Institute for Biomedical Engineering, Science and Technology
(Toronto Metropolitan University and St. Michael's Hospital)
 
Department of Chemical Engineering (Toronto Metropolitan University)

Li M, Joung D, Hughes B, Waldman SD, Kozinski JA, Hwang DK (2016)

Scientific Reports 6:30463.

Surface wrinkled particles are ubiquitous in nature and present in different sizes and shapes, such as plant pollens and peppercorn seeds. These natural wrinkles provide the particles with advanced functions to survive and thrive in nature. In this work, by combining flow lithography and plasma treatment, we have developed a simple method that can rapidly create wrinkled non-spherical particles, mimicking the surface textures in nature. Due to the oxygen inhibition in flow lithography, the non-spherical particles synthesized in a microfluidic channel are covered by a partially cured polymer (PCP) layer. When exposed to plasma treatment, this PCP layer rapidly buckles, forming surface-wrinkled particles. We designed and fabricated various particles with desired shapes and sizes. The surfaces of these shapes were tuned to created wrinkle morphologies by controlling UV exposure time and the washing process. We further demonstrated that wrinkles on the particles significantly promoted cell attachment without any chemical modification, potentially providing a new route for cell attachment for various biomedical applications.

Hayami JWS, Waldman SD, Amsden BG (2016)

Macromolecular Bioscience 16(7):1083-1095.

Chondrocyte-seeded, photo-cross-linked hydrogels prepared from solutions containing 50% mass fractions of methacrylated glycol chitosan or methacrylated hyaluronic acid (MHA) with methacrylated chondroitin sulfate (MCS) are cultured in vitro under static conditions over 35 d to assess their suitability for load-bearing soft tissue repair. The photo-cross-linked hydrogels have initial equilibrium moduli between 100 and 300 kPa, but only the MHAMCS hydrogels retain an approximately constant modulus (264 ± 5 kPa) throughout the culture period. Visually, the seeded chondrocytes in the MHAMCS hydrogels are well distributed with an apparent constant viability in culture. Multicellular aggregates are surrounded by cartilaginous matrix, which contain aggrecan and collagen II. Thus, co-cross-linked MCS and MHA hydrogels may be suited for use in an articular cartilage or nucleus pulposus repair applications.

Weber JF, Waldman SD (2016)

Journal of Orthopaedic Research 34(2):231-239.

Cellular mechanosensitivity is an important factor during the mechanical stimulation of tissue engineered cartilage. While the application of mechanical stimuli improves tissue growth and properties, chondrocytes also rapidly desensitize under prolonged loading thereby limiting its effectiveness. One potential method to mitigate load-induced desensitization is by superimposing noise on the loading waveforms ("stochastic resonance"). Thus, the purpose of this study was to investigate the effects of stochastic resonance on chondrocyte matrix metabolism. Chondrocyte-seeded agarose gels were subjected to dynamic compressive loading, with or without, superimposed vibrations of different amplitudes and frequency bandwidths. Changes in matrix biosynthesis were determined by radioisotope incorporation and subsequent effects on intracellular calcium signaling were evaluated by confocal microscopy. Although dependent on the duration of loading, superimposed vibrations improved cellular sensitivity to mechanical loading by further increasing matrix synthesis between 20-60%. Stochastic resonance also appeared to limit load-induced desensitization by maintaining sensitivity under desensitized loading conditions. While superimposed vibrations had little effect on the magnitude of intracellular calcium signaling, recovery of mechanosensitivity after stimulation was achieved at a faster rate suggesting that less time may be required between successive loading applications. Thus, stochastic resonance appears to be a valuable tool during the mechanical stimulation of cartilage constructs, even when suboptimal stimulation conditions are used.

Li M1, Hakimi N, Perez R, Waldman S, Kozinski JA, Hwang DK (2015)

Advanced Materials 27(11):1880-1886.

Partial polymerization during photolitho­graphy is precisely controlled to obtain a partially cured (PCP) layer on the formed 3D microstructures. Upon plasma treatment, a 3D surface with morphologically tunable and spatially controllable wrinkles is obtained. The fabrication process is characterized and its ability to make various wrinkled microstructures is demonstrated. Experiments show cells can sense 3D wrinkled microstructures, attach, and bridge between them.

Zhao Y, Waldman SD, Flynn LE (2015)

Journal of Tissue Engineering and Regenerative Medicine 9(7):826-837.

Stem cell interactions through paracrine cell signalling can regulate a range of cell responses, including metabolic activity, proliferation and differentiation. Moving towards the development of optimized tissue-engineering strategies with adipose-derived stem cells (ASCs), the focus of this study was on developing indirect co-culture models to study the effects of mature adipocytes, chondrocytes and osteoblasts on bovine ASC multilineage differentiation. For each lineage, ASC differentiation was characterized by histology, gene expression and protein expression, in the absence of key inductive differentiation factors for the ASCs. Co-culture with each of the mature cell populations was shown to successfully induce or enhance lineage-specific differentiation of the ASCs. In general, a more homogeneous but lower-level differentiation response was observed in co-culture as compared to stimulating the bovine ASCs with inductive differentiation media. To explore the role of the Wnt canonical and non-canonical signalling pathways within the model systems, the effects of the Wnt inhibitors WIF-1 and DKK-1 on multilineage differentiation in co-culture were assessed. The data indicated that Wnt signalling may play a role in mediating ASC differentiation in co-culture with the mature cell populations.

Hayami JWS, Waldman SD, Amsden BG (2015)

European Polymer Journal 72:687-690.

Photo-cross-linked hydrogels produced from solution blends of methacrylated glycol chitosan (MGC), hyaluronic acid (MHA) and chondroitin sulfate (MCS) were examined for their potential use as load bearing soft tissue (LBST) repair constructs. The effect of the degree of prepolymer methacrylation (X, Y or Z; based on a repeating dimer unit) on the final hydrogel properties was investigated using solutions of 6% w/v for MGC (6%MGC-X, where X = 12%, 26% or 58%) and MHA (6%MHA-Y, where Y = 14%, 42% or 96%) and 20% w/v for MCS (20%MCS-Z, where Z = 16%, 26% or 45%). The goal was to adjust the cross-link density to produce hydrogels with moduli greater than 100 kPa to be suitable for load bearing applications while also minimizing swelling after cross-linking (±10% change in volume), and maintaining high viability and high metabolic activity of the encapsulated chondrocytes. These objectives were achieved by cross-linking solution blends of either the 6%MGC-12 or 6%MHA-42 with the 20%MCS-45 prepolymer at 50% mass fraction (5050 MGC12MCS45 and 5050 MHA42MCS45). Chondrocyte viability within blended hydrogels were greater than 70% after 24 h of culture, but metabolic activity was highest in the MHA based hydrogels (single component and blended) over a 35 day culture period. Overall, the high initial modulus, low swelling and enhanced metabolic activity of the encapsulated chondrocytes within the 5050 MHA42MCS45 hydrogels suggests they may be suitable for use in a reparative load bearing soft tissue construct.