An in vitro assessment of the thermoreversible PLGA-PEG-PLGA copolymer: Implications for Descemet's membrane endothelial keratoplasty.

BACKGROUND: To explore the use of a thermoreversible copolymer gel coating to prevent donor tissue scrolling in Descemet's membrane endothelial keratoplasty (DMEK). METHODS: PLGA-PEG-PLGA triblock copolymer was synthesised via ring opening polymerisation. Two formulations were fabricated and gelation properties characterised using rheological analyses. Endothelial cytotoxicity of the copolymer was assessed using a Trypan Blue exclusion assay. Thickness of the copolymer gel coating on the endothelial surface was analysed using anterior segment optical coherence tomography (OCT) (RTVue-100, Optovue Inc.). Gold nanoparticles were added to the copolymer to aid visualisation using OCT. Prevention of Descemet membrane donor scrolling was represented via a novel, in vitro, immersion of copolymer coated donor graft material. RESULTS: Two different formulations of PLGA-PEG-PLGA copolymer were successfully fabricated and the desired peak gelling temperature of 24°C was achieved by polymer blending. Application of 20%, 30% and 40% (wt/vol) polymer concentrations resulted in a statistically significant increase in polymer thickness on the endothelium (p < 0.001). There was no detectable endothelial cytotoxicity. The polymer was easy to apply to the endothelium and prevented scrolling of the DMEK graft. CONCLUSION: This PLGA-PEG-PLGA thermoreversible copolymer gel could be exploited as a therapeutic aid for preventing DMEK graft scrolling.

Droplet Microfluidic Optimisation Using Micropipette Characterisation of Bio-Instructive Polymeric Surfactants.

Droplet microfluidics can produce highly tailored microparticles whilst retaining monodispersity. However, these systems often require lengthy optimisation, commonly based on a trial-and-error approach, particularly when using bio-instructive, polymeric surfactants. Here, micropipette manipulation methods were used to optimise the concentration of bespoke polymeric surfactants to produce biodegradable (poly(d,l-lactic acid) (PDLLA)) microparticles with unique, bio-instructive surface chemistries. The effect of these three-dimensional surfactants on the interfacial tension of the system was analysed. It was determined that to provide adequate stabilisation, a low level (0.1% (w/v)) of poly(vinyl acetate-co-alcohol) (PVA) was required. Optimisation of the PVA concentration was informed by micropipette manipulation. As a result, successful, monodisperse particles were produced that maintained the desired bio-instructive surface chemistry.

In vitro, in silico and in vivo study challenges the impact of bronchial thermoplasty on acute airway smooth muscle mass loss.

Bronchial thermoplasty is a treatment for asthma. It is currently unclear whether its histopathological impact is sufficiently explained by the proportion of airway wall that is exposed to temperatures necessary to affect cell survival.Airway smooth muscle and bronchial epithelial cells were exposed to media (37-70°C) for 10 s to mimic thermoplasty. In silico we developed a mathematical model of airway heat distribution post-thermoplasty. In vivo we determined airway smooth muscle mass and epithelial integrity pre- and post-thermoplasty in 14 patients with severe asthma.In vitro airway smooth muscle and epithelial cell number decreased significantly following the addition of media heated to ≥65°C. In silico simulations showed a heterogeneous heat distribution that was amplified in larger airways, with <10% of the airway wall heated to >60°C in airways with an inner radius of ∼4 mm. In vivo at 6 weeks post-thermoplasty, there was an improvement in asthma control (measured via Asthma Control Questionnaire-6; mean difference 0.7, 95% CI 0.1-1.3; p=0.03), airway smooth muscle mass decreased (absolute median reduction 5%, interquartile range (IQR) 0-10; p=0.03) and epithelial integrity increased (14%, IQR 6-29; p=0.007). Neither of the latter two outcomes was related to improved asthma control.Integrated in vitro and in silico modelling suggest that the reduction in airway smooth muscle post-thermoplasty cannot be fully explained by acute heating, and nor did this reduction confer a greater improvement in asthma control.

Fungal Attachment-Resistant Polymers for the Additive Manufacture of Medical Devices.

This study reports the development of the first copolymer material that (i) is resistant to fungal attachment and hence biofilm formation, (ii) operates via a nonkilling mechanism, i.e., avoids the use of antifungal actives and the emergence of fungal resistance, (iii) exhibits sufficient elasticity for use in flexible medical devices, and (iv) is suitable for 3D printing (3DP), enabling the production of safer, personalized medical devices. Candida albicans (C. albicans) can form biofilms on in-dwelling medical devices, leading to potentially fatal fungal infections in the human host. Poly(dimethylsiloxane) (PDMS) is a common material used for the manufacture of medical devices, such as voice prostheses, but it is prone to microbial attachment. Therefore, to deliver a fungal-resistant polymer with key physical properties similar to PDMS (e.g., flexibility), eight homopolymers and 30 subsequent copolymers with varying glass transition temperatures (Tg) and fungal antiattachment properties were synthesized and their materials/processing properties studied. Of the copolymers produced, triethylene glycol methyl ether methacrylate (TEGMA) copolymerized with (r)-α-acryloyloxy-ß,ß-dimethyl-γ-butyrolactone (AODMBA) at a 40:60 copolymer ratio was found to be the most promising candidate by meeting all of the above criteria. This included demonstrating the capability to successfully undergo 3DP by material jetting, via the printing of a voice prosthesis valve-flap using the selected copolymer.

Bioactive coatings on 3D printed scaffolds for bone regeneration: Use of Laponite® to deliver BMP-2 in an ovine femoral condyle defect model.

Biomaterial-based approaches for bone regeneration seek to explore alternative strategies to repair non-healing fractures and critical-sized bone defects. Fracture non-union occurs due to a number of factors resulting in the formation of bone defects. Rigorous evaluation of the biomaterials in relevant models and assessment of their potential to translate towards clinical use is vital. Large animal experimentation can be used to model fracture non-union while scaling-up materials for clinical use. Growth factors modulate cell phenotype, behaviour and initiate signalling pathways leading to changes in matrix deposition and tissue formation. Bone morphogenetic protein-2 (BMP-2) is a potent osteogenic growth factor, with a rapid clearance time in vivo necessitating clinical use at a high dose, with potential deleterious side-effects. The current studies have examined the potential for Laponite® nanoclay coated poly(caprolactone) trimethacrylate (PCL-TMA900) scaffolds to bind BMP-2 for enhanced osteoinduction in a large animal critical-sized bone defect. An ovine femoral condyle defect model confirmed PCL-TMA900 scaffolds coated with Laponite®/BMP-2 produced significant bone formation compared to the uncoated PCL-TMA 900 scaffold in vivo, assessed by micro-computed tomography (µCT) and histology. This indicated the ability of Laponite® to deliver the bioactive BMP-2 on the PCL-TMA900 scaffold. Bone formed around the Laponite®/BMP-2 coated PCL-TMA900 scaffold, with no erroneous bone formation observed away from the scaffold material confirming localisation of BMP-2 delivery. The current studies demonstrate the ability of a nanoclay to localise and deliver bioactive BMP-2 within a tailored octet-truss scaffold for efficacious bone defect repair in a large animal model with significant implications for translation to the clinic.

Glycerol-based sustainably sourced resin for volumetric printing.

Volumetric Additive Manufacturing (VAM) represents a revolutionary advancement in the field of Additive Manufacturing, as it allows for the creation of objects in a single, cohesive process, rather than in a layer-by-layer approach. This innovative technique offers unparalleled design freedom and significantly reduces printing times. A current limitation of VAM is the availability of suitable resins with the required photoreactive chemistry and from sustainable sources. To support the application of this technology, we have developed a sustainable resin based on polyglycerol, a bioderived (e.g., vegetable origin), colourless, and easily functionisable oligomer produced from glycerol. To transform polyglycerol-6 into an acrylate photo-printable resin we adopted a simple, one-step, and scalable synthesis route. Polyglycerol-6-acrylate fulfils all the necessary criteria for volumetric printing (transparency, photo-reactivity, viscosity) and was successfully used to print a variety of models with intricate geometries and good resolution. The waste resin was found to be reusable with minimal performance issues, improving resin utilisation and minimising waste material. Furthermore, by incorporating dopants such as poly(glycerol) adipate acrylate (PGA-A) and 10,12-pentacosadyinoic acid (PCDA), we demonstrated the ability to print objects with a diverse range of functionalities, including temperature sensing probes and a polyester excipient, highlighting the potential applications of these new resins.

Tissue engineering in the development of replacement technologies.

The field of tissue engineering is generating new scaffolds, bioreactors and methods for stimulating cells within complex cultures, with the aim of recreating the conditions under which cells form functional tissues. Hitherto, the primary focus of this field has been on clinical applications. However, there are many methods of in vitro tissue engineering that represent new opportunities in 3D cell culture and could be the basis for new replacement methods that either replace the use of a tissue isolated from an animal or the use of a living animal. This chapter presents an overview of tissue engineering and provides tissue-specific examples of recent advances.

Mineralizing Coating on 3D Printed Scaffolds for the Promotion of Osseointegration.

Design and fabrication of implants that can perform better than autologous bone grafts remain an unmet challenge for the hard tissue regeneration in craniomaxillofacial applications. Here, we report an integrated approach combining additive manufacturing with supramolecular chemistry to develop acellular mineralizing 3D printed scaffolds for hard tissue regeneration. Our approach relies on an elastin-like recombinamer (ELR) coating designed to trigger and guide the growth of ordered apatite on the surface of 3D printed nylon scaffolds. Three test samples including a) uncoated nylon scaffolds (referred to as "Uncoated"), b) ELR coated scaffolds (referred to as "ELR only"), and c) ELR coated and in vitro mineralized scaffolds (referred to as "Pre-mineralized") were prepared and tested for in vitro and in vivo performance. All test samples supported normal human immortalized mesenchymal stem cell adhesion, growth, and differentiation with enhanced cell proliferation observed in the "Pre-mineralized" samples. Using a rabbit calvarial in vivo model, 'Pre-mineralized' scaffolds also exhibited higher bone ingrowth into scaffold pores and cavities with higher tissue-implant integration. However, the coated scaffolds ("ELR only" and "Pre-mineralized") did not exhibit significantly more new bone formation compared to "Uncoated" scaffolds. Overall, the mineralizing coating offers an opportunity to enhance integration of 3D printed bone implants. However, there is a need to further decipher and tune their immunologic response to develop truly osteoinductive/conductive surfaces.

Ink-jet 3D printing as a strategy for developing bespoke non-eluting biofilm resistant medical devices.

Chronic infection as a result of bacterial biofilm formation on implanted medical devices is a major global healthcare problem requiring new biocompatible, biofilm-resistant materials. Here we demonstrate how bespoke devices can be manufactured through ink-jet-based 3D printing using bacterial biofilm inhibiting formulations without the need for eluting antibiotics or coatings. Candidate monomers were formulated and their processability and reliability demonstrated. Formulations for in vivo evaluation of the 3D printed structures were selected on the basis of their in vitro bacterial biofilm inhibitory properties and lack of mammalian cell cytotoxicity. In vivo in a mouse implant infection model, Pseudomonas aeruginosa biofilm formation on poly-TCDMDA was reduced by ∼99% when compared with medical grade silicone. Whole mouse bioluminescence imaging and tissue immunohistochemistry revealed the ability of the printed device to modulate host immune responses as well as preventing biofilm formation on the device and infection of the surrounding tissues. Since 3D printing can be used to manufacture devices for both prototyping and clinical use, the versatility of ink-jet based 3D-printing to create personalised functional medical devices is demonstrated by the biofilm resistance of both a finger joint prosthetic and a prostatic stent printed in poly-TCDMDA towards P. aeruginosa and Staphylococcus aureus.

Review of emerging nanotechnology in bone regeneration: progress, challenges, and perspectives.

The application of nanotechnology to regenerative medicine has increased over recent decades. The development of materials that can influence biology at the nanoscale has gained interest as our understanding of the interactions between cells and biomaterials at the nanoscale has grown. Materials that are either nanostructured or influence the nanostructure of the cellular microenvironment have been developed and shown to have advantages over their microscale counterparts. There are several reviews which have been published that discuss how nanomaterials have been used in regenerative medicine, particularly in bone regeneration. Most of these studies have explored this concept in specific areas, such as the application of glass-based nanocomposites, nanotechnology for targeted drug delivery to stimulate bone repair, and the progress in nanotechnology for the treatment of osteoporosis. In this review paper, the impact of nanotechnology in biomaterials development for bone regeneration will be discussed highlighting specifically, nanostructured materials that influence mechanical properties, biocompatibility, and osteoinductivity.

Mixed polymer and bioconjugate core/shell electrospun fibres for biphasic protein release.

Effective regenerative medicine requires delivery systems which can release multiple components at appropriate levels and at different phases of tissue growth and repair. However, there are few biomaterials and encapsulation techniques that are fully suitable for the loading and controlled release of multiple proteins. In this study we describe how proteins were physically and chemically loaded into a single coaxial electrospun fibre scaffold to obtain bi-phasic release profiles. Cyto-compatible polymers were used to construct the scaffold, using polyethylene oxide (PEO) for the core and polycaprolactone (PCL) reacted or mixed with (bis-aminopropyl)polyether (Jeffamine ED2003; JFA) for the shell. Horseradish peroxidase (HRP), a model protein, was loaded in the core and functionalised onto the scaffold surface by coupling of protein carboxyl groups to the available polymer amine groups. Fibre morphologies were evaluated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and functional group content was determined using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF SIMS). Hydrophobicity profiles of the fibres before and after protein loading were evaluated by water contact angle (WCA) and the mechanical properties of the electrospun scaffolds were determined by performing tensile tests. The electrospun fibre scaffolds generated by reacting PEO/PCL with 1,6-diaminohexane and those from mixing PEO/PCL with JFA were further characterised for protein conjugation and release. Fibres prepared by the mixed PEO/PCL/JFA system were found to be the most appropriate for the simultaneous release of protein from the core and the immobilisation of another protein on the shell of the same scaffold. Moreover, JFA enhanced scaffold properties in terms of porosity and elasticity. Finally, we successfully demonstrated the cytocompatibility and cell response to protein-loaded and -conjugated scaffolds using HepG2 cells. Enhanced cell attachment (2.5 fold) was demonstrated using bovine serum albumin (BSA)-conjugated scaffolds, and increased metabolic activity observed with retinoic acid (RA)-loaded scaffolds (2.7 fold).

Bespoke 3D-Printed Polydrug Implants Created via Microstructural Control of Oligomers.

Controlling the microstructure of materials by means of phase separation is a versatile tool for optimizing material properties. Phase separation has been exploited to fabricate intricate microstructures in many fields including cell biology, tissue engineering, optics, and electronics. The aim of this study was to use phase separation to tailor the spatial location of drugs and thereby generate release profiles of drug payload over periods ranging from 1 week to months by exploiting different mechanisms: polymer degradation, polymer diluent dissolution, and control of microstructure. To achieve this, we used drop-on-demand inkjet three-dimensional (3D) printing. We predicted the microstructure resulting from phase separation using high-throughput screening combined with a model based on the Flory-Huggins interaction parameter and were able to show that drug release from 3D-printed objects can be predicted from observations based on single drops of mixtures. We demonstrated for the first time that inkjet 3D printing yields controllable phase separation using picoliter droplets of blended photoreactive oligomers/monomers. This new understanding gives us hierarchical compositional control, from droplet to device, allowing release to be "dialled up" without manipulation of device geometry. We exemplify this approach by fabricating a biodegradable, long-term, multiactive drug delivery subdermal implant ("polyimplant") for combination therapy and personalized treatment of coronary heart disease. This is an important advance for implants that need to be delivered by cannula, where the shape is highly constrained and thus the usual geometrical freedoms associated with 3D printing cannot be easily exploited, which brings a hitherto unseen level of understanding to emergent material properties of 3D printing.

Discovery of synergistic material-topography combinations to achieve immunomodulatory osteoinductive biomaterials using a novel in vitro screening method: The ChemoTopoChip.

Human mesenchymal stem cells (hMSCs) are widely represented in regenerative medicine clinical strategies due to their compatibility with autologous implantation. Effective bone regeneration involves crosstalk between macrophages and hMSCs, with macrophages playing a key role in the recruitment and differentiation of hMSCs. However, engineered biomaterials able to simultaneously direct hMSC fate and modulate macrophage phenotype have not yet been identified. A novel combinatorial chemistry-topography screening platform, the ChemoTopoChip, is used here to identify materials suitable for bone regeneration by screening 1008 combinations in each experiment for human immortalized mesenchymal stem cell (hiMSCs) and human macrophage response. The osteoinduction achieved in hiMSCs cultured on the "hit" materials in basal media is comparable to that seen when cells are cultured in osteogenic media, illustrating that these materials offer a materials-induced alternative to osteo-inductive supplements in bone-regeneration. Some of these same chemistry-microtopography combinations also exhibit immunomodulatory stimuli, polarizing macrophages towards a pro-healing phenotype. Maximum control of cell response is achieved when both chemistry and topography are recruited to instruct the required cell phenotype, combining synergistically. The large combinatorial library allows us for the first time to probe the relative cell-instructive roles of microtopography and material chemistry which we find to provide similar ranges of cell modulation for both cues. Machine learning is used to generate structure-activity relationships that identify key chemical and topographical features enhancing the response of both cell types, providing a basis for a better understanding of cell response to micro topographically patterned polymers.

Exploiting Generative Design for 3D Printing of Bacterial Biofilm Resistant Composite Devices.

As the understanding of disease grows, so does the opportunity for personalization of therapies targeted to the needs of the individual. To bring about a step change in the personalization of medical devices it is shown that multi-material inkjet-based 3D printing can meet this demand by combining functional materials, voxelated manufacturing, and algorithmic design. In this paper composite structures designed with both controlled deformation and reduced biofilm formation are manufactured using two formulations that are deposited selectively and separately. The bacterial biofilm coverage of the resulting composites is reduced by up to 75% compared to commonly used silicone rubbers, without the need for incorporating bioactives. Meanwhile, the composites can be tuned to meet user defined mechanical performance with ±10% deviation. Device manufacture is coupled to finite element modelling and a genetic algorithm that takes the user-specified mechanical deformation and computes the distribution of materials needed to meet this under given load constraints through a generative design process. Manufactured products are assessed against the mechanical and bacterial cell-instructive specifications and illustrate how multifunctional personalization can be achieved using generative design driven multi-material inkjet based 3D printing.

Maintenance of pluripotency in human embryonic stem cells cultured on a synthetic substrate in conditioned medium.

Realizing the potential clinical and industrial applications of human embryonic stem cells (hESCs) is limited by the need for costly, labile, or undefined growth substrates. Here we demonstrate that trypsin passaging of the hESC lines, HUES7 and NOTT1, on oxygen plasma etched tissue culture polystyrene (PE-TCPS) in conditioned medium is compatible with pluripotency. This synthetic culture surface is stable at room temperature for at least a year and is readily prepared by placing polystyrene substrates in a radio frequency oxygen plasma generator for 5 min. Modification of the polystyrene surface chemistry by plasma etching was confirmed by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS), which identified elemental and molecular changes as a result of the treatment. Pluripotency of hESCs cultured on PE-TCPS was gauged by consistent proliferation during serial passage, expression of stem cell markers (OCT4, TRA1-60, and SSEA-4), stable karyotype and multi-germlayer differentiation in vitro, including to pharmacologically responsive cardiomyocytes. Generation of cost-effective, easy-to-handle synthetic, defined, stable surfaces for hESC culture will expedite stem cell use in biomedical applications.

Investigating the feasibility of spatially offset Raman spectroscopy for in-vivo monitoring of bone healing in rat calvarial defect models.

A wide range of biomaterials and tissue-engineered scaffolds are being investigated to support and stimulate bone healing in animal models. Using phantoms and rat cadavers, we investigated the feasibility of using spatially offset Raman spectroscopy (SORS) to monitor changes in collagen concentration at levels similar to those expected to occur in vivo during bone regeneration (0-0.84 g/cm3 ). A partial least squares (PLS) regression model was developed to quantify collagen concentration in plugs consisting of mixtures or collagen and hydroxyapatite (predictive power of ±0.16 g/cm3 ). The PLS model was then applied on SORS spectra acquired from rat cadavers after implanting the collagen: hydroxyapatite plugs in drilled skull defects. The PLS model successfully predicting the profile of collagen concentration, but with an increased predictive error of ±0.30 g/cm3 . These results demonstrate the potential of SORS to quantify collagen concentrations, in the range relevant to those occurring during new bone formation.

Bioinspired Precision Engineering of Three-Dimensional Epithelial Stem Cell Microniches.

Maintenance of the epithelium relies on stem cells residing within specialized microenvironments, known as epithelial crypts. Two-photon polymerization (2PP) is a valuable tool for fabricating 3D micro/nanostructures for stem cell niche engineering applications. Herein, biomimetic gelatin methacrylate-based constructs, replicating the precise geometry of the limbal epithelial crypt structures (limbal stem cell "microniches") as an exemplar epithelial niche, are fabricated using 2PP. Human limbal epithelial stem cells (hLESCs) are seeded within the microniches in xeno-free conditions to investigate their ability to repopulate the crypts and the expression of various differentiation markers. Cell proliferation and a zonation in cell phenotype along the z-axis are observed without the use of exogenous signaling molecules. Significant differences in cell phenotype between cells located at the base of the microniche and those situated towards the rim are observed, demonstrating that stem cell fate is strongly influenced by its location within a niche and the geometrical details of where it resides. This study provides insight into the influence of the niche's spatial geometry on hLESCs and demonstrates a flexible approach for the fabrication of biomimetic crypt-like structures in epithelial tissues. This has significant implications for regenerative medicine applications and can ultimately lead to implantable synthetic "niche-based" treatments.

Stem cells from the dental apical papilla in extracellular matrix hydrogels mitigate inflammation of microglial cells.

After spinal cord injury (SCI) chronic inflammation hampers regeneration. Influencing the local microenvironment after SCI may provide a strategy to modulate inflammation and the immune response. The objectives of this work were to determine whether bone or spinal cord derived ECM hydrogels can deliver human mesenchymal stem cells from the apical papilla (SCAP) to reduce local inflammation and provide a regenerative microenvironment. Bone hydrogels (8 and 10 mg/ml, B8 and B10) and spinal cord hydrogels (8 mg/ml, S8) supplemented with fibrin possessed a gelation rate and a storage modulus compatible with spinal cord implantation. S8 and B8 impact on the expression of anti and pro-inflammatory cytokines (Arg1, Nos2, Tnf) in LPS treated microglial cells were assessed using solubilised and solid hydrogel forms. S8 significantly reduced the Nos2/Arg1 ratio and solubilised B8 significantly reduced Tnf and increased Arg1 whereas solid S8 and B8 did not impact inflammation in microglial cells. SCAP incorporation within ECM hydrogels did not impact upon SCAP immunoregulatory properties, with significant downregulation of Nos2/Arg1 ratio observed for all SCAP embedded hydrogels. Tnf expression was reduced with SCAP embedded in B8, reflecting the gene expression observed with the innate hydrogel. Thus, ECM hydrogels are suitable vehicles to deliver SCAP due to their physical properties, preservation of SCAP viability and immunomodulatory capacity.

A thermoresponsive three-dimensional fibrous cell culture platform for enzyme-free expansion of mammalian cells.

A three-dimensional thermoresponsive fibrous scaffold system for the subsequent extended culture and enzyme-free passaging of a range of mammalian cell types is presented. Poly(PEGMA188) was incorporated with poly(ethylene terephthalate) (PET) via blend-electrospinning to render the fibre thermoresponsive. Using primary human corneal stromal stem cells as an therapeutically relevant exemplar, cell adhesion, viability, proliferation and phenotype on this fibrous culture system over numerous thermal enzyme-free passages is described. We also illustrate the versatility of this system with respect to fabricating thermoresponsive fibres from biodegradable polymers and for the culture of diverse mammalian cell types including mesenchymal stem cells, colon adenocarcinoma cells and NIH-3T3 fibroblasts. This thermoresponsive scaffold system combines the advantages of providing a physiologically relevant environment to maintain a desirable cell phenotype, allowing routine enzyme-free passaging and expansion of cultured cells, whilst offering mechanical support for cell growth. The system described in this study presents a versatile platform for biomedical applications and more specifically for the expansion of mammalian cells destined for the clinic. STATEMENT OF SIGNIFICANCE: The lack of three-dimensional (3D) cell culture environments significantly impacts mammalian cell morphology, proliferation and phenotype in vitro. A versatile, 3D fibrous scaffold system for the extended culture and passaging of a range of clinically-relevant cell types is presented herein. This methodology can be used to fabricate thermoresponsive fibres from polymer blends of any polymer amenable to electrospinning and with a thermoresponsive component. A variety of mammalian cells cultured on the thermoresponsive system were detached from the surface solely by lowering the temperature whilst retaining high viability, a desirable cell phenotype, and supported long-term cell proliferation over numerous thermal enzyme-free passages. This is a significant advance for in vitro expansion of diverse cell types destined for the clinic.

Spatially-offset Raman spectroscopy for monitoring mineralization of bone tissue engineering scaffolds: feasibility study based on phantom samples.

Using phantom samples, we investigated the feasibility of spatially-offset Raman spectroscopy (SORS) as a tool for monitoring non-invasively the mineralization of bone tissue engineering scaffold in-vivo. The phantom samples consisted of 3D-printed scaffolds of poly-caprolactone (PCL) and hydroxyapatite (HA) blends, with varying concentrations of HA, to mimic the mineralisation process. The scaffolds were covered by a 4 mm layer of skin to simulate the real in-vivo measurement conditions. At a concentration of HA approximately 1/3 that of bone (~0.6 g/cm3), the characteristic Raman band of HA (960 cm-1) was detectable when the PCL:HA layer was located at 4 mm depth within the scaffold (i.e. 8 mm below the skin surface). For the layers of the PCL:HA immediately under the skin (i.e. top of the scaffold), the detection limit of HA was 0.18 g/cm3, which is approximately one order of magnitude lower than that of bone. Similar results were also found for the phantoms simulating uniform and inward gradual mineralisation of the scaffold, indicating the suitability of SORS to detect early stages of mineralisation. Nevertheless, the results also show that the contribution of the materials surrounding the scaffold can be significant and methods for subtraction need to be investigated in the future. In conclusion, these results indicate that spatially-offset Raman spectroscopy is a promising technique for in-vivo longitudinal monitoring scaffold mineralization and bone re-growth.