How to build a brain

Your cells are magnificent little things, every single one is full of complex microsystems all working together to keep you going. They’re more intricate and advanced than any machines we can make, but sometimes… they need a little help to get going. Stem cells are like tiny teenagers, they’re full of potential but they need a kick in the pants to get going, and that’s where I come in. After a stroke, patients are left with chunks of damaged brain tissue. Now, instead of trying to rebuild the incredibly complex human brain from scratch, I’d much give cells the support and encouragement they need to rebuild it themselves. My research goal is to rebuild damaged brain tissue, but in truth, stem cells will be doing all the actual building, I’m just making materials that tell them how to build a brain

Novel Growth Factor Delivery Systems from Self-Assembling Peptide (SAP) Hydrogels

Growth factors are important signalling molecules in regenerative medicine and tissue engineering, but their inherent instability, lasting only minute to hours in vivo, presents an obstacle to sustained and controlled delivery. This is particularly difficult to achieve in the brain, where the blood brain barrier (BBB) prevents systemic delivery. For this reason, much research is currently directed at incorporating growth factors into supportive tissue engineering materials that mimic the natural extracellular matrix (ECM). In this case temporally controlled and sequential delivery must come from selectively delaying the release of some growth factors from the material. Here, we aim to develop novel growth factor delivery systems to provide temporally controlled growth factor delivery from self-assembling peptide (SAP) hydrogel materials specifically. We use minimalist and tissue-specific Fmoc-SAP hydrogels, a novel class of material designed around biologically recognisable peptide sequences, engineered to self-assemble at physiological conditions into supportive nanofibres. We demonstrate the biocompatibility of three distinct sequences in vivo with cell grafts into an intact brain, as well as the tissue-specificity of the materials, with the brain protein laminin derived SAPs showing superior performance. We also demonstrate their ability to improve cell graft treatment efficacy in an ischemic brain injury in rats, showing improved sensorimotor recovery, increased neuronal differentiation, and reduced cortical atrophy compared to the unsupported cell graft treatment. We demonstrate that these materials stabilise growth factors to provide sustained delivery, with release detected out to 6 weeks. Sustained delivery of growth factors is a common goal in growth factor delivery, and here we go beyond that by providing novel systems for temporally controlled delivery, allowing the sequential delivery of multiple growth factors required to achieve their full therapeutic potential. We have successfully demonstrated systems to provide a short delay of 4 hours, a long delay of 6 days, and stimuli-responsive control of the delivery profiles. Covalent attachment of the polysaccharide chitosan to the growth factor increased physical associations with the SAP nanofibres, delaying its release by 4 hours. Using emulsion electrospinning to create polymer nanofibres loaded with growth factor, we then cut short fibres to mix into the SAP hydrogel. The polymer provided an additional barrier to diffusion, delaying the release from the hydrogel by 6 days. Covalent attachment of growth factor to UV-sensitive nanoparticles allowed for counter-intuitive control over growth factor delivery, with UV exposure reducing the growth factor released. We were also able to use this system to tune the shape of the temporal release profile to provide a constant dose delivery with no initial burst. These novel systems demonstrate an improved level of control of growth factor delivery without sacrificing the tissue engineering material properties, and represent a significant contribution to the field of tissue engineering

Extraction of DNA staining dyes from DNA using hydrophobic ionic liquids

The partition of oligonucleotides and DNA staining dyes into a few hydrophobic ionic liquids has been studied, where the oligonucleotides remain in the aqueous phase and all the DNA staining dyes are extracted in the ionic liquid phase, allowing the separation of these two.University of Waterloo || Canadian Foundation for Innovation || Natural Sciences and Engineering Research Council || Ontario Ministry of Research and Innovation |

Peptide-Based Scaffolds Support Human Cortical Progenitor Graft Integration to Reduce Atrophy and Promote Functional Repair in a Model of Stroke

Stem cell transplants offer significant hope for brain repair following ischemic damage. Pre-clinical work suggests that therapeutic mechanisms may be multi-faceted, incorporating bone-fide circuit reconstruction by transplanted neurons, but also protection/regeneration of host circuitry. Here, we engineered hydrogel scaffolds to form "bio-bridges" within the necrotic lesion cavity, providing physical and trophic support to transplanted human embryonic stem cell-derived cortical progenitors, as well as residual host neurons. Scaffolds were fabricated by the self-assembly of peptides for a laminin-derived epitope (IKVAV), thereby mimicking the brain's major extracellular protein. Following focal ischemia in rats, scaffold-supported cell transplants induced progressive motor improvements over 9 months, compared to cell- or scaffold-only implants. These grafts were larger, exhibited greater neuronal differentiation, and showed enhanced electrophysiological properties reflective of mature, integrated neurons. Varying graft timing post-injury enabled us to attribute repair to both neuroprotection and circuit replacement. These findings highlight strategies to improve the efficiency of stem cell grafts for brain repair

Scaffolds formed via the non-equilibrium supramolecular assembly of the synergistic ECM peptides RGD and PHSRN demonstrate improved cell attachment in 3D

Self-assembling peptides (SAPs) are a relatively new class of low molecular weight gelators which immobilize their solvent through the spontaneous formation of (fibrillar) nanoarchitectures. As peptides are derived from proteins, these hydrogels are ideal for use as biocompatible scaffolds for regenerative medicine. Importantly, due to the propensity of peptide sequences to act as signals in nature, they are easily functionalized to be cell instructive via the inclusion of bioactive epitopes. In nature, the fibronectin peptide sequence, arginine-glycine-aspartic acid (RGD) synergistically promotes the integrin α5β1mediated cell adhesion with another epitope, proline-histidine-serine-arginine-asparagine (PHSRN); however most functionalization strategies focus on RGD alone. Here, for the first time, we discuss the biomimetic inclusion of both these sequences within a self-assembled minimalistic peptide hydrogel. Here, based on our work with Fmoc-FRGDF (N-flourenylmethyloxycarbonyl phenylalanine-arginine-glycine-aspartic acid-phenylalanine), we show it is possible to present two epitopes simultaneously via the assembly of the epitopes by the coassembly of two SAPs, and compare this to the effectiveness of the signals in a single peptide; Fmoc-FRGDF: Fmoc-PHSRN (N-flourenylmethyloxycarbonyl-proline-histidine-serine-arginine-asparagine) and Fmoc-FRGDFPHSRN (N-flourenylmethyloxycarbonyl-phenylalanine-arginine-glycine-asparticacidphenylalanine- proline-histidine-serine-arginine-asparagine). We show both produced self-supporting hydrogel underpinned by entangled nanofibrils, however, the stiffness of coassembled hydrogel was over two orders of magnitude higher than either Fmoc-FRGDF or Fmoc-FRGDFPHSRN alone. In-vitro three-dimensional cell culture of human mammary fibroblasts on the hydrogel mixed peptide showed dramatically improved adhesion, spreading and proliferation over Fmoc-FRGDF. However, the long peptide did not provide effective cell attachment. The results demonstrated the selective synergy effect of PHSRN with RGD is an effective way to augment the robustness and functionality of self-assembled bioscaffolds

Coassembled nanostructured bioscaffold reduces the expression of proinflammatory cytokines to induce apoptosis in epithelial cancer cells

The local inflammatory environment of the cell promotes the growth of epithelial cancers. Therefore, controlling inflammation locally using a material in a sustained, non-steroidal fashion can effectively kill malignant cells without significant damage to surrounding healthy cells. A promising class of materials for such applications is the nanostructured scaffolds formed by epitope presenting minimalist self-assembled peptides; these are bioactive on a cellular length scale, while presenting as an easily handled hydrogel. Here, we show that the assembly process can distribute an anti-inflammatory polysaccharide, fucoidan, localized to the nanofibers within the scaffold to create a biomaterial for cancer therapy. We show that it supports healthy cells, while inducing apoptosis in cancerous epithelial cells, as demonstrated by the significant down-regulation of gene and protein expression pathways associated with epithelial cancer progression. Our findings highlight an innovative material approach with potential applications in local epithelial cancer immunotherapy and drug delivery

Solubility of nanocrystalline scorodite and amorphous ferric arsenate: Implications for stabilization of arsenic in mine wastes

Solubility experiments were performed on nanocrystalline scorodite and amorphous ferric arsenate. Nanocrystalline scorodite occurs as stubby prismatic crystals measuring about 50 nm and having a specific surface area of 39.88 ± 0.07 m2/g whereas ferric arsenate is amorphous and occurs as aggregated clusters measuring about 50–100 nm with a specific surface area of 17.95 ± 0.19 m2/g. Similar to its crystalline counterpart, nanocrystalline scorodite has a solubility of about 0.25 mg/L at around pH 3–4 but has increased solubilities at low and high pH (i.e. 6). Nanocrystalline scorodite dissolves incongruently at about pH > 2.5 whereas ferric arsenate dissolution is incongruent at all the pH ranges tested (pH 2–5). It appears that the solubility of scorodite is not influenced by particle size. The dissolution rate of nanocrystalline scorodite is 2.64 × 10−10 mol m−2 s−1 at pH 1 and 3.25 × 10−11 mol m−2 s−1 at pH 2. These rates are 3–4 orders of magnitude slower than the oxidative dissolution of pyrite and 5 orders of magnitude slower than that of arsenopyrite. Ferric arsenate dissolution rates range from 6.14 × 10−9 mol m−2 s−1 at pH 2 to 1.66 × 10−9 mol m−2 s−1 at pH 5. Among the common As minerals, scorodite has the lowest solubility and dissolution rate. Whereas ferric arsenate is not a suitable compound for As control in mine effluents, nanocrystalline scorodite that can be easily precipitated at ambient pressure and temperature conditions would be satisfactory in meeting the regulatory guidelines at pH 3–4

Dynamic and Responsive Growth Factor Delivery from Electrospun and Hydrogel Tissue Engineering Materials

Tissue engineering scaffolds are designed to mimic physical, chemical, and biological features of the extracellular matrix, thereby providing a constant support that is crucial to improved regenerative medicine outcomes. Beyond mechanical and structural support, the next generation of these materials must also consider the more dynamic presentation and delivery of drugs or growth factors to guide new and regenerating tissue development. These two aspects are explored expansively separately, but they must interact synergistically to achieve optimal regeneration. This review explores common tissue engineering materials types, electrospun polymers and hydrogels, and strategies used for incorporating drug delivery systems into these scaffolds.K. F. Bruggeman was supported by a Natural Sciences and Engineering Research Council of Canada (NSERC) Postgraduate Scholarship Doctoral (PGS D) award. R. J. Williams was supported via an Alfred Deakin Research Fellowship (NHMRC Dementia Research Leadership Fellowship, GNT1135657)

Dynamic and responsive growth factor delivery from electrospun and hydrogel tissue engineering materials

Tissue engineering scaffolds are designed to mimic physical, chemical, and biological features of the extracellular matrix, thereby providing a constant support that is crucial to improved regenerative medicine outcomes. Beyond mechanical and structural support, the next generation of these materials must also consider the more dynamic presentation and delivery of drugs or growth factors to guide new and regenerating tissue development. These two aspects are explored expansively separately, but they must interact synergistically to achieve optimal regeneration. This review explores common tissue engineering materials types, electrospun polymers and hydrogels, and strategies used for incorporating drug delivery systems into these scaffolds