Sharon Lee Edwards

Carbon nanotubes in scaffolds for tissue engineering

Carbon nanotubes are hollow graphitic cylinders of nanoscale dimensions. They are electrically conductive, chemically and thermally stable, and exceptionally strong. Given this unique combination of properties there has been much interest in carbon nanotubes, and finding applications for them. One application where this combination of properties may prove useful is in the area of tissue regeneration, incorporating carbon nanotubes into scaffolds for tissue engineering. It is believed that carbon nanotubes may improve scaffold properties and enhance tissue regeneration. This report aims to discuss the suitability of carbon nanotubes as a biomaterial for scaffold production, and the fabrication, properties and performance of carbon nanotube-based scaffolds.

A preclinical evaluation of alternative synthetic biomaterials for fascial defect repair using a rat abdominal hernia model.

Introduction Fascial defects are a common problem in the abdominal wall and in the vagina leading to hernia or pelvic organ prolapse that requires mesh enhancement to reduce operation failure. However, the long-term outcome of synthetic mesh surgery may be unsatisfactory due to post-surgical complications. We hypothesized that mesh fabricated from alternative synthetic polymers may evoke a different tissue response, and provide more appropriate mechanical properties for hernia repair. Our aim was to compare the in vivo biocompatibility of new synthetic meshes with a commercial mesh. Methods We have fabricated 3 new warp-knitted synthetic meshes from different polymers with different tensile properties polyetheretherketone (PEEK), polyamide (PA) and a composite, gelatin coated PA (PA+G). The rat abdominal hernia model was used to implant the meshes (25×35 mm, n = 24/ group). After 7, 30, 60, 90 days tissues were explanted for immunohistochemical assessment of foreign body reaction and tissue integration, using CD31, CD45, CD68, alpha-SMA antibodies. The images were analysed using an image analysis software program. Biomechanical properties were uniaxially evaluated using an Instron Tensile® Tester. Results This study showed that the new meshes induced complex differences in the type of foreign body reaction over the time course of implantation. The PA, and particularly the composite PA+G meshes, evoked a milder early inflammatory response, and macrophages were apparent throughout the time course. Our meshes led to better tissue integration and new collagen deposition, particularly with the PA+G meshes, as well as greater and sustained neovascularisation compared with the PP meshes. Conclusion PA, PA+G and PEEK appear to be well tolerated and are biocompatible, evoking an overlapping and different host tissue response with time that might convey mechanical variations in the healing tissue. These new meshes comprising different polymers may provide an alternative option for future treatment of fascial defects.

Characterisation of clinical and newly fabricated meshes for pelvic organ prolapse repair.

Clinical meshes used in pelvic organ prolapse (POP) repair are predominantly manufactured from monofilament polypropylene (PP). Complications from the use of these meshes in transvaginal kits, including mesh exposure and pain, have prompted two public health notifications by the FDA. The aim of this study was to compare several clinical PP POP meshes to new fabricated POP meshes, knitted from alternative polymers, for their mechanical properties using standard and clinically relevant multi-axial testing methods. Five new meshes were warp knitted to different architectures and weights from polyamide and polyetheretherketone monofilaments. A composite mesh of a polyamide mesh incorporating a gelatin layer was also fabricated to enable the potential delivery of cells on these meshes. Meshes were assessed for their structural characteristics and mechanical properties, using uniaxial stiffness, permanent strain, bending rigidity and multi-axial burst strength methods. Results were compared to three clinical urogynaecological polypropylene meshes: Polyform®, Gynemesh(TM)PS, and IntePro®. New fabricated meshes were uniaxially less stiff (less than 0.24 N/mm and 1.20 N/mm in toe and linear regions, respectively) than the Gynemesh (0.48 N/mm and 2.08 N/mm in toe and linear regions, respectively) and IntePro (0.57 N/mm in toe region) clinical meshes, with the gelatin coated PA mesh exhibiting lower permanent strain than Polyform clinical mesh (8.1% vs. 23.5%). New meshes had lower burst stiffness than Polyform (less than 16.9 N/mm for new meshes and 26.6N/mm for Polyform). Within the new mesh prototypes, the PA meshes, either uncoated (4.7-5.7 μN m) or with gelatin coating (16.7 μN m) possessed lower bending rigidity than both Polyform and Gynemesh (46.2 μN m and 36.4 μN m, respectively). The new fabricated mesh designs were of similar architecture, but with some improved mechanical properties, compared to clinical POP meshes. Multi-axial analysis of new and clinical mesh designs provides greater discriminatory power in analysing mesh mechanical properties for clinical applications.

Influence of Reproductive Status on Tissue Composition and Biomechanical Properties of Ovine Vagina

Objective To undertake a comprehensive analysis of the biochemical tissue composition and passive biomechanical properties of ovine vagina and relate this to the histo-architecture at different reproductive stages as part of the establishment of a large preclinical animal model for evaluating regenerative medicine approaches for surgical treatment of pelvic organ prolapse. Methods Vaginal tissue was collected from virgin (n = 3), parous (n = 6) and pregnant sheep (n = 6; mean gestation; 132 d; term = 145 d). Tissue histology was analyzed using H+E and Massons Trichrome staining. Biochemical analysis of the extracellular matrix proteins used a hydroxyproline assay to quantify total collagen, SDS PAGE to measure collagen III/I+III ratios, dimethylmethylene blue to quantify glycosaminoglycans and amino acid analysis to quantify elastin. Uniaxial tensiometry was used to determine the Youngs modulus, maximum stress and strain, and permanent strain following cyclic loading. Results Vaginal tissue of virgin sheep had the lowest total collagen content and permanent strain. Parous tissue had the highest total collagen and lowest elastin content with concomitant high maximum stress. In contrast, pregnant sheep had the highest elastin and lowest collagen contents, and thickest smooth muscle layer, which was associated with low maximum stress and poor dimensional recovery following repetitive loading. Conclusion Pregnant ovine vagina was the most extensible, but the weakest tissue, whereas parous and virgin tissues were strong and elastic. Pregnancy had the greatest impact on tissue composition and biomechanical properties, compatible with significant tissue remodeling as demonstrated in other species. Biochemical changes in tissue protein composition coincide with these altered biomechanical properties.

Induction of endometrial mesenchymal stem cells into tissue-forming cells suitable for fascial repair

Pelvic organ prolapse is a major hidden burden affecting almost one in four women. It is treated by reconstructive surgery, often augmented with synthetic mesh. To overcome the growing concerns of using current synthetic meshes coupled with the high risk of reoperation, a tissue engineering strategy has been developed, adopting a novel source of mesenchymal stem cells. These cells are derived from the highly regenerative endometrial lining of the uterus (eMSCs) and will be delivered in vivo using a new gelatin-coated polyamide scaffold. In this study, gelatin properties were optimized by altering the gelatin concentration and extent of crosslinking to produce the desired gelation and degradation rate in culture. Following cell seeding of uncoated polyamide (PA) and gelatin-coated meshes (PA+G), the growth rate of eMSCs on the PA+G scaffolds was more than that on the PA alone, without compromising cell shape. eMSCs cultured on the PA+G scaffold retained their phenotype, as demonstrated by W5C5/SUSD2 (eMSC-specific marker) immunocytochemistry. Additionally, eMSCs were induced to differentiate into smooth muscle cells (SMC), as shown by immunofluorescence for smooth muscle protein 22 and smooth muscle myosin heavy chain. eMSCs also differentiated into fibroblast-like cells when treated with connective tissue growth factor with enhanced detection of Tenascin-C and collagen type I as well as new tissue formation, as seen by Massons trichrome. In summary, it was demonstrated that the PA+G scaffold is an appropriate platform for eMSC delivery, proliferation and differentiation into SMC and fibroblasts, with good biocompatibility and the capacity to regenerate neo-tissue.

A review of TiO 2 NTs on Ti metal: Electrochemical synthesis, functionalization and potential use as bone implants

Degenerative diseases of bone such as osteoarthritis and osteoporosis can lead to bone fractures and immobility, compromising quality of life. Titanium (Ti)-based implants have been intensively investigated for bone repair, with these implants, demonstrating improved outcomes compared to stainless steel and cobalt-chrome alloys, owing to superior mechanical properties and biocompatibility. However, osseointegration between the Ti-based implants and the surrounding bone tissue needs to be improved. Surface modification of Ti-based implants provides a solution for addressing this, with electrochemical anodization becoming a realistic approach for the fabrication of hierarchical structured for example nanotubes (NTs), implant surfaces. Using this technique, biocompatibility and osteogenesis of the implant may be improved, by providing an appropriate site for bone cell attachment. In this review, we discuss the anodization of Ti-based implants as an approach for creating titanium dioxide nanotubes (TiO2 NTs) on the implant surface. We further discuss the various ways of functionalizing the NT surface, to reduce post-operative infection and improve implant biocompatibility and osseointegration.

Regional variation in tissue composition and biomechanical properties of postmenopausal ovine and human vagina.

Objective There are increasing numbers of reports describing human vaginal tissue composition in women with and without pelvic organ prolapse with conflicting results. The aim of this study was to compare ovine and human posterior vaginal tissue in terms of histological and biochemical tissue composition and to assess passive biomechanical properties of ovine vagina to further characterise this animal model for pelvic organ prolapse research. Study Design Vaginal tissue was collected from ovariectomised sheep (n = 6) and from postmenopausal women (n = 7) from the proximal, middle and distal thirds. Tissue histology was analyzed using Massons Trichrome staining; total collagen was quantified by hydroxyproline assays, collagen III/I+III ratios by delayed reduction SDS PAGE, glycosaminoglycans by dimethylmethylene blue assay, and elastic tissue associated proteins (ETAP) by amino acid analysis. Youngs modulus, maximum stress/strain, and permanent strain following cyclic loading were determined in ovine vagina. Results Both sheep and human vaginal tissue showed comparable tissue composition. Ovine vaginal tissue showed significantly higher total collagen and glycosaminoglycan values (p<0.05) nearest the cervix. No significant differences were found along the length of the human vagina for collagen, GAG or ETAP content. The proximal region was the stiffest (Youngs modulus, p<0.05), strongest (maximum stress, p<0.05) compared to distal region, and most elastic (permanent strain). Conclusion Sheep tissue composition and mechanical properties showed regional differences along the postmenopausal vaginal wall not apparent in human vagina, although the absolute content of proteins were similar. Knowledge of this baseline variation in the composition and mechanical properties of the vaginal wall will assist future studies using sheep as a model for vaginal surgery.

Changes in pelvic organ prolapse mesh mechanical properties following implantation in rats

BACKGROUND Pelvic organ prolapse (POP) is a multifactorial disease that manifests as the herniation of the pelvic organs into the vagina. Surgical methods for prolapse repair involve the use of a synthetic polypropylene mesh. The use of this mesh has led to significantly higher anatomical success rates compared with native tissue repairs, and therefore, despite recent warnings by the Food and Drug Administration regarding the use of vaginal mesh, the number of POP mesh surgeries has increased over the last few years. However, mesh implantation is associated with higher postsurgery complications, including pain and erosion, with higher consecutive rates of reoperation when placed vaginally. Little is known on how the mechanical properties of the implanted mesh itself change in vivo. It is assumed that the mechanical properties of these meshes remain unchanged, with any differences in mechanical properties of the formed mesh-tissue complex attributed to the attached tissue alone. It is likely that any changes in mesh mechanical properties that do occur in vivo will have an impact on the biomechanical properties of the formed mesh-tissue complex. OBJECTIVE The objective of the study was to assess changes in the multiaxial mechanical properties of synthetic clinical prolapse meshes implanted abdominally for up to 90 days, using a rat model. Another objective of the study was to assess the biomechanical properties of the formed mesh-tissue complex following implantation. STUDY DESIGN Three nondegradable polypropylene clinical synthetic mesh types for prolapse repair (Gynemesh PS, Polyform Lite, and Restorelle) and a partially degradable polypropylene/polyglecaprone mesh (UltraPro) were mechanically assessed before and after implantation (n = 5/ mesh type) in Sprague Dawley rats for 30 (Gynemesh PS, Polyform Lite, and Restorelle) and 90 (UltraPro and Polyform Lite) days. Stiffness and permanent extension following cyclic loading, and breaking load, of the preimplanted mesh types, explanted mesh-tissue complexes, and explanted meshes were assessed using a multi-axial (ball-burst) method. RESULTS The 4 clinical meshes varied from each other in weight, thickness, porosity, and pore size and showed significant differences in stiffness and breaking load before implantation. Following 30 days of implantation, the mechanical properties of some mesh types altered, with significant decreases in mesh stiffness and breaking load, and increased permanent extension. After 90 days these changes were more obvious, with significant decreases in stiffness and breaking load and increased permanent extension. Similar biomechanical properties of formed mesh-tissue complexes were observed for mesh types of different preimplant stiffness and structure after 90 days implantation. CONCLUSION This is the first study to report on intrinsic changes in the mechanical properties of implanted meshes and how these changes have an impact on the estimated tissue contribution of the formed mesh-tissue complex. Decreased mesh stiffness, strength, and increased permanent extension following 90 days of implantation increase the biomechanical contribution of the attached tissue of the formed mesh-tissue complex more than previously thought. This needs to be considered when using meshes for prolapse repair.

Nonwoven Scaffolds of Improved Design for the Tissue Engineering of the Anterior Cruciate Ligament

ABSTRACT This work is concerned with improving nonwoven scaffold design for the tissue engineering of the anterior cruciate ligament. When designing a scaffold two important design criteria to consider are scaffolds internal structure and biocompatibility, both of which are addressed in this paper. The role of a scaffold is to provide a framework for cells to attach, proliferate and secrete extra cellular matrix. The scaffold also acts as a template, directing the growth of cells and newly formed tissue. It is the scaffolds internal structure, together with polymer surface chemistry and morphology, which directly influence the cellular activities that lead to tissue formation. With regard to scaffolds internal structure, structural parameters are discussed in relation to specific scaffold function; for example the effect of scaffold pore-size on cell proliferation, migration and nutrient supply. Another structural factor discussed is the role of fibre orientation as a means of guiding and organising new tissue growth. With the aim of creating a scaffold of optimum design, for the tissue engineering of the anterior cruciate ligament, nonwoven scaffolds of differing structure have been constructed. In order to understand the relationship between manufacturing method and scaffold structure characterisation techniques have been employed to analyse the structural parameters of these scaffolds. Obtained scaffold structural properties are discussed in relation to manufacturing method. Regarding the second scaffold criteria biocompatibility tests have been conducted by the authors on a range of generic fibre types. The results of these tests are provided in the form of cell attachment, with reference to fibre morphology.

Ovine multiparity is associated with diminished vaginal muscularis, increased elastic fibres and vaginal wall weakness: implication for pelvic organ prolapse

Pelvic Organ Prolapse (POP) is a major clinical burden affecting 25% of women, with vaginal delivery a major contributing factor. We hypothesised that increasing parity weakens the vagina by altering the extracellular matrix proteins and smooth muscle thereby leading to POP vulnerability. We used a modified POP-quantification (POP-Q) system and a novel pressure sensor to measure vaginal wall weakness in nulliparous, primiparous and multiparous ewes. These measurements were correlated with histological, biochemical and biomechanical properties of the ovine vagina. Primiparous and multiparous ewes had greater displacement of vaginal tissue compared to nulliparous at points Aa, Ap and Ba and lower pressure sensor measurements at points equivalent to Ap and Ba. Vaginal wall muscularis of multiparous ewes was thinner than nulliparous and had greater elastic fibre content. Collagen content was lower in primiparous than nulliparous ewes, but collagen organisation did not differ. Biomechanically, multiparous vaginal tissue was weaker and less stiff than nulliparous. Parity had a significant impact on the structure and function of the ovine vaginal wall, as the multiparous vaginal wall was weaker and had a thinner muscularis than nulliparous ewes. This correlated with “POP-Q” and pressure sensor measurements showing greater tissue laxity in multiparous compared to nulliparous ewes.