Delayed degradation of poly(lactide-co-glycolide) accelerates hydrolysis of poly(ε-caprolactone) in ternary composite scaffolds

Graded or random - Effect of pore distribution in 3D titanium scaffolds on corrosion performance and response of hMSCs

Researchers agree that the ideal scaffold for tissue engineering should possess a 3D and highly porous structure, biocompatibility to encourage cell/tissue growth, suitable surface chemistry for cell attachment and differentiation, and mechanical properties that match those of the surrounding tissues. However, there is no consensus on the optimal pore distribution. In this study, we investigated the effect of pore distribution on corrosion resistance and performance of human mesenchymal stem cells (hMSC) using titanium scaffolds fabricated by laser beam powder bed fusion (PBF-LB). We designed two scaffold architectures with the same porosities (i.e., 75 %) but different distribution of pores of three sizes (200, 500, and 700 μm). The pores were either grouped in three zones (graded, GRAD) or distributed randomly (random, RAND). Microfocus X-ray computed tomography revealed that the chemically polished scaffolds had the porosity of 69 ± 4 % (GRAD) and 71 ± 4 % (RAND), and that the GRAD architecture had the higher surface area (1580 ± 101 vs 991 ± 62 mm2) and the thinner struts (221 ± 37 vs 286 ± 14 μm). The electrochemical measurements demonstrated that the apparent corrosion rate of chemically polished GRAD scaffold decreased with the immersion time extension, while that for polished RAND was increased. The RAND architecture outperformed the GRAD one with respect to hMSC proliferation (over two times higher although the GRAD scaffolds had 85 % higher initial cell retention) and migration from a monolayer. Our findings demonstrate that the pore distribution affects the biological properties of the titanium scaffolds for bone tissue engineering.

Influence of Polymeric Microparticle Size and Loading Concentration on 3D Printing Accuracy and Degradation Behavior of Composite Scaffolds

Successful employment of 3D printing for delivery of therapeutic biomolecules requires protection of their bioactivity on exposure to potentially inactivating conditions. Although intermediary encapsulation of the biomolecules in polymeric particulate delivery vehicles is a promising strategy for this objective, the inclusion of such particles in 3D printing formulations may critically impact the accuracy or precision of 3D printed scaffolds relative to their intended designed architectures, as well as the degradation behavior of both the scaffolds and the included particles. The present work aimed to elucidate the effect of poly(d,l-lactic-co-glycolic acid) particle size and loading concentration on material accuracy, machine precision, and degradation of 3D printed poly(ɛ-caprolactone)-based scaffolds. Using a main effects analysis, the sizes and loading concentrations of particle delivery vehicles investigated were found to have neither a beneficial nor disadvantageous influence on the metrics of printing quality such as material accuracy and machine precision. Meanwhile, particle loading concentration was determined to influence degradation rate, whereas printing temperature affected the trends in composite weight-average molecular weight. Neither of the two particle-related parameters (concentration nor diameter) was found to exhibit a significant effect on intra-fiber nor inter-fiber porosity. These findings evidence the capacity for controlled loading of particulate delivery vehicles in 3D printed scaffolds while preserving construct accuracy and precision, and with predictable dictation of composite degradation behavior for potential controlled release of encapsulated biomolecules.

Effect of adipose-derived stem cells seeding and surgical prefabrication on composite scaffold vascularization

The study aimed to evaluate an angiogenic effect of adipose-derived stem cells (ASCs) seeding and surgical prefabrication (placing a vascular pedicle inside the scaffold) on developed composite scaffolds made of poly-ε-caprolactone (PCL), β-tricalcium phosphate (β-TCP), and poly (lactic-co-glycolic acid) (PLGA) (PCL+β-TCP+PLGA). Moreover, we aimed to compare our data with previously tested PCL scaffolds to assess whether the new material has better angiogenic properties. The study included 18 inbred male WAG rats. There were three scaffold groups (six animals each): with non-seeded PCL+β-TCP+PLGA scaffolds, with PCL+β-TCP+PLGA scaffolds seeded with ASCs and with PCL+β-TCP+PLGA scaffolds seeded with ASCs and osteogenic-induced. Each rat was implanted with two scaffolds in the inguinal region (one prefabricated and one non-prefabricated). After 2 months from implantation, the scaffolds were explanted, and vessel density was determined by histopathological examination. Prefabricated ASC-seeded PCL+β-TCP+PLGA scaffolds promoted greater vessel formation than non-seeded scaffolds (19.73 ± 5.46 vs 12.54 ± 0.81; p = .006) and those seeded with osteogenic-induced ASCs (19.73 ± 5.46 vs 11.87±2.21; p = .004). The developed composite scaffold promotes vessel formation more effectively than the previously described PCL scaffold.

3D-Printed Polycaprolactone Implants Modified with Bioglass and Zn-Doped Bioglass

In this work, composite filaments in the form of sticks and 3D-printed scaffolds were investigated as a future component of an osteochondral implant. The first part of the work focused on the development of a filament modified with bioglass (BG) and Zn-doped BG obtained by injection molding. The main outcome was the manufacture of bioactive, strong, and flexible filament sticks of the required length, diameter, and properties. Then, sticks were used for scaffold production. We investigated the effect of bioglass addition on the samples mechanical and biological properties. The samples were analyzed by scanning electron microscopy, optical microscopy, infrared spectroscopy, and microtomography. The effect of bioglass addition on changes in the SBF mineralization process and cell morphology was evaluated. The presence of a spatial microstructure within the scaffolds affects their mechanical properties by reducing them. The tensile strength of the scaffolds compared to filaments was lower by 58-61%. In vitro mineralization experiments showed that apatite formed on scaffolds modified with BG after 7 days of immersion in SBF. Scaffold with Zn-doped BG showed a retarded apatite formation. Innovative 3D-printing filaments containing bioglasses have been successfully applied to print bioactive scaffolds with the surface suitable for cell attachment and proliferation.

Colonization versus encapsulation in cell-laden materials design: porosity and process biocompatibility determine cellularization pathways

Seeding materials with living cells has been-and still is-one of the most promising approaches to reproduce the complexity and the functionality of living matter. The strategies to associate living cells with materials are limited to cell encapsulation and colonization, however, the requirements for these two approaches have been seldom discussed systematically. Here we propose a simple two-dimensional map based on materials' pore size and the cytocompatibility of their fabrication process to draw, for the first time, a guide to building cellularized materials. We believe this approach may serve as a straightforward guideline to design new, more relevant materials, able to seize the complexity and the function of biological materials. This article is part of the theme issue 'Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 1)'.

Statistical degradation modelling of Poly(D,L-lactide-co-glycolide) copolymers for bioscaffold applications

This methodology permits to simulate the performance of different Poly(D,L-lactide-co-glycolide) copolymer formulations (PDLGA) in the human body, to identify the more influencing variables on hydrolytic degradation and, thus, to estimate biopolymer degradation level. The PDLGA characteristic degradation trends, caused by hydrolysis processes, have been studied to define their future biomedical applications as dental scaffolds. For this purpose, the mass loss, pH, glass transition temperature (Tg) and absorbed water mass of the different biopolymers have been obtained from samples into a phosphate-buffered saline solution (PBS) with initial pH of 7.4, at 37°C (human body conditions). The mass loss has been defined as the variable that characterize the biopolymer degradation level. Its dependence relationship with respect to time, pH and biopolymer formulation has been modelled using statistical learning tools. Namely, generalized additive models (GAM) and nonlinear mixed-effects regression with logistic and asymptotic functions have been applied. GAM model provides information about the relevant variables and the parametric functions that relate mass loss, pH and time. Mixed effects are introduced to model and estimate the degradation properties, and to compare the PDLGA biopolymer populations. The degradation path for each polymer formulation has been estimated and compared with respect to the others for helping to use the proper polymer for each specific medical application, performing selection criteria. It was found that the mass loss differences in PDLGA copolymers are strongly related with the way the pH decay versus time, due to carboxylic acid groups formation. This may occur in those environments in which the degradation products remain relatively confined with the non degraded mass. This is the case emulated with the present experimental procedure. The results show that PDLGA polymers degradation degree, in terms of half life and degradation rate, is increasing when acid termination is included, when DL-lactide molar ratio is reduced, decreasing the midpoint viscosity, or when glycolide is not included.

X-ray physics-based CT-to-composition conversion applied to a tissue engineering scaffold, enabling multiscale simulation of its elastic behavior

Nowadays, the assessment of the mechanical competence of tissue engineering scaffolds based on computer simulations is a well-accepted technology. Typically, such simulations are performed by means of the Finite Element (FE) method, with the underlying structural model being created based on micro-computed tomography (microCT). Here, this analysis modality is applied to a new, ternary composite, consisting of PHBV, i.e. poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PLGA, i.e. poly(lactic-co-glycolide), as well as of TCP, i.e. tricalcium phosphate hydrate. The studied scaffold structure is made up by fibers of this new composite material, manufactured by means of the rapid prototyping method. The data collected from microCT is utilized for adequately defining the mechanical properties of the FE model. In particular, the three-dimensional field of grey values is interpreted in terms of the underlying field of attenuation coefficients, taking into account the photon energy employed in microCT imaging, eventually allowing for calculation of the three-dimensionally distributed, voxel-specific composition of the studied material. For the sake of keeping the FE simulations as efficient as possible, groups of voxels are combined into one finite element; the grey value of the latter is obtained by volume averaging. Employing a two-step micromechanical homogenization scheme, the experimentally accessible stiffness of the three constituents (PHBV, PLGA, and TCP) is then, finite element by finite element, upscaled to the composition-dependent stiffness of the composite material. The plausibility and adequacy of the FE model is demonstrated by simulating the effects of uniaxial compression on the scaffold structure, in terms of resulting stress and strain fields, highlighting the importance of the fiber junctions (as they are the mechanically most stressed regions), and that neglecting the material heterogeneity would lead to a potentially significant underestimation of stresses and strains. Finally, a comparison is made of the employed analysis modality of microCT data with a previously pursued, simplified analysis strategy, highlighting the conceptual superiority of the former, and pointing out the application limits of the latter.

Biodegradable fiducial markers for X-ray imaging – soft tissue integration and biocompatibility

This study aims at investigation of material for innovative fiducial markers for soft tissue in X-ray based medical imaging. NH₃ plasma modified P[LAcoCL] combined with BaSO₄ and hydroxyapatite as radio-opaque fillers appears to be a promising material systems for this application.

Synthesis, Properties, and In Vitro Hydrolytic Degradation of Poly(d,l-lactide-co-glycolide-co-ε-caprolactone)

Random copolymers of poly(d,l-lactide-co-glycolide-co-ε-caprolactone) (PLGC) were synthesized by the ring-opening polymerization of d,l-lactide (DLLA), glycolide (GA), andε-caprolactone (CL). The effects of CL on the copolymers were evaluated to prepare suitable copolymers with controlled properties. Our results showed that the CL content significantly influenced the thermal and mechanical properties of the copolymers and that the CL content in compositions could be altered to control properties of random copolymers. The in vitro hydrolytic degradation of the resulting implants showed that the degradation rate of PLGC was lower than that of PLGA, which could markedly reduce acidic degradation products. Finally, we demonstrated that higher CL contents in compositions slowed degradation rates.