Uncovering the relationship between macrophages and polypropylene surgical mesh

Currently, in vitro testing examines the cytotoxicity of biomaterials but fails to consider how materials respond to mechanical forces and the immune response to them; both are crucial for successful long-term implantation. A notable example of this failure is polypropylene mid-urethral mesh used in the treatment of stress urinary incontinence (SUI). The mesh was largely successful in abdominal hernia repair but produced significant complications when repurposed to treat SUI. Developing more physiologically relevant in vitro test models would allow more physiologically relevant data to be collected about how biomaterials will interact with the body. This study investigates the effects of mechanochemical distress (a combination of oxidation and mechanical distention) on polypropylene mesh surfaces and the effect this has on macrophage gene expression. Surface topology of the mesh was characterised using SEM and AFM; ATR-FTIR, EDX and Raman spectroscopy was applied to detect surface oxidation and structural molecular alterations. Uniaxial mechanical testing was performed to reveal any bulk mechanical changes. RT-qPCR of selected pro-fibrotic and pro-inflammatory genes was carried out on macrophages cultured on control and mechanochemically distressed PP mesh. Following exposure to mechanochemical distress the mesh surface was observed to crack and craze and helical defects were detected in the polymer backbone. Surface oxidation of the mesh was seen after macrophage attachment for 7 days. These changes in mesh surface triggered modified gene expression in macrophages. Pro-fibrotic and pro-inflammatory genes were upregulated after macrophages were cultured on mechanochemically distressed mesh, whereas the same genes were down-regulated in macrophages exposed to control mesh. This study highlights the relationship between macrophages and polypropylene surgical mesh, thus offering more insight into the fate of an implanted material than existing in vitro testing.

Surfactant-free gelatin-stabilised biodegradable polymerised high internal phase emulsions with macroporous structures

High internal phase emulsion (HIPE) templating is a well-established method for the generation of polymeric materials with high porosity (>74%) and degree of interconnectivity. The porosity and pore size can be altered by adjusting parameters during emulsification, which affects the properties of the resulting porous structure. However, there remain challenges for the fabrication of polyHIPEs, including typically small pore sizes (∼20-50 μm) and the use of surfactants, which can limit their use in biological applications. Here, we present the use of gelatin, a natural polymer, during the formation of polyHIPE structures, through the use of two biodegradable polymers, polycaprolactone-methacrylate (PCL-M) and polyglycerol sebacate-methacrylate (PGS-M). When gelatin is used as the internal phase, it is capable of stabilising emulsions without the need for an additional surfactant. Furthermore, by changing the concentration of gelatin within the internal phase, the pore size of the resulting polyHIPE can be tuned. 5% gelatin solution resulted in the largest mean pore size, increasing from 53 μm to 80 μm and 28 μm to 94 µm for PCL-M and PGS-M respectively. In addition, the inclusion of gelatin further increased the mechanical properties of the polyHIPEs and increased the period an emulsion could be stored before polymerisation. Our results demonstrate the potential to use gelatin for the fabrication of surfactant-free polyHIPEs with macroporous structures, with potential applications in tissue engineering, environmental and agricultural industries.

Self-Assembling Peptide Hydrogel Matrices Improve the Neurotrophic Potential of Human Adipose-Derived Stem Cells

Despite advances in microsurgical techniques, treatment options to restore prior function following peripheral nerve injury remain unavailable, and autologous nerve grafting remains the therapy of choice. Recent experimental work has focused on the development of artificial constructs incorporating smart biomaterials and stem cells, aspiring to match/improve the outcomes of nerve autografting. Chemically stimulated human adipose-derived stem cells (dhASC) can improve nerve regeneration outcomes; however, these properties are lost when chemical stimulation is withdrawn, and survival rate upon transplantation is low. It is hypothesized that interactions with synthetic hydrogel matrices could maintain and improve neurotrophic characteristics of dhASC. dhASC are cultured on PeptiGel-Alpha 1 and PeptiGel-Alpha 2 self-assembling peptide hydrogels, showing comparable viability to collagen I control gels. Culturing dhASC on Alpha 1 and Alpha 2 substrates allow the maintenance of neurotrophic features, such as the expression of growth factors and neuroglial markers. Both Alpha 1 and Alpha 2 substrates are suitable for the culture of peripheral sensory neurons, permitting sprouting of neuronal extensions without the need of biological extracellular matrices, and preserving neuronal function. PeptiGel substrates loaded with hdASC are proposed as promising candidates for the development of tissue engineering therapies for the repair of peripheral nerve injuries.

Tuning of hydrogel stiffness using a two-component peptide system for mammalian cell culture

Self-assembling peptide hydrogels (SAPHs) represent emerging cell cultures systems in several biomedical applications. The advantages of SAPHs are mainly ascribed to the absence of toxic chemical cross-linkers, the presence of ECM-like fibrillar structures and the possibility to produce hydrogels with a large range of different mechanical properties. We will present a two-component peptide system with tuneable mechanical properties, consisting of a small pentapeptide (SFFSF-NH2 , SA5N) that acts as a gelator and a larger 21-mer peptide (SFFSF-GVPGVGVPGVG-SFFSF, SA21) designed as a physical cross-linker. The hydrogels formed by different mixtures of the two peptides are made up mainly of antiparallel β-sheet nanofibers entangling in an intricate network. The effect of the addition of SA21 on the morphology of the hydrogels was investigated by atomic force microscopy and transmission electron microscopy and correlated to the mechanical properties of the hydrogel. Finally, the biocompatibility of the hydrogels using 2D cell cultures was tested. © 2018 The Authors. journal Of Biomedical Materials Research Part A Published By Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 535-544, 2019.

Peptide hydrogel in vitro non-inflammatory potential

Peptide‐based hydrogels have attracted significant interest in recent years as these soft, highly hydrated materials can be engineered to mimic the cell niche with significant potential applications in the biomedical field. Their potential use in vivo in particular is dependent on their biocompatibility, including their potential to cause an inflammatory response. In this work, we investigated in vitro the inflammatory potential of a β‐sheet forming peptide (FEFEFKFK; F: phenylalanine, E: glutamic acid; K: lysine) hydrogel by encapsulating murine monocytes within it (3D culture) and using the production of cytokines, IL‐β, IL‐6 and TNFα, as markers of inflammatory response. No statistically significant release of cytokines in our test sample (media + gel + cells) was observed after 48 or 72 h of culture showing that our hydrogels do not incite a pro‐inflammatory response in vitro. These results show the potential biocompatibility of these hydrogels and therefore their potential for in vivo use. The work also highlighted the difference in monocyte behaviour, proliferation and morphology changes when cultured in 2D vs. 3D. © 2016 The Authors Journal of Peptide Science published by European Peptide Society and John Wiley & Sons Ltd.

Controlled Generation of Microspheres Incorporating Extracellular Matrix Fibrils for Three-Dimensional Cell Culture

A growing body of evidence suggests that studying cell biology in classical two-dimensional formats, such as cell culture plasticware, results in misleading, non-physiological findings. For example, some aspects of cancer biology cannot be observed in 2D, but require 3D culture methods to recapitulate observations in vivo. Therefore, we developed a microsphere-based model to permit 3D cell culture incorporating physiological extracellular matrix components. Bio-electrospraying was chosen as it is the most advanced method to produce microspheres, with THP-1 cells as a model cell line. Bio-electrospraying parameters, such as nozzle size, polymer flow rate, and voltage, were systematically optimized to allow stable production of size controlled microspheres containing extracellular matrix material and human cells. We investigated the effect of bio-electrospraying parameters, alginate type and cell concentration on cell viability using trypan blue and propidium iodide staining. Bio-electrospraying had no effect on cell viability nor the ability of cells to proliferate. Cell viability was similarly minimally affected by encapsulation in all types of alginate tested (MVM, MVG, chemical- and food-grade). Cell density of 5 × 10⁶ cells ml^-1 within microspheres was the optimum for cell survival and proliferation. The stable generation of microspheres incorporating cells and extracellular matrix for use in a 3D cell culture will benefit study of many diverse diseases and permit investigation of cellular biology within a 3D matrix.

Sexually dimorphic gene expression in the brains of mature zebrafish

The molecular signalling pathways mediating sexual dimorphism have principally been investigated in the gonads, and to a lesser extent in other organs. The brain plays a central role in coordinating sexual function, including the regulation of reproductive development, maturation and sexual behaviour in both sexes. In this study, we investigated sex-related differences in gene expression in the brains of breeding zebrafish (Danio rerio) to establish a greater understanding of the sex-specific physiology of the brain in lower vertebrates. The brain transcriptomic profiles of males and females were interrogated to identify the genes showing sexually dimorphic gene expression. 42 genes were differentially expressed between the sexes, from which 18 genes were over-expressed in males and 24 genes were over-expressed in females. In males, these included deiodinase, iodothyronine, type II and ribosomal protein S8, and in females, superoxide dismutase [Cu-Zn], sprouty-4, frizzled 10 and testis enhanced gene transcript. Estrogen responsive elements were found in the regulatory regions for 3 genes over-expressed in males and 7 genes over-expressed in females. We have demonstrated the existence of dimorphic patterns of gene expression in the brain of a sexually mature, non-mammalian, vertebrate model, with implications for studies into reproduction and chemical disruption of brain function.

Molecular basis of sex and reproductive status in breeding zebrafish

The zebrafish ( Danio rerio) is used extensively as a model species for studies on vertebrate development and for assessing chemical effects on reproduction. Despite this, the molecular mechanisms controlling zebrafish reproduction are poorly understood. We analyzed the transcriptomic profiles of the gonads of individual zebrafish, using a 17k oligonucleotide microarray, to define the molecular basis of sex and reproductive status in sexually mature fish. The gonadal transcriptome differed substantially between sexes. Among the genes overexpressed in females, 11 biological processes were overrepresented including mitochondrion organization and biogenesis, and cell growth and/or maintenance. Among the genes overexpressed in males, six biological processes were overrepresented including protein biosynthesis and protein metabolism. Analysis of the expression of gene families known to be involved in reproduction identified a number of genes differentially expressed between ovaries and testes including a number of sox genes and genes belonging to the insulin-like growth factor and the activin-inhibin pathways. Real-time quantitative PCR confirmed the expression profiles for nine of the most differentially expressed genes and indicated that many transcripts are likely to be switched off in one of the sexes in the gonads of adult fish. Significant differences were seen between the gonad transcriptomes of individual reproductively active females reflecting their stage of maturation, whereas the testis transcriptomes were remarkably similar between individuals. In summary, we have identified molecular processes associated with (gonadal) sex specificity in breeding zebrafish and established a strong relationship between individual ovarian transcriptomes and reproductive status in females.

Microfluidic chip-based synthesis of alginate microspheres for encapsulation of immortalized human cells

Cellular transplantation is a promising technology with great clinical potential in regenerative medicine and disease management. However, effective control over patient immunological response is essential. The encapsulation of cells within hydrogel microspheres is an increasingly prevalent method for the protection of cellular grafts from immune rejection. Microfluidic "chip" reactors present elegant solutions to several capsule generation issues, including the requirement for intercapsule uniformity, high reproducibility, and sterile, good manufacturing practice compliance. This study presents a novel method for the on-chip production of stable, highly monodisperse alginate microspheres and demonstrates its utility in the encapsulation of an immortalized human-derived cell line. Four populations of immortalized human embryonic kidney cells (HEK293) were encapsulated on chip within monodisperse alginate capsules. Cell viability measurements were recorded for each of the four encapsulated populations for 90 days.