Freeze-Drying as a Novel Biofabrication Method for Achieving a Controlled Microarchitecture within Large, Complex Natural Biomaterial Scaffolds

The biofabrication of large scaffolds from natural biomaterials into complex 3D shapes with controllable microarchitecture remains a major challenge. Freeze-drying (or lyophilization) is a technique used to create bioactive scaffolds with a porous architecture and is typically only used to generate scaffolds in planar 3D geometries. Here we report the development of a new biofabrication process to form a collagen-based scaffold into a large, complex geometry which has a large height to width ratio, and a controlled porous microarchitecture. This biofabrication process was validated through the successful development of a heart valve shaped scaffold, fabricated from a collagen-glycosaminoglycan co-polymer. Notably, despite the significant challenges in using freeze-drying to create such a structure, the resultant scaffold had a uniform, homogeneous pore architecture throughout. This was achieved through optimization of the freeze-drying mold and freezing parameters. We believe this to be the first demonstration of using freeze-drying to create a large, complex scaffold geometry with a controlled, porous architecture using natural materials. This study validates the potential of using freeze-drying for development of organ-specific scaffold geometries for tissue engineering applications, which up until now might not have been considered feasible

Adhesion Molecules Associated with Female Genital Tract Infection

Altres ajuts: Marie Curie Career Integration Grant i una beca Fundació Dexeus Salut de la DonaEfforts to develop vaccines that can elicit mucosal immune responses in the female genital tract against sexually transmitted infections have been hampered by an inability to measure immune responses in these tissues. The differential expression of adhesion molecules is known to confer site-dependent homing of circulating effector T cells to mucosal tissues. Specific homing molecules have been defined that can be measured in blood as surrogate markers of local immunity (e.g. α4β7 for gut). Here we analyzed the expression pattern of adhesion molecules by circulating effector T cells following mucosal infection of the female genital tract in mice and during a symptomatic episode of vaginosis in women. While CCR2, CCR5, CXCR6 and CD11c were preferentially expressed in a mouse model of Chlamydia infection, only CCR5 and CD11c were clearly expressed by effector T cells during bacterial vaginosis in women. Other homing molecules previously suggested as required for homing to the genital mucosa such as α4β1 and α4β7 were also differentially expressed in these patients. However, CD11c expression, an integrin chain rarely analyzed in the context of T cell immunity, was the most consistently elevated in all activated effector CD8+ T cell subsets analyzed. This molecule was also induced after systemic infection in mice, suggesting that CD11c is not exclusive of genital tract infection. Still, its increase in response to genital tract disorders may represent a novel surrogate marker of mucosal immunity in women, and warrants further exploration for diagnostic and therapeutic purposes

Mechanics of the linea alba and suture-based wound closure

THESIS 11111Over the past thirty years, there has been a dramatic change in the methodology of abdominal surgery. The introduction of digitalisation, miniaturisation, improved optics, novel imaging techniques and computerised information systems in the operating theatre in the form of minimally invasive laparoscopic surgery have greatly reduced risk to the patient and the length of time required to complete the surgery. However, there are still medical situations that require the more invasive laparotomy surgery and it is estimated that the same number of people (two million for each laparoscopic and laparotomy surgeries) undergo the procedure in the USA each year. Unfortunately, despite the medical advances in recent years, incisional hernia can form post-operatively, having a prevalence of approximately 1-5% for laparoscopic surgery and as high as 20% for open laparotomies. There are claims that the risk of incisional hernia is related to the quality of wound closure. This thesis therefore aims to develop a novel wound closure method that will reduce the risk of incisional hernia occurring. The design of a novel wound closure method requires a fundamental understanding of the mechanical properties of the tissue involved. To achieve this, the tensile mechanical characterisation of the porcine and human linea alba, as determined by uniaxial and equi-load biaxial testing using image-based strain measurement methods is presented due to the limited data available in the literature and which use less accurate methods of stretch measurement. Significant anisotropy was observed in the tissue of both species with deformation heavily biased in the longitudinal direction under equal application of load. It was found that the response of porcine linea alba to uniaxial and biaxial loading is similar to that of human linea alba, permitting the use of a porcine model for investigations into wound closure methodology. Additionally, a finite element model of the uniaxial experiments quantified the effect of clamping and tissue dimensions (which are suboptimal for tensile testing) on the porcine uniaxial results. A correction factor was produced that was used to scale the porcine uniaxial data to account for the effects of clamping. These results provide an improved assessment of the mechanical properties of the porcine and human linea alba to help further an understanding of wound closure. The suture pullout characteristics of both porcine and human linea alba are investigated to ascertain an optimal placement of sutures for surgical wound closure. This is performed again in response to the very limited data available in the literature. It was found that the relationship between pullout force of the suture, bite separation and bite depth is quadratic and characterises low separation and high depth as optimal parameters. Of the parameters used in the study, it was found that resistance to pullout could be improved by as much as 290%. Both human and porcine tissue were observed to exhibit the same behaviour, again corroborating the use of a porcine model for investigations into wound closure methodology. Orientation of suture application was also found to significantly affect the magnitude of suture pullout. Suture styles applied longitudinally across a transverse defect were observed to be more beneficial and it was concluded that it could especially reduce the risk of laparoscopic incisional hernia. Since the abdomen is itself a pressurised vessel, it is generally described as being subjected to multi-axial loading; not solely in the direction of the abdominal muscles aponeurotic processes. To more adequately describe the effect that suture-based wound closure has on the apposition of the linea alba laparotomy defect, it is necessary to create an environment that adequately reflects an in-vivo standpoint. To this end, deformation tests on porcine linea alba (intact abdominal wall) with a suture-closed laparotomy incision were performed on a surrogate abdominal rig. This was done in order to more accurately ascertain the optimum bite depth and bite separation of a continuous suture to be used to close a laparotomy defect through quantitative measurement of wound apposition. The conclusions proved to be the same as that of uniaxial suture pullout, validating uniaxial pullout as a reliable source. Theoretical and experimental evaluation of suture pullout was also investigated in order to predict the pressure of suture pullout beyond what is capable of the surrogate rig. However, the theoretical model tended to under-predict the experimental results due to the types of assumptions used. In conclusion, a detailed understanding of the mechanics of the linea alba and suture-based wound closure has been developed and used to improve upon clinical methodologies and could potentially reduce the risk of post-operative complications. Two clinical recommendations were developed and accepted by a surgical consultant. A suture bite depth of 16mm and a bite separation of 5mm is advised for laparotomy closure and transverse incisions closed using longitudinal applications of suture are advised for laparoscopic closure to help minimise the risk of incisional hernia

Uniaxial and biaxial mechanical properties of porcine linea alba

Incisional hernia is a severe complication post-laparoscopic/laparotomy surgery that is commonly associated with the linea alba. However, the few studies on the mechanical properties of the linea alba in the literature appear contradictory, possible due to challenges with the physical dimensions of samples and variations in protocol. This study focuses on the tensile mechanical characterisation of the porcine linea alba, as determined by uniaxial and equi-load biaxial testing using image-based strain measurement methods. Results show that the linea alba demonstrated a non-linear elastic, anisotropic behaviour which is often observed in biological soft tissues. The transverse direction (parallel to fibres) was found to be approximately eight times stiffer than the longitudinal (cross-fibre) direction under both uniaxial and equi-load biaxial loading. The equi-load biaxial tensile tests revealed that contraction could occur in the transverse direction despite increasing load, probably due to the anisotropy of the tissue. Optical surface marker tracking and digital image correlation methods were found to greatly improve the accuracy of stretch measurement, resulting in a 75% change in the apparent stiffness compared to using strain derived from machine cross-head displacement. Additionally, a finite element model of the experiments using a combination of an Ogden and fibre exponential power law model for the linea alba was implemented to quantify the effect of clamping and tissue dimensions (which are suboptimal for tensile testing) on the results. The preliminary model results were used to apply a correction factor to the uniaxial experimental data prior to inverse optimisation to derive best fit material parameters for the fibre reinforced Ogden model. Application of the model to the equi-load biaxial case showed some differences compared to the experimental data, suggesting a more complex anisotropic model may be necessary to capture biaxial behaviour. These results provide an improved assessment of the mechanical properties of the porcine linea alba for wound closure and other studie

Advanced Material Catheter (AMCath), a minimally invasive endocardial catheter for the delivery of fast-gelling covalently cross-linked hyaluronic acid hydrogels

Injectable hydrogels that aim to mechanically stabilise the weakened left ventricle wall to restore cardiac function or to deliver stem cells in cardiac regenerative therapy have shown promising data. However, the clinical translation of hydrogel-based therapies has been limited due to difficulties injecting them through catheters. We have engineered a novel catheter, Advanced Materials Catheter (AMCath), that overcomes translational hurdles associated with delivering fast-gelling covalently cross-linked hyaluronic acid hydrogels to the myocardium. We developed an experimental technique to measure the force required to inject such hydrogels and determined the mechanical/viscoelastic properties of the resulting hydrogels. The preliminary in vivo feasibility of delivering fast-gelling hydrogels through AMCath was demonstrated by accessing the porcine left ventricle and showing that the hydrogel was retained in the myocardium post-injection (three 200 μL injections delivered, 192, 204 and 183 μL measured). However, the mechanical properties of the hydrogels were reduced by passage through AMCath (≤20.62% reduction). We have also shown AMCath can be used to deliver cardiopoietic adipose-derived stem cell-loaded hydrogels without compromising the viability (80% viability) of the cells in vitro. Therefore, we show that hydrogel/catheter compatibility issues can be overcome as we have demonstrated the minimally invasive delivery of a fast-gelling covalently cross-linked hydrogel to the beating myocardium.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: AMCARE consortium (FP7/2007-2013) under Grant Agreement No.604531

Advanced Material Catheter (AMCath), a minimally invasive endocardial catheter for the delivery of fast-gelling covalently cross-linked hyaluronic acid hydrogels

Injectable hydrogels that aim to mechanically stabilise the weakened left ventricle wall to restore cardiac function or to deliver stem cells in cardiac regenerative therapy have shown promising data. However, the clinical translation of hydrogel-based therapies has been limited due to difficulties injecting them through catheters. We have engineered a novel catheter, Advanced Materials Catheter (AMCath), that overcomes translational hurdles associated with delivering fast-gelling covalently cross-linked hyaluronic acid hydrogels to the myocardium. We developed an experimental technique to measure the force required to inject such hydrogels and determined the mechanical/viscoelastic properties of the resulting hydrogels. The preliminary in vivo feasibility of delivering fast-gelling hydrogels through AMCath was demonstrated by accessing the porcine left ventricle and showing that the hydrogel was retained in the myocardium post-injection (three 200 μL injections delivered, 192, 204 and 183 μL measured). However, the mechanical properties of the hydrogels were reduced by passage through AMCath (≤20.62% reduction). We have also shown AMCath can be used to deliver cardiopoietic adipose-derived stem cell-loaded hydrogels without compromising the viability (80% viability) of the cells in vitro. Therefore, we show that hydrogel/catheter compatibility issues can be overcome as we have demonstrated the minimally invasive delivery of a fast-gelling covalently cross-linked hydrogel to the beating myocardium.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: AMCARE consortium (FP7/2007-2013) under Grant Agreement No.604531.peer-reviewe

Nurses, midwives and key stakeholders experiences and perceptions on requirements to demonstrate the maintenance of professional competence: an Irish study

Aim: To present the qualitative findings from a study on the development of scheme(s) to give evidence of maintenance of professional competence for nurses and midwives. Background: Key issues in maintenance of professional competence include notions of self- assessment, verification of engagement and practice hours, provision of an evidential record, the role of the employer and articulation of possible consequences for non-adherence with the requirements. Schemes to demonstrate the maintenance of professional competence have application to nurses, midwives and regulatory bodies and healthcare employers worldwide. Design: A mixed methods approach was used. This included an online survey of nurses and midwives and focus groups with nurses and midwives and other key stakeholders. The qualitative data are reported in this study. Methods: Focus groups were conducted among a purposive sample of nurses, midwives and key stakeholders from January–May 2015. A total of 13 focus groups with 91 participants contributed to the study. Findings: Four major themes were identified: Definitions and Characteristics of Competence; Continuing Professional Development and Demonstrating Competence; Assessment of Competence; The Nursing and Midwifery Board of Ireland and employers as regulators and enablers of maintaining professional competence. Conclusion: Competence incorporates knowledge, skills, attitudes, professionalism, application of evidence and translating learning into practice. It is specific to the nurse's/midwife's role, organizational needs, patient's needs and the individual nurse's/midwife's learning needs. Competencies develop over time and change as nurses and midwives work in different practice areas. Thus, role-specific competence is linked to recent engagement in practice