1. Production of dermal inspired collagen architectures by lyophilisation and electrophoretic deposition
- Author
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Smith, Patricia and Cameron, Ruth
- Subjects
Biomaterials ,Collagen ,Electrophoretic Deposition ,Freeze Drying ,Lyophilisation ,MicroCT ,Tissue Engineering - Abstract
Collagen scaffolds have been used successfully as dermal regeneration templates in clinical applications, but most do not recapitulate the natural tissue structure and are often combined with synthetic membranes to afford additional barrier properties. This work aimed to produce dermal-inspired collagen structures that better replicate the native dermal and epidermal structure and function. Aqueous suspensions of 1% w/v insoluble collagen type I were freeze-dried to create porous collagen sponges c. 32-35mm in diameter with varying thicknesses. Freeze-drying comprised an ice nucleation and growth phase, followed by sublimation to leave an interconnected pore network. The effects of changing process parameters on the resulting pore structure were analysed using micro-computed X-ray tomography and scanning electron microscopy. The target pore structure consisted of a majority "reticular" region of < 125µm pores with a thin upper region of >150µm pores to mimic the open papillary dermal ECM. An "annealing" step at -20°C for 24h following ice nucleation increased mean pore size by 20-30µm in samples over 6mm thick but had no effect on samples thinner than this. Extending time at equilibrium (TAE) during freezing increased pore size significantly, with TAE and pore size following a power law relationship, the exponent 1/n experimentally determined to be n=6.21. Annealing temperature was identified as a critical parameter influencing the rate of ice crystal coarsening and a heat source was introduced to increase the temperature gradient through the scaffold thickness after freezing. After process optimisation, differential coarsening through the thickness of c. 4-5mm thick scaffolds was observed in samples annealed above c. -3°C. Annealing for 100min near 0°C produced scaffolds with upper regions of mean pore size above 160µm, while lower regions remained comparable with the 95-105µm mean pore size of non-annealed controls. To address the requirement for barrier properties to mimic the native epidermis, direct current electrophoretic deposition (DC-EPD) was investigated as a method to produce collagen membranes. DC-EPD was applied to suspended collagen scaffolds to produce well-adhered, continuous, and defect-free scaffold-film bilayers. Carbodiimide crosslinking of scaffolds to 10% of the standard 5:1 carbodiimide:COO-(Col) ratio was found to be sufficient to maintain the scaffold structure during DC-EPD processing. By controlling the overall resistance of the deposition cell, deposition yields approaching 100% were achieved in under 20min. The barrier properties of collagen scaffold-film bilayers produced by freeze-drying and DC-EPD were assessed. The water vapour transmission rate (WVTR) across scaffolds and scaffold-film bilayers was compared. The film addition reduced the WVTR from 0.862-0.660g/Pa/m²/d, the latter within the recommended range for wound cover. Finally, human dermal fibroblast (HDF) infiltration into nude scaffolds and scaffold-film bilayers (seeded either on the film, or scaffold side) was investigated. The film-seeded bilayers significantly impeded HDF infiltration compared to nude scaffolds, whereas the scaffold-seeded bilayers showed a small reduction in infiltration compared to nude controls. Bilayers seeded on both surfaces showed similar HDF population counts on both surfaces after 14 days.
- Published
- 2022
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