ß receptor II conditional knockout (cKO) mice. Histological analysis of the teeth at postnatal day 7 (P7) showed altered enamel matrix composition in the cKO mice as compared to the floxed mice that had enamel similar to the wild-type mice. The µCT and SEM analyses revealed decreased mineral content in the cKO enamel concomitant with increased attrition and thinner enamel crystallites. Although the mRNA levels remained unaltered, immunostaining revealed increased amelogenin, ameloblastin, and enamelin localization in the cKO enamel at the maturation stage. Interestingly, KLK4 mRNA levels were significantly reduced in the cKO teeth along with a slight increase in MMP-20 levels, suggesting that normal enamel maturation is regulated by TGF-ß signaling through the expression of KLK4. Thus, our study indicates that TGF-ß signaling plays an important role in ameloblast functions and enamel maturation.

Abstract A tendon’s ordered extracellular matrix (ECM) is essential for transmitting force but is also highly prone to injury. How tendon cells embedded within and surrounding this dense ECM orchestrate healing is not well understood. Here, we identify a specialized quiescent Scx +/Axin2 + population in mouse and human tendons that initiates healing and is a major functional contributor to repair. Axin2 + cells express stem cell markers, expand in vitro, and have multilineage differentiation potential. Following tendon injury, Axin2 + -descendants infiltrate the injury site, proliferate, and differentiate into tenocytes. Transplantation assays of Axin2-labeled cells into injured tendons reveal their dual capacity to significantly proliferate and differentiate yet retain their Axin2 + identity. Specific loss of Wnt secretion in Axin2 + or Scx + cells disrupts their ability to respond to injury, severely compromising healing. Our work highlights an unusual paradigm, wherein specialized Axin2 + /Scx + cells rely on self-regulation to maintain their identity as key organizers of tissue healing.

Introduction In Brazil, approximately 5% are born with a congenital disorder, potentially fatal without surgery. This study aims to evaluate the relationship between gastrointestinal congenital malformation (GICM) mortality, health indicators, and socioeconomic factors in Brazil.Methods GICM admissions (Q39–Q45) between 2012 and 2019 were collected using national databases. Patient demographics, socioeconomic factors, clinical management, outcomes, and the healthcare workforce density were also accounted for. Pediatric Surgical Workforce density and the number of neonatal intensive care units in a region were extracted from national datasets and combined to create a clinical index termed ‘NeoSurg’. Socioeconomic variables were combined to create a socioeconomic index termed ‘SocEcon’. Simple linear regression was used to investigate if the temporal changes of both indexes were significant. The correlation between mortality and the different indicators in Brazil was evaluated using Pearson’s correlation coefficient.Results Over 8 years, Brazil recorded 12804 GICM admissions. The Southeast led with 6147 cases, followed by the Northeast (2660), South (1727), North (1427), and Midwest (843). The North and Northeast reported the highest mortality, lowest NeoSurg, and SocEcon Index rates. Nevertheless, mortality rates declined across regions from 7.7% (2012) to 3.9% (2019), a 51.7% drop. The North and Midwest experienced the most substantial reductions, at 63% and 75%, respectively. Mortality significantly correlated with the indexes in nearly all regions (p

ABSTRACT The 35th Brazilian Congress of Surgery marked a turning point for surgical education in the country. For the first time, the Brazilian College of Surgeons included Global Surgery on the main congressional agenda, providing a unique opportunity to rethink how surgical skills are taught from a public health perspective. This discussion prompts us to consider why and how Global Surgery education should be expanded in Brazil. Although Brazilian researchers and institutions have contributed to the fields expansion since 2015, Global Surgery education initiatives are still incipient in our country. Relying on successful strategies can be a starting point to promote the area among national surgical practitioners. In this editorial, we discuss potential strategies to expand Global Surgery education opportunities and propose a series of recommendations at the national level.

Abstract Although adoptive T cell therapy provides the T cell pool needed for immediate tumor debulking, the infused T cells generally have a narrow repertoire for antigen recognition and limited ability for long-term protection. Here, we present a hydrogel that locally delivers adoptively transferred T cells to the tumor site while recruiting and activating host antigen-presenting cells with GMCSF or FLT3L and CpG, respectively. T cells alone loaded into these localized cell depots provided significantly better control of subcutaneous B16-F10 tumors than T cells delivered through direct peritumoral injection or intravenous infusion. T cell delivery combined with biomaterial-driven accumulation and activation of host immune cells prolonged the activation of the delivered T cells, minimized host T cell exhaustion, and enabled long-term tumor control. These findings highlight how this integrated approach provide both immediate tumor debulking and long-term protection against solid tumors, including against tumor antigen escape.

Immunotherapy has emerged as a promising strategy to eradicate cancer cells. Particularly, the development of cancer vaccines to induce a potent and sustained antigen-specific T cell response has become a center of attention. Herein, we describe a novel immunotherapy based on magnetic nanoparticles (MNP) covalently modified with the OVA254-267 antigen and a CpG oligonucleotide via disulfide bonds. The MNP-CpG-COVA significantly enhances dendritic cell activation and CD8+ T cell antitumoral response against B16-OVA melanoma cells in vitro. Notably, the immune response induced by the covalently modified MNP is more potent and sustained over time than that triggered by the free components, highlighting the advantage of nanoformulations in immunotherapies. What is more, the nanoparticles are stable in the blood after in vivo administration and induce potent levels of systemic tumor-specific effector CD8 + T cells. Overall, our findings highlight the potential of covalently functionalized MNP to induce robust immune responses against mouse melanoma.

‘Manufacturing CAR-T cells is a streamlined and highly regulated procedure involving T-cell-expansion and activation on a standardised platform. Here, the authors show that a personalized approach, taking the phenotypic attributes of individual patients’ T cells into account, leads to more efficient CAR-T cell manufacturing and better CAR-T cell functionality.

Objective In this study, we assess the delivery of congenital pediatric surgical care under Brazil’s system of universal health coverage and evaluate differences in delivery between public and private sectors.Methods A cross-sectional national survey of pediatric surgeons in Brazil was conducted. Participants were asked which of 23 interventions identified through the Disease Control Priorities 3 (Surgical Interventions for Congenital Anomalies) they perform and to report barriers faced while providing surgical care. Responses were weighted by state and stratified by sector (public vs private).Results A sample of 352 responses was obtained and weighted to represent 1378 practicing pediatric surgeons registered in Brazil during the survey time. 73% spend the majority of their time working in the public sector (‘Sistema Único de Saúde’ and Foundation hospitals), and most of them also work in the private sector. Generally, Brazilian pediatric surgeons have the expertise to provide thoracic, abdominal, and urologic procedures. Surgeons working mostly in the public sector were more likely to report a lack of access to essential medications (25% vs 9%, p

Abstract Multicellular spheroids made of stem cells can act as building blocks that fuse to capture complex aspects of native in vivo environments, but the effect of hydrogel viscoelasticity on cell migration from spheroids and their fusion remains largely unknown. Here, we investigated the effect of viscoelasticity on migration and fusion behavior of mesenchymal stem cell (MSC) spheroids using hydrogels with a similar elasticity but different stress relaxation profiles. Fast relaxing (FR) matrices were found to be significantly more permissive to cell migration and consequent fusion of MSC spheroids. Mechanistically, inhibition of ROCK and Rac1 pathways prevented cell migration. Moreover, the combination of biophysical and biochemical cues provided by fast relaxing hydrogels and platelet‐derived growth factor (PDGF) supplementation, respectively, resulted in a synergistic enhancement of migration and fusion. Overall, these findings emphasize the important role of matrix viscoelasticity in tissue engineering and regenerative medicine strategies based on spheroids.

Abstract Neutrophils are essential effector cells for mediating rapid host defense and their insufficiency arising from therapy‐induced side‐effects, termed neutropenia, can lead to immunodeficiency‐associated complications. In autologous hematopoietic stem cell transplantation (HSCT), neutropenia is a complication that limits therapeutic efficacy. Here, we report the development and in vivo evaluation of an injectable, biodegradable hyaluronic acid (HA)‐based scaffold, termed HA cryogel, with myeloid responsive degradation behavior. In mouse models of immune deficiency, we show that the infiltration of functional myeloid‐lineage cells, specifically neutrophils, is essential to mediate HA cryogel degradation. Post‐HSCT neutropenia in recipient mice delayed degradation of HA cryogels by up to 3 weeks. We harnessed the neutrophil‐responsive degradation to sustain the release of granulocyte colony stimulating factor (G‐CSF) from HA cryogels. Sustained release of G‐CSF from HA cryogels enhanced post‐HSCT neutrophil recovery, comparable to pegylated G‐CSF, which, in turn, accelerated cryogel degradation. HA cryogels are a potential approach for enhancing neutrophils and concurrently assessing immune recovery in neutropenic hosts.

The immunosuppressive tumour microenvironment impairs immunotherapy in poorly immunogenic cancer. Here, the authors load an alginate gel with GM-CSF, CpG oligonucleotides and doxorubicin-iRGD to promote immunogenic death of tumour cells and improve immunotherapy efficacy in triple negative breast cancer models.

Staphylococcus aureus bacteremia (SAB) remains a clinically challenging infection despite extensive investigation. Repurposing medications approved for other indications is appealing as clinical safety profiles have already been established. Ticagrelor, a reversible adenosine diphosphate receptor antagonist that prevents platelet aggregation, is indicated for patients suffering from acute coronary syndrome (ACS). However, some clinical data suggest that patients treated with ticagrelor are less likely to have poor outcomes due to S. aureus infection. There are several potential mechanisms by which ticagrelor may affect S. aureus virulence. These include direct antibacterial activity, up-regulation of the innate immune system through boosting platelet-mediated S. aureus killing, and prevention of S. aureus adhesion to host tissues. In this Pearl, we review the clinical data surrounding ticagrelor and infection as well as explore the evidence surrounding these proposed mechanisms of action. While more evidence is needed before antiplatelet medications formally become part of the arsenal against S. aureus infection, these potential mechanisms represent exciting pathways to target in the host/pathogen interface.

Background Pancreatic pseudocysts may develop after high-grade pancreatic injuries in children. Many resolve without intervention, and the management of symptomatic pseudocysts that persist remains controversial, with various open, percutaneous and laparoscopic approaches to intervention described. Successful endoscopic cyst gastrostomy has been reported in children with pancreatic pseudocysts of mixed etiology.Methods The trauma registry and electronic medical record of a level 1 pediatric trauma center were queried for children with a symptomatic pseudocyst following pancreatic trauma over a 12-year period, from 2008 to 2019.Results We describe a case series of five consecutive children with persistent symptomatic pancreatic pseudocysts following blunt abdominal trauma all successfully treated with endoscopic cyst gastrostomy.Discussion Endoscopic cyst gastrostomy appears to be safe and effective in the management of symptomatic pancreatic pseudocysts in children following pancreatic trauma.Level of evidence 5 – retrospective case series.

Background Many organizations have issued recommendations to limit elective surgery during the coronavirus disease 2019 (COVID-19) pandemic. We surveyed providers of children’s surgical care working in low-income and middle-income countries (LMICs) to understand their perspectives on surgical management in the wake of the COVID-19 pandemic and how they were subsequently modifying their surgical care practices.Methods A survey of children’s surgery providers in LMICs was performed. Respondents reported how their perioperative practice had changed in response to COVID-19. They were also presented with 26 specific procedures and asked which of these procedures they were allowed to perform and which they felt they should be allowed to perform. Changes in surgical practice reported by respondents were analyzed thematically.Results A total of 132 responses were obtained from 120 unique institutions across 30 LMICs. 117/120 institutions (97.5%) had issued formal guidance on delaying or limiting elective children’s surgical procedures. Facilities in LICs were less likely to have issued guidance on elective surgery compared with middle-income facilities (82% in LICs vs 99% in lower middle-income countries and 100% in upper middle-income countries, p=0.036). Although 122 (97%) providers believed cases should be limited during a global pandemic, there was no procedure where more than 61% of providers agreed cases should be delayed or canceled.Conclusions There is little consensus on which procedures should be limited or delayed among LMIC providers. Expansion of testing capacity and local, context-specific guidelines may be a better strategy than international consensus, given the disparities in availability of preoperative testing and the lack of consensus towards which procedures should be delayed.

The instability of DNA nanostructures in physiological environments has hampered their use as therapeutics and diagnostic agents inin vivoapplications. Here, the authors show that coating DNA origami with oligolysine-PEG moieties improves their pharmacokinetic properties in mouse models.

Immunotherapeutic treatments in head and neck cancer clinical trials include cancer vaccines targeting foreign viral antigens or mutational neoantigens derived from cancer-expressed proteins. Anti-tumor immune responses place cancer cells under selective pressure to lose or downregulate target antigens; therefore, vaccination against virus- or host- “driver” oncogenes are proposed as a strategy to overcome immune escape. Herein, we demonstrate the impact of immunogenic viral antigens on anti-tumor response and immune editing in MOC2-E6E7, a syngeneic murine oral cancer cell line expressing HPV-16 E6 and E7 oncoproteins. Using orthotopic syngeneic models, we observed in vivo tumor growth kinetics of MOC2-E6E7 is delayed in immunocompetent mice compared to parental MOC2 tumors. In contrast, tumor growth remained similar in Rag1-/- mice lacking adaptive immunity. MOC2-E6E7 tumors demonstrated an “inflamed” or immune-activated tumor microenvironment and greater infiltration of CD8+ T cells compared to MOC2. By real-time PCR, we detected downregulation of E6 and E7 genes in MOC2-E6E7 tumors only in immunocompetent mice, suggesting the loss of ectopic viral antigen expression due to immune editing. We then assessed the efficacy of a biomaterials-based mesoporous silica rod (MSR) cancer vaccine targeting HPV-16 E7 in our model. Vaccination induced robust infiltration of antigen-specific CD8+ T cells, which led to tumor growth delay and modestly prolonged survival in MOC2-E6E7 tumors. Increased efficacy was seen in a separate head and neck cancer tumor model, mEER, which obligately expresses E7 antigen. Collectively, our data highlight the need for both immunogenicity and ‘driver’ status of target antigens to be considered in cancer vaccine design.

The use of autologous cells harvested and subsequently transplanted in an intraoperative environment constitutes a new approach to promote regeneration. Usually cells are isolated by selection methods such as fluorescence- or magnetic- activated cell sorting with residual binding of the antibodies or beads. Thus, cell-based therapies would benefit from the development of new devices for cell isolation that minimally manipulate the target cell population. In the clinic, 5 to 10 percent of fractures do not heal properly and CD31+ cells have been identified as promising candidates to support bone regeneration. The aim of this project was to develop and prototype a simple system to facilitate the enrichment of CD31+ cells from whole blood. After validating the specificity of a commercially available aptamer for CD31, we combined this aptamer with traditional magnetic bead strategies, which led to enrichment of CD31+ cells with a purity of 91±10%. Subsequently, the aptamer was attached to agarose beads (Ø = 100-165 um) that were incorporated into a column-based system to enable capture and subsequent release of the CD31+ enriched cells. Different parameters were investigated to allow a biophysical-based cell release from beads, and a simple mixing was found sufficient to release initially bound cells from the optimized column without the need for any chemicals that promote disassociation. The system led to a significant enrichment of CD31+ cells (initial population: 63±9%, released: 87±3%) with excellent cell viability (released: 97±1%). The composition of the released CD31+ fraction indicated an enrichment of the monocyte population. The angiogenic and osteogenic potential of the released cell population were confirmed in vitro. These results and the simplicity of this system highlight the potential of such approach to enable cell enrichment strategies in intraoperative settings.

In calcific aortic valve disease (CAVD), microcalcifications originating from nanoscale calcifying vesicles disrupt the aortic valve (AV) leaflets, which consist of three (biomechanically) distinct layers: the fibrosa, spongiosa, and ventricularis. CAVD has no pharmacotherapy and lacks in vitro models as a result of complex valvular biomechanical features surrounding resident mechanosensitive valvular interstitial cells (VICs). We measured layer-specific mechanical properties of the human AV and engineered a three-dimensional (3D)-bioprinted CAVD model that recapitulates leaflet layer biomechanics for the first time. Human AV leaflet layers were separated by microdissection, and nanoindentation determined layer-specific Young’s moduli. Methacrylated gelatin (GelMA)/methacrylated hyaluronic acid (HAMA) hydrogels were tuned to duplicate layer-specific mechanical characteristics, followed by 3D-printing with encapsulated human VICs. Hydrogels were exposed to osteogenic media (OM) to induce microcalcification, and VIC pathogenesis was assessed by near infrared or immunofluorescence microscopy. Median Young’s moduli of the AV layers were 37.1, 15.4, and 26.9 kPa (fibrosa/spongiosa/ventricularis, respectively). The fibrosa and spongiosa Young’s moduli matched the 3D 5% GelMa/1% HAMA UV-crosslinked hydrogels. OM stimulation of VIC-laden bioprinted hydrogels induced microcalcification without apoptosis. We report the first layer-specific measurements of human AV moduli and a novel 3D-bioprinted CAVD model that potentiates microcalcification by mimicking the native AV mechanical environment. This work sheds light on valvular mechanobiology and could facilitate high-throughput drug-screening in CAVD.

Testing new antiangiogenic drugs for cancer treatment requires the use of animal models, since stromal cells and extracellular matrices mediate signals to endothelial cells that cannot be fully reproduced in vitro. Most methods used for analysis of antiangiogenic drugs in vivo utilized histologic examination of tissue specimens, which often requires large sample sizes to obtain reliable quantitative data. Furthermore, these assays rely on the analysis of murine vasculature that may not be correlated with the responses of human endothelial cells. Here, we engineered human blood vessels in immunodeficient mice with human endothelial cells expressing luciferase, demonstrated that these cells line functional blood vessels, and quantified angiogenesis over time using a photon counting-based method. In a proof-of-principle experiment with PTK/ZK, a small molecule inhibitor of vascular endothelial growth factor (VEGF) tyrosine kinase receptors, a strong correlation was observed between the decrease in bioluminescence (9.12-fold) in treated mice and the actual decrease in microvessel density (9.16-fold) measured after retrieval of the scaffolds and immunohistochemical staining of endothelial cells. The method described here allows for quantitative and noninvasive investigation into the effects of anti-cancer drugs on human angiogenesis in a murine host.

Microparticles based on segmented polyurethane were synthesized by polycondensation of a series of diols having various molecular weight with tolyene-2,4-diisocyanate in water-in-oil emulsion. The resulting spherical microparticles were 6-10 µm in diameter following the Gauss distribution. The size of microcapsules at maximum distribution band increases with growing PEG length. It was observed that with higher length of PEG wall surfaces of capsules become more stable mechanically, however a capsule itself is no more brittle and rough. Some aggregation also occurs for microparticles based on PEG 4200. Since respiratory way of drug administration considers size of particles within 1-10 µm as the most applicable, the resulting PU microparticles could be an ideal candidate as domain for respirable antiTB drug administration.

Embryonic skeletogenesis involves proliferation, condensation and subsequent chondrogenic differentiation of mesenchymal precursor cells, and the strains and stresses inherent to these processes have been hypothesized to influence skeletal development. The aim of this study was to determine the effect of growth-mimicking strain on the process of early skeletal development in vitro. To this end, we applied continuous uniaxial strain to embryonic skeletal precursor cells in micromass culture. Strain was applied at different times of culture to specifically address the effect of mechanical loading on the sequential stages of cellular proliferation, condensation and differentiation. We found that growth-mimicking strain at all three times did not affect proliferation or chondrogenic differentiation under the tested conditions. However, the timing of the applied strain did play a role in the density of mesenchymal condensations. This finding suggests that a mechanically dynamic environment, and specifically strain, can influence skeletal patterning. The growth-mimicking micromass model presented here may be a useful tool for further studies into the role of mechanical loading in early skeletal development.

As the role of mechanical force in cellular signaling gained recognition, investigators designed a number of devices to deliver controlled regimens of mechanical force to cultured cells. One type of device uses thin silicone-rubber membranes to support monolayer cell adhesion and to transmit mechanical force in the form of biaxial strain. We have observed that cell attachment and spreading are impaired on these membranes compared to polystyrene, even when both are passively coated with identical amounts of extracellular matrix. The purpose of these studies was to quantify the efficiency and stability of passive matrix adsorption onto commercially available elastic culture substrates. A theoretically saturating density (1 μg/cm2) of fibronectin was added to each well, and the initial efficiency of adsorption to the walls and elastic membranes was found to be 31 ± 2% of the protein added. Strikingly, when the protein adsorbed specifically to the membranes was quantified after seven days, only 10–26 ng/cm2 fibronectin were present, revealing that most of the adsorption is to the sides of the wells. These results indicate that the adsorption of matrix proteins to silicone-rubber substrates is relatively inefficient and that investigators who use these systems must be aware of this fact and design their experiments accordingly.

Human embryonic and induced pluripotent stem cells (hESC/hiPSC) are promising cell sources for the derivation of large numbers of specific cell types for tissue engineering and cell therapy applications. We have describe a directed differentiation protocol that generates fibroblasts from both hESC and hiPSC (EDK/iPDK) that support the repair and regeneration of epithelial tissue in engineered, 3D skin equivalents. In the current study, we analyzed the secretory profiles of EDK and iPDK cells to investigate the production of factors that activate and promote angiogenesis. Analysis of in vitro secretion profiles from EDK and iPDK cells demonstrated the elevated secretion of pro-angiogenic soluble mediators, including VEGF, HGF, IL-8, PDGF-AA, and Ang-1, that stimulated endothelial cell sprouting in a 3D model of angiogenesis in vitro. Phenotypic analysis of EDK and iPDK cells during the course of differentiation from hESCs and iPSCs revealed that both cell types progressively acquired pericyte lineage markers NG2, PDGFRβ, CD105, and CD73 and demonstrated transient induction of pericyte progenitor markers CD31, CD34, and Flk1/VEGFR2. Furthermore, when co-cultured with endothelial cells in 3D fibrin-based constructs, EDK and iPDK cells promoted self-assembly of vascular networks and vascular basement membrane deposition. Finally, transplantation of EDK cells into mice with hindlimb ischemia significantly reduced tissue necrosis and improved blood perfusion, demonstrating the potential of these cells to stimulate angiogenic responses in vivo. These findings demonstrate that stable populations of pericyte-like angiogenic cells can be generated with high efficiency from hESC and hiPSC using a directed differentiation approach. This provides new cell sources and opportunities for vascular tissue engineering and for the development of novel strategies in regenerative medicine.

Current efforts in surface functionalization have not produced a robust technique capable of creating specific two-dimensional microscale geometrical arrays composed of multiple proteins. Such a capability is desirable for engineering substrates in sensing and cell patterning applications where at least two different protein functionalities in a specific configuration are required. Here we introduce a new approach for the creation of arrays of microscale geometries. We demonstrate our approach with a biomimetic structure inspired by the immunological synapse, a cell-cell interfacial structure characterized by two concentric rings of proteins: an outer adhesion protein structure and an inner recognition ligand core. The power of the technique lies in its ability to pattern any protein in any defined geometry as well as to create arrays in parallel.

Alginate hydrogels are widely used for cell encapsulation and transplantation, and they are frequently surface reinforced with secondary polymers to enhance their mechanical rigidity and stability. We hypothesized that the molecular weight (MW) of the polymer utilized to reinforce alginate would be an important factor in their stability, particularly when the gel network was homogeneously reinforced with the polymer. This hypothesis was investigated with alginate hydrogels cross-linked with Ca2+, and reinforced throughout the bulk of the gel with poly(ethyleneimine) (PEI) having different MWs. Interactions between the two polymers became significant following gelation, leading to higher elastic moduli (E) than gels with no PEI. The decrease in E of gels incubated in isotonic salt solutions over time, utilized as an indication of gel break down, was ameliorated with an increase in the MW of the PEI. In addition, the dependencies of the moduli and visco-elasticity on the temperature also became smaller with the use of high MW PEI. This is likely due to the limited mobility of high MW PEI, leading to a higher energy for dissociation. The stable interactions between the alginate and PEI prevented alterations of the pore structure in the gels, and slowed the deterioration of gel properties even under continuous agitation in a bioreactor. The results of this study will likely be useful in designing alginate encapsulation strategies for various applications.