The formation of a functional retinal pigment epithelium occurs on porous polytetrafluoroethylene substrates independently of the surface chemistry

Subretinal transplantation of functioning retinal pigment epithelial (RPE) cells may have the potential to preserve or restore vision in patients affected by blinding diseases such as age-related macular degeneration (AMD). One of the critical steps in achieving this is the ability to grow a functioning retinal pigment epithelium, which may need a substrate on which to grow and to aid transplantation. Tailoring the physical and chemical properties of the substrate should help the engineered tissue to function in the long term. The purpose of the study was to determine whether a functioning monolayer of RPE cells could be produced on expanded polytetrafluoroethylene substrates modified by either an ammonia plasma treatment or an n-Heptylamine coating, and whether the difference in surface chemistries altered the extracellular matrix the cells produced. Primary human RPE cells were able to form a functional, cobblestone monolayer on both substrates, but the formation of an extracellular matrix to exhibit a network structure took months, whereas on non-porous substrates with the same surface chemistry, a similar appearance was observed after a few weeks. This study suggests that the surface chemistry of these materials may not be the most critical factor in the development of growth of a functional monolayer of RPE cells as long as the cells can attach and proliferate on the surface. This has important implications in the design of strategies to optimise the clinical outcomes of subretinal transplant procedures

Inflammasome components ASC and AIM2 modulate the acute phase of biomaterial implant-induced foreign body responses

Detailing the inflammatory mechanisms of biomaterial-implant induced foreign body responses (FBR) has implications for revealing targetable pathways that may reduce leukocyte activation and fibrotic encapsulation of the implant. We have adapted a model of poly(methylmethacrylate) (PMMA) bead injection to perform an assessment of the mechanistic role of the ASC-dependent inflammasome in this process. We first demonstrate that ASC(-/-) mice subjected to PMMA bead injections had reduced cell infiltration and altered collagen deposition, suggesting a role for the inflammasome in the FBR. We next investigated the NLRP3 and AIM2 sensors because of their known contributions in recognising damaged and apoptotic cells. We found that NLRP3 was dispensable for the fibrotic encapsulation; however AIM2 expression influenced leukocyte infiltration and controlled collagen deposition, suggesting a previously unexplored link between AIM2 and biomaterial-induced FBR.Susan N. Christo, Kerrilyn R. Diener, Jim Manavis, Michele A. Grimbaldeston, Akash Bachhuka, Krasimir Vasilev & John D. Haybal

Surface functionalization of exposed core glass optical fiber for metal ion sensing

One of the biggest challenges associated with exposed core glass optical fiber-based sensing is the availability of techniques that can be used to generate reproducible, homogeneous and stable surface coating. We report a one step, solvent free method for surface functionalization of exposed core glass optical fiber that allows achieving binding of fluorophore of choice for metal ion sensing. The plasma polymerization-based method yielded a homogeneous, reproducible and stable coating, enabling high sensitivity aluminium ion sensing. The sensing platform reported in this manuscript is versatile and can be used to bind different sensing molecules opening new avenues for optical fiber-based sensing.Akash Bachhuka, Sabrina Heng, Krasimir Vasilev, Roman Kostecki, Andrew Abell and Heike Ebendorff-Heideprie

Modulation of macrophages differentiation by nanoscale-engineered geometric and chemical features

Macrophage differentiation into M1 (inflammatory) and M2 (healing) phenotypes plays a vital role in determining the fate of biomaterials. The biophysical properties of the extracellular matrix are known to affect macrophage behavior. Mimicking these special biophysical properties of the extracellular matrix has led to increasing interest in biomaterial constructs with tailor-engineered surface nanotopographical and chemical properties. However, a significant gap of knowledge exists in the role played by the combinational effect of surface nanotopography and chemistry. To address this gap, we have fabricated nanoporous surfaces of controlled pore size (30, 65, and 200 nm) and lateral spacing with uniform outermost surface chemistry tailored with amines (NH2), carboxyl (COOH−) and hydrocarbon (CH3−) functionalities. We show that the combinatory effects of surface properties can direct the differentiation of macrophages to the pro-healing M2 phenotype. This is most evident on the surface featuring nanopores of 200 nm and −COOH functionality. Overall, the concentration of pro-inflammatory cytokines significantly decreases, while the concentration of anti-inflammatory cytokines increases many folds on nanotopographically, and chemically, modified surfaces compared to their planar counterparts. Our data provide pioneering knowledge that could provide pathways to tuning inflammatory and foreign body responses and instruct the design of tailor-engineered biomaterial implants to enable better clinical outcomes.A. Bachhuka, R. Madathiparambil Visalakshan, C. S. Law, A. Santos, H. Ebendorff-Heidepriem, S. Karnati, and K. Vasile

The interplay between surface nanotopography and chemistry modulates collagen I and III deposition by human dermal fibroblasts

The events within the foreign body response are similar to, but ultimately different than, the wound healing cascade. Collagen production by fibroblasts is known to play a vital role in wound healing and device fibrous encapsulation. However, the influence of surface nanotopography on collagen deposition by these cells has not been reported so far. To address this gap, we have developed model substrata having surface nanotopography of controlled height of 16, 38, and 68 nm and tailored outermost surface chemistry of amines, carboxyl acid, and pure hydrocarbon. Fibroblast adhesion was reduced on nanotopographically modified surfaces compared to the smooth control. Furthermore, amine and acid functionalized surfaces showed increased cell proliferation over hydrophobic hydrocarbon surfaces. Collagen III production increased from day 3 to day 8 and then decreased from day 8 to day 16 on all surfaces, while collagen I deposition increased throughout the duration of 16 days. Our data show that the initial collagen I and III deposition can be modulated by selecting desired combinations of surface nanotopography and chemistry. This study provides useful knowledge that could help in tuning fibrous capsule formation and in turn govern the fate of implantable biomaterial devices.Akash Bachhuka, John Dominic Hayball, Louise E. Smith and Krasimir Vasile

Effect of surface chemical functionalities on collagen deposition by primary human dermal fibroblasts

Surface modification has been identified as an important technique that could improve the response of the body to implanted medical devices. Collagen production by fibroblasts is known to play a vital role in wound healing and device fibrous encapsulation. However, how surface chemistry affects collagen I and III deposition by these cells has not been systematically studied. Here, we report how surface chemistry influences the deposition of collagen I and III by primary human dermal fibroblasts. Amine (NH3), carboxyl acid (COOH), and hydrocarbon (CH3) surfaces were generated by plasma deposition. This is a practically relevant tool to deposit a functional coating on any type of substrate material. We show that fibroblasts adhere better and proliferate faster on amine-rich surfaces. In addition, the initial collagen I and III production is greater on this type of coating. These data indicates that surface modification can be a promising route for modulating the rate and level of fibrous encapsulation and may be useful in informing the design of implantable biomedical devices to produce more predictable clinical outcomes.Akash Bachhuka, John Hayball, Louise E. Smith and K. Vasile

Surface modification by allylamine plasma polymerization promotes osteogenic differentiation of human adipose-derived stem cells

Tuning the material properties in order to control the cellular behavior is an important issue in tissue engineering. It is now well-established that the surface chemistry can affect cell adhesion, proliferation, and differentiation. In this study, plasma polymerization, which is an appealing method for surface modification, was employed to generate surfaces with different chemical compositions. Allylamine (AAm), acrylic acid (AAc), 1,7-octadiene (OD), and ethanol (ET) were used as precursors for plasma polymerization in order to generate thin films rich in amine (-NH2), carboxyl (-COOH), methyl (-CH3), and hydroxyl (-OH) functional groups, respectively. The surface chemistry was characterized by X-ray photoelectron spectroscopy (XPS), the wettability was determined by measuring the water contact angles (WCA) and the surface topography was imaged by atomic force microscopy (AFM). The effects of surface chemical compositions on the behavior of human adipose-derive stem cells (hASCs) were evaluated in vitro: Cell Count Kit-8 (CCK-8) analysis for cell proliferation, F-actin staining for cell morphology, alkaline phosphatase (ALP) activity analysis, and Alizarin Red S staining for osteogenic differentiation. The results show that AAm-based plasma-polymerized coatings can promote the attachment, spreading, and, in turn, proliferation of hASCs, as well as promote the osteogenic differentiation of hASCs, suggesting that plasma polymerization is an appealing method for the surface modification of scaffolds used in bone tissue engineering.Xujie Liu, Qingling Feng, Akash Bachhuka and Krasimir Vasile

A spiropyran with enhanced fluorescence: a bright, photostable and red-emitting calcium sensor

Abstract not availableGeorgina M. Sylvia, Sabrina Heng, Akash Bachhuka, Heike Ebendorff-Heidepriem, Andrew D. Abel

Surface nanotopography mediated albumin adsorption, unfolding and modulation of early innate immune responses

Surface roughness plays an important role in regulating protein adsorption to biomaterial surfaces and modulating the subsequent inflammatory response. In this study, we examined the role of surface nanotopography on albumin adsorption, unfolding and subsequent immune responses. To achieve the objectives of the study, we create model surfaces of hill-like nanoprotrusions by covalently immobilizing gold nanoparticles (AuNPs) of predetermined sizes (16, 38, and 68 nm) on a functional plasma polymer layer. The amount of adsorbed albumin increased with the increase in surface area caused by greater surface nanotopography scales. Circular dichroism spectroscopy was used to evaluate albumin conformational changes and pointed to loss of α-helical structure on all model surfaces with the greatest conformational changes found on the smooth surface and the surface with largest nanotopography features. Studies with differentiated THP-1 cells (dTHP-1) demonstrated that immune cells interacted with surface adsorbed albumin via their scavenger receptors, which could bind to exposed peptide sequences caused by surface induced unfolding of the albumin. Pre-adsorption of albumin resulted in an overall decrease in the level of expression of pro-inflammatory cytokines from dTHP-1 cells. On the other hand, pre-adsorption of albumin led in an increase in the production of anti-inflammatory markers, which suggests a switch to the M2 pro-healing phenotype. The knowledge obtained from this study could instruct the design of healthcare materials where the generation of targeted surface nanotopography and pre-adsorption of albumin may enhance the biomaterial biocompatibility and lead to faster wound healing.Panthihage Ruvini L. Dabare, Akash Bachhuka, Emma Parkinson-Lawrence, Krasimir Vasile