Meltblown Polylactic Acid Nanowebs as a Tissue Engineering Scaffold

Application of Tendon-Derived Matrix and Carbodiimide Crosslinking Matures the Engineered Tendon-Like Proteome on Meltblown Scaffolds

Background: Tendon injuries are increasingly common and heal by fibrosis rather than scar-less regeneration. Tissue engineering seeks to improve repair using synthetic polymer scaffolds with biomimetic factors to enhance the regenerative potential. Methods: In this study, we compared three groups, namely, poly(lactic acid) (PLA) meltblown scaffolds, PLA meltblown scaffolds coated with tendon-derived matrix (TDM), and PLA meltblown scaffolds with carbodiimide crosslinked TDM (2.5:1:1 EDC:NHS:COOH ratio) (EDC-TDM) and determined their potential for engineered tendon development. We cultured human adipose stem cells (hASCs) for 28 days on meltblown scaffolds (n = 4-6/group) and measured tensile mechanical function, matrix synthesis, and matrix composition using biochemical assays and proteomics. Results: Coating PLA meltblown scaffolds with TDM improved yield stretch and stress at 28 days compared with PLA. Matrix synthesis rates for TDM or EDC-TDM were similar to PLA. Proteomic analysis revealed that hASCs produced a collagen-rich extracellular matrix, with many tendon-related matrix proteins. Coating scaffolds with TDM led to an increase in collagen type I whereas EDC-TDM scaffolds had an increase in glycoproteins and ECM regulators compared with other groups, consistent with increased maturity of the newly deposited matrix. Conclusions: TDM coating and crosslinking of meltblown scaffolds demonstrated matricellular benefits for the proteome of engineered tendon development but provided fewer clear benefits toward mechanical, biochemical, and rate of matrix accumulation than expected, and that previous work with electrospun scaffolds would suggest. However, electrospun scaffolds have different fiber structure and microarchitecture than meltblown, suggesting that further consideration of these differences and refinement of TDM application methods to meltblown scaffolds is required.

Generation of Bio-Based, Shape- and Temperature-Stable Three-Dimensional Nonwoven Structures Using Different Polyhydroxyalkanoates

Recent research has shown the potential of polyhydroxyalkanoates (PHAs), particularly poly(3-hydroxybutyrate) (P3HB), to form nonwoven structures with fine fiber diameter distributions ranging from 2.5 µm to 20 µm during the meltblow process. The shortcomings of existing fabrics of this type include high brittleness, low elongation at break (max. 3%), and a lack of flexibility. Furthermore, the high melt adhesion and the special crystallization kinetics of PHAs have commonly been regarded as constraints in filament and nonwoven processing so far. However, these two properties have now been used to elaborate a three-dimensional fiber arrangement on a matrix, resulting in the creation of dimensionally and temperature-stable "nonwoven-parts". Moreover, this study investigated the PHA copolymer poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), revealing a similar processability to P3HB and PHBV in the meltblow process. A significant increase in the (peak load) elongation in the machine direction was observed, reaching values between 5% and 10%, while the tensile strength retained unaltered. The addition of the bio-based plasticizer acetyltributylcitrate (ATBC) to PHBH resulted on an increase in elongation up to 15%. The three-dimensional fabric structure of PHBH exhibited complete resilience to compression, a property that differentiates it from both P3HB and PHBV. However, the addition of the plasticizer to P3HB did not lead to any improvements. This interesting array of properties results in moderate air permeability and hydrophobicity, leading to impermeability to water.

Influence of Rheological and Morphological Characteristics of Polyhydroxybutyrate on Its Meltblown Process Behavior

Polyhydroxybutyrate (PHB) is a promising biopolymer. However, processing PHB in pure form in thermoplastic processes is limited due to its rapid degradation, very low initial crystallization rate, strong post-crystallization, and its low final stretchability. In this article, we screened commercial PHBs for morphological characteristics, rheological properties, and "performance" in the meltblown process in order to reveal process-relevant properties and overcome the shortcoming of PHB in thermoplastic processes for fiber formation. An evaluation of degradation (extruded (meltblown) material vs. granules) was performed via rheological and SEC analysis. The study revealed large differences in the minimum melt temperature (175 up to 200 °C) and the grade-dependent limitation of accessible throughput on a 500 mm plant. The average fiber diameter could be lowered from around 10 μm to 2.4 μm in median, which are the finest reported values in the literature so far. It was found that the determination of the necessary process temperature can be predicted well from the complex shear viscosity. Different to expectations, it became apparent that a broader initial molar mass distribution (>8) is suitable to overcome the state-of-the art limitations of PHAs in order to stabilize fiber formation, increase the productivity, and obtain better resistance towards thermal degradation in process. Accordingly, longer polymer chain fractions could be more affected by degradation than medium and short polymer chains in the distribution. Further, a low initial narrow distributed molar mass resulted in too brittle fabrics.

Effects of Process Parameters on Structure and Properties of Melt-Blown Poly(Lactic Acid) Nonwovens for Skin Regeneration

Skin regeneration requires a three-dimensional (3D) scaffold for cell adhesion, growth and proliferation. A type of the scaffold offering a 3D structure is a nonwoven material produced via a melt-blown technique. Process parameters of this technique can be adapted to improve the cellular response. Polylactic acid (PLA) was used to produce a nonwoven scaffold by a melt-blown technique. The key process parameters, i.e., the head and air temperature, were changed in the range from 180–270 °C to obtain eight different materials (MB1–MB8). The relationships between the process parameters, morphology, porosity, thermal properties and the cellular response were explored in this study. The mean fiber diameters ranged from 3 to 120 µm. The average material roughness values were between 47 and 160 µm, whereas the pore diameters ranged from 5 to 400 µm. The calorimetry thermograms revealed a correlation between the temperature parameters and crystallization. The response of keratinocytes and macrophages exhibited a higher cell viability on thicker fibers. The cell-scaffold interaction was observed via SEM after 7 days. This result proved that the features of melt-blown nonwoven scaffolds depended on the processing parameters, such as head temperature and air temperature. Thanks to examinations, the most suitable scaffolds for skin tissue regeneration were selected.