RESUMEN
We applied a recently developed method, laser metrology, to characterize the influence of collector rotation on porosity gradients of electrospun polycaprolactone (PCL) widely investigated for use in tissue engineering. The prior- and post-sintering dimensions of PCL scaffolds were compared to derive quantitative, spatially-resolved porosity 'maps' from net shrinkage. Deposited on a rotating mandrel (200 RPM), the central region of deposition reaches the highest porosity, ~92%, surrounded by approximately symmetrical decreases to ~89% at the edges. At 1100 RPM, a uniform porosity of ~88-89% is observed. At 2000 RPM, the lowest porosity, ~87%, is found in the middle of the deposition, rebounding to ~89% at the edges. Using a statistical model of random fiber network, we demonstrated that these relatively small changes in porosity values produce disproportionately large variations in pore size. The model predicts an exponential dependence of pore size on porosity when the scaffold is highly porous (e.g., >80%) and, accordingly, the observed porosity variation is associated with dramatic changes in pore size and ability to accommodate cell infiltration. Within the thickest regions most likely to 'bottleneck' cell infiltration, pore size decreases from ~37 to 23 µm (38%) when rotational speeds increased from 200 to 2000 RPM. This trend is corroborated by electron microscopy. While faster rotational speeds ultimately overcome axial alignment induced by cylindrical electric fields associated with the collector geometry, it does so at the cost of eliminating larger pores favoring cell infiltration. This puts the bio-mechanical advantages associated with collector rotation-induced alignment at odds with biological goals. A more significant decrease in pore size from ~54 to ~19 µm (65%), well below the minimum associated with cellular infiltration, is observed from enhanced collector biases. Finally, similar predictions show that sacrificial fiber approaches are inefficient in achieving cell-permissive pore sizes.
Asunto(s)
Ingeniería de Tejidos , Andamios del Tejido , Porosidad , Poliésteres , Rayos LáserRESUMEN
Vascular endothelial growth factor (VEGF) is a key regulator of abnormal blood vessel growth. As such, bevacizumab-based inhibition of VEGF has been the clinically adopted strategy to treat colorectal and breast cancers as well as age-related macular degeneration (AMD). However, as the treatment of vascular diseases often requires a high drug concentration for a long period, the burst release of bevacizumab remains a critical limitation in anti-VEGF-based therapies. Maintaining bevacizumab at high concentrations over extended periods remains challenging due to insufficient drug loading capacity and drug-device interactions. We report the development of a polymeric based bi-layered capsule that could address these challenges by extending the release over one year, thereby providing an effective platform enabling treatment of chronic vascular diseases. Remarkably, the developed capsules have a bi-layered structure which ensures the structural integrity of the injectable capsules and appropriate diffusion of bevacizumab by providing optimal physical trapping and electrostatic interaction. Meanwhile, the central hollow design enables a higher drug loading to meet the need for long-term release of bevacizumab for several months to one year. Using an in vitro drug release assay, we demonstrated that the bi-layered capsule could produce longer-term local drug administration by intravitreal injection compared to previously reported devices. The capsules also present minimal toxicity and maintain anti-VEGF potency, suggesting that our approach may have the potential to treat vascular-related diseases using bevacizumab.
Asunto(s)
Ranibizumab , Factor A de Crecimiento Endotelial Vascular , Inhibidores de la Angiogénesis/uso terapéutico , Bevacizumab , Inyecciones Intravítreas , Agudeza VisualRESUMEN
Electrospinning has been used widely for drug delivery applications due to its versatility and ease of modification of spun fiber properties. Net drug loading and release is typically limited by the inherent surface-area of the sample. In a relatively novel approach, sintering of electrospun fiber was used to create a capsule favoring long-term delivery. We showed that electrospun polycaprolactone (PCL) retained its initial morphology out to 1042â¯days of in vitro exposure, illustrating its potential for extended performance. Sintering decreased the electrospun pore size by 10- and 28-fold following 56 and 57⯰C exposures, respectively. At 58 and 59⯰C, the PCL capsules lost all apparent surface porosity, but entrapped pores were observed in the 58⯰C cross-section. The use of Rhodamine B (RhB, 479.02â¯gâ¯mol-1), Rose Bengal (RB, 1017.64â¯gâ¯mol-1) and albumin-fluorescein isothiocyanate conjugate from bovine serum (BSA-FITC, ~66,000â¯gâ¯mol-1) as model compounds demonstrated that release (RhBâ¯>â¯RBâ¯â«â¯BSA-FITC) is controlled both by molecular weight and available porosity. Interestingly, the ranking of release following sintering was 57â¯>â¯56â¯>â¯59â¯>â¯58⯰C; COMSOL simulations explored the effects of capsule wall thickness and porosity on release rate. It was hypothesized that model drug adsorption on the available fiber surface-area (57 versus 56⯰C) and entrapped porosity (59 versus 58⯰C) could have also attributed to the observed ranking of release rates. While the 56 and 57⯰C exposures allowed the bulk of the release to occur in <1â¯day, the capsules sintered at 58 and 59⯰C exhibited release that continued after 12â¯days of exposure.
Asunto(s)
Preparaciones de Acción Retardada/administración & dosificación , Sistemas de Liberación de Medicamentos/métodos , Poliésteres/química , Simulación por Computador , Liberación de Fármacos , Modelos Moleculares , Rodaminas/química , Rosa Bengala/química , Albúmina Sérica Bovina/química , TemperaturaRESUMEN
Suture retention strength (SRS) is commonly used as a measure the ability of sutures to adhere implants to surrounding tissue. While SRS is widely employed, surprisingly its effects on graft microstructure have not been characterized. This is particularly germane to the broad utilization of electrospun implants in tissue engineering. These implants need to retain their initial nanoscale topography while simultaneously preserving clinically critical mechanical properties. We examined the suture-driven microstructural deformation of polycaprolactone electrospun to form both square and tubular SRS samples. The impact of fiber orientation (generally parallel or random orientation, orthogonally aligned) on the SRS of these vascular tissue equivalents was analyzed and compared to native and decellularized porcine vasculature. The initial state of the fiber clearly dictates the overall efficiency of scaffold utilization. SRS values for as-spun fibers at a thickness of 300 µm were found to be in the range of 1.59-4.78 N for the three orientations. Unexpectedly, random fibers provided the optimal SRS values based on both resistance to suture motion and the percentage of scaffold involvement. A "V-shaped" failure morphology is observed for both electrospun scaffolds and native tissue during SRS testing. Post-test fiber alignment in the tensile direction was visible in all initial fiber orientations similar to that of native tissue. These findings are significant as they allow us to employ new, counterintuitive biomimetic design criteria for nanofiber-based scaffolds in which reliable mechanical integration with the surrounding tissues via suture-based methods is important. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1525-1534, 2016.