Growth factor sustained delivery from poly‐lactic‐co‐glycolic acid microcarriers and its mass transfer modeling by finite element in a dynamic and static three‐dimensional environment bioengineered with stem cells

Abstract

Poly-lactic-co-glycolic acid (PLGA) microcarriers (0.8 ± 0.2 μm) have been fabricated with a load of 20 μg/g PLGA by an emulsion-based-proprietary technology to sustained deliver human bone morphogenetic protein 2 (hBMP2), a growth factor largely used for osteogenic induction. hBMP2 release profile, measured in vitro, showed a moderate "burst" release of 20% of the load in first 3 days, followed by a sustained release of 3% of the load along the following 21 days. PLGA microbeads loaded with fluorescent marker (8 mg/g PLGA ) and hydroxyapatite (30 mg/g PLGA ) were also fabricated and successfully dispersed within three-dimensional (3D) alginate scaffold (Ca-alginate 2% wt/wt) in a range between 50 and 200 mg/cm 3 ; the presence of microcarriers within the scaffold induced a variation of its stiffness between 0.03 and 0.06 MPa; whereas the scaffold surface area was monitored always in the range of 190-200 m 2 /g. Uniform microcarriers dispersion was obtained up to 200 mg/cm 3 ;higher loading values in the 3D scaffold produced large aggregates. The release data and the surface area were, then, used to simulate by finite element modeling the hBMP2 mass transfer within the 3D hydrogel bioengineered with stem cells, in dynamic and static cultivations. The simulation was developed with COMSOL Multiphysics ® giving a good representation of hBMP2 mass balances along microbeads (bulk eroded) and on cell surface (cell binding). hBMP2 degradation rate was also taken into account in the simulations. hBMP2 concentration of 20 ng/cm 3 was set as a target because it has been described as the minimum effective value for stem cells stimulation versus the osteogenic phenotype. The sensitivity analysis suggested the best microbeads/cells ratio in the 3D microenvironment, along 21 days of cultivations in both static and dynamic cultivation (perfusion) conditions. The simulated formulation was so assembled experimentally using human mesenchymal stem cells and an improved scaffold stiffness up to 0.09 MPa (n = 3; p ≤ 0.01) was monitored after 21 days of cultivation; moreover a uniform extracellular matrix deposition within the 3D system was detected by Von Kossa staining, especially in dynamic

3D Biomimetic Scaffold for Growth Factor Controlled Delivery: An In-Vitro Study of Tenogenic Events on Wharton’s Jelly Mesenchymal Stem Cells

“…Despite several works reporting the concentration of 100 ng/mL as optimal for induction of stem cell commitment toward a tenogenic phenotype, when it was supplemented in the culture medium (wherein the 3D construct was immersed), we did not observe tenogenic gene up-regulation, probably because these indications mainly refer to monolayer cultures in conventional flasks [ 13 , 15 , 16 ]. Furthermore, hGDF-5 was already reported to commit WJ-MSCs towards a tenogenic phenotype [ 13 ] and the mechanical input provided was expected to improve the overall growth factor mass transfer within the 3D system [ 32 ], allowing its active transport through the cells loaded within the 3D scaffold [ 50 ]. However, in our case, a subsequent commitment was not observed in the above-described culture conditions.…”

“…This hydrolysis reaction promotes bulk erosion of the polymer and then further drug release. These mechanisms compete and overlap over the release time assuring a quite linear drug release along the first 15 days [ 29 , 50 , 59 , 66 ]. Therefore, the release profile can display a nonlinear behavior, especially when an extremely low drug loading is adopted, as was likely the case here.…”

“…Poly-lactic acid (PLA) and poly-lactic-co-glycolic acid (PLGA) carriers (FDA-approved bioresorbable polymers) have been recently applied. These carriers can act as micro-environmental regulators within a 3D bioengineered scaffold, providing a spatio-temporally controlled delivery of biomolecules [ 43 , 44 ], in both pharmaceutical [ 45 , 46 , 47 ] and biomedical [ 48 , 49 , 50 ] fields.…”

Chondrogenic Commitment of human Bone Marrow Mesenchymal Stem Cells cultured under perfusion within a 3D collagen environment releasing hTGF\(\beta\)1

“…The estimated hTGFβ1 release within the scaffold is presented inFigure 3d. A burst release of 20 ng/mL is observed at day 1, a mean amount of 4 ng/mL/day for the following 5 days, and 0.5 ng/mL/day are delivered in the following days, except at day 13, when a spike of 5 ng/mL results from PLGA burst de-polymerization (Trucillo et al, 2019). An overall amount of 45 ng of hTGFβ1 is thus delivered in each scaffold over the 16 days of culture time (Reyes et al, 2012).…”

“…These carriers can be easily immobilized within the hydrogel matrix, and the controlled delivery of their cargo within the 3D scaffold can be accomplished. As a consequence, it is possible to optimize the cells/carrier ratio to maintain a constant growth factor concentration within the 3D system (Trucillo et al, 2019).…”