Tissue Mimic Research Articles

Attenuation estimation of soft tissue with reference-free minimization of system effects

Estimation of ultrasonic attenuation coefficient (AC) is essential for quantifying and characterizing the features of tissue microstructure. In the conventional AC estimation methods, a well-specified reference phantom is commonly used for minimizing the diffraction and transmit pulse related effects on the ultrasound radio-frequency (RF) signal. In this paper, a novel AC estimation technique is proposed avoiding the need of using any reference data, where the undesired system effects on the RF data are minimized through point spread function (PSF) separation and band-pass filtering of the envelope signal of the tissue reflectivity function (TRF). An improved and computationally efficient non-parametric cepstrum-based technique is used for separating the TRF and PSF from the measured RF signal. The Hilbert transform based temporal envelope is introduced to smooth out the unwanted effects of discontinuity and noise in the TRF and PSF signals. Finally, a band-pass filter based log power approximation of the TRF-envelope is applied to estimate the center frequency component of the attenuating power spectra with reduced diffraction effect. Assuming continuity of AC within a small uniform region, an exponentially weighted-average of logarithmic signal power of the neighboring blocks at the center frequency is measured for different depths, with a view to fit a regression line for obtaining an average AC value from its slope. Comparative results of the proposed reference-free AC estimation method with other conventional reference-based methods are presented for tissue-mimicking (TM) phantoms, in vivo breast and liver data. For the TM phantoms, the AC estimates using the new algorithm are within 10% deviation of the actual values. The obtained results for the breasts, normal livers, and fatty livers are 0.44 ± 0.23 dB/cm-MHz, 0.55 ± 0.21 dB/cm-MHz, and 0.61 ± 0.20 dB/cm-MHz, respectively, which are consistent with the literature-reported AC values. Different from reference-based methods, the novel technique is free from the bias that may result from the dissimilarity between acoustic property of the reference and sample.

Building blocks for a European Organ-on-Chip roadmap

This paper summarizes the outcome of the Organ-on-Chip (OoC) ORCHID Strategy workshop (Leiden, the Netherlands, 17 January 2019) intended to establish a European OoC roadmap through expert discussions, conclusions and recommendations. The workshop identified six specific building blocks for the OoC roadmap: (1) application, (2) specification, (3) qualification, (4) standardization, (5) production and upscaling, and (6) adoption. Complementary aspects relating to ethics and communication were also addressed. Priorities, methods and targets for the roadmap were proposed for each building block. General consensus was reached on the potential contribution of the newly founded European Organ-on-Chip Society (EUROoCS), which could facilitate deployment of each block. EUROoCS would ideally initiate and catalyze dialogue between OoC developers, end users and regulators. The dialogue should address qualification, open technology platforms, standardization and implementation of OoC technology, as well as ethical aspects of human tissue mimics, training the next generation of OoC researchers, dissemination and communication.

Galvanicdisplacement-induced codeposition of reduced-graphene-oxide/silver on alloy fibers for non-destructive SPME@SERS analysis of antibiotics.

This work describes the integration of solid-phase microextraction (SPME) and surface-enhanced Raman spectroscopy (SERS) by codeposition of a hybrid consisting of reduced graphene oxide and silver on silver-copper alloy fibers. The morphology and structure of the coating were characterized by a variety of microscopic and spectroscopic techniques that confirmed the hybrid structure of the material. A galvanic-displacement-induced process is assumed to be involved during the codeposition of the hybrid coating on the alloy. In this process, Ag(I)is reduced to Ag(0) by Cu(0), and the presence of conjugated domains in GO facilitates the long-range transfer of electrons from Cu toAg+. Simultaneously,GO accepts electrons and is converted into RGO.The hybrid coating exhibits a high SERS enhancement factor and good spatial uniformity. The needle-like coated alloy fibers are shown to be a viable tool for non-destructive sampling and SERS-based determination of trace levels of the antibiotics sulfadiazine and sulfamethoxazole in a spiked tissue mimic. The SERS peaks at 1149cm-1 for sulfadiazine and 1144cm-1 forsulfamethoxazole areselected as the reference peaks in the quantitative analysis. The linear range is from 0.01 to 100μg·cm-3. The detection limits are 1.9ng·cm-3 for sulfadiazine and 4.4ng·cm-3 for sulfamethoxazole. Graphical abstract Schematic presentation of I: Galvanic-displacement-induced reduction of graphene oxide (brown films) and Ag+ (purple dots) onsilver-copperalloy; II: Codeposition of reduced-graphene-oxide (grey films)/Ag (blue stars) on alloy fiber; III: Non-destructive SPME of antibiotics from spiked tissue mimic; IV: SERS detection using Raman spectroscope.

Composite hydrogel: A high fidelity soft tissue mimic for surgery

Accurate tissue phantoms are difficult to design due to the complex non-linear viscoelastic properties of real soft tissues. A composite hydrogel, resulting from a mix of poly(vinyl) alcohol and phytagel, is able to reproduce the viscoelastic responses of different soft tissues due to its compositional tunability. The aim of this work is to demonstrate the flexibility of the composite hydrogel in mimicking the interactions between surgical tools and various soft tissues, such as brain, lung and liver. Therefore compressive stiffness, insertion forces and frictional forces were used as matching criteria to determine the hydrogel compositions for each soft tissue. A full map of the behaviour of the synthetic material is provided for these three characteristics and the compositions found to best match the mechanical response of brain, lung and liver are reported. The optimised hydrogel samples are then tested and shown to mimic the behaviour of the three tissues with unprecedented fidelity. The effect of each hydrogel constituent on the compressive stiffness, needle insertion and frictional forces is also detailed in this work to explain their individual contributions and synergistic effects. This study opens important opportunities for the realisation of surgical planning and training devices and tools for in-vitro tissue testing.

Performance of multiphase scaffolds for bone repair based on two-photon polymerized poly(d,l-lactide-co-ɛ-caprolactone), recombinamers hydrogel and nano-HA

Multiphase hybrids were fabricated from poly(d,l-lactide-co-ɛ-caprolactone) (PLCL) copolymer scaffolds impregnated with silk-elastin-like recombinamers (SELRs) hydrogel containing 2 wt% hydroxyapatite nanoparticles (nHA). The PLCL scaffolds, triply-periodic minimal surface geometry, were manufactured using two-photon stereolithography. In vitro degradation studies were conducted on PLCL scaffolds in inflamed tissue mimic media (pH ~ 4.5–6.5) or phosphate buffered saline (PBS) at 37 °C. Compression test revealed instant shape recovery of PLCL scaffolds after compression to 70% strain, ideal for arthroscopic delivery. Degradation of these scaffolds was accelerated in acidic media, where mass loss and compressive properties at day 56 were about 2–6 times lower than the scaffolds degraded in PBS. No significant difference was seen in the compressive properties between PLCL scaffolds and the hybrids due to the order of magnitude difference between the hydrogels and the PLCL scaffolds. Moreover, degradation properties of the hybrids did not significantly change by inclusion of SELR+/−nHA nanocomposite hydrogels. The hybrids lost approximately 40% and 84% of their initial weight and mechanical properties, respectively after 112 days of degradation. Cytotoxicity assessment revealed no cytotoxic effects of PLCL or PLCL-SELR+/−2%nHA scaffolds on bone marrow-derived human Mesenchymal Stem Cells. These findings highlight the potential of these hybrid constructs for bone and cartilage repair.

Microfluidics Fabrication of Soft Microtissues and Bottom‐Up Assembly

AbstractSoft microtissues comprising living cells and supportive matrices have attracted the attention of researchers for their potential as in vitro organ models that represent the patient's tissue heterogeneity, as well as building blocks for artificial organs or regenerative tissues. Microfluidics is known for its capability to produce monodisperse microstructures in high‐throughput. This review summarizes the progress on microfluidics fabrication of hydrogel‐based microstructures and soft microtissues, and the challenges faced by this field. It mainly focuses on the strengths and limitations of microfluidics fabrication of extracellular matrix (ECM)‐based microtissues as in vitro tissue mimics. ECM‐based microtissues hold promise to alter the course of regenerative and precision medicine.

Cartilage tissue formation through assembly of microgels containing mesenchymal stem cells

Current clinical approaches to treat articular cartilage degeneration provide only a limited ability to regenerate tissue with long-term durability and functionality. In this application, injectable bulk hydrogels and microgels containing stem cells can provide a suitable environment for tissue regeneration. However insufficient cell–cell interactions, low differentiation efficiency and poor tissue adhesion hinder the formation of high-quality hyaline type cartilage. Here, we have designed a higher order tissue-like structure using injectable cell-laden microgels as the building blocks to achieve human bone marrow-derived mesenchymal stem cell (hBMSC) long-term maintenance and chondrogenesis. We have demonstrated that a 4-arm poly(ethylene glycol)-N-hydroxysuccinimide (NHS) crosslinker induces covalent bonding between the microgel building blocks as well as the surrounding tissue mimic. The crosslinking process assembles the microgels into a 3D construct and preserves the viability and cellular functions of the encapsulated hBMSCs. This assembled microgel construct encourages upregulation of chondrogenic markers in both gene and glycosaminoglycan (GAG) expression levels. In addition, the regenerated tissue in the assembled microgels stained positively with Alcian blue and Safranin O exhibiting unique hyaline-like cartilage features. Furthermore, the immunostaining showed a favourable distribution and significantly higher content of type II collagen in the assembled microgels when compared to both the bulk hydrogel and pellet cultures. Collectively, this tissue adhesive hBMSC-laden microgel construct provides potential clinical opportunities for articular cartilage repair and other applications in regenerative medicine. Statement of SignificanceA reliable approach to reconstruct durable and fully functional articular cartilage tissue is required for effective clinical therapies. Here, injectable hydrogels together with cell-based therapies offer new treatment strategies in cartilage repair. For effective cartilage regeneration, the injectable hydrogel system needs to be bonded to the surrounding tissue and at the same time needs to be sufficiently stable for prolonged chondrogenesis. In this work, we utilised injectable hBMSC-laden microgels as the building blocks to create an assembled construct via N-hydroxysuccinimide-amine coupling. This crosslinking process also allows for rapid bonding between the assembled microgels and a surrounding tissue mimic. The resultant assembled microgel-construct provides both a physically stable and biologically dynamic environment for hBMSC chondrogenesis, leading to the production of a mature hyaline type cartilage structure.

Expression of H3.3 G34W Distinguishes Giant Cell Tumor of Bone From Its Major Giant Cell-containing Bone and Soft Tissue Mimics, in Particular Aneurysmal Bone Cyst and Giant Cell Tumor of Soft Tissue

*Department of Pathology, Ghent University Hospital †CRIG, Cancer Research Institute Ghent Ghent University, Ghent, Belgium The author did not received funding for this work from any of the following organizations: National Institutes of Health (NIH); Wellcome Trust; Howard Hughes Medical Institute (HHMI); or others. The author declares no conflict of interest.

Sparse Ultrasound Image Reconstruction From a Shape-Sensing Single-Element Forward-Looking Catheter.

Minimally invasive procedures, such as intravascular and intracardiac interventions, may benefit from guidance with forward-looking (FL) ultrasound. In this work, we investigate FL ultrasound imaging using a single-element transducer integrated in a steerable catheter, together with an optical shape sensing (OSS) system. We tested the feasibility of the proposed device by imaging the surface of a tissue-mimicking (TM) phantom and an ex vivo human carotid plaque. While manually steering the catheter tip, ultrasound A-lines are acquired at 60 Hz together with the catheter shape from the OSS system, resulting in a two-dimensional sparse and irregularly sampled data set. We implemented an adaptive Normalized Convolution (NC) algorithm to interpolate the sparse data set by applying an anisotropic Gaussian kernel that is rotated according to the local direction of the catheter scanning pattern. To choose the Gaussian widths tangential ( ${\sigma _t}$) and normal ( ${\sigma _n}$) to the scanning pattern, an exhaustive search was implemented based on RMSE computation on simulated data. Simulations showed that the sparse data set contains only 5% of the original information. The chosen widths, ${\sigma _n} = \text{250}\;\mu {\textrm{m}}$ and ${\sigma _t} = \text{100}\;\mu{\textrm{m}}$, are used to successfully reconstruct the surface of the phantom with a contrast ratio of 0.9. The same kernel is applied successfully to the carotid plaque data. The proposed approach enables FL imaging with a single ultrasound element, mounted on a steerable device. This principle may find application in a variety of image-guided interventions, such as chronic total occlusion (CTO) recanalization.

Controlled drug release from ultrasound-visualized elastic eccentric microcapsules using different resonant modes.

Ultrasound controlled drug delivery and release has attracted increased attention for targeted delivery of drug. In this report, we present a strategy for targeted drug delivery by using ultrasound to image the location of drug carriers, as well as simultaneously controlling the release rate of drug from elastic eccentric microcapsules (EEMs), based on their mode shapes (MSs) and resonant natural frequencies (NFs). We prepared a series of EEMs with various diameters of inner spherical cavities using a microfluidic chip. The EEMs could be visualized by an ultrasound imaging system within a tissue mimic (i.e. phantom). Using theoretical modeling techniques, we investigated the effects of MSs and NFs on the resonant modes of EEMs. Guided by this modelling, we applied external ultrasonic stimuli at various levels of low frequency to regulate the release rate of Rhodamine 6G (R6G, as a model drug) from EEMs. To further demonstrate the control of drug release and evaluate the efficacy of the encapsulated drugs on cancer cells, we released an anticancer drug, doxorubicin hydrochloride (DOX), from the EEMs and tested the viability of cancer cells in vitro. The results show that this novel strategy holds great promise towards development of a controlled drug release system visualized and triggered by ultrasound.

Effect of Tissue Inhomogeneity in Soft Tissue Sarcomas: From Real Cases to Numerical and Experimental Models

Electrochemotherapy is an established treatment option for patients with superficially metastatic tumors, mainly malignant melanoma and breast cancer. Based on preliminary experiences, electrochemotherapy has the potential to be translated in the treatment of larger and deeper neoplasms, such as soft tissue sarcomas. However, soft tissue sarcomas are characterized by tissue inhomogeneity and, consequently, by variable electrical characteristic of tumor tissue. The inhomogeneity in conductivity represents the cause of local variations in the electric field intensity. Crucially, this fact may hamper the achievement of the electroporation threshold during the electrochemotherapy procedure. In order to evaluate the effect of tissue inhomogeneity on the electric field distribution, we first performed ex vivo analysis of some clinical cases to quantify the inhomogeneity area. Subsequently, we performed some simulations where the electric field intensity was evaluated by means of finite element analysis. The results of the simulation models are finally compared to an experimental model based on potato and tissue mimic materials. Tissue mimic materials are materials where the conductivity can be suitably designed. The coupling of computation and experimental results could be helpful to show the effect of the inhomogeneity in terms of variation in electric field distribution and characteristics.

Solitary Fibrous Tumour of Pelvic Soft Tissue Mimicking A Prostatic Mass: Diagnosis and Management

Solitary fibrous tumor (SFT) is a rare soft tissue tumor occurring rarely in extrapleural sites like the pelvis. We here present a case of SFT of the pelvis which was initially diagnosed radiologically as a mass arising from prostate and on biopsy found to be a solitary fibrous tumor. On exploration, there was a well encapsulated tumor in retro-vesical space separate from prostate. Histopathology with Immuno-histochemistry confirmed the diagnosis of SFT. We retrospectively reviewed the literature to avoid such confusion in future. Pubmed search was made with the following keywords: solitary fibrous tumor, treatment, soft tissue, pelvis, radiology, and histopathology.

Tunable denture adhesives using biomimetic principles for enhanced tissue adhesion in moist environments.

Mussel adhesive proteins have proven to be promising biomimetic adhesive candidates for soft tissues and here for the first time we have adapted marine adhesive technology into a denture fixative application. Importantly, we have incorporated a soft tissue mimic in our in vitro adhesion technique that more closely resembles the oral mucosa than previously studied substrates. The novel biomimetic-modified adhesives showed the ability to score the highest adhesive bonding out of all the formulations included in this study, across all moisture levels. This paper will be of major interest to the Acta Biomaterialia readership since the study has illustrated the potential of biomimetic principles in the design of effective prosthodontic tissue adhesives in a series of purpose-designed in vitro experiments in the context of the challenging features of the oral environment.

Models and tissue mimics for brain shift simulations

Capturing the deformation of human brain during neurosurgical operations is an extremely important task to improve the accuracy or surgical procedure and minimize permanent damage in patients. This study focuses on the development of an accurate numerical model for the prediction of brain shift during surgical procedures and employs a tissue mimic recently developed to capture the complexity of the human tissue. The phantom, made of a composite hydrogel, was designed to reproduce the dynamic mechanical behaviour of the brain tissue in a range of strain rates suitable for surgical procedures. The use of a well-controlled, accessible and MRI compatible alternative to real brain tissue allows us to rule out spurious effects due to patient geometry and tissue properties variability, CSF amount uncertainties, and head orientation. The performance of different constitutive descriptions is evaluated using a brain–skull mimic, which enables 3D deformation measurements by means of MRI scans. Our combined experimental and numerical investigation demonstrates the importance of using accurate constitutive laws when approaching the modelling of this complex organic tissue and supports the proposal of a hybrid poro-hyper-viscoelastic material formulation for the simulation of brain shift.

The Role of Vasculature Engineering in Dental Pulp Regeneration

Creating an optimal microenvironment that supports angiogenesis, cell-cell cross talk, cell migration, and differentiation is crucial for pulp/dentin regeneration. It was shown that dental stem cells being seeded onto a scaffold and transplanted in vivo could give rise to a new tissue similar to that of the native pulp. However, the unique structure of the tooth with a pulp space encased within hard dentin allows only a single blood supply from a small apical opening located at the apex of the root canals. Therefore, a further strategy that can address this limitation such as the incorporation of endothelial/endothelial progenitor cells or cells with high angiogenic potential into the transplant is required so that the added cells can contribute to the vascularization within the implant. However, the placement of 2 or more different cell types inside 3-dimensional porous scaffolds is technologically challenging. In contrast to the conventional scaffolding approach, self-assembly of monodispersed cells into 3-dimensional tissue mimics permits true physiological interactions between and among different types of cells without any influence from a secondary material. In this review, we discuss potential strategies that can be used in vasculature engineering in dental pulp regeneration with a specific emphasis on combining prevascularization and scaffold-based or scaffold-free approaches.

Surface Enhanced Spatially Offset Raman Spectroscopy Detection of Neurochemicals Through the Skull.

The ability to noninvasively detect neurotransmitters through the skull would aid in understanding brain function and the development of neurological diseases. Surface enhanced spatially offset Raman spectroscopy (SESORS) is a powerful technique that combines the sensitivity of surface-enhanced Raman spectroscopy (SERS) with the ability of spatially offset Raman spectroscopy (SORS) to probe subsurface layers. Here we present SERS measurements of neurotransmitters (melatonin, serotonin, and epinephrine) at various concentrations followed by the SESORS measurements of the neurotransmitters to a concentration as low as 100 μM in a brain tissue mimic through a cat skull. Principal components analysis was performed to distinguish between the surface bone layer and the subsurface layer, comprised of a brain tissue mimic modified with neurotransmitters, and to determine if each individual neurotransmitter could be accurately identified.

Pattern analysis of laser-tattoo interactions for picosecond- and nanosecond-domain 1,064-nm neodymium-doped yttrium-aluminum-garnet lasers in tissue-mimicking phantom

During laser treatment for tattoo removal, pigment chromophores absorb laser energy, resulting in fragmentation of the ink particles via selective photothermolysis. The present study aimed to outline macroscopic laser-tattoo interactions in tissue-mimicking (TM) phantoms treated with picosecond- and nanosecond-domain lasers. Additionally, high-speed cinematographs were captured to visualize time-dependent tattoo-tissue interactions, from laser irradiation to the formation of photothermal and photoacoustic injury zones (PIZs). In all experimental settings using the nanosecond or picosecond laser, tattoo pigments fragmented into coarse particles after a single laser pulse, and further disintegrated into smaller particles that dispersed toward the boundaries of PIZs after repetitive delivery of laser energy. Particles fractured by picosecond treatment were more evenly dispersed throughout PIZs than those fractured by nanosecond treatment. Additionally, picosecond-then-picosecond laser treatment (5-pass-picosecond treatment + 5-pass-picosecond treatment) induced greater disintegration of tattoo particles within PIZs than picosecond-then-nanosecond laser treatment (5-pass-picosecond treatment + 5-pass-nanosecond treatment). High-speed cinematography recorded the formation of PIZs after repeated reflection and propagation of acoustic waves over hundreds of microseconds to a few milliseconds. The present data may be of use in predicting three-dimensional laser-tattoo interactions and associated reactions in surrounding tissue.

3D Microtissue Models to Analyze the Effects of Ultralow Dose LPS on Vascular Sprouting Dynamics in the Tumor Microenvironment.

Lipopolysaccharide (LPS) plays a major role in innate immune responses and has been shown to impact vascular dynamics when present at high concentrations. However, the impact of ultralow levels of LPS (<100 pg/mL), present in the body during states of chronic inflammation, on vascular dynamics is unclear. In this study, we have integrated a 3D collagen hydrogel tissue mimic with advanced imaging and cell characterization assays to assess the potential impact of chronic inflammation on vascular dynamics, and uncover any alterations in the vascular response to low vs high dose LPS in the context of tumor progression. Accounting for both frequency of sprouting and invasiveness of the sprouts, the treatments of ultralow dose LPS with vascular endothelial growth factor (VEGF), a potent angiogenic promoter and present in excess in the tumor microenvironment, produced enhanced vascular development of human brain microvascular endothelial cells (HBMECs) in our in vitro model. There was no evidence of altered proliferation or apoptosis among the various VEGF treatment groups, indicating an enhanced migratory endothelial cell phenotype results from exposure to ultralow dose LPS with VEGF. The lack of enhanced vascular development upon treatments of high doses of LPS in the presence of VEGF could be partially attributed to an LPS dose-dependent increase in the activation of NF-κB. This study provides insight into the dynamic regulation of vascular development by varying levels of LPS and the potential role of chronic inflammation to prime a pro-angiogenic microenvironment and contribute to tumor progression.

Imaging tissue-mimic with light sheet microscopy: A comparative guideline

Tissue mimics (TMs) on the scale of several hundred microns provide a beneficial cell culture configuration for in vitro engineered tissue and are currently under the spotlight in tissue engineering and regenerative medicine. Due to the cell density and size, TMs are fairly inaccessible to optical observation and imaging within these samples remains challenging. Light Sheet Fluorescence Microscopy (LSFM)- an emerging and attractive technique for 3D optical sectioning of large samples- appears to be a particularly well-suited approach to deal with them. In this work, we compared the effectiveness of different light sheet illumination modalities reported in the literature to improve resolution and/or light exposure for complex 3D samples. In order to provide an acute and fair comparative assessment, we also developed a systematic, computerized benchmarking method. The outcomes of our experiment provide meaningful information for valid comparisons and arises the main differences between the modalities when imaging different types of TMs.

Peptide and nucleic acid-directed self-assembly of cationic nanovehicles through giant unilamellar vesicle modification: Targetable nanocomplexes for in vivo nucleic acid delivery.

The efficient targeted delivery of nucleic acids in vivo provides some of the greatest challenges to the development of genetic therapies. Giant unilamellar lipid vesicles (GUVs) have been used mainly as cell and tissue mimics and are instrumental in studying lipid bilayers and interactions. Here, the GUVs have been modified into smaller nanovesicles. We have then developed novel nanovesicle complexes comprising self-assembling mixtures of the nanovesicles, plasmid DNA or siRNA, and targeting peptide ligands. Their biophysical properties were studied and their transfection efficiency was investigated. They transfected cells efficiently without any associated cytotoxicity and with targeting specificity, and in vivo they resulted in very high and tumour-specific uptake and in addition, efficiently transfected the lung. The peptide-targeted nanovesicle complexes allow for the specific targeted enhancement of nucleic acid delivery with improved biosafety over liposomal formulations and represent a promising tool to improve our arsenal of safe, non-viral vectors to deliver therapeutic cargos in a variety of disorders.