Co-electrospraying of tumour cell mimicking hollow polymeric microspheres for diffusion magnetic resonance imaging.

Diffusion magnetic resonance imaging (dMRI) is considered as a useful tool to study solid tumours. However, the interpretation of dMRI signal and validation of quantitative measurements of is challenging. One way to address these challenges is by using a standard reference material that can mimic tumour cell microstructure. There is a growing interest in using hollow polymeric microspheres, mainly prepared by multiple steps, as mimics of cells in healthy and diseased tissue. The present work reports on tumour cell-mimicking materials composed of hollow microspheres for application as a standard material in dMRI. These microspheres were prepared via one-step co-electrospraying process. The shell material was poly(d,l-lactic-co-glycolic acid) (PLGA) polymers with different molecule weights and/or ratios of glycolic acid-to-lactic, while the core was polyethylene glycol (PEG) or ethylene glycol. The resultant co-electrosprayed products were characterised by optical microscopy, scanning electron microscopy (SEM) and synchrotron X-ray micro-CT. These products were found to have variable structures and morphologies, e.g. from spherical particles with/without surface hole, through beaded fibres to smooth fibres, which mainly depend on PLGA composition and core materials. Only the shell material of PLGA polymer with ester terminated, Mw 50,000-75,000 g mol-1, and lactide:glycolide 85:15 formed hollow microspheres via the co-electrospraying process using the core material of 8 wt% PEG/chloroform as the core. A water-filled test object (or phantom) was designed and constructed from samples of the material generated from co-electrosprayed PLGA microspheres and tested on a 7 T MRI scanner. The preliminary MRI results provide evidence that hollow PLGA microspheres can restrict/hinder water diffusion as cells do in tumour tissue, implying that the phantom may be suitable for use as a quantitative validation and calibration tool for dMRI.

Poly(vinylphosphonic acid-co-acrylic acid) hydrogels: The effect of copolymer composition on osteoblast adhesion and proliferation.

There is a clinical need for a synthetic bone graft substitute that can be used at sites of surgical intervention to promote bone regeneration. Poly(vinylphosphonic acid-co-acrylic acid) (PVPA-co-AA) has recently been identified as a potential candidate for use in bone tissue scaffolds. It is hypothesized that PVPA-co-AA can bind to divalent calcium ions on bone mineral surfaces to control matrix mineralization and promote bone formation. In this study, hydrogels of PVPA-co-AA have been produced and the effect of copolymer composition on the structure and properties of the gels was investigated. It was found that an increase in VPA content led to the production of hydrogels with high porosities and greater swelling capacities. Consequently, improved cell adhesion and proliferation was observed on these hydrogels, as well as superior cell spreading morphologies. Furthermore, whereas poly(acrylic acid) gels were shown to be relatively brittle, an increase in VPA content created more flexible hydrogels that can be more easily molded into bone defect sites. Therefore, this work demonstrates that the mechanical and cell adhesion properties of PVPA-co-AA hydrogels can be tuned for the specific application by altering the copolymer composition. © 2017 The Authors Journal of Biomedical Materials Research Part A Published by Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 255-264, 2018.

The unique calcium chelation property of poly(vinyl phosphonic acid-co-acrylic acid) and effects on osteogenesis in vitro.

There is a clear clinical need for a bioactive bone graft substitute. Poly(vinyl phosphonic acid-co-acrylic acid) (PVPA-co-AA) has been identified as a promising candidate for bone regeneration but there is little evidence to show its direct osteogenic effect on progenitor or mature cells. In this study mature osteoblast-like cells (SaOS-2) and human bone marrow-derived mesenchymal stem cells (hBM-MSCs) were cultured with PVPA-co-AA polymers with different VPA:AA ratio and at different concentrations in vitro. We are the first to report the direct osteogenic effect of PVPA-co-AA polymer on bone cells and, more importantly, this effect was dependent on VPA:AA ratio and concentration. Under the optimized conditions, PVPA-co-AA polymer not only has an osteoconductive effect, enhancing SaOS-2 cell mineralization, but also has an osteoinductive effect to promote hBM-MSCs' osteogenic differentiation. Notably, the same PVPA-co-AA polymer at different concentrations could lead to differential osteogenic effects on both SaOS-2 and hBM-MSCs in vitro. This study furthers knowledge of the PVPA-co-AA polymer in osteogenic studies, which is critical when utilizing the PVPA-co-AA polymer for the design of novel bioactive polymeric tissue engineering scaffolds for future clinical applications. © 2017 The Authors Journal of Biomedical Materials Research Part A Published by Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 168-179, 2018.

A biomimetic tumor tissue phantom for validating diffusion-weighted MRI measurements.

PURPOSE: To develop a biomimetic tumor tissue phantom which more closely reflects water diffusion in biological tissue than previously used phantoms, and to evaluate the stability of the phantom and its potential as a tool for validating diffusion-weighted (DW) MRI measurements. METHODS: Coaxial-electrospraying was used to generate micron-sized hollow polymer spheres, which mimic cells. The bulk structure was immersed in water, providing a DW-MRI phantom whose apparent diffusion coefficient (ADC) and microstructural properties were evaluated over a period of 10 months. Independent characterization of the phantom's microstructure was performed using scanning electron microscopy (SEM). The repeatability of the construction process was investigated by generating a second phantom, which underwent high resolution synchrotron-CT as well as SEM and MR scans. RESULTS: ADC values were stable (coefficients of variation (CoVs) < 5%), and varied with diffusion time, with average values of 1.44 ± 0.03 µm2 /ms (Δ = 12 ms) and 1.20 ± 0.05 µm2 /ms (Δ = 45 ms). Microstructural parameters showed greater variability (CoVs up to 13%), with evidence of bias in sphere size estimates. Similar trends were observed in the second phantom. CONCLUSION: A novel biomimetic phantom has been developed and shown to be stable over 10 months. It is envisaged that such phantoms will be used for further investigation of microstructural models relevant to characterizing tumor tissue, and may also find application in evaluating acquisition protocols and comparing DW-MRI-derived biomarkers obtained from different scanners at different sites. Magn Reson Med 80:147-158, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Development of multisubstituted hydroxyapatite nanopowders as biomedical materials for bone tissue engineering applications.

Ionic substitutions have been proposed as a tool to control the functional behavior of synthetic hydroxyapatite (HA), particularly for Bone Tissue Engineering applications. The effect of simultaneous substitution of different levels of carbonate (CO3 ) and silicon (Si) ions in the HA lattice was investigated. Furthermore, human bone marrow-derived mesenchymal stem cells (hMSCs) were cultured on multi-substituted HA (SiCHA) to determine if biomimetic chemical compositions were osteoconductive. Of the four different compositions investigates, SiCHA-1 (0.58 wt % Si) and SiCHA-2 (0.45 wt % Si) showed missing bands for CO3 and Si using FTIR analysis, indicating competition for occupation of the phosphate site in the HA lattice; 500°C was considered the most favorable calcination temperature as: (i) the powders produced possessed a similar amount of CO3 (2-8 wt %) and Si (<1.0 wt %) as present in native bone; and (ii) there was a minimal loss of CO3 and Si from the HA structure to the surroundings during calcination. Higher Si content in SiCHA-1 led to lower cell viability and at most hindered proliferation, but no toxicity effect occurred. While, lower Si content in SiCHA-2 showed the highest ALP/DNA ratio after 21 days culture with hMSCs, indicating that the powder may stimulate osteogenic behavior to a greater extent than other powders. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1775-1785, 2017.

Defining a turnover index for the correlation of biomaterial degradation and cell based extracellular matrix synthesis using fluorescent tagging techniques.

Non-destructive protocols which can define a biomaterial's degradation and its associated ability to support proliferation and/or promote extracellular matrix deposition will be an essential in vitro tool. In this study we investigate fluorescently tagged biomaterials, with varying rates of degradation and their ability to support cell proliferation and osteogenic differentiation. Changes in fluorescence of the biomaterials and the release of fluorescent soluble by-products were confirmed as accurate methods to quantify degradation. It was demonstrated that increasing rates of the selected biomaterials' degradation led to a decrease in cell proliferation and concurrently an increase in osteogenic matrix production. A novel turnover index (TI), which directly describes the effect of degradation of a biomaterial on cell behaviour, was calculated. Lower TIs for proliferation and high TIs for osteogenic marker production were observed on faster degrading biomaterials, indicating that these biomaterials supported an upregulation of osteogenic markers. This TI was further validated using an ex vivo chick femur model, where the faster degrading biomaterial, fibrin, led to an increased TI for mineralisation within an epiphyseal defect. This in vitro tool, TI, for monitoring the effect of biomaterial degradation on extracellular matrix production may well act as predictor of the selected biomaterials' performance during in vivo studies. STATEMENT OF SIGNIFICANCE: This paper outlines a novel metric, Turnover Index (TI), which can be utilised in tissue-engineering for the comparison of a range of biomaterials. The metric sets out to define the relationship between the rate of degradation of biomaterials with the rate of cell proliferation and ECM synthesis, ultimately allowing us to tailor material for set clinical requirements. We have discovered some novel comparative findings that cells cultured on biomaterials with increased rates of degradation have lower rates of proliferation but alternatively have a greater production of osteogenic markers compared to materials which degrade slower. By making comparisons in a rigorous manner, we can begin to define a useful matrix for materials which ultimately may aid for clinical selection.

The application of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) scaffolds for tendon repair in the rat model.

Tendon injuries and defects present a substantial burden to global healthcare economies. There are no synthetic/biosynthesised implants available which can restore full function or match the mechanical properties of native tendon. Therefore, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) was investigated for its utility as a scaffold in a rat Achilles tendon repair model. Porous PHBHHx tubes and fibres were prepared with particle leaching and extrusion methods, respectively. Collagen gels reinforced by polymer fibres were inserted into the lumen of scaffold tubes to create the operational scaffold unit. Mechanical testing demonstrated that PHBHHx scaffolds had comparable mechanical properties to rat tendon, with maximal loads of 23.73 ± 1.08 N, compared to 17.35 ± 1.76 N in undamaged rat Achilles tendon. Sprague-Dawley (SD) rats were split into four experimental groups: control, PHBHHx scaffold only, PHBHHx scaffold and collagen, PHBHHx scaffold, collagen and tenocyte compositions for implantation to repair an induced Achilles tendon defect. No secondary immune response to PHBHHx was observed over a 40 days period of implantation. Movement was restored in PHBHHx scaffold-collagen-tenocyte recipient rats at an earlier time point than in other experimental groups, with complete load-bearing and function returning 20 days post-surgery as determined by the Achilles Functional Index. In vitro testing of tendon constructs after 40 days demonstrated reductions in PHBHHx molecular weight and polydispersity index accompanied by an increase in mean chain length indicating degradation of smaller polymer chain subunits. Similarly a reduction in PHBHHx tube ultimate tensile strength and elastic modulus was observed. Histological analysis provided evidence of tissue remodelling and cell alignment. In summary, PHBHHx scaffolds have been successfully applied in an in vivo tendon repair model raising promise for future utility in tissue engineering applications.

One-step recovery of marrow stromal cells on nanofibers.

This study describes the one-step isolation and expansion of marrow stromal cells (MSCs) directly onto the implantable nanofibrous scaffolds. Coverslips were first coated with either aligned or random configurations of poly L,D lactic acid, poly lactic-glycolic acid, and poly-epsilon-caprolactone and then seeded with fresh bone marrow aspirate. Colony-forming units were quantified and the differentiation capacities of the recovered cells were explored. Further optimization was provided by exploring the impact of hyperoxic (21% O(2)) and physiologically approximate (2% O(2)) on cell recovery. Aligned nanofibers in 2% O(2) were identified as being superior for isolation of MSCs. Isolated cells formed colonies following the direction of nanofibers, indicating potential for guided tissue regeneration. The isolated MSCs demonstrated retention of multipotency. These findings offer a rapid, cost-effective method of producing a stem-cell-seeded scaffold for regeneration of multiple tissue types.