The biophysical properties of Basal lamina gels depend on the biochemical composition of the gel

Fluid preservation in brain banking: a review

Fluid preservation is nearly universally used in brain banking to store fixed tissue specimens for future research applications. However, the effects of long-term immersion on neural circuitry and biomolecules are not well characterized. As a result, there is a need to synthesize studies investigating fluid preservation of brain tissue. We searched PubMed and other databases to identify studies measuring the effects of fluid preservation in nervous system tissue. We categorized studies based on the fluid preservative used: formaldehyde solutions, buffer solutions, alcohol solutions, storage after tissue clearing, and cryoprotectant solutions. We identified 91 studies containing 197 independent observations of the effects of long-term storage on cellular morphology. Most studies did not report any significant alterations due to long-term storage. When present, the most frequent alteration was decreased antigenicity, commonly attributed to progressive crosslinking by aldehydes that renders biomolecules increasingly inaccessible over time. To build a mechanistic understanding, we discuss biochemical aspects of long-term fluid preservation. A subset of lipids appears to be chemical altered or extracted over time due to incomplete retention in the crosslinked gel. Alternative storage fluids mitigate the problem of antigen masking but have not been extensively characterized and may have other downsides. We also compare fluid preservation to cryopreservation, paraffin embedding, and resin embedding. Overall, existing evidence suggests that fluid preservation provides maintenance of neural architecture for decades, including precise structural details. However, to avoid the well-established problem of overfixation caused by storage in high concentration formaldehyde solutions, fluid preservation procedures can use an initial fixation step followed by an alternative long-term storage fluid. Further research is warranted on optimizing protocols and characterizing the generalizability of the storage artifacts that have been identified.

The extracellular matrix - immune microenvironment crosstalk in cancer therapy: Challenges and opportunities

Targeting the tumour immune microenvironment (TIME) by cancer immunotherapy has led to improved patient outcomes. However, response to these treatments is heterogeneous and cancer-type dependant. The therapeutic activity of classical cancer therapies such as chemotherapy, radiotherapy, and surgical oncology is modulated by alterations of the TIME. A major regulator of immune cell function and resistance to both immune and classical therapies is the extracellular matrix (ECM). Concurrently, cancer therapies reshape the TIME as well as the ECM, causing both pro- and anti-tumour responses. Accordingly, the TIME-ECM crosstalk presents attractive opportunities to improve therapy outcomes. Here, we review the molecular crosstalk between the TIME and the ECM in cancer and its implications in cancer progression and clinical intervention. Additionally, we discuss examples and future directions of ECM and TIME co-targeting in combination with oncological therapies including surgery, chemotherapy, and radiotherapy.

Small leucine rich proteoglycans: Biology, function and their therapeutic potential in the ocular surface

Small leucine rich proteoglycans (SLRPs) are the largest family of proteoglycans, with 18 members that are subdivided into five classes. SLRPs are small in size and can be present in tissues as glycosylated and non-glycosylated proteins, and the most studied SLRPs include decorin, biglycan, lumican, keratocan and fibromodulin. SLRPs specifically bind to collagen fibrils, regulating collagen fibrillogenesis and the biomechanical properties of tissues, and are expressed at particularly high levels in fibrous tissues, such as the cornea. However, SLRPs are also very active components of the ECM, interacting with numerous growth factors, cytokines and cell surface receptors. Therefore, SLRPs regulate major cellular processes and have a central role in major fundamental biological processes, such as maintaining corneal homeostasis and transparency and regulating corneal wound healing. Over the years, mutations and/or altered expression of SLRPs have been associated with various corneal diseases, such as congenital stromal corneal dystrophy and cornea plana. Recently, there has been great interest in harnessing the various functions of SLRPs for therapeutic purposes. In this comprehensive review, we describe the structural features and the related functions of SLRPs, and how these affect the therapeutic potential of SLRPs, with special emphasis on the use of SLRPs for treating ocular surface pathologies.

A novel modelling and simulation approach for the hindered mobility of charged particles in biological hydrogels

This article presents a novel computational model to study the selective filtering of biological hydrogels due to the surface charge and size of diffusing particles. It is the first model that includes the random three-dimensional fibre orientation and connectivity of the biopolymer network and that accounts for elastic deformations of the fibres by means of beam theory. As a key component of the model, novel formulations are proposed both for the electrostatic and repulsive steric interactions between a spherical particle and a beam. In addition to providing a thorough validation of the model, the presented computational studies yield new insights into the underlying mechanisms of hindered particle mobility, especially regarding the influence of the aforementioned aspects that are unique to this model. It is found that the precise distribution of fibre and thus charge agglomerations in the network have a crucial influence on the mobility of oppositely charged particles and gives rise to distinct motion patterns. Considering the high practical significance for instance with respect to targeted drug release or infection defence, the provided proof of concept motivates further advances of the model towards a truly predictive computational tool that allows a case- and patient-specific assessment for real (biological) systems.

An investigational study of a dual-layer, chorion-free amnion patch as a protective barrier following lumbar laminectomy in a sheep model

The inherent properties of the human amniotic membrane (HAM) suggest its potential for use as a physical barrier during surgery to protect neural elements and vessels from the surrounding environment. The objective of this study was to evaluate the effect of a dual-layer, chorion-free amnion patch (DLAM; ViaShield®, Globus Medical Inc., Audubon, PA, USA) processed from HAM as a protective barrier following lumbar laminectomy in a sheep model. A multiplex immunoassay was performed to quantify the inherent cytokines present in the amnion after processing. Twelve skeletally mature female crossbred Suffolk sheep were randomly divided into two equal post-operative periods (4 and 10 weeks). Each sheep underwent a laminectomy at L3 and L5, and one of the surgical sites randomly received the DLAM treatment. At each postsurgical time point, the extent of epidural fibrosis and neurohistopathological responses at the laminectomy sites was assessed based on epidural fibrosis-dura tenacity scores and decalcified histology, respectively. Immunoassay results showed that inflammatory mediators and immunomodulatory cytokines were present in the amnion after processing, but no proangiogenic cytokines were detected. At 10 weeks, tissue tenacity was significantly less in the DLAM treatment group when compared with the operative control (1.2 ± 0.4 vs. 2.8 ± 0.4, p < 0.05), demonstrating the ability of DLAM to act as a barrier and cover the dura. Gross observations showed fewer fibroblasts in the DLAM group in comparison with the control at both post-operative time points. Fibroblast infiltration analysis indicated that at both 4 and 10 weeks, there were significantly more infiltrated fibroblasts in the operative control sites than in the DLAM-treated sites, expressed as a percentage of the total number of fibroblasts present (4 weeks: 72.3 ± 10.2% vs. 10.8 ± 10.1%, p < .05; 10 weeks: 84.9 ± 15.8% vs. 43.1 ± 11.6%, p < .05). Additionally, fibroblasts travelled further into the dura in the operative control group compared with the DLAM-treated group at both time points. In conclusion, this study found that DLAM reduced fibroblast infiltration and tissue tenacity following lumbar laminectomy in a sheep animal model. These findings support the potential use of DLAM in clinical practice as a protective barrier for neural elements and anterior vessels.

Preventing Obstructions of Nanosized Drug Delivery Systems by the Extracellular Matrix

Although nanosized drug delivery systems are promising tools for the treatment of severe diseases, the extracellular matrix (ECM) constitutes a major obstacle that endangers therapeutic success. Mobility of diffusing species is restricted not only by small pore size (down to as low as 3 nm) but also by electrostatic interactions with the network. This article evaluates commonly used in vitro models of ECM, analytical methods, and particle types with respect to their similarity to native conditions in the target tissue. In this cross-study evaluation, results from a wide variety of mobility studies are analyzed to discern general principles of particle-ECM interactions. For instance, cross-linked networks and a negative network charge are essential to reliably recapitulate key features of the native ECM. Commonly used ECM mimics comprised of one or two components can lead to mobility calculations which have low fidelity to in vivo results. In addition, analytical methods must be tailored to the properties of both the matrix and the diffusing species to deliver accurate results. Finally, nanoparticles must be sufficiently small to penetrate the matrix pores (ideally R_d/p < 0.5; d = particle diameter, p = pore size) and carry a neutral surface charge to avoid obstructions. Larger (R_d/p >> 1) or positively charged particles are trapped.

Engineered basement membranes: from in vivo considerations to cell-based assays

Engineered basement membranes are required to mimic in vivo properties within cell-based assays.

The particle in the spider's web: transport through biological hydrogels

Biological hydrogels such as mucus, extracellular matrix, biofilms, and the nuclear pore have diverse functions and compositions, but all act as selectively permeable barriers to the diffusion of particles. Each barrier has a crosslinked polymeric mesh that blocks penetration of large particles such as pathogens, nanotherapeutics, or macromolecules. These polymeric meshes also employ interactive filtering, in which affinity between solutes and the gel matrix controls permeability. Interactive filtering affects the transport of particles of all sizes including peptides, antibiotics, and nanoparticles and in many cases this filtering can be described in terms of the effects of charge and hydrophobicity. The concepts described in this review can guide strategies to exploit or overcome gel barriers, particularly for applications in diagnostics, pharmacology, biomaterials, and drug delivery.

Interactions between circulating nanoengineered polymer particles and extracellular matrix components in vitro

A simple and modular flow-based system is used to rapidly screen fundamental interactions of soft polymer particles with biologically relevant microenvironments under flow-conditions.

Influence of PEGylation on nanoparticle mobility in different models of the extracellular matrix

Nanoparticle transport inside the extracellular matrix (ECM) is a crucial factor affecting the therapeutic success. In this work, two in vitro ECM models - a neutrally charged collagen I network with an effective pore size of 0.47μm and Matrigel, a basement membrane matrix with strong negative charge and effective pore size of 0.14μm - were assessed for barrier function in the context of diffusing nanoparticles. Nanoparticles with a size of 120nm were coated with poly(ethylene glycol) (PEG) of different molecular weights - 2, 5 and 20kDa - over a range of gradually increasing coating densities - precisely 0.2, 2, 8 and 20PEG/nm². The PEG corona was imaged in its native state without any drying process by atomic force microscopy, revealing that the experimentally determined arrangement of PEG at the surface did not match with what was theoretically expected. In a systematic investigation of nanoparticle mobility via fluorescence recovery after photobleaching, increasing both PEG MW and PEGylation density gradually improved diffusion properties predominately in collagen. Due to its smaller pore size and electrostatic obstruction, diffusion coefficients were about ten times lower in Matrigel than in the collagen network and an extension of the PEG MW and density did not necessarily lead to better diffusing particles. Consequently, collagen gels were revealed to be a poor model for nanoparticle mobility assessment, as neither their pore size nor their electrostatic properties reflect the expected in vivo conditions. In Matrigel, diffusion proceeded according to a sigmoidal increase with gradually increasing PEG densities showing threshold zeta potentials of 11.6mV (PEG_2kDa) and 13.8mV (PEG_5kDa), below which particles were regarded as mobile. Irrespective of the molecular weight particles with a PEGylation density lower than 2PEG/nm² were defined as immobile and those with a PEG coverage of more than 8PEG/nm² as mobile.

A microfluidics approach to study the accumulation of molecules at basal lamina interfaces

For an efficient distribution of drugs and drug carriers through biological barriers such as the vascular system, the size and surface properties of nanoparticles and molecules play a key role. To screen for important parameters which determine the ability of drugs or drug carriers to translocate through complex biological barriers, an in vitro assay which correctly predicts the behavior of those objects in vivo would be highly desirable. Here, we present a microfluidic setup to probe the diffusive spreading of molecules with different net charges and molecular weights through a basal lamina interface - a biopolymer system which contributes to the barrier function of the vascular system and the skin. From our data, we find a charge dependent accumulation of molecules at the gel interface which is consistent with transient binding of those molecules to the gel constituents. We also observe a similar charge-dependent accumulation of molecules in living mice where the test molecules colocalize with collagen IV, a key component of the basal lamina. Our assay may serve as a platform to perform penetration experiments with even more complex interfaces combining cellular barriers with biopolymer coatings.