Development of melt electrospun composite scaffolds for bone regeneration

This thesis was a step forward in the development of an effective and patient-specific treatment for bone tissue loss using synthetic tissue engineered constructs. A novel polycaprolactone/strontium-substituted bioactive glass composite was fabricated into scaffolds with highly ordered fibre structure and promising osteogenic potential using an advanced additive manufacturing technique known as melt-electrospinning. The findings of this thesis provide an indispensable link in our understanding of future cell-free treatment for bone defects utilising fully synthetic bioactive scaffolds. The thesis also developed several histological assessment tools for evaluating current and future tissue engineered bone constructs utilised in pre-clinical animal studies

Improved fabrication of melt electrospun tissue engineering scaffolds using direct writing and advanced electric field control

Direct writing melt electrospinning is an additive manufacturing technique capable of the layer-by-layer fabrication of highly ordered 3d tissue engineering scaffolds from micron-diameter fibres. The utility of these scaffolds, however, is limited by the maximum achievable height of controlled fibre deposition, beyond which the structure becomes increasingly disordered. A source of this disorder is charge build-up on the deposited polymer producing unwanted coulombic forces. In this study we introduce a novel melt electrospinning platform with dual voltage power supplies to reduce undesirable charge effects and improve fibre deposition control. We produced and characterised several 90° cross-hatched fibre scaffolds using a range of needle/collector plate voltages. Fibre thickness was found to be sensitive only to overall potential and invariant to specific tip/collector voltage. We also produced ordered scaffolds up to 200 layers thick (fibre spacing 1 mm, diameter 40 μm) and characterised structure in terms of three distinct zones; ordered, semi-ordered and disordered. Our in vitro analysis indicates successful cell attachment and distribution throughout the scaffolds, with little evidence of cell death after seven days. This study demonstrates the importance of electrostatic control for reducing destabilising polymer charge effects and enabling the fabrication of morphologically suitable scaffolds for tissue engineering

Effects of scaffold architecture on cranial bone healing

Scaffolds for bone tissue engineering should be designed to optimize cell migration, enhance new bone formation and give mechanical support. In the present study, we used polycaprolactone-tricalciumphosphate (PCL/TCP) scaffolds with two different fibre lay down patterns which were coated with hydroxyapatite and gelatine as an approach for optimizing bone regeneration in a critical sized calvarial defect. After 12 weeks bone regeneration was quantified using microCT analysis, biomechanical testing and histological evaluation. Notably, the experimental groups containing coated scaffolds showed lower bone formation and lower biomechanical properties within the defect compared to the uncoated scaffolds. Surprisingly, the different lay down pattern of the fibres resulted in different bone formation and biomechanical properties; namely 0/60/120° scaffolds revealed lower bone formation and biomechanical properties compared to the 0/90° scaffolds in all the experimental groups. The different architecture of the scaffold fibres may have an effect on nutrition supply as well as the attachment of the newly formed matrix to the scaffold. Therefore, future bone regeneration strategies utilising scaffolds should consider scaffold architecture as an important factor during the scaffold optimisation stages in order to move closer to a clinical application

Development of mechanically enhanced polycaprolactone composites by a functionalized titanate nanofiller for melt electrowriting in 3D printing

Three-dimensional (3D) printing technologies are widely applied in various industries and research fields and are currently the subject of intensive investigation and development. However, high-performance materials that are suitable for 3D printing are still in short supply, which is a major limitation for 3D printing, particularly for biomedical applications. The physicochemical properties of single constituent materials may not be sufficient to meet the needs of modern biotechnology development and production. To enhance the materials’ performance and broaden their applications, this work designed and tested a series of titanate nanofiller (nanowire and nanotube)-enhanced polycaprolactone (PCL) composites that were 3D-printable and provided superior mechanical properties. By grafting two different functional groups (phenyl- and thiol-terminated ligands), the nanofiller surface showed improved hydrophobicity, which significantly improved their dispersion in the PCL matrix. After characterizing the surface modification, we evaluated the significance of the homogeneity of the ceramic nanofiller in terms of printability, formability, and mechanical strength. Melt electrowriting additive manufacturing was used to fabricate microfibers of PCL and PCL/nanofiller composites. Improved nanofiller dispersion enabled intact and uniform sample morphology, and in contrast, nanofiller aggregation greatly varied the viscosity during the printing process, which could result in poorly printed structures. Importantly, the modified ceramic/PCL composite delivered enhanced and stable mechanical properties, where its Young’s modulus was measured to be 1.67 GPa, which is more than 7 times higher compared to that of pristine PCL (0.22 GPa). Retaining the cell safety properties (comparable to PCL), the concept of enhancing biocompatible polymers with modified nanofillers shows great potential in the field of customized 3D printing for biomedicine

Enzyme-degradable 3D multi-material microstructures

There exists a growing need for smart materials suitable for use in biomedical applications. Herein, a photoresist that can be used to fabricate a biocompatible material entirely degradable by the enzyme chymotrypsin is introduced. The photoresist is based on a crosslinker with a tyramine moiety that is recognized and cleaved by the enzyme chymotrypsin. Macroscopic films as well as microstructures are fabricated via the use of direct laser writing. Multi-material boxing ring microstructures are generated and selectively degraded by the enzyme. Cell biocompatibility studies indicate that cells are able to attach and proliferate over one week on the material. A photoresist that is biocompatible and can be entirely removed by a biocompatible stimulus such as an enzyme can potentially be used as an easily removed tissue engineering scaffold and is especially promising for basic cell biology research.</p

The Patenting and Technological Trends in Hernia Mesh Implants

Described as a projection (prolapse) of tissue through a fascial defect in the abdominal wall, hernias are associated with significant rates of complications, recurrence, and reoperations. This literature review is aimed at providing an overview of the prosthetic surgical meshes used for the repairing of hernia defects. The review was carried out using two specialized online databases: Espacenet, from the European Patent Office (EPO), and WIPO from the World Intellectual Property Organization. Of the 56 patents selected from 2008 to 2018, China was the largest contributor with 55% (31 patents) of the total patent applicant filings, followed by the United States of America (US), with 29% (16 patents). Although the majority of patent applications (39 documents) had at least one company (industry) assigned to the patent application, 4 patents were solely from academic research. Our data showed that only 13 industry applicants have had their products included in the market, and the majority of meshes available on the market are still made from polypropylene. Chemical, physical, and mesh surface modifications have been implemented, and a few reviews describing mesh design, composition, and mechanical properties are available. However, to date, the ideal mesh implant from a clinical point of view has not been developed.</p

Role of <i>SiPHR1</i> in the Response to Low Phosphate in Foxtail Millet via Comparative Transcriptomic and Co-Expression Network Analyses

Enhancing the absorption and utilization of phosphorus by crops is an important aim for ensuring food security worldwide. However, the gene regulatory network underlying phosphorus use in foxtail millet remains unclear. In this study, the molecular mechanism underlying low-phosphorus (LP) responsiveness in foxtail millet was evaluated using a comparative transcriptome analysis. LP reduced the chlorophyll content in shoots, increased the anthocyanin content in roots, and up-regulated purple acid phosphatase and phytase activities as well as antioxidant systems (CAT, POD, and SOD). Finally, 13 differentially expressed genes related to LP response were identified and verified using transcriptomic data and qRT-PCR. Two gene co-expression network modules related to phosphorus responsiveness were positively correlated with POD, CAT, and PAPs. Of these, SiPHR1, functionally annotated as PHOSPHATE STARVATION RESPONSE 1, was identified as an MYB transcription factor related to phosphate responsiveness. SiPHR1 overexpression in Arabidopsis significantly modified the root architecture. LP stress caused cellular, physiological, and phenotypic changes in seedlings. SiPHR1 functioned as a positive regulator by activating downstream genes related to LP tolerance. These results improve our understanding of the molecular mechanism underlying responsiveness to LP stress, thereby laying a theoretical foundation for the genetic modification and breeding of new LP-tolerant foxtail millet varieties

Materials Design Innovations in Optimizing Cellular Behavior on Melt Electrowritten (MEW) Scaffolds

The field of melt electrowriting (MEW) has seen significant progress, bringing innovative advancements to the fabrication of biomaterial scaffolds, and creating new possibilities for applications in tissue engineering and beyond. Multidisciplinary collaboration across materials science, computational modeling, AI, bioprinting, microfluidics, and dynamic culture systems offers promising new opportunities to gain deeper insights into complex biological systems. As the focus shifts towards personalized medicine and reduced reliance on animal models, the multidisciplinary approach becomes indispensable. This review provides a concise overview of current strategies and innovations in controlling and optimizing cellular responses to MEW scaffolds, highlighting the potential of scaffold material, MEW architecture, and computational modeling tools to accelerate the development of efficient biomimetic systems. Innovations in material science and the incorporation of biologics into MEW scaffolds have shown great potential in adding biomimetic complexity to engineered biological systems. These techniques pave the way for exciting possibilities for tissue modeling and regeneration, personalized drug screening, and cell therapies.</p

Highly substituted calcium silicates 3D printed with complex architectures to produce stiff, strong and bioactive scaffolds for bone regeneration

Bone's outstanding biomechanical performance is derived from cooperative interactions between its composition and microarchitecture. Towards developing bioceramic scaffolds with similar biomechanical performance for repairing large bone defects under load, we have developed 13 new bioceramic compositions by doping various concentrations of iron and magnesium into Baghdadite (a Zr-Ca-Silicate: Ca3ZrSi2O9). The resulting bioceramics were printed into scaffolds with precisely controlled internal and external shapes using a versatile photopolymerization-based stereolithography technique. The biomechanical performance of new compositions and scaffolds were determined using mechanical tests with in situ imaging, in vitro cell study, an in vivo animal study, histological analysis, and microcomputed tomography. Mg-doped Baghdadite with composition Ca3Mg0.1Zr0.9Si2O8.9 demonstrated superior bioactivity and mechanical properties, compared to Baghdadite. 3D printed Mg-doped Baghdadite scaffolds with 35% porosity and designed architecture matched the stiffness and strength of cortical bone. These scaffolds were 2–5 times stronger than other bioceramic and bioglass scaffolds with the same porosity made with photopolymerization techniques. In vivo bone ingrowth was 2.2 times higher in Mg-doped Baghdadite than Baghdadite, effectively transforming these mechanically brittle scaffolds into deformable and tough ceramic-bone composites. Mg-doped Baghdadite scaffolds demonstrate a combination of favorable mechanical properties and bone regeneration capacity that show their potential for clinical success.</p