The effect of mean pore size in collagen-glycosaminoglycan scaffolds on cell migration and differentiation for bone tissue engineering applications

Tissue engineering was born from the belief that primary cells could be isolated from a patient, expanded in vitro and seeded onto a substrate that could be grafted back into the patient (Yang et a/, 2001) providing a biological alternative to transplantations and prosthesis. There are three main components in tissue engineering, scaffolds, cells and signalling mechanisms that make up the tissue engineering triad. This thesis focuses on the interplay between cell behaviour and scaffold structural properties. Recent studies from our laboratory have developed novel freeze-drying techniques to vary the structure of collagen-glycosaminoglycan (GAG) scaffolds producing scaffolds with mean pores ranging from 85 pm - 325 pm (Haugh et a/, 2010). The general aim of this thesis was to investigate, using this range of scaffolds, the effect of mean pore size on cell behaviour in the scaffolds and see how this behaviour varies with different cell types. A non-linear effect was seen on initial cell attachment but ultimately scaffolds with the largest pores size of 325 pm facilitated optimal osteoblast attachment, proliferation and migration. A comparison of stem cell (MSC) behaviour to semi-differentiated osteoblasts in the scaffolds demonstrated a similar non-linear effect on cell attachment but poorer MSC migration was observed highlighting the difference in cell type behaviour. Further analysis shed some light on this effect whereby MSCs were physically bigger cells and less motile. Longer term studies were carried out to determine the effect of mean pore size on osteoblast differentiation, matrix mineralisation and cell-mediated contraction. The largest scaffold mean pore size of 325 pm facilitated improved cell distribution, an earlier onset of osteogenic differentiation and a higher level of mineralisation. The final study of this thesis investigated the potential of human amniotic fluid derived stem cells as a readily accessible source of pluripotent stem cells (AFSCs). These cells demonstrated osteogenic differentiation and an ability to attach to the collagen-GAG scaffold. In conclusion, mean pore size was shown to have an effect on cell behaviour in collagen-GAG scaffolds. Ultimately the larger pores of 325 pm facilitate optimal cell attachment, migration, osteogenic differentiation, matrix mineralisation and cellmediated contraction. In addition, the osteogenic potential of a readily accessible source of pluripotent stem cells has demonstrated their future potential in bone tissue engineering

Twenty years of load theory—Where are we now, and where should we go next?

Selective attention allows us to ignore what is task-irrelevant and focus on what is task-relevant. The cognitive and neural mechanisms that underlie this process are key topics of investigation in cognitive psychology. One of the more prominent theories of attention is perceptual load theory, which suggests that the efficiency of selective attention is dependent on both perceptual and cognitive load. It is now more than 20 years since the proposal of load theory, and it is a good time to evaluate the evidence in support of this influential model. The present article supplements and extends previous reviews (Lavie, Trends in Cognitive Sciences, 9, 75–82. doi:10.​1016/​j.​tics.​2004.​12.​004, 2005, Current Directions in Psychological Science, 19, 143–148. doi:10.​1177/​0963721410370295​, 2010) by examining more recent research in what appears to be a rapidly expanding area. The article comprises five parts, examining (1) evidence for the effects of perceptual load on attention, (2) cognitive load, (3) individual differences under load, (4) alternative theories and criticisms, and (5) the future of load theory. We argue that the key next step for load theory will be the application of the model to real-world tasks. The potential benefits of applied attention research are numerous, and there is tentative evidence that applied research would provide strong support for the theory itself, as well as real-world benefits related to activities in which attention is crucial, such as driving and education

Novel freeze-drying methods to produce a range of collagen-glycosaminoglycan scaffolds with tailored mean pore sizes.

The pore structure of three-dimensional scaffolds used in tissue engineering has been shown to significantly influence cellular activity. As the optimal pore size is dependant on the specifics of the tissue engineering application, the ability to alter the pore size over a wide range is essential for a particular scaffold to be suitable for multiple applications. With this in mind, the aim of this study was to develop methodologies to produce a range of collagen-glycosaminoglycan (CG) scaffolds with tailored mean pore sizes. The pore size of CG scaffolds is established during the freeze-drying fabrication process. In this study, freezing temperature was varied (−10 degrees C to −70 degrees C) and an annealing step was introduced to the process to determine their effects on pore size. Annealing is an additional step in the freeze-drying cycle that involves raising the temperature of the frozen suspension to increase the rate of ice crystal growth. The results show that the pore size of the scaffolds decreased as the freezing temperature was reduced. Additionally, the introduction of an annealing step during freeze-drying was found to result in a significant increase (40%) in pore size. Taken together, these results demonstrate that the methodologies developed in this study can be used to produce a range of CG scaffolds with mean pore sizes from 85 to 325 microm. This is a substantial improvement on the range of pore sizes that were possible to produce previously (96-150 microm). The methods developed in this study provide a basis for the investigation of the effects of pore size on both in vitro and in vivo performance and for the determination of the optimal pore structure for specific tissue engineering applications

Crosslinking and Mechanical Properties Significantly Influence Cell Attachment, Proliferation, and Migration Within Collagen Glycosaminoglycan Scaffolds.

Crosslinking and the resultant changes in mechanical properties have been shown to influence cellular activity within collagen biomaterials. With this in mind, we sought to determine the effects of crosslinking on both the compressive modulus of collagen-glycosaminoglycan scaffolds and the activity of osteoblasts seeded within them. Dehydrothermal, 1-ethyl-3-3-dimethyl aminopropyl carbodiimide and glutaraldehyde crosslinking treatments were first investigated for their effect on the compressive modulus of the scaffolds. After this, the most promising treatments were used to study the effects of crosslinking on cellular attachment, proliferation, and infiltration. Our experiments have demonstrated that a wide range of scaffold compressive moduli can be attained by varying the parameters of the crosslinking treatments. 1-Ethyl-3-3-dimethyl aminopropyl carbodiimide and glutaraldehyde treatments produced the stiffest scaffolds (fourfold increase when compared to dehydrothermal crosslinking). When cells were seeded onto the scaffolds, the stiffest scaffolds also showed increased cell number and enhanced cellular distribution when compared to the other groups. Taken together, these results indicate that crosslinking can be used to produce collagen-glycosaminoglycan scaffolds with a range of compressive moduli, and that increased stiffness enhances cellular activity within the scaffolds

Fool me twice: How effective is debriefing in false memory studies?

Deception is often necessary in false memory studies, especially when the study aims to explore the effect of misinformation on memory. At the end of the study, participants are debriefed, but does this eliminate the influence of misinformation? In the current study, we followed up 630 participants six months after they participated in a study in which they were exposed to fabricated political news stories. We compared the memories of these â continuing participantsâ for both novel and previously seen news stories to the memories of 474 newly recruited participants. Relative to new recruits, continuing participants were less likely to report a false memory for a story that they had been previously exposed to, and they were also less likely to report a false memory for a novel fake news story. Continuing participants were more likely to report a memory for previously seen true events than novel true events. Both groups of participants reported enjoying the experience and feeling confident that they understood which stories were fabricated. Importantly, this study did not find any negative long-term effects of participating in our false memory experiment, and even exhibited some positive effects

3D-printed gelatin methacrylate scaffolds with controlled architecture and stiffness modulate the fibroblast phenotype towards dermal regeneration

Impaired skin wound healing due to severe injury often leads to dysfunctional scar tissue formation as a result of excessive and persistent myofibroblast activation, characterised by the increased expression of α-smooth muscle actin (αSMA) and extracellular matrix (ECM) proteins. Yet, despite extensive research on impaired wound healing and the advancement in tissue-engineered skin substitutes, scar formation remains a significant clinical challenge. This study aimed to first investigate the effect of methacrylate gelatin (GelMA) biomaterial stiffness on human dermal fibroblast behaviour in order to then design a range of 3D-printed GelMA scaffolds with tuneable structural and mechanical properties and understand whether the introduction of pores and porosity would support fibroblast activity, while inhibiting myofibroblast-related gene and protein expression. Results demonstrated that increasing GelMA stiffness promotes myofibroblast activation through increased fibrosis-related gene and protein expression. However, the introduction of a porous architecture by 3D printing facilitated healthy fibroblast activity, while inhibiting myofibroblast activation. A significant reduction was observed in the gene and protein production of αSMA and the expression of ECM-related proteins, including fibronectin I and collagen III, across the range of porous 3D-printed GelMA scaffolds. These results show that the 3D-printed GelMA scaffolds have the potential to improve dermal skin healing, whilst inhibiting fibrosis and scar formation, therefore potentially offering a new treatment for skin repair.The authors acknowledge funding from Science Foundation Ireland under the M-ERA.NET program, Transnational Call 2016 (17/US/3437; Ireland), EU BlueHuman Interreg Atlantic Area Project (grant EAPA_151/2016) and Science Foundation Ireland, through the Advanced Materials and BioEngineering Research Centre (AMBER; grants 12/RC/2278 and 12/RC/2278_P2)

A collagen-hydroxyapatite scaffold allows for binding and co-delivery of recombinant bone morphogenetic proteins and bisphosphonates.

An emerging paradigm in orthopedics is that a bone-healing outcome is the product of the anabolic (bone-forming) and catabolic (bone-resorbing) outcomes. Recently, surgical and tissue engineering strategies have emerged that combine recombinant human bone morphogenetic proteins (rhBMPs) and bisphosphonates (BPs) in order to maximize anabolism and minimize catabolism. Collagen-based scaffolds that are the current surgical standard can bind rhBMPs, but not BPs. We hypothesized that a biomimetic collagen-hydroxyapatite (CHA) scaffold would bind both agents and produce superior in vivo outcomes. Consistent with this concept, in vitro elution studies utilizing rhBMP-2 ELISA assays and scintillation counting of (14)C-radiolabeled zoledronic acid (ZA) confirmed delayed release of both agents from the CHA scaffold. Next, scaffolds were tested for their capacity to form ectopic bone after surgical implantation into the rat hind limb. Using CHA, a significant 6-fold increase in bone volume was seen in rhBMP-2/ZA groups compared to rhBMP-2 alone, confirming the ability of ZA to enhance rhBMP-2 bone formation. CHA scaffolds were found to be capable of generating mineralized tissue in the absence of rhBMP-2. This study has implications for future clinical treatments of critical bone defects. It demonstrates the relative advantages of co-delivering anabolic and anti-catabolic agents using a multicomponent scaffold system

False memories for fake news during Ireland's abortion referendum

The current study examined false memories in the week preceding the 2018 Irish abortion referendum. Participants (N = 3,140) viewed six news stories concerning campaign events—two fabricated and four authentic. Almost half of the sample reported a false memory for at least one fabricated event, with more than one third of participants reporting a specific memory of the event. “Yes” voters (those in favor of legalizing abortion) were more likely than “no” voters to “remember” a fabricated scandal regarding the campaign to vote “no,” and “no” voters were more likely than “yes” voters to “remember” a fabricated scandal regarding the campaign to vote “yes.” This difference was particularly strong for voters of low cognitive ability. A subsequent warning about possible misinformation slightly reduced rates of false memories but did not eliminate these effects. This study suggests that voters in a real-world political campaign are most susceptible to forming false memories for fake news that aligns with their beliefs, in particular if they have low cognitive ability

Mechanomodulatory biomaterials prospects in scar prevention and treatment

Scarring is a major clinical issue that affects a considerable number of patients. The associated problems go beyond the loss of skin functionality, as scars bring aesthetic, psychological, and social difficulties. Therefore, new strategies are required to improve the process of healing and minimize scar formation. Research has highlighted the important role of mechanical forces in the process of skin tissue repair and scar formation, in addition to the chemical signalling. A more complete understanding of how engi- neered biomaterials can modulate these mechanical stimuli and modify the mechanotransduction signals in the wound microenvironment is expected to enable scar tissue reduction. The present review aims to provide an overview of our current understanding of skin biomechanics and mechanobiology underlying wound healing and scar formation, with an emphasis on the development of novel mechanomodulatory wound dressings with the capacity to offload mechanical tension in the wound environment. Further- more, a broad overview of current challenges and future perspectives of promising mechanomodulatory biomaterials for this application are provided.The authors would like to acknowledge Portuguese Foun dation for Science and Technology (FCT) for funding the research project Dressing4Scars M-ERA-NET2/0013/2016, and LP da Silva (2020.01541.CEECIND/CP1600/CT0024), and to Norte-01-0145-FEDER-02219015 (MT Cerqueira)