A comparison of two versus five epineural sutures to achieve successful polyethylene glycol (PEG) nerve fusion in a rat sciatic nerve repair model.

Background: We compared rates of successful polyethylene glycol (PEG) nerve fusion between two epineural suture repairs (2SR) and five epineural suture repairs (5SR) in a rat sciatic nerve transection neurorrhaphy model. We hypothesise that the two and five epineural neural suture repair groups will achieve a similar rate of PEG fusion. Methods: Twenty-five Lewis rats underwent bilateral sciatic nerve transection. Primary neurorrhaphy (PN) consisting of 2SR in one hind limb and 5SR in the contralateral hind limb was performed utilizing PEG fusion. Successful PEG fusion was confirmed by a distal muscle twitch after nerve stimulation proximal to the nerve fusion site. Sciatic nerve conduction velocity (SNCV) across the repair site and the force generated by tibialis anterior muscle (TAM) contraction were also compared between the 2SR and 5SR groups. Results: Success rates were 100% for the 2SR and the 5SR groups. No statistically significant differences in SNCV (P = 0.444) or isometric tetanic TAM contractile force (P = 0.820) were observed between 2SR and 5SR in the setting of PEG fusion. Conclusion: These findings demonstrate no significant difference in successful PEG fusion between the 2SR and 5SR groups. In addition, the findings demonstrate no statistically significant differences in SNCV or isometric tetanic TAM contractile force following sciatic nerve transection when performing a 2SR or 5SR PN in the setting of PEG fusion. Successful PEG fusion can be achieved acutely with either a two or five-epineural suture repair in a rat model.

Revealing Early Spatial Patterns of Cellular Responsivity in Fiber-Reinforced Microenvironments.

Due to responses to reviewer comments, we are slightly above the word limit for the abstract. The revised version is included in the main manuscript text. Please let us know if this is an issue, and we can revise to try to get under the word limit. Thank you.

Synthesis and Photopatterning of Synthetic Thiol-Norbornene Hydrogels.

Hydrogels are a class of soft biomaterials and the material of choice for a myriad of biomedical applications due to their biocompatibility and highly tunable mechanical and biochemical properties. Specifically, light-mediated thiol-norbornene click reactions between norbornene-modified macromers and di-thiolated crosslinkers can be used to form base hydrogels amenable to spatial biochemical modifications via subsequent light reactions between pendant norbornenes in the hydrogel network and thiolated peptides. Macromers derived from natural sources (e.g., hyaluronic acid, gelatin, alginate) can cause off-target cell signaling, and this has motivated the use of synthetic macromers such as poly(ethylene glycol) (PEG). In this study, commercially available 8-arm norbornene-modified PEG (PEG-Nor) macromers were reacted with di-thiolated crosslinkers (dithiothreitol, DTT) to form synthetic hydrogels. By varying the PEG-Nor weight percent or DTT concentration, hydrogels with a stiffness range of 3.3 kPa-31.3 kPa were formed. Pendant norbornene groups in these hydrogels were used for secondary reactions to either increase hydrogel stiffness (by reacting with DTT) or to tether mono-thiolated peptides to the hydrogel network. Peptide functionalization has no effect on bulk hydrogel mechanics, and this confirms that mechanical and biochemical signals can be independently controlled. Using photomasks, thiolated peptides can also be photopatterned onto base hydrogels, and mesenchymal stem cells (MSCs) attach and spread on RGD-functionalized PEG-Nor hydrogels. MSCs encapsulated in PEG-Nor hydrogels are also highly viable, demonstrating the ability of this platform to form biocompatible hydrogels for 2D and 3D cell culture with user-defined mechanical and biochemical properties.

Engineering transcriptional regulation for cell-based therapies.

A major aim in the field of synthetic biology is developing tools capable of responding to user-defined inputs by activating therapeutically relevant cellular functions. Gene transcription and regulation in response to external stimuli are some of the most powerful and versatile of these cellular functions being explored. Motivated by the success of chimeric antigen receptor (CAR) T-cell therapies, transmembrane receptor-based platforms have been embraced for their ability to sense extracellular ligands and to subsequently activate intracellular signal transduction. The integration of transmembrane receptors with transcriptional activation platforms has not yet achieved its full potential. Transient expression of plasmid DNA is often used to explore gene regulation platforms in vitro. However, applications capable of targeting therapeutically relevant endogenous or stably integrated genes are more clinically relevant. Gene regulation may allow for engineered cells to traffic into tissues of interest and secrete functional proteins into the extracellular space or to differentiate into functional cells. Transmembrane receptors that regulate transcription have the potential to revolutionize cell therapies in a myriad of applications, including cancer treatment and regenerative medicine. In this review, we will examine current engineering approaches to control transcription in mammalian cells with an emphasis on systems that can be selectively activated in response to extracellular signals. We will also speculate on the potential therapeutic applications of these technologies and examine promising approaches to expand their capabilities and tighten the control of gene regulation in cellular therapies.

Mesenchymal stem cells enhance targeted bone growth from injectable hydrogels with BMP-2 peptides.

Osteoporosis is the most common chronic metabolic bone disease, and the prevalence of osteoporotic fractures is rapidly increasing with the aging population. While bisphosphonates can reduce bone loss and risk of fracture, these drugs are systemic, rely on long-term use, and patient compliance is low. Recombinant human bone morphogenetic protein-2 (BMP-2) is an FDA-approved protein that can offer a more targeted therapeutic than systemic treatments. DWIVA is a peptide sequence corresponding to the wrist epitope of BMP-2, and DWIVA-functionalized hydrogels feature osteoinductive propertiesin vitro and in vivo. This study reports that self-forming DWIVA-functionalized hydrogels injected into the intramedullary canal of rat femurs induce a local increase in trabecular bone in as little as 2 weeks. Increases in bone volume, trabecular thickness, and trabeculae count from DWIVA-laden hydrogels persist for at least 4 weeks, and the inclusion of mesenchymal stem cells (MSCs) significantly enhances the development of mineralized bone. Histological analysis of decalcified femurs also shows that hydrogel injections containing DWIVA peptide and MSCs stimulate unmineralized bone tissue formation and induce an increased count of osteoblasts and osteoclasts at the injection site after 4 weeks. Overall, the MSC-laden DWIVA peptide-functionalized hydrogels presented rapidly induce targeted bone formation and have the potential to form nascent bone within bones in jeopardy of an osteoporotic fracture such as the femur.

Fibrin Glue Acutely Blocks Distal Muscle Contraction after Confirmed Polyethylene Glycol Nerve Fusion: An Animal Study.

Background: Polyethylene glycol (PEG) is a synthetic, biodegradable, and hyperosmotic material promising in the treatment of acute peripheral nerve injuries. Our team set out to investigate the impact of fibrin glue upon PEG fusion in a rat model. Methods: Eighteen rats underwent sciatic nerve transection and PEG fusion. Electrophysiologic testing was performed to measure nerve function and distal muscle twitch. Fibrin glue was applied and testing repeated. Due to preliminary findings, fibrin glue was applied to an uncut nerve in five rodents and testing was conducted before and after glue application. Mann-Whitney U tests were used to compare median values between outcome measures. A Shapiro-Wilk test was used to determine normality of data for each comparison, significance set at a P value less than 0.05. Results: PEG fusion was confirmed in 13 nerves with no significant change in amplitude (P = 0.054), latency (P = 0.114), or conduction velocity (P = 0.114). Stimulation of nerves following PEG fusion produced distal muscle contraction in 100% of nerves. Following application of fibrin glue, there was a significant reduction in latency (P = 0.023), amplitude (P < 0.001), and conduction velocity (P = 0.023). Stimulation of the nerve after application of fibrin glue did not produce distal muscle twitch. Five uncut nerves with fibrin glue application blocked distal muscle contraction following stimulation. Conclusions: Our data suggest that fibrin glue alters the nerve's function. The immediate confirmation of PEG fusion via distal muscle twitch is blocked with application fibrin glue in this experimental model. Survival and functional outcome studies are necessary to understand if this has implications on the long-term functional outcomes.

A 3D-printed blood-brain barrier model with tunable topology and cell-matrix interactions.

Recent developments in digital light processing (DLP) can advance the structural and biochemical complexity of perfusablein vitromodels of the blood-brain barrier. Here, we describe a strategy to functionalize complex, DLP-printed vascular models with multiple peptide motifs in a single hydrogel. Different peptides can be clicked into the walls of distinct topologies, or the peptide motifs lining channel walls can differ from those in the bulk of the hydrogel. The flexibility of this approach is used to both characterize the effects of various bioactive domains on endothelial coverage and tight junction formation, in addition to facilitating astrocyte attachment in the hydrogel surrounding the endothelialized vessel to mimic endothelial-astrocyte interaction. Peptides derived from proteins mediating cell-extracellular matrix (e.g. RGD and IKVAV) and cell-cell (e.g. HAVDI) adhesions are used to mediate endothelial cell attachment and coverage. HAVDI and IKVAV-lined channels exhibit significantly greater endothelialization and increased zonula-occluden-1 (ZO-1) localization to cell-cell junctions of endothelial cells, indicative of tight junction formation. RGD is then used in the bulk hydrogel to create an endothelial-astrocyte co-culture model of the blood-brain barrier that overcomes the limitations of previous platforms incapable of complex topology or tunable bioactive domains. This approach yields an adjustable, biofabricated platform to interrogate the effects of cell-matrix interaction on blood-brain barrier mechanobiology.

A Pilot Remote Curriculum to Enhance Resident and Medical Student Understanding of Machine Learning in Healthcare.

BACKGROUND: Despite the expanding role of machine learning (ML) in health care and patient expectations for clinicians to understand ML-based tools, few for-credit curricula exist specifically for neurosurgical trainees to learn basic principles and implications of ML for medical research and clinical practice. We implemented a novel, remotely delivered curriculum designed to develop literacy in ML for neurosurgical trainees. METHODS: A 4-week pilot medical elective was designed specifically for trainees to build literacy in basic ML concepts. Qualitative feedback from interested and enrolled students was collected to assess students' and trainees' reactions, learning, and future application of course content. RESULTS: Despite 15 interested learners, only 3 medical students and 1 neurosurgical resident completed the course. Enrollment included students and trainees from 3 different institutions. All learners who completed the course found the lectures relevant to their future practice as clinicians and researchers and reported improved confidence in applying and understanding published literature applying ML techniques in health care. Barriers to ample enrollment and retention (e.g., balancing clinical responsibilities) were identified. CONCLUSIONS: This pilot elective demonstrated the interest, value, and feasibility of a remote elective to establish ML literacy; however, feedback to increase accessibility and flexibility of the course encouraged our team to implement changes. Future elective iterations will have a semiannual, 2-week format, splitting lectures more clearly between theory (the method and its value) and application (coding instructions) and will make lectures open-source prerequisites to allow tailoring of student learning to their planned application of these methods in their practice and research.

The World Neurosurgery Global Champions Program: First-Year Experience of a Model Initiative for Reducing Disparities in Global Neurosurgical Literature.

OBJECTIVE: Most surgical journals are published in English, representing a challenge for researchers from non-Anglophone countries. We describe the implementation, workflow, outcomes, and lessons learned from the WORLD NEUROSURGERY Global Champions Program (GCP), a novel journal-specific English language editing program for articles rejected because of poor English grammar or usage. METHODS: The GCP was advertised via the journal website and social media. Applicants were selected to be a reviewer for the GCP if they demonstrated English proficiency on writing samples supplied in their application. The demographics of GCP members and characteristics and outcomes of articles edited by the GCP during its first year were reviewed. Surveys of GCP members and authors who used the service were conducted. RESULTS: Twenty-one individuals became part of the GCP, representing 8 countries and 16 languages apart from English. A total of 380 manuscripts were peer reviewed by the editor-in-chief, who determined these manuscripts to have potentially worthwhile content but needed to be rejected due to poor language. The authors of these manuscripts were informed of the existence of this language assistance program. Forty-nine articles (12.9%) were edited by the GCP in 41.6 ± 22.8 days. Of 40 articles resubmitted to WORLD NEUROSURGERY, 24 (60.0%) were accepted. GCP members and authors understood the purpose and workflow of the program and recognized improvements in article quality and the probability of acceptance through their participation. CONCLUSIONS: The WORLD NEUROSURGERY Global Champions Program mitigated a critical barrier to publication in an English language journal for authors from non-Anglophone countries. This program promotes research equity by providing a free, largely medical student and trainee operated, English language editing service. This model or a similar service can be replicated by other journals.

Recent Advances in Antimicrobial Peptide Hydrogels.

Advances in the number and type of available biomaterials have improved medical devices such as catheters, stents, pacemakers, prosthetic joints, and orthopedic devices. The introduction of a foreign material into the body comes with a risk of microbial colonization and subsequent infection. Infections of surgically implanted devices often lead to device failure, which leads to increased patient morbidity and mortality. The overuse and improper use of antimicrobials has led to an alarming rise and spread of drug-resistant infections. To overcome the problem of drug-resistant infections, novel antimicrobial biomaterials are increasingly being researched and developed. Hydrogels are a class of 3D biomaterials consisting of a hydrated polymer network with tunable functionality. As hydrogels are customizable, many different antimicrobial agents, such as inorganic molecules, metals, and antibiotics have been incorporated or tethered to them. Due to the increased prevalence of antibiotic resistance, antimicrobial peptides (AMPs) are being increasingly explored as alternative agents. AMP-tethered hydrogels are being increasingly examined for antimicrobial properties and practical applications, such as wound-healing. Here, we provide a recent update, from the last 5 years of innovations and discoveries made in the development of photopolymerizable, self-assembling, and AMP-releasing hydrogels.

Leveraging published randomized controlled trials to inform clinical trial design: a simulation-based study of laminectomy versus laminectomy and fusion.

OBJECTIVE: The US-based Spinal Laminectomy versus Instrumented Pedicle Screw (SLIP) trial reported improvement in disability following laminectomy with fusion versus laminectomy alone for patients with lumbar spondylolisthesis. Despite using similar methods, a concurrent Swedish trial investigating the same question did not reach the same conclusion. The authors performed a simulation-based analysis to elucidate potential causes of these divergent results. METHODS: The mean and standard deviation of the preoperative and 2-year postoperative Oswestry Disability Index (ODI) scores for each study group (laminectomy with fusion and laminectomy alone) were collected from the spondylolisthesis stratum of the Swedish trial and used to create a MATLAB simulator using linear transformations to predict postoperative ODI distributions. Applying this simulator to both varied and published preoperative ODI distributions from the SLIP trial, the authors simulated the results of the US-based trial using treatment effects from the Swedish study and compared simulated US results to those published in the SLIP trial. RESULTS: Simulated US results showed that as preoperative disability increased, the difference in postoperative ODI scores grew between treatment groups and increasingly favored laminectomy alone (p < 0.0001). In 100 simulations of a similarly sized US trial, the average mean change in ODI scores postoperatively was significantly higher than was published for laminectomy alone in the SLIP trial (-21.3 vs -17.9), whereas it was significantly lower than published for fusion (-16.9 vs -26.3). CONCLUSIONS: The expected benefit of surgical treatments for spondylolisthesis varied according to preoperative disability. Adapting Swedish-estimated treatment effects to the US context mildly overapproximated the improvement in postoperative disability scores for laminectomy, but more severely underapproximated the improvement reported for laminectomy and fusion in the SLIP trial. The observed heterogeneity between these studies is influenced more by patient response to fusion than response to laminectomy. This analysis paves the way for future studies on the impact of preoperative treatment group heterogeneity, differences in surgical methods, and empirical design on reported clinical benefits. Although bayesian reanalysis of published randomized controlled trial data is susceptible to biases that typically limit post hoc analyses, the authors' method offers a simple and cost-effective approach to improve the understanding of published clinical trial results and their implications for future studies.

Evaluation of first and second trimester maternal thyroid profile on the prediction of gestational diabetes mellitus and post load glycemia.

Maternal thyroid alterations have been widely associated with the risk of gestational diabetes mellitus (GDM). This study aims to 1) test the first and the second trimester full maternal thyroid profile on the prediction of GDM, both alone and combined with non-thyroid data; and 2) make that prediction independent of the diagnostic criteria, by evaluating the effectiveness of the different maternal variables on the prediction of oral glucose tolerance test (OGTT) post load glycemia. Pregnant women were recruited in Concepción, Chile. GDM diagnosis was performed at 24-28 weeks of pregnancy by an OGTT (n = 54 for normal glucose tolerance, n = 12 for GDM). 75 maternal thyroid and non-thyroid parameters were recorded in the first and the second trimester of pregnancy. Various combinations of variables were assessed for GDM and post load glycemia prediction through different classification and regression machine learning techniques. The best predictive models were simplified by variable selection. Every model was subjected to leave-one-out cross-validation. Our results indicate that thyroid markers are useful for the prediction of GDM and post load glycemia, especially at the second trimester of pregnancy. Thus, they could be used as an alternative screening tool for GDM, independently of the diagnostic criteria used. The final classification models predict GDM with cross-validation areas under the receiver operating characteristic curve of 0.867 (p<0.001) and 0.920 (p<0.001) in the first and the second trimester of pregnancy, respectively. The final regression models predict post load glycemia with cross-validation Spearman r correlation coefficients of 0.259 (p = 0.036) and 0.457 (p<0.001) in the first and the second trimester of pregnancy, respectively. This investigation constitutes the first attempt to test the performance of the whole maternal thyroid profile on GDM and OGTT post load glycemia prediction. Future external validation studies are needed to confirm these findings in larger cohorts and different populations.

Directional Deep Brain Stimulation-A Step in the Right Direction? A Systematic Review of the Clinical and Therapeutic Efficacy of Directional Deep Brain Stimulation in Parkinson Disease.

BACKGROUND: The use of directional deep brain stimulation (dDBS) electrodes for the treatment of movement disorders such as Parkinson disease (PD) has become relatively widespread. However, the efficacy of dDBS relative to its omnidirectional deep brain stimulation (oDBS) counterpart is not well characterized. This systematic review aims to synthesize the literature comparing clinical and therapeutic outcomes of dDBS relative to oDBS in patients with PD. METHODS: A systematic literature search for studies with comparative clinical outcome data between dDBS and oDBS was performed across the PubMed, Ovid MEDLINE, and Web of Science databases. Data including therapeutic window (TW) and surrogate measures and the Unified Parkinson's Disease Rating Scale score were collected and summarized across multiple time periods. RESULTS: Ten studies met the eligibility criteria. Three of these studies evaluated motor performance in the form of Unified Parkinson's Disease Rating Scale III, with none finding differences between dDBS and oDBS. Two studies assessed quality-of-life measures with neither finding differences between dDBS and oDBS. TW or a surrogate measure was assessed in 6 studies; 5 studies found an increase or strong trend toward increase in dDBS relative to oDBS. CONCLUSIONS: The current evidence, although limited by bias, does suggest that dDBS in the treatment of PD yields improvements in motor symptoms and quality of life that are comparable to oDBS; TW and surrogate measures are consistently improved in patients with PD under a directional configuration relative to omnidirectional.

Self-Forming Norbornene-Tetrazine Hydrogels with Independently Tunable Properties.

Although photopolymerization reactions are commonly used to form hydrogels, these strategies rely on light and may not be suitable for delivering therapeutics in a minimally invasive manner. Here, hyaluronic acid (HA) macromers are modified with norbornene (Nor) or tetrazine (Tet) and upon mixing click into covalently crosslinked Nor-Tet hydrogels via a Diels-Alder reaction. By incorporating a high degree of Nor and Tet substitution, Nor-Tet hydrogels with a broad range in elastic moduli (5 to 30 kPa) and fast gelation times (1 to 5 min) are achieved. By pre-coupling methacrylated HANor macromers with thiolated peptides via a Michael addition reaction, Nor-Tet hydrogels are peptide-functionalized without affecting their physical properties. Mesenchymal stem cells (MSCs) on RGD-functionalized Nor-Tet hydrogels adhere and exhibit stiffness-dependent differences in matrix mechanosensing. Fluid properties of Nor-Tet hydrogel solutions allow for injections through narrow syringe needles and can locally deliver viable cells and peptides. Substituting HA with enzymatically degradable gelatin also results in cell-responsive Nor-Tet hydrogels, and MSCs encapsulated in Nor-Tet hydrogels preferentially differentiate into adipocytes or osteoblasts, based on 3D cellular spreading regulated by stable (HA) and degradable (gelatin) macromers.

Plant Tissue Parenchyma and Vascular Bundles Selectively Regulate Stem Cell Mechanosensing and Differentiation.

Introduction: Plant tissues are plentiful, diverse, and due to convergent evolution are structurally similar to many animal tissues. Decellularized plant tissues feature microtopographies that resemble cancellous bone (porous parenchyma) and skeletal muscle (fibrous vascular bundles). However, the use of plant tissues as an inexpensive and abundant biomaterial for controlling stem cell behavior has not been widely explored. Methods: Celery plant tissues were cut cross-sectionally (porous parenchyma) or longitudinally (fibrous vascular bundles) and decellularized. Human mesenchymal stem cells (MSCs) were then cultured atop plant tissues and confocal imaging of single cells was used to evaluate the early effects of microtopography on MSC adhesion, morphology, cytoskeletal alignment, Yes-associated protein (YAP) signaling, and downstream lineage commitment to osteogenic or myogenic phenotypes. Results: Microtopography was conserved post plant tissue decellularization and MSCs attached and proliferated on plant tissues. MSCs cultured on porous parenchyma spread isotropically along the periphery of plant tissue pores. In contrast, MSCs cultured on vascular bundles spread anisotropically and aligned in the direction of fibrous vascular bundles. Differences in microtopography also influenced MSC nuclear YAP localization and actin anisotropy, with higher values observed on fibrous tissues. When exposed to osteogenic or myogenic culture medium, MSCs on porous parenchyma had a higher percentage of cells stain positive for bone biomarker alkaline phosphatase, whereas myoblast determination protein 1 (MyoD) was significantly upregulated for MSCs on fibrous vascular bundles. Conclusions: Together, these results show that plant tissues are an abundant biomaterial with defined microarchitecture that can reproducibly regulate MSC morphology, mechanosensing, and differentiation. Supplementary Information: The online version of this article contains supplementary material available 10.1007/s12195-022-00737-9.

[Analysis of a clinical ethics committee activities at a general hospital]. / Experiencia del Comité de Ética Asistencial del Hospital Carlos van Buren entre los años 2007-2020.

BACKGROUND: Clinical Ethics Committees are deliberative groups whose main functions are to assess cases with ethical-clinical conflicts, to generate institutional protocols for preventive purposes, and to train health teams. AIM: To analyze the activity of a clinical ethics committee of a general hospital in the period 2007-2020. MATERIAL AND METHODS: A retrospective analysis of all session records, annual reports, case resolution and documents generated by the Clinical Ethics Committee of Carlos van Buren Hospital in Valparaíso, Chile, between 2007 and 2020, was carried out. RESULTS: On average, 12 cases are analyzed per year. Sixty percent correspond to requests from pediatric units and in 78% of these cases there was at least one neurological disease. In 62% of cases, the main ethical dilemma was adequacy of therapeutic effort, followed by dilemmas related to the exercise of autonomy in 18.2%. In education, two courses are identified aimed to doctors, residents, and other members of the health team. Regarding normative functions, several documents were generated at the request of the Hospital management or in different clinical situations. During COVID-19 pandemia, the active role of the committee was linked to the three main functions, namely evaluating cases, participating in morbidity and mortality meetings for preventive purposes, and issuing guidelines and recommendations for action. The active participation of Pediatric Neurology residents in the Committee, for educational and administrative purposes, stands out. CONCLUSIONS: The three main functions described for the ethics committees were exerted by this Committee during the evaluated period. The impact of our recommendations remain to be objectively evaluated.

Human induced mesenchymal stem cells display increased sensitivity to matrix stiffness.

The clinical translation of mesenchymal stem cells (MSCs) is limited by population heterogeneity and inconsistent responses to engineered signals. Specifically, the extent in which MSCs respond to mechanical cues varies significantly across MSC lines. Although induced pluripotent stem cells (iPSCs) have recently emerged as a novel cell source for creating highly homogeneous MSC (iMSC) lines, cellular mechanosensing of iMSCs on engineered materials with defined mechanics is not well understood. Here, we tested the mechanosensing properties of three human iMSC lines derived from iPSCs generated using a fully automated platform. Stiffness-driven changes in morphology were comparable between MSCs and iMSCs cultured atop hydrogels of different stiffness. However, contrary to tissue derived MSCs, no significant changes in iMSC morphology were observed between iMSC lines atop different stiffness hydrogels, demonstrating a consistent response to mechanical signals. Further, stiffness-driven changes in mechanosensitive biomarkers were more pronounced in iMSCs than MSCs, which shows that iMSCs are more adaptive and responsive to mechanical cues than MSCs. This study reports that iMSCs are a promising stem cell source for basic and applied research due to their homogeneity and high sensitivity to engineered mechanical signals.

Porous Scaffold-Hydrogel Composites Spatially Regulate 3D Cellular Mechanosensing.

Cells encapsulated in 3D hydrogels exhibit differences in cellular mechanosensing based on their ability to remodel their surrounding hydrogel environment. Although cells in tissue interfaces feature a range of mechanosensitive states, it is challenging to recreate this in 3D biomaterials. Human mesenchymal stem cells (MSCs) encapsulated in methacrylated gelatin (GelMe) hydrogels remodel their local hydrogel environment in a time-dependent manner, with a significant increase in cell volume and nuclear Yes-associated protein (YAP) localization between 3 and 5 days in culture. A finite element analysis model of compression showed spatial differences in hydrogel stress of compressed GelMe hydrogels, and MSC-laden GelMe hydrogels were compressed (0-50%) for 3 days to evaluate the role of spatial differences in hydrogel stress on 3D cellular mechanosensing. MSCs in the edge (high stress) were significantly larger, less round, and had increased nuclear YAP in comparison to MSCs in the center (low stress) of 25% compressed GelMe hydrogels. At 50% compression, GelMe hydrogels were under high stress throughout, and this resulted in a consistent increase in MSC volume and nuclear YAP across the entire hydrogel. To recreate heterogeneous mechanical signals present in tissue interfaces, porous polycaprolactone (PCL) scaffolds were perfused with an MSC-laden GelMe hydrogel solution. MSCs in different pore diameter (~280-430 µm) constructs showed an increased range in morphology and nuclear YAP with increasing pore size. Hydrogel stress influences MSC mechanosensing, and porous scaffold-hydrogel composites that expose MSCs to diverse mechanical signals are a unique biomaterial for studying and designing tissue interfaces.

The living interface between synthetic biology and biomaterial design.

Recent far-reaching advances in synthetic biology have yielded exciting tools for the creation of new materials. Conversely, advances in the fundamental understanding of soft-condensed matter, polymers and biomaterials offer new avenues to extend the reach of synthetic biology. The broad and exciting range of possible applications have substantial implications to address grand challenges in health, biotechnology and sustainability. Despite the potentially transformative impact that lies at the interface of synthetic biology and biomaterials, the two fields have, so far, progressed mostly separately. This Perspective provides a review of recent key advances in these two fields, and a roadmap for collaboration at the interface between the two communities. We highlight the near-term applications of this interface to the development of hierarchically structured biomaterials, from bioinspired building blocks to 'living' materials that sense and respond based on the reciprocal interactions between materials and embedded cells.