In vitro studies on space-conforming self-assembling silk hydrogels as a mesenchymal stem cell-support matrix suitable for minimally invasive brain application

Abstract

Advanced cell therapies require robust delivery materials and silk is a promising contender with a long clinical track record. Our aim was to optimise self-assembling silk hydrogels as a mesenchymal stem cell (MSC)-support matrix that would allow future minimally invasive brain application. We used sonication energy to programme the transition of silk (1–5% w/v) secondary structure from a random coil to a stable β-sheet configuration. This allowed fine tuning of self-assembling silk hydrogels to achieve space conformity in the absence of any silk hydrogel swelling and to support uniform cell distribution as well as cell viability. Embedded cells underwent significant proliferation over 14 days in vitro, with the best proliferation achieved with 2% w/v hydrogels. Embedded MSCs showed significantly better viability in vitro after injection through a 30G needle when the gels were in the pre-gelled versus post-gelled state. Silk hydrogels (4% w/v) with physical characteristics matching brain tissue were visualised in preliminary in vivo experiments to exhibit good space conformity in an ischemic cavity (intraluminal thread middle cerebral artery occlusion model) in adult male Sprague-Dawley rats (n = 3). This study informs on optimal MSC-hydrogel matrix conditions for minimally invasive application as a platform for future experiments targeting brain repair.

Evaluation of Neurosecretome from Mesenchymal Stem Cells Encapsulated in Silk Fibroin Hydrogels

“…These in vivo studies were performed using SF solutions with a polymer concentration of 2%. It has been previously shown that the viability of MSCs within SF hydrogels decreases drastically in 4–6% polymer concentrations 31,32 with stiffness ranges that possibly are not adequate for intracerebral applications. Consequently, gels with a fibroin concentration of 2% were used in this study, to encapsulate cells and examine their neurosecretome activity.

Figure 1Characterization of silk fibroin hydrogels.

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“…In relation to silk, a previous study reported that MSCs survive for up to 10 days in culture when encapsulated in SF hydrogels while they have a moderate proliferation rate 56 . Parallel studies have examined the effect of SF stiffness on MSCs survival, finding that MSCs viability inside SF hydrogels is drastically reduced at polymer concentrations higher than 4–6% 31,32 .…”

“…In our work, we tested cell adhesion under serum conditions to establish a link with the secretome analysis and our previous in vivo study 23 , where MSCs implantation with SF hydrogels were performed in the brain striatum, exposed to extracellular matrix components regularly found in serum. We also sought to establish a comparison with previous studies that examined MSCs adhesion and growth on the top or inside SF under serum conditions 31,32,52 . Specific research is needed to clarify the influence of non-serum environments in the cellular adherence and secretome activity of MSCs in contact with SF.…”

Neurorestoration Approach by Biomaterials in Ischemic Stroke

“…The most widespread natural compounds for application in the restoration of tissue defects and improvements in the adverse microenvironment are fibrin, HA-methylcellulose, chitosan, and collagen (Hopkins et al, 2013;Medelin et al, 2018;Osama et al, 2018).…”

Allogeneic Mesenchymal Stem Cells and Biomaterials: The Perfect Match for Cardiac Repair?

“…In a recent study in rat MI model, cellulose nanofibers modified with chitosan/silk fibroin multilayers was tested, showing a higher cell viability, improved LVEF, and a reduced adverse ventricular remodeling in the treated hearts [ 50 ]. Interestingly, self-assembling silk hydrogels have been designed as support for MSC where controllable gel-kinetics could be modified to achieve uniform cell distribution, viability, and space conformity [ 51 ].…”