Effects of bone surface topography and chemistry on macrophage polarization.

Surface structure plays a crucial role in determining cell behavior on biomaterials, influencing cell adhesion, proliferation, differentiation, as well as immune cells and macrophage polarization. While grooves and ridges stimulate M2 polarization and pits and bumps promote M1 polarization, these structures do not accurately mimic the real bone surface. Consequently, the impact of mimicking bone surface topography on macrophage polarization remains unknown. Understanding the synergistic sequential roles of M1 and M2 macrophages in osteoimmunomodulation is crucial for effective bone tissue engineering. Thus, exploring the impact of bone surface microstructure mimicking biomaterials on macrophage polarization is critical. In this study, we aimed to sequentially activate M1 and M2 macrophages using Poly-L-Lactic acid (PLA) membranes with bone surface topographical features mimicked through the soft lithography technique. To mimic the bone surface topography, a bovine femur was used as a model surface, and the membranes were further modified with collagen type-I and hydroxyapatite to mimic the bone surface microenvironment. To determine the effect of these biomaterials on macrophage polarization, we conducted experimental analysis that contained estimating cytokine release profiles and characterizing cell morphology. Our results demonstrated the potential of the hydroxyapatite-deposited bone surface-mimicked PLA membranes to trigger sequential and synergistic M1 and M2 macrophage polarizations, suggesting their ability to achieve osteoimmunomodulatory macrophage polarization for bone tissue engineering applications. Although further experimental studies are required to completely investigate the osteoimmunomodulatory effects of these biomaterials, our results provide valuable insights into the potential advantages of biomaterials that mimic the complex microenvironment of bone surfaces.

Mesenchymal stem cells derived-exosomes enhanced amniotic membrane extract promotes corneal keratocyte proliferation.

Amniotic membrane extract (AME) and Wharton's jelly mesenchymal stem cells derived-exosomes (WJ-MSC-Exos) are promising therapeutic solutions explored for their potential in tissue engineering and regenerative medicine, particularly in skin and corneal wound healing applications. AME is an extract form of human amniotic membrane and known to contain a plethora of cytokines and growth factors, making it a highly attractive option for topical applications. Similarly, WJ-MSC-Exos have garnered significant interest for their wound healing properties. Although WJ-MSC-Exos and AME have been used separately for wound healing research, their combined synergistic effects have not been studied extensively. In this study, we evaluated the effects of both AME and WJ-MSC-Exos, individually and together, on the proliferation of corneal keratocytes as well as their ability to promote in vitro cell migration, wound healing, and their impact on cellular morphology. Our findings indicated that the presence of both exosomes (3 × 105 Exo/mL) and AME (50 µg/mL) synergistically enhance the proliferation of corneal keratocytes. Combined use of these solutions (3 × 105 Exo/mL + 50 µg/mL) increased cell proliferation compared to only 50 µg/mL AME treatment on day 3 (**** p < 0.0001). This mixture treatment (3 × 105 Exo/mL + 50 µg/mL) increased wound closure rate compared to isolated WJ-MSC-Exo treatment (3 × 105 Exo/mL) (*p < 0.05). Overall, corneal keratocytes treated with AME and WJ-MSC-Exo (3 × 105 Exo/mL + 50 µg/mL) mixture resulted in enhanced proliferation and wound healing tendency. Utilization of combined use of AME and WJ-MSC-Exo can pave the way for a promising foundation for corneal repair research.

Bone surface mimicked PDMS membranes stimulate osteoblasts and calcification of bone matrix.

Cellular microenvironments play a crucial role in cell behavior. In addition to the biochemical cues present in the microenvironments, biophysical and biomechanical properties on surfaces have an impact on cellular functionality and eventually cellular fate. Effects of surface topography on cell behavior are being studied extensively in the literature. However, these studies often try to replicate topographical features of tissue surfaces by using techniques such as chemical etching, photolithography, and electrospinning, which may result in the loss of crucial micro- and nano- features on the tissue surfaces such as bone. This study investigates the topographical effects of bone surface by transferring its surface features onto polydimethylsiloxane (PDMS) membranes using soft lithography from a bovine femur. Our results have shown that major features on bone surfaces were successfully transferred onto PDMS using soft lithography. Osteoblast proliferation and calcification of bone matrix have significantly increased along with osteoblast-specific differentiation and maturation markers such as osteocalcin (OSC), osterix (OSX), collagen type I alpha 1 chain (COL1A1), and alkaline phosphatase (ALP) on bone surface mimicked (BSM) PDMS membranes in addition to a unidirectional alignment of osteoblast cells compared to plain PDMS surfaces. This presented bone surface mimicking method can provide a versatile native-like platform for further investigation of intracellular pathways regarding osteoblast growth and differentiation.