Tuning foreign body response with tailor-engineered nanoscale surface modifications: fundamentals to clinical applications

Biomaterials are omnipresent in today's healthcare services and are employed in various applications, including implants, sensors, healthcare accessories, and drug delivery systems. Unfavorable host immunological responses frequently jeopardize the efficacy of biomaterials. As a result, surface modification has received much attention in controlling inflammatory responses since it helps camouflage the biomaterial from the host immune system, influencing the foreign body response (FBR) from protein adsorption to fibrous capsule formation. Surfaces with controlled nanotopography and chemistry, among other surface modification methodologies, have effectively altered the immune response to biomaterials. However, the field is still in its early stages, with only a few studies showing a synergistic effect of surface chemistry and nanotopography on inflammatory and wound healing pathways. Therefore, this review will concentrate on the individual and synergistic effects of surface chemistry and nanotopography on FBR modulation and the molecular processes known to modulate these responses. This review will also provide insights into crucial research gaps and advancements in various tactics for modulating FBR, opening new paths for future research. This will further aid in improving our understanding of the immune response to biomaterials, developing advanced surface modification techniques, designing immunomodulatory biomaterials, and translating discoveries into clinical applications.

Plasma polymerized bio-interface directs fibronectin adsorption and functionalization to enhance "epithelial barrier structure" formation via FN-ITG β1-FAK-mTOR signaling cascade

BACKGROUND

Transepithelial medical devices are increasing utilized in clinical practices. However, the damage of continuous natural epithelial barrier has become a major risk factor for the failure of epithelium-penetrating implants. How to increase the "epithelial barrier structures" (focal adhesions, hemidesmosomes, etc.) becomes one key research aim in overcoming this difficulty. Directly targeting the in situ "epithelial barrier structures" related proteins (such as fibronectin) absorption and functionalization can be a promising way to enhance interface-epithelial integration.

METHODS

Herein, we fabricated three plasma polymerized bio-interfaces possessing controllable surface chemistry. Their capacity to adsorb and functionalize fibronectin (FN) from serum protein was compared by Liquid Chromatography-Tandem Mass Spectrometry. The underlying mechanisms were revealed by molecular dynamics simulation. The response of gingival epithelial cells regarding the formation of epithelial barrier structures was tested.

RESULTS

Plasma polymerized surfaces successfully directed distinguished protein adsorption profiles from serum protein pool, in which plasma polymerized allylamine (ppAA) surface favored adsorbing adhesion related proteins and could promote FN absorption and functionalization via electrostatic interactions and hydrogen bonds, thus subsequently activating the ITG β1-FAK-mTOR signaling and promoting gingival epithelial cells adhesion.

CONCLUSION

This study offers an effective perspective to overcome the current dilemma of the inferior interface-epithelial integration by in situ protein absorption and functionalization, which may advance the development of functional transepithelial biointerfaces. Tuning the surface chemistry by plasma polymerization can control the adsorption of fibronectin and functionalize it by exposing functional protein domains. The functionalized fibronectin can bind to human gingival epithelial cell membrane integrins to activate epithelial barrier structure related signaling pathway, which eventually enhances the formation of epithelial barrier structure.

Mechanistic Insight in Surface Nanotopography Driven Cellular Migration

Cellular migration plays a vital role in many physiological processes. To elucidate the role of surface nanotopography on the downstream signaling pathways underlying cell migration, model surfaces having well-defined hill-like surface nanotopography and uniform surface chemistry were designed and implemented using plasma polymerization and covalent attachment of nanoparticles of predetermined size. A scratch wound assay, immunostaining, and gene expression of focal adhesion (FA) proteins were performed to determine the influence of surface nanotopography on cell migration. The results of this study demonstrate that the gap closure between cell monolayers is faster on surfaces having greater nanoscale topography. The phenomenon is predominantly driven by cell migration and was independent from cell proliferation. Qualitative and quantitative assessment of proteins involved in the signaling pathways underlying cell migration showed significant modulation by surface nanotopography. Specifically, focal adhesion sites decreased with the increase in surface nanotopography scale while the expression of FA proteins increased. This implies that nanotopography mediated modulation of cell migration is directly governed by the recruitment of receptor and adapter proteins responsible for cell-surface interaction. The results of this study indicate that biomaterial devices and constructs having rationally designed surface nanotopography and chemistry could be utilized to regulate wound healing and tissue regeneration.

Synergistic Effect of Surface Chemistry and Surface Topography Gradient on Osteogenic/Adipogenic Differentiation of hMSCs

Much attention has been paid to understanding the individual effects of surface chemistry or topography on cell behavior. However, the synergistic influence of both surface chemistry and surface topography on differentiation of human mesenchymal stem cells (hMSCs) should also be addressed. Here, gold nanoparticles were immobilized in an increasing number density manner to achieve a surface topography gradient; a thin film rich in amine (-NH₂) or methyl (-CH₃) chemical groups was plasma-polymerized to adjust the surface chemistry of the outermost layer (ppAA and ppOD, respectively). hMSCs were cultured on these model substrates with defined surface chemistry and surface topography gradient. The morphology and focal adhesion (FA) formation of hMSCs were first examined. hMSC differentiation was then co-induced in osteogenic and adipogenic medium, as well as in the presence of extracellular-signal-regulated kinase1/2 (ERK1/2) and RhoA/Rho-associated protein kinase (ROCK) inhibitors. The results show that the introduction of nanotopography could enhance FA formation and osteogenesis but inhibited adipogenesis on both ppAA and ppOD surfaces, indicating that the surface chemistry could regulate hMSC differentiation, in a surface topography-dependent manner. RhoA/ROCK and ERK1/2 signaling pathways may participate in this process. This study demonstrated that surface chemistry and surface topography can jointly affect cell morphology, FA formation, and thus osteogenic/adipogenic differentiation of hMSCs. These findings highlight the importance of the synergistic effect of different material properties on regulation of cell response, which has important implications in designing functional biomaterials.

Chronic Obstructive Pulmonary Disease and the Cardiovascular System: Vascular Repair and Regeneration as a Therapeutic Target

Chronic obstructive pulmonary disease (COPD) is a major cause of morbidity and mortality worldwide and encompasses chronic bronchitis and emphysema. It has been shown that vascular wall remodeling and pulmonary hypertension (PH) can occur not only in patients with COPD but also in smokers with normal lung function, suggesting a causal role for vascular alterations in the development of emphysema. Mechanistically, abnormalities in the vasculature, such as inflammation, endothelial dysfunction, imbalances in cellular apoptosis/proliferation, and increased oxidative/nitrosative stress promote development of PH, cor pulmonale, and most probably pulmonary emphysema. Hypoxemia in the pulmonary chamber modulates the activation of key transcription factors and signaling cascades, which propagates inflammation and infiltration of neutrophils, resulting in vascular remodeling. Endothelial progenitor cells have angiogenesis capabilities, resulting in transdifferentiation of the smooth muscle cells via aberrant activation of several cytokines, growth factors, and chemokines. The vascular endothelium influences the balance between vaso-constriction and -dilation in the heart. Targeting key players affecting the vasculature might help in the development of new treatment strategies for both PH and COPD. The present review aims to summarize current knowledge about vascular alterations and production of reactive oxygen species in COPD. The present review emphasizes on the importance of the vasculature for the usually parenchyma-focused view of the pathobiology of COPD.

Plasma polymer surface modified expanded polytetrafluoroethylene promotes epithelial monolayer formation in vitro and can be transplanted into the dystrophic rat subretinal space

The aim of this study was to evaluate whether the surface modification of expanded polytetrafluoroethylene (ePTFE) using an n-heptylamine (HA) plasma polymer would allow for functional epithelial monolayer formation suitable for subretinal transplant into a non-dystrophic rat model. Freshly isolated iris pigment epithelial (IPE) cells from two rat strains (Long Evans [LE] and Dark Agouti [DA]) were seeded onto HA, fibronectin-coated n-heptylamine modified (F-HA) and unmodified ePFTE and fibronectin-coated tissue culture (F-TCPS) substrates. Both F-HA ePTFE and F-TCPS substrates enabled functional monolayer formation with both strains of rat. Without fibronectin coating, only LE IPE formed a monolayer on HA-treated ePTFE. Functional assessment of both IPE strains on F-HA ePTFE demonstrated uptake of POS that increased significantly with time that was greater than control F-TCPS. Surgical optimization using Healon GV and mixtures of Healon GV: phosphate buffered saline (PBS) to induce retinal detachment demonstrated that only Healon GV:PBS allowed F-HA ePTFE substrates to be successfully transplanted into the subretinal space of Royal College of Surgeons rats, where they remained flat beneath the neural retina for up to 4 weeks. No apparent substrate-induced inflammatory response was observed by fundus microscopy or immunohistochemical analysis, indicating the potential of this substrate for future clinical applications.

Field Deployable Method for Gold Detection Using Gold Pre-Concentration on Functionalized Surfaces

Keywords: surface chemistry, plasma polymerization, salinization, gold sensing.

Nanotopography-based strategy for the precise manipulation of osteoimmunomodulation in bone regeneration

Immune cells play vital roles in regulating bone dynamics. Successful bone regeneration requires a favourable osteo-immune environment. The high plasticity and diversity of immune cells make it possible to manipulate the osteo-immune response of immune cells, thus modulating the osteoimmune environment and regulating bone regeneration. With the advancement in nanotechnology, nanotopographies with different controlled surface properties can be fabricated. On tuning the surface properties, the osteo-immune response can be precisely modulated. This highly tunable characteristic and immunomodulatory effects make nanotopography a promising strategy to precisely manipulate osteoimmunomdulation for bone tissue engineering applications. This review first summarises the effects of the immune response during bone healing to show the importance of regulating the immune response for the bone response. The plasticity of immune cells is then reviewed to provide rationales for manipulation of the osteoimmune response. Subsequently, we highlight the current types of nanotopographies applied in bone biomaterials and their fabrication techniques, and explain how these nanotopographies modulate the immune response and the possible underlying mechanisms. The effects of immune cells on nanotopography-mediated osteogenesis are emphasized, and we propose the concept of "nano-osteoimmunomodulation" to provide a valuable strategy for the development of nanotopographies with osteoimmunomodulatory properties that can precisely regulate bone dynamics.

Nanotopography mediated osteogenic differentiation of human dental pulp derived stem cells

Advanced medical devices, treatments and therapies demand an understanding of the role of interfacial properties on the cellular response. This is particularly important in the emerging fields of cell therapies and tissue regeneration. In this study, we evaluate the role of surface nanotopography on the fate of human dental pulp derived stem cells (hDPSC). These stem cells have attracted interest because of their capacity to differentiate to a range of useful lineages but are relatively easy to isolate. We generated and utilized density gradients of gold nanoparticles which allowed us to examine, on a single substrate, the influence of nanofeature density and size on stem cell behavior. We found that hDPSC adhered in greater numbers and proliferated faster on the sections of the gradients with higher density of nanotopography features. Furthermore, greater surface nanotopography density directed the differentiation of hDPSC to osteogenic lineages. This study demonstrates that carefully tuned surface nanotopography can be used to manipulate and guide the proliferation and differentiation of these cells. The outcomes of this study can be important in the rational design of culture substrates and vehicles for cell therapies, tissue engineering constructs and the next generation of biomedical devices where control over the growth of different tissues is required.

The Role of Controlled Surface Topography and Chemistry on Mouse Embryonic Stem Cell Attachment, Growth and Self-Renewal

The success of stem cell therapies relies heavily on our ability to control their fate in vitro during expansion to ensure an appropriate supply. The biophysical properties of the cell culture environment have been recognised as a potent stimuli influencing cellular behaviour. In this work we used advanced plasma-based techniques to generate model culture substrates with controlled nanotopographical features of 16 nm, 38 nm and 68 nm in magnitude, and three differently tailored surface chemical functionalities. The effect of these two surface properties on the adhesion, spreading, and self-renewal of mouse embryonic stem cells (mESCs) were assessed. The results demonstrated that physical and chemical cues influenced the behaviour of these stem cells in in vitro culture in different ways. The size of the nanotopographical features impacted on the cell adhesion, spreading and proliferation, while the chemistry influenced the cell self-renewal and differentiation.

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.

Surface nanotopography guides kidney-derived stem cell differentiation into podocytes

Stem cells have enormous potential for developing novel therapies for kidney disease but our current inability to direct their differentiation to specialised renal cells presents a barrier to their use in renal bioengineering and drug development programmes. Here, a plasma-based technology was used to produce a range of biocompatible substrates comprising controlled surface nanotopography and tailored outermost chemical functionalities. These novel substrata were used to investigate the response of mouse kidney-derived stem cells to changes in both substrate nanotopography and surface chemistry. The stem cells proliferated to a similar extent on all substrates, but specific combinations of nanotopography and surface chemistry promoted differentiation into either podocyte or proximal tubule-like cells. The data reveal that high density of surface nanodefects in association with amine rich chemistry primarily lead to differentiation into podocytes while surfaces with low amine content constituted better substrates for differentiation into proximal tubule cells regardless of the surface nanotopographic profile. Thus plasma coated nanorough substrate may provide useful platform for guiding the fate kidney stem cell in vitro.

STATEMENT OF SIGNIFICANCE

Adult kidney-derived stem cells have been identified as a promising way to regenerate damaged nephrons. Artificial growth platforms capable to guide the stem cells differentiation into useful cell lineages are needed to expand regenerative cell therapies for chronic kidney diseases. Chemically homogeneous growth substrates endowed with nanotopography gradients were generated via plasma assisted methods in order to investigate the effect of physical cues on the proliferation and differentiation of kidney-derived stem cells. For the first time it is shown that the surface density of the nano-structures had a greater impact on fate of the stem cells than their size. Careful design of the growth substrate nanotopography may help directing the differentiation into either podocytes or proximal tubule cells.

Tuning Chemistry and Topography of Nanoengineered Surfaces to Manipulate Immune Response for Bone Regeneration Applications

Osteoimmunomodulation has informed the importance of modulating a favorable osteoimmune environment for successful materials-mediated bone regeneration. Nanotopography is regarded as a valuable strategy for developing advanced bone materials, due to its positive effects on enhancing osteogenic differentiation. In addition to this direct effect on osteoblastic lineage cells, nanotopography also plays a vital role in regulating immune responses, which makes it possible to utilize its immunomodulatory properties to create a favorable osteoimmune environment. Therefore, the aim of this study was to advance the applications of nanotopography with respect to its osteoimmunomodulatory properties, aiming to shed further light on this field. We found that tuning the surface chemistry (amine or acrylic acid) and scale of the nanotopography (16, 38, and 68 nm) significantly modulated the osteoimmune environment, including changes in the expression of inflammatory cytokines, osteoclastic activities, and osteogenic, angiogenic, and fibrogenic factors. The generated osteoimmune environment significantly affected the osteogenic differentiation of bone marrow stromal cells, with carboxyl acid-tailored 68 nm surface nanotopography offering the most promising outcome. This study demonstrated that the osteoimmunomodulation could be manipulated via tuning the chemistry and nanotopography, which implied a valuable strategy to apply a "nanoengineered surface" for the development of advanced bone biomaterials with favorable osteoimmunomodulatory properties.

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.

The contribution of inflammasome components on macrophage response to surface nanotopography and chemistry

Implantable devices have become an established part of medical practice. However, often a negative inflammatory host response can impede the integration and functionality of the device. In this paper, we interrogate the role of surface nanotopography and chemistry on the potential molecular role of the inflammasome in controlling macrophage responses. To achieve this goal we engineered model substrata having precisely controlled nanotopography of predetermined height and tailored outermost surface chemistry. Bone marrow derived macrophages (BMDM) were harvested from genetically engineered mice deficient in the inflammasome components ASC, NLRP3 and AIM2. These cells were then cultured on these nanoengineered substrata and assessed for their capacity to attach and express pro-inflammatory cytokines. Our data provide evidence that the inflammasome components ASC, NLRP3 and AIM2 play a role in regulating macrophage adhesion and activation in response to surface nanotopography and chemistry. The findings of this paper are important for understanding the inflammatory consequences caused by biomaterials and pave the way to the rational design of future implantable devices having controlled and predictable inflammatory outcomes.

The Role of Surface Nanotopography and Chemistry on Primary Neutrophil and Macrophage Cellular Responses

Synthetic materials employed for enhancing, replacing, or restoring biological functionality may be compromised by the host immune responses that they evoke. Surface modification has attracted substantial attention as a tool to modulate the host response to synthetic materials; however, how surface nanotopography combined with chemistry affects immune effector cell responses is still poorly understood. To address this open question, a unique set of model surfaces with controlled surface nanotopography in the range of 16, 38, and 68 nm has been generated. Tailored outermost surface chemistry that was amine, carboxyl, or methyl group rich has been provided. The combinations of these properties yield 12 surface types that are subject to functional assays assessing key immune effector cells, namely, primary neutrophil and macrophage responses in vitro. The data demonstrate that surface nanotopography leads to enhanced matrix metalloproteinase-9 production from primary neutrophils, and a decrease in pro-inflammatory cytokine secretion from primary macrophages. Together, these results are the first to directly compare the immunomodulatory effects of the cooperative interplay between surface nanotopography and chemistry.

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.

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.

Surface Chemical Gradient Affects the Differentiation of Human Adipose-Derived Stem Cells via ERK1/2 Signaling Pathway

To understand the role of surface chemistry on cell behavior and the associated molecular mechanisms, we developed and utilized a surface chemical gradient of amine functional groups by carefully adjusting the gas composition of 1,7-octadiene (OD) and allylamine (AA) of the plasma phase above a moving substrate. The chemical gradient surface used in the present work shows an increasing N/C ratio and wettability from the OD side toward the AA side with no change in surface topography. Under standard culture conditions (with serum), human adipose-derived stem cells (hASCs) adhesion and spreading area increased toward the AA side of the gradient. However, there were no differences in cell behavior in the absence of serum. These results, supported by the trends in proteins adsorption on the gradient surface, demonstrated that surface chemistry affects the response of hASCs through cell-adhesive serum proteins, rather than interacting directly with the cells. The expression of p-ERK and the osteogenic differentiation increased toward the AA side of the gradient, while adipogenic differentiation decreased in the same direction; however, when the activation of ERK1/2 was blocked by PD98059, the levels of osteogenic or adipogenic differentiation on different regions of the chemical gradient were the same. This indicates that ERK1/2 may be an important downstream signaling pathway of surface chemistry directed stem cell fate.

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.