Modulation of Cellular Colonization of Porous Polyurethane Scaffolds via the Control of Pore Interconnection Size and Nanoscale Surface Modifications

Silk biomaterials for corneal tissue engineering: From research approaches to therapeutic potentials; A review

The corneal complications can result in opacity and eventual blindness. Furthermore, a shortage of available donors constrains the existing therapeutic options. Therefore, one of the most promising strategies involves the application of biomaterials, particularly silk. Silk has garnered significant attention among these biomaterials due to its natural origin and diverse features derived from different sources. One of the most critical factors of silk is its transparency, which is crucial for the cornea, and there are no concerns about infection. This material also possesses several advantages, including cost-effectiveness in production, biocompatibility in vivo and in vitro, biodegradation, and desirable mechanical characteristics. Modifications in the topographical structure, porosity, and crystallinity of silk enhance its properties and optimize its suitability for wound dressing, efficient drug delivery systems, and various cornea-related treatments. In each layer, silk was examined as a single biomaterial or blended with the others, so, this review aims to explore silk as a potential material for corneal regenerative medicine from a novel viewpoint. By considering a range of studies, a classification system has been developed that categorizes the utilization of silk in the various layers of the cornea and sub-categorizes the different modifications and applications of silk.

Enhanced Ear Cartilage Regeneration with Dual-Network LT-GelMA/F127DA Hydrogel Featuring Nanomicelle Integration

Tissue-engineered cartilage, supported by advancements in photo-cross-linkable hydrogels, offers a promising solution for the repair and regeneration of damaged cartilage in anatomically complex and mechanically demanding sites. Low-temperature soluble GelMA (LT-GelMA) remains in a liquid state at room temperature, allowing for easier handling; however, it has limitations in mechanical strength and structural stability. To address these limitations, we developed a novel dual-network hydrogel combining LT-GelMA with Pluronic F127-diacrylate (F127DA). The resulting hydrogel uniquely integrates the low-temperature solubility of LT-GelMA with the enhanced mechanical strength provided by photo-cross-linkable F127DA nanomicelles. Additionally, the hydrogel exhibits controlled swelling and biodegradation rates. In vitro studies revealed a significant increase in chondrocyte viability by day 7 in formulations with higher F127DA concentrations. In vivo, the hydrogel demonstrated superior neo-cartilage formation in a subcutaneous nude mouse model, as indicated by increased deposition of cartilage-specific extracellular matrix components at 4 and 8 weeks. In summary, we developed a hydrogel with fluidity at room temperature and enhanced mechanical performance. These results indicate that the LT-GelMA/F127DA hydrogel effectively addresses the current gaps in cartilage tissue engineering. The hydrogel's superior performance, especially in promoting cartilage regeneration, positions it as a promising alternative for reconstructive surgery, representing a significant improvement over existing cartilage repair strategies.

A Bioglass-Poly(lactic-co-glycolic Acid) Scaffold@Fibrin Hydrogel Construct to Support Endochondral Bone Formation

Bone tissue engineering using stem cells to build bone directly on a scaffold matrix often fails due to lack of oxygen at the injury site. This may be avoided by following the endochondral ossification route; herein, a cartilage template is promoted first, which can survive hypoxic environments, followed by its hypertrophy and ossification. However, hypertrophy is so far only achieved using biological factors. This work introduces a Bioglass-Poly(lactic-co-glycolic acid@fibrin (Bg-PLGA@fibrin) construct where a fibrin hydrogel infiltrates and encapsulates a porous Bg-PLGA. The hypothesis is that mesenchymal stem cells (MSCs) loaded in the fibrin gel and induced into chondrogenesis degrade the gel and become hypertrophic upon reaching the stiffer, bioactive Bg-PLGA core, without external induction factors. Results show that Bg-PLGA@fibrin induces hypertrophy, as well as matrix mineralization and osteogenesis; it also promotes a change in morphology of the MSCs at the gel/scaffold interface, possibly a sign of osteoblast-like differentiation of hypertrophic chondrocytes. Thus, the Bg-PLGA@fibrin construct can sequentially support the different phases of endochondral ossification purely based on material cues. This may facilitate clinical translation by decreasing in-vitro cell culture time pre-implantation and the complexity associated with the use of external induction factors.

Emerging albumin hydrogels as personalized biomaterials

Developing biomaterials-based tissue engineering scaffolds with personalized features and intrinsic biocompatibility is appealing and urgent. Through utilizing various strategies, albumin, as the most abundant protein in plasma, could be fabricated into sustainable, cost-effective, and potentially personalized hydrogels that would display enormous biological applications. To date, much of the albumin-based research is primarily engrossed in using albumin as a therapeutic molecule or a drug carrier, not much as a scaffold for tissue engineering. For this reason, we have come up with a detailed and insightful review of recent progress in albumin-based hydrogels having an emphasis on production techniques, material characteristics, and biological uses. It is envisioned that albumin-based scaffolds would be appealing and useful platforms to meet current tissue engineering needs and achieve the goal of clinical translation to benefit patients. STATEMENT OF SIGNIFICANCE: The creation of autologous material-based scaffolds is a potential method for preventing immunological reactions and obtaining the best therapeutic results. Patient-derived albumin hydrogels may consequently provide improved opportunities for personalized treatment due to their abundant supply and minimal immunogenicity. To provide a detailed and insightful summary on albumin-based hydrogels, this review includes latest comprehensive information on their preparation procedures, features, and applications in 3D printing and other biomedical applications. The challenges, along with the future potential for implementing albumin-based hydrogels in clinics, have also been addressed.

Hyperelastic, shape-memorable, and ultra-cell-adhesive degradable polycaprolactone-polyurethane copolymer for tissue regeneration

Novel polycaprolactone-based polyurethane (PCL-PU) copolymers with hyperelasticity, shape-memory, and ultra-cell-adhesion properties are reported as clinically applicable tissue-regenerative biomaterials. New isosorbide derivatives (propoxylated or ethoxylated ones) were developed to improve mechanical properties by enhanced reactivity in copolymer synthesis compared to the original isosorbide. Optimized PCL-PU with propoxylated isosorbide exhibited notable mechanical performance (50 MPa tensile strength and 1150% elongation with hyperelasticity under cyclic load). The shape-memory effect was also revealed in different forms (film, thread, and 3D scaffold) with 40%-80% recovery in tension or compression mode after plastic deformation. The ultra-cell-adhesive property was proven in various cell types which were reasoned to involve the heat shock protein-mediated integrin (α5 and αV) activation, as analyzed by RNA sequencing and inhibition tests. After the tissue regenerative potential (muscle and bone) was confirmed by the myogenic and osteogenic responses in vitro, biodegradability, compatible in vivo tissue response, and healing capacity were investigated with in vivo shape-memorable behavior. The currently exploited PCL-PU, with its multifunctional (hyperelastic, shape-memorable, ultra-cell-adhesive, and degradable) nature and biocompatibility, is considered a potential tissue-regenerative biomaterial, especially for minimally invasive surgery that requires small incisions to approach large defects with excellent regeneration capacity.

PoreScript: Semi-automated pore size algorithm for scaffold characterization

The scaffold pore size influences many critical physical aspects of tissue engineering, including tissue infiltration, biodegradation rate, and mechanical properties. Manual measurements of pore sizes from scanning electron micrographs using ImageJ/FIJI are commonly used to characterize scaffolds, but these methods are both time-consuming and subject to user bias. Current semi-automated analysis tools are limited by a lack of accessibility or limited sample size in their verification process. The work here describes the development of a new MATLAB algorithm, PoreScript, to address these limitations. The algorithm was verified using three common scaffold fabrication methods (e.g., salt leaching, gas foaming, emulsion templating) with varying pore sizes and shapes to demonstrate the versatility of this new tool. Our results demonstrate that the pore size characterization using PoreScript is comparable to manual pore size measurements. The PoreScript algorithm was further evaluated to determine the effect of user-input and image parameters (relative image magnification, pixel intensity threshold, and pore structure). Overall, this work validates the accuracy of the PoreScript algorithm across several fabrication methods and provides user-guidance for semi-automated image analysis and increased throughput of scaffold characterization.

In vitro two-step granuloma formation model for testing innate immune response to implants and coatings

The extensive innate immune response to implanted biomaterials contributes significantly to their sub-par performance and failure. Granuloma formation is one of such reactions which results in multi-cell type clusters in line with the immune reaction to implanted materials. However, currently no in vitro model of granuloma formation exists that takes into account the arrival of multiple cell types (immune cells and connective tissue cells) to the implant insertion site. In this study, we developed a two-step model based on stimulated macrophage seeding followed by fibroblast introduction after a physiologically relevant time period for mimicking initial steps of immune reaction to biomaterials and inducing granuloma like behavior. Both LPS and TNF-α induction resulted in granuloma like formations which persisted longer than the control conditions. Introduction of human fibroblasts resulted in the colonization of the surfaces where the cell numbers and the collagen secretion were dependent on the microenvironment. In order to demonstrate the capacity of our model system to monitor the reaction to a given coating, a validated antimicrobial coating (Polyarginine (PAR)/Hyaluronic acid (HA)) was used as a testing bed. The coating prevented the adhesion of macrophages while allowing the adhesion of the fibroblast at the time of their arrival. Similar to its antimicrobial activity, macrophage metabolic activity and M2 differentiation in the presence of PAR was dependent to its chain length. The incorporation of fibroblasts resulted in decreased TNF-α and increased IL-1RA secretion especially in stimulation conditions. The pro- and anti-inflammatory cytokine secretions were low for PAR/HA coatings in line with the decreased number of macrophage presence. In the presence of complex PBMC population, the coating resulted in slightly less cellular attachment, without any significant cytokine secretion; the absence of inflammatory reaction was also demonstrated in vivo in a mouse model. The described in vitro granuloma testing system can control the macrophage reaction as a function of stimulation. It can also be used for testing new biomaterials for the potential innate immune responses and also for validation of implant coatings beyond their primary function from the immune response point of view.

Three-dimensional Culture and Chondrogenic Differentiation of Mesenchymal Stem Cells in Interconnected Collagen Scaffolds

Interconnected scaffolds are useful for promoting the chondrogenic differentiation of stem cells. Collagen scaffolds with interconnected pore structures were fabricated with poly(lactic acid-co-glycolic acid) (PLGA) sponge templates. The PLGA-templated collagen scaffolds were used to culture human bone marrow-derived mesenchymal stem cells (hMSCs) to investigate their promotive effect on the chondrogenic differentiation of hMSCs. The cells adhered to the scaffolds with a homogeneous distribution and proliferated with culture time. The expression of chondrogenesis-related genes was upregulated, and abundant cartilaginous matrices were detected. After subcutaneous implantation, the PLGA-templated collagen scaffolds further enhanced the production of cartilaginous matrices and the mechanical properties of the implants. The good interconnectivity of the PLGA-templated collagen scaffolds promoted chondrogenic differentiation. In particular, the collagen scaffolds prepared with large pore-bearing PLGA sponge templates showed the highest promotive effect.

Hydrogel foams from liquid foam templates: Properties and optimisation

Hydrogel foams are an important sub-class of macroporous hydrogels. They are commonly obtained by integrating closely-packed gas bubbles of 10-1000 μm into a continuous hydrogel network, leading to gas volume fractions of more than 70% in the wet state and close to 100% in the dried state. The resulting wet or dried three-dimensional architectures provide hydrogel foams with a wide range of useful properties, including very low densities, excellent absorption properties, a large surface-to-volume ratio or tuneable mechanical properties. At the same time, the hydrogel may provide biodegradability, bioabsorption, antifungal or antibacterial activity, or controlled drug delivery. The combination of these properties are increasingly exploited for a wide range of applications, including the biomedical, cosmetic or food sector. The successful formulation of a hydrogel foam from an initially liquid foam template raises many challenging scientific and technical questions at the interface of hydrogel and foam research. Goal of this review is to provide an overview of the key notions which need to be mastered and of the state of the art of this rapidly evolving field at the interface between chemistry and physics.

Nerve Guidance Conduits with Hierarchical Anisotropic Architecture for Peripheral Nerve Regeneration

Nerve guidance conduits with multifunctional features could offer microenvironments for improved nerve regeneration and functional recovery. However, the challenge remains to optimize multiple cues in nerve conduit systems due to the interplay of these factors during fabrication. Here, a modular assembly for the fabrication of nerve conduits is utilized to address the goal of incorporating multifunctional guidance cues for nerve regeneration. Silk-based hollow conduits with suitable size and mechanical properties, along with silk nanofiber fillers with tunable hierarchical anisotropic architectures and microporous structures, are developed and assembled into conduits. These conduits supported improves nerve regeneration in terms of cell proliferation (Schwann and PC12 cells) and growth factor secretion (BDNF, brain-derived neurotrophic factor) in vitro, and the in vivo repair and functional recovery of rat sciatic nerve defects. Nerve regeneration using these new conduit designs is comparable to autografts, providing a path towards future clinical impact.

Improving the colonization and functions of Wharton's Jelly-derived mesenchymal stem cells by a synergetic combination of porous polyurethane scaffold with an albumin-derived hydrogel

The development of neo-tissues assisted by artificial scaffolds is continually progressing, but the reproduction of the extracellular environment surrounding cells is quite complex. While synthetic scaffolds can support cell growth, they lack biochemical cues that can prompt cell proliferation or differentiation. In this study, Wharton's Jelly-derived mesenchymal stem cells are seeded on a polyurethane (PU) scaffold combined with a hydrogel based on bovine serum albumin (BSA). BSA hydrogel is obtained through thermal treatment. While such treatment leads to partial unfolding of the protein, we show that the extent of denaturation is small enough to maintain its bioactivity, such as protein binding. Therefore, BSA provides a suitable playground for cells inside the scaffold, allowing higher spreading, proliferation and matrix secretions. Furthermore, the poor mechanical properties of the hydrogel are compensated for by the porous PU scaffold, whose architecture is well controlled. We show that even though PU by itself can allow cell adhesion and protein secretion, cell proliferation is 3.5 times higher in the PU + BSA scaffolds as compared to pure PU after 21 d, along with the non-collagenous protein secretions (389 versus 134 μmmg ^-1). Conversely, the secretion of sulphated glycosaminoglycans is 12.3-fold higher in the scaffold made solely of PU. Thereby, we propose a simple approach to generating a hybrid material composed of a combination of PU and BSA hydrogel as a promising scaffold for tissue regeneration.

The Overview of Porous, Bioactive Scaffolds as Instructive Biomaterials for Tissue Regeneration and Their Clinical Translation

Porous scaffolds have been employed for decades in the biomedical field where researchers have been seeking to produce an environment which could approach one of the extracellular matrixes supporting cells in natural tissues. Such three-dimensional systems offer many degrees of freedom to modulate cell activity, ranging from the chemistry of the structure and the architectural properties such as the porosity, the pore, and interconnection size. All these features can be exploited synergistically to tailor the cell-material interactions, and further, the tissue growth within the voids of the scaffold. Herein, an overview of the materials employed to generate porous scaffolds as well as the various techniques that are used to process them is supplied. Furthermore, scaffold parameters which modulate cell behavior are identified under distinct aspects: the architecture of inert scaffolds (i.e., pore and interconnection size, porosity, mechanical properties, etc.) alone on cell functions followed by comparison with bioactive scaffolds to grasp the most relevant features driving tissue regeneration. Finally, in vivo outcomes are highlighted comparing the accordance between in vitro and in vivo results in order to tackle the future translational challenges in tissue repair and regeneration.

Construction and application of textile-based tissue engineering scaffolds: a review

Tissue engineering (TE) provides a practicable method for tissue and organ repair or substitution. As the most important component of TE, a scaffold plays a critical role in providing a growing environment for cell proliferation and functional differentiation as well as good mechanical support. And the restorative effects are greatly dependent upon the nature of the scaffold including the composition, morphology, structure, and mechanical performance. Medical textiles have been widely employed in the clinic for a long time and are being extensively investigated as TE scaffolds. However, unfortunately, the advantages of textile technology cannot be fully exploited in tissue regeneration due to the ignoring of the diversity of fabric structures. Therefore, this review focuses on textile-based scaffolds, emphasizing the significance of the fabric design and the resultant characteristics of cell behavior and extracellular matrix reconstruction. The structure and mechanical behavior of the fabrics constructed by various textile techniques for different tissue repairs are summarized. Furthermore, the prospect of structural design in the TE scaffold preparation was anticipated, including profiled fibers and some unique and complex textile structures. Hopefully, the readers of this review would appreciate the importance of structural design of the scaffold and the usefulness of textile-based TE scaffolds in tissue regeneration.

Validation of Milner's visco-elastic theory of sintering for the generation of porous polymers with finely tuned morphology

Sacrificial sphere templating has become a method of choice to generate macro-porous materials with well-defined, interconnected pores. For this purpose, the interstices of a sphere packing are filled with a solidifying matrix, from which the spheres are subsequently removed to obtain interconnected voids. In order to control the size of the interconnections, viscous sintering of the initial sphere template has proven a reliable approach. To predict how the interconnections evolve with different sintering parameters, such as time or temperature, Frenkel's model has been used with reasonable success over the last 70 years. However, numerous investigations have shown that the often complex flow behaviour of the spheres needs to be taken into account. To this end, S. Milner [arXiv:1907.05862] developed recently a theoretical model which improves on some key assumptions made in Frenkel's model, leading to a slightly different scaling. He also extended this new model to take into account the visco-elastic response of the spheres. Using an in-depth investigation of templates of paraffin spheres, we provide here the first systematic comparison with Milner's theory. Firstly, we show that his new scaling describes the experimental data slightly better than Frenkel's scaling. We then show that the visco-elastic version of his model provides a significantly improved description of the data over a wide parameter range. We finally use the obtained sphere templates to produce macro-porous polyurethanes with finely controlled pore and interconnection sizes. The general applicability of Milner's theory makes it transferable to a wide range of formulations, provided the flow properties of the sphere material can be quantified. It therefore provides a powerful tool to guide the creation of sphere packings and porous materials with finely controlled morphologies.

Electrical conductivity and tortuosity of solid foam: Effect of pore connections

Numerical and analytical methods at both micro- and mesoscales are used to study how the electrical resistivity and the high-frequency tortuosity of solid foam are modified by the presence of membranes that partially or totally close the cell windows connecting neighbor pores. Finite-element-method simulations are performed on two pores connected by a single-holed membrane and on well-ordered Kelvin foam. For two pores connected by a single-holed membrane, we show that the equation for pore access resistance obtained by Sahu and Zwolak [Phys. Rev. E 98, 012404 (2018)2470-004510.1103/PhysRevE.98.012404] can predict, after a few modifications, the electrical resistivity at the membrane scale for a large range of membrane apertures. Considering these analytical results, we build a pore-network model by using two kinds of conductances at the pore scale: interpore conductance and intrapore conductance. Local interpore resistances govern foam electrical conductivity at small membrane aperture size, but when the membrane aperture has the same order of magnitude as the pore size, the intrapore resistances are no longer negligible. An important success of this pore-network model is that it can be used to study the effects of percolation on the foam electrical conductivity by using pore-network simulations on larger samples containing a few thousand pores and having different proportions of closed membrane randomly distributed over the sample. The tortuosity is found to be drastically larger than one in foam containing membranes with small apertures or a significant fraction of closed membranes.