LAPONITE® nanorods regulating degradability, acidic-alkaline microenvironment, apatite mineralization and MC3T3-E1 cells responses to poly(butylene succinate) based bio-nanocomposite scaffolds

Gelatin Methacryloyl (GelMA)-Based Biomaterial Inks: Process Science for 3D/4D Printing and Current Status

Tissue engineering for injured tissue replacement and regeneration has been a subject of investigation over the last 30 years, and there has been considerable interest in using additive manufacturing to achieve these goals. Despite such efforts, many key questions remain unanswered, particularly in the area of biomaterial selection for these applications as well as quantitative understanding of the process science. The strategic utilization of biological macromolecules provides a versatile approach to meet diverse requirements in 3D printing, such as printability, buildability, and biocompatibility. These molecules play a pivotal role in both physical and chemical cross-linking processes throughout the biofabrication, contributing significantly to the overall success of the 3D printing process. Among the several bioprintable materials, gelatin methacryloyl (GelMA) has been widely utilized for diverse tissue engineering applications, with some degree of success. In this context, this review will discuss the key bioengineering approaches to identify the gelation and cross-linking strategies that are appropriate to control the rheology, printability, and buildability of biomaterial inks. This review will focus on the GelMA as the structural (scaffold) biomaterial for different tissues and as a potential carrier vehicle for the transport of living cells as well as their maintenance and viability in the physiological system. Recognizing the importance of printability toward shape fidelity and biophysical properties, a major focus in this review has been to discuss the qualitative and quantitative impact of the key factors, including microrheological, viscoelastic, gelation, shear thinning properties of biomaterial inks, and printing parameters, in particular, reference to 3D extrusion printing of GelMA-based biomaterial inks. Specifically, we emphasize the different possibilities to regulate mechanical, swelling, biodegradation, and cellular functionalities of GelMA-based bio(material) inks, by hybridization techniques, including different synthetic and natural biopolymers, inorganic nanofillers, and microcarriers. At the close, the potential possibility of the integration of experimental data sets and artificial intelligence/machine learning approaches is emphasized to predict the printability, shape fidelity, or biophysical properties of GelMA bio(material) inks for clinically relevant tissues.

Tracking cellular uptake, intracellular trafficking and fate of nanoclay particles in human bone marrow stromal cells

Clay nanoparticles, in particular synthetic smectites, have generated interest in the field of tissue engineering and regenerative medicine due to their utility as cross-linkers for polymers in biomaterial design and as protein release modifiers for growth factor delivery. In addition, recent studies have suggested a direct influence on the osteogenic differentiation of responsive stem and progenitor cell populations. Relatively little is known however about the mechanisms underlying nanoclay bioactivity and in particular the cellular processes involved in nanoclay-stem cell interactions. In this study we employed confocal microscopy, inductively coupled plasma mass spectrometry and transmission electron microscopy to track the interactions between clay nanoparticles and human bone marrow stromal cells (hBMSCs). In particular we studied nanoparticle cellular uptake mechanisms and uptake kinetics, intracellular trafficking pathways and the fate of endocytosed nanoclay. We found that nanoclay particles present on the cell surface as μm-sized aggregates, enter hBMSCs through clathrin-mediated endocytosis, and their uptake kinetics follow a linear increase with time during the first week of nanoclay addition. The endocytosed particles were observed within the endosomal/lysosomal compartments and we found evidence for both intracellular degradation of nanoclay and exocytosis as well as an increase in autophagosomal activity. Inhibitor studies indicated that endocytosis was required for nanoclay upregulation of alkaline phosphatase activity but a similar dependency was not observed for autophagy. This study into the nature of nanoclay-stem cell interactions, in particular the intracellular processing of nanosilicate, may provide insights into the mechanisms underlying nanoclay bioactivity and inform the successful utilisation of clay nanoparticles in biomaterial design.

Tissue adhesive hemostatic microneedle arrays for rapid hemorrhage treatment

Blood loss by hemorrhaging wounds accounts for over one-third of ∼5 million trauma fatalities worldwide every year. If not controlled in a timely manner, exsanguination can take lives within a few minutes. Developing new biomaterials that are easy to use by non-expert patients and promote rapid blood coagulation is an unmet medical need. Here, biocompatible, and biodegradable microneedle arrays (MNAs) based on gelatin methacryloyl (GelMA) biomaterial hybridized with silicate nanoplatelets (SNs) are developed for hemorrhage control. The SNs render the MNAs hemostatic, while the needle-shaped structure increases the contact area with blood, synergistically accelerating the clotting time from 11.5 min to 1.3 min in vitro. The engineered MNAs reduce bleeding by ∼92% compared with the untreated injury group in a rat liver bleeding model. SN-containing MNAs outperform the hemostatic effect of needle-free patches and a commercial hemostat in vivo via combining micro- and nanoengineered features. Furthermore, the tissue adhesive properties and mechanical interlocking support the suitability of MNAs for wound closure applications. These hemostatic MNAs may enable rapid hemorrhage control, particularly for patients in developing countries or remote areas with limited or no immediate access to hospitals.

Hydrogel Based on Nanoclay and Gelatin Methacrylate Polymeric Matrix as a Potential Osteogenic Application

A nanocomposite hydrogel has potentially applicability in the induction of osteogenesis. The hydrogel was synthesized using 1% gelatin methacrylate (GelMA), a biodegradable and bioactive polymer containing the structure of gelatin, denatured collagen derived from the extracellular bone matrix, and 6% laponite (Lap), a synthetic phyllosilicate of nanosized particles. Initially, 0.6 g of Lap was added to deionized water, and then a solution of GelMA/Igarcure was added under stirring and UV light for crosslinking. The spectra in the Fourier-transform infrared region showed bands that indicate the interaction between gelatin and methacrylate anhydride. X-ray diffraction patterns confirmed the presence of Lap and GelMA in the hydrogel. The thermogravimetric analysis suggested an increase in the thermal stability of the hydrogel with the presence of clay mineral. Rheological analysis showed that the hydrogel had a viscosity that allowed its injectability. The hydrogel did not show acute toxicity at any of the concentrations tested according to the Artemia salina lethality test. It showed cell viability more significant than 80% in the MTT test, which makes it suitable for in vivo osteogenic induction tests. The cell differentiation test showed the differentiation of stem cells into osteogenic cells. It indicates a material with the potential for osteogenic induction and possible application in bone tissue engineering.

Immunomodulatory Microgels Support Proregenerative Macrophage Activation and Attenuate Fibroblast Collagen Synthesis

Scars composed of fibrous connective tissues are natural consequences of injury upon incisional wound healing in soft tissues.  Hydrogels that feature a sustained presentation of immunomodulatory cytokines are known to modulate wound healing. However, existing immunomodulatory hydrogels lack interconnected micropores to promote cell ingrowth. Other limitations include invasive delivery procedures and harsh synthesis conditions that are incompatible with drug molecules. Here, hybrid nanocomposite microgels containing interleukin-10 (IL-10) are reported to modulate tissue macrophage phenotype during wound healing. The intercalation of laponite nanoparticles in the polymer network yields microgels with tissue-mimetic elasticity (Young's modulus in the range of 2-6 kPa) and allows the sustained release of IL-10 to promote the differentiation of macrophages toward proregenerative phenotypes. The porous interstitial spaces between microgels promote fibroblast proliferation and fast trafficking (an average speed of ≈14.4 µm h^-1 ). The incorporation of hyaluronic acid further enhances macrophage infiltration. The coculture of macrophages and fibroblasts treated with transforming growth factor-beta 1 resulted in a twofold reduction in collagen-I production for microgels releasing IL-10 compared to the IL-10 free group. The new microgels show potential toward regenerative healing by harnessing the antifibrotic behavior of host macrophages.

Laponite/amoxicillin-functionalized PLA nanofibrous as osteoinductive and antibacterial scaffolds

In this study, Amoxicillin (AMX) was loaded on laponite (LAP) nanoplates and then immobilized on the surface of electrospun polylactic acid (PLA) nanofibers to fabricate scaffolds with osteoinductive and antibacterial activities. The highest loading efficiency (49%) was obtained when the concentrations of AMX and LAP were 3 mg/mL and 1 mg/mL, respectively. FTIR and XRD spectroscopies and zeta potentiometry confirmed the successful encapsulating of AMX within LAP nanoplates. The immobilization of AMX-loaded LAPs on the surface of PLA nanofibers was verified by SEM and FTIR spectroscopy. In vitro release study showed a two-phase AMX release profile for the scaffolds; an initial burst release within the first 48 h and a later sustained release up to 21 days. In vitro antibacterial tests against Staphylococcus aureus and Escherichia coli presented the ability of scaffolds to inhibit the growth of both bacteria. The biocompatibility assays revealed the attachment and viability of human bone marrow mesenchymal stem cells (hBMSCs) cultured on the surface of scaffolds (p ≤ 0.05). The increased ALKALINE PHOSPHATASE (ALP) activity (p ≤ 0.001), calcium deposition, and expression of ALP and OSTEONECTIN genes indicated the osteoinductivity of functionalized scaffolds for hBMSCs. These LAP/AMX-functionalized scaffolds might be desirable candida for the treatment of bone defects.

Nanosilicate-Functionalized Polycaprolactone Orchestrates Osteogenesis and Osteoblast-Induced Multicellular Interactions for Potential Endogenous Vascularized Bone Regeneration

Massive oral and maxillofacial bone defect regeneration remains a major clinical challenge due to the absence of functionalized bone grafts with ideal mechanical and proregeneration properties. In the present study, Laponite (LAP), a synthetic nanosilicate, is incorporated into polycaprolactone (PCL) to develop a biomaterial for bone regeneration. It is explored whether LAP-embedded PCL would accelerate bone regeneration by orchestrating osteoblasts to directly and indirectly induce bone regeneration processes. The results confirmed the presence of LAP in PCL, and LAP is distributed in the exfoliated structure without aggregates. Incorporation of LAP in PCL slightly improved the compressive properties. LAP-embedded PCL is biocompatible and exerts pronounced enhancements in cell viability, osteogenic differentiation, and extracellular matrix formation of osteoblasts. Furthermore, osteoblasts cultured on LAP-embedded PCL facilitate angiogenesis of vessel endothelial cells and alleviate osteoclastogenesis of osteoclasts in a paracrine manner. The addition of LAP to the PCL endows favorable bone formation in vivo. Based upon these results, LAP-embedded PCL shows great potential as an ideal bone graft that exerts both space-maintaining and vascularized bone regeneration synergistic effects and can be envisioned for oral and maxillofacial bone defect regeneration.

The role of lithium in the osteogenic bioactivity of clay nanoparticles

LAPONITE® clay nanoparticles are known to exert osteogenic effects on human bone marrow stromal cells (HBMSCs), most characteristically, an upregulation in alkaline phosphatase activity and increased calcium deposition. The specific properties of LAPONITE® that impart its bioactivity are not known. In this study the role of lithium, a LAPONITE® degradation product, was investigated through the use of lithium salts and lithium modified LAPONITE® formulations. In contrast to intact particles, lithium ions applied at concentrations equivalent to that present in LAPONITE®, failed to induce any significant increase in alkaline phosphatase (ALP) activity. Furthermore, no significant differences were observed in ALP activity with modified clay structures and the positive effect on osteogenic gene expression did not correlate with the lithium content of modified clays. These results suggest that other properties of LAPONITE® nanoparticles, and not their lithium content, are responsible for their bioactivity.

Adaptation of MC3T3 cell line to Dulbecco's Modified Eagle's medium

Seeding cells directly into a new medium subjects the cells to stress due to certain differences in medium formulation. As a result, it seems necessary for cells to be adapted to a new medium, in order to save the properties of the cells and to achieve reliable results from the tests. The MC3T3 osteoblastic cell line is recommended to be cultured in Alpha Minimum Essential Medium (α-MEM). However, Dulbecco's Modified Eagle's medium (DMEM) is widely used for its culture. Therefore, in the present paper, two sequential methodologies were applied to adapt the MC3T3 cells to DMEM. In sequential adaptation 1, 10 vol.% DMEM was added to the original medium every day, while in sequential adaptation 2, the old medium was changed to a new medium having 20 vol.% higher DMEM content after each passage. Cells were monitored and compared to direct cell adaptation, while they were growing. The results showed that in the direct cell adaptation, increase in the number of cells was very slow. In contrast, the two sequential adaptation processes were more efficient where sequential adaptation 2 resulted in a higher number of cells in fewer days; 88 % greater than sequential adaptation 1 when it was believed that the cells were adapted. Furthermore, the statistical analysis was conducted by stepwise regression analysis and mathematical models were provided, which can predict the number of cells by day of culture.

A Novel Bilayer Polycaprolactone Membrane for Guided Bone Regeneration: Combining Electrospinning and Emulsion Templating

Guided bone regeneration is a common dental implant treatment where a barrier membrane (BM) is used between epithelial tissue and bone or bone graft to prevent the invasion of the fast-proliferating epithelial cells into the defect site to be able to preserve a space for infiltration of slower-growing bone cells into the periodontal defect site. In this study, a bilayer polycaprolactone (PCL) BM was developed by combining electrospinning and emulsion templating techniques. First, a 250 µm thick polymerised high internal phase emulsion (polyHIPE) made of photocurable PCL was manufactured and treated with air plasma, which was shown to enhance the cellular infiltration. Then, four solvent compositions were investigated to find the best composition for electrospinning a nanofibrous PCL barrier layer on PCL polyHIPE. The biocompatibility and the barrier properties of the electrospun layer were demonstrated over four weeks in vitro by histological staining. Following in vitro assessment of cell viability and cell migration, cell infiltration and the potential of PCL polyHIPE for supporting blood vessel ingrowth were further investigated using an ex-ovo chick chorioallantoic membrane assay. Our results demonstrated that the nanofibrous PCL electrospun layer was capable of limiting cell infiltration for at least four weeks, while PCL polyHIPE supported cell infiltration, calcium and mineral deposition of bone cells, and blood vessel ingrowth through pores.

Interactions at scaffold interfaces: Effect of surface chemistry, structural attributes and bioaffinity

Effective regenerative medicine relies on understanding the interplay between biomaterial implants and the adjoining cells. Scaffolds contribute by presenting sites for cellular adhesion, growth, proliferation, migration, and differentiation which lead to regeneration of tissues over desired periods of time. The fabrication and recruitment of scaffolds often fail to consider the interactions that occur at the interfaces, thereby risking rejection. This lack of knowledge on interfacial microenvironments and related exchanges often causes reduced cellular interactions, poor cell survival and intervention failure. Successful regenerative therapy requires scaffolds with bespoke biocompatibility, optimum pore structure, and cues for cell attachments. These factors determine the development of cellular affinity in scaffolds. For biomedical applications, a detailed understanding of scaffolds and their interfaces is required for better tuning of biomaterials to suit the microenvironments. In this review, we discuss the role of biointerfaces with a focus on surface chemistry, pore structure, scaffold hydro-affinity and their biointeractions. An understanding of the effect of scaffold interfacial properties is crucial for enhancing the progress of tissue engineering towards clinical applications.