Investigation of wound healing process guided by nano-scale topographic patterns integrated within a microfluidic system

Nanocomposite Based on Bacterial Cellulose and Silver Nanoparticles Improve Wound Healing Without Exhibiting Toxic Effect

Wound healing is an important and complex process, containing a multifaceted process governed by sequential yet overlapping phases. Certain treatments can optimize local physiological conditions and improve wound healing. Silver nanoparticles (AgNP) are widely known for their antimicrobial activity. On the other hand, bacterial cellulose (BC) films have been used as a dressing that temporarily substitutes the skin, offering many advantages in optimizing wound healing, in addition to being highly biocompatible. Considering the promising activities of AgNP and BC films, the present study aimed to evaluate the wound healing activity in Wistar Hannover rats using a nanocomposite based on bacterial cellulose containing AgNP (AgBC). In a period of 21 days, its influence on the wound area, microbial growth, histopathological parameters, and collagen content were analyzed. In addition, toxicity indicators were assessed, such as weight gain, water consumption, and creatinine and alanine transaminase levels. After 14 days of injury, the animals treated with AgBC showed a significant increase in wound contraction. The treatment with AgBC significantly reduced the number of microbial colonies compared to other treatments in the first 48 h after the injury. At the end of the 21 experimental days, an average wound contraction rate greater than 97 % in relation to the initial area was observed, in addition to a significant increase in the amount of collagen fibers at the edge of the wounds, lower scores of necrosis, angiogenesis and inflammation, associated with no systemic toxicity. Therefore, it is concluded that the combination of preexisting products to form a new nanocomposite based on BC and AgNP amplified the biological activity of these products, increasing the effectiveness of wound healing and minimizing possible toxic effects of silver.

Surface Deformation of Biocompatible Materials: Recent Advances in Biological Applications

The surface topography of substrates is a crucial factor that determines the interaction with biological materials in bioengineering research. Therefore, it is important to appropriately modify the surface topography according to the research purpose. Surface topography can be fabricated in various forms, such as wrinkles, creases, and ridges using surface deformation techniques, which can contribute to the performance enhancement of cell chips, organ chips, and biosensors. This review provides a comprehensive overview of the characteristics of soft, hard, and hybrid substrates used in the bioengineering field and the surface deformation techniques applied to the substrates. Furthermore, this review summarizes the cases of cell-based research and other applications, such as biosensor research, that utilize surface deformation techniques. In cell-based research, various studies have reported optimized cell behavior and differentiation through surface deformation, while, in the biosensor and biofilm fields, performance improvement cases due to surface deformation have been reported. Through these studies, we confirm the contribution of surface deformation techniques to the advancement of the bioengineering field. In the future, it is expected that the application of surface deformation techniques to the real-time interaction analysis between biological materials and dynamically deformable substrates will increase the utilization and importance of these techniques in various fields, including cell research and biosensors.

Contact Guidance of Connective Tissue Fibroblasts on Submicrometer Anisotropic Topographical Cues Is Dependent on Tissue of Origin, β1 Integrins, and Tensin-1 Recruitment

The substratum topography of both natural and synthetic materials is a prominent regulator of cell behaviors including adhesion, migration, matrix fibrillogenesis, and cell phenotype. Connective tissue fibroblasts are known to respond to repeating groove topographical modifications by aligning and exhibiting directed migration, a phenomenon termed contact guidance. Although both reside in collagen rich connective tissues, dermal and gingival fibroblasts are known to exhibit differences in phenotype during wound healing, with gingival tissue showing a fetal-like scarless response. Differences in adhesion formation and maturation are known to underlie both a scarring phenotype and cell response to topographical features. Utilizing repeating groove substrates with periodicities of 600, 900, and 1200 nm (depth, 100 nm), we investigated the roles of integrins αvβ3 and β1 associated adhesions on contact guidance of human gingival (HGFs) and dermal fibroblasts (HDFs). HGFs showed a higher degree of orientation with the groove long axis than HDFs, with alignment of both vinculin and tensin-1 evident on 600 and 900 nm periodicities in both cell types. Orientation with grooves of any periodicity in HGFs and HDFs did not alter the adhesion number or area compared to smooth control surfaces. Growth of both cell types on all periodicities reduced fibronectin fibrillogenesis compared to control surfaces. Independent inhibition of integrin αvβ3 and β1 in both cell types induced changes in spreading up to 6 h and reduced alignment with the groove long axis. At 24 h post-seeding with blocking antibodies, HGFs recovered orientation, but in HDFs, blocking of β1, but not αvβ3 integrins, inhibited alignment. Blocking of β1 and αvβ3 in HDFs, but not HGFs, inhibited tensin-1-associated fibrillar adhesion formation. Furthermore, inhibition of β1 integrins in HDFs, but not HGFs, resulted in recruitment of tensin-1 to αvβ3 focal adhesions, preventing HDFs from aligning with the groove long axis. Our work demonstrates that tensin-1 localization with specific integrins in adhesion sites is an important determinant of contact guidance. This work emphasizes further the need for tissue-specific biomaterials, when integration into host tissues is required.

Fabrication of Scratched Nanogrooves for Highly Oriented Cell Alignment and Application as a Wound Healing Dressing

Using improper wound care materials may cause impaired wound healing, which can involve scar formation and infection. Herein, we propose a facile method to fabricate a cell-alignment scaffold, which can effectively enhance cell growth and migration, leading to the reproduction of cellular arrangements and restoration of tissues. The principle is scratching a diamond lapping film that gives uniaxial nanotopography on substrates. Cells are seeded to follow the geometric cue via contact guidance, resulting in highly oriented cell alignment. Remarkable biocompatibility is also demonstrated by the high cell viability on various substrates. In vivo studies in a wound healing model in mice show that the scratched film supports directed cell guidance on the nanostructure, with significantly reduced wound areas and inhibition of excessive collagen deposition. Rapid recovery of the epidermis and dermis is also shown by histological analyses, suggesting the potential application of the scratching technique as an advanced wound dressing material for effective tissue regeneration.

Bioelectronic microfluidic wound healing: a platform for investigating direct current stimulation of injured cell collectives

Upon cutaneous injury, the human body naturally forms an electric field (EF) that acts as a guidance cue for relevant cellular and tissue repair and reorganization. However, the direct current (DC) flow imparted by this EF can be impacted by a variety of diseases. This work delves into the impact of DC stimulation on both healthy and diabetic in vitro wound healing models of human keratinocytes, the most prevalent cell type of the skin. The culmination of non-metal electrode materials and prudent microfluidic design allowed us to create a compact bioelectronic platform to study the effects of different sustained (12 hours galvanostatic DC) EF configurations on wound closure dynamics. Specifically, we compared if electrotactically closing a wound's gap from one wound edge (i.e., uni-directional EF) is as effective as compared to alternatingly polarizing both the wound's edges (i.e., pseudo-converging EF) as both of these spatial stimulation strategies are fundamental to the eventual translational electrode design and strategy. We found that uni-directional electric guidance cues were superior in group keratinocyte healing dynamics by enhancing the wound closure rate nearly three-fold for both healthy and diabetic-like keratinocyte collectives, compared to their non-stimulated respective controls. The motility-inhibited and diabetic-like keratinocytes regained wound closure rates with uni-directional electrical stimulation (increase from 1.0 to 2.8% h^-1) comparable to their healthy non-stimulated keratinocyte counterparts (3.5% h^-1). Our results bring hope that electrical stimulation delivered in a controlled manner can be a viable pathway to accelerate wound repair, and also by providing a baseline for other researchers trying to find an optimal electrode blueprint for in vivo DC stimulation.

Spatially selective cell treatment and collection for integrative drug testing using hydrodynamic flow focusing and shifting

Hydrodynamic focusing capable of readily producing and controlling laminar flow facilitates drug treatment of cells in existing microfluidic culture devices. However, to expand applications of such devices to multiparameter drug testing, critical limitations in current hydrodynamic focusing microfluidics must be addressed. Here we describe hydrodynamic focusing and shifting as an advanced microfluidics tool for spatially selective drug delivery and integrative cell-based drug testing. We designed and fabricated a co-flow focusing, three-channel microfluidic device with a wide cell culture chamber. By controlling inlet flow rates of sample and two side solutions, we could generate hydrodynamic focusing and shifting that mediated precise regulation of the path and width of reagent and drug stream in the microfluidic device. We successfully validated a hydrodynamic focusing and shifting approach for spatially selective delivery of DiI, a lipophilic fluorophore, and doxorubicin, a chemotherapeutic agent, to tumor cells in our device. Moreover, subsequent flowing of a trypsin EDTA solution over the cells that were exposed to doxorubicin flow allowed us to selectively collect the treated cells. Our approach enabled downstream high-resolution microscopy of the cell suspension to confirm the nuclear delivery of doxorubicin into the tumor cells. In the device, we could also evaluate in situ the cytotoxic effect of doxorubicin to the tumor cells that were selectively treated by hydrodynamic flow focusing and shifting. These results show that hydrodynamic focusing and shifting enable a fast and robust approach to spatially treat and then collect cells in an optimized microfluidic device, offering an integrative assay tool for efficient drug screening and discovery.

Engineered Nanotechnology: An Effective Therapeutic Platform for the Chronic Cutaneous Wound

The healing of chronic wound infections, especially cutaneous wounds, involves a complex cascade of events demanding mutual interaction between immunity and other natural host processes. Wound infections are caused by the consortia of microbial species that keep on proliferating and produce various types of virulence factors that cause the development of chronic infections. The mono- or polymicrobial nature of surface wound infections is best characterized by its ability to form biofilm that renders antimicrobial resistance to commonly administered drugs due to poor biofilm matrix permeability. With an increasing incidence of chronic wound biofilm infections, there is an urgent need for non-conventional antimicrobial approaches, such as developing nanomaterials that have intrinsic antimicrobial-antibiofilm properties modulating the biochemical or biophysical parameters in the wound microenvironment in order to cause disruption and removal of biofilms, such as designing nanomaterials as efficient drug-delivery vehicles carrying antibiotics, bioactive compounds, growth factor antioxidants or stem cells reaching the infection sites and having a distinct mechanism of action in comparison to antibiotics-functionalized nanoparticles (NPs) for better incursion through the biofilm matrix. NPs are thought to act by modulating the microbial colonization and biofilm formation in wounds due to their differential particle size, shape, surface charge and composition through alterations in bacterial cell membrane composition, as well as their conductivity, loss of respiratory activity, generation of reactive oxygen species (ROS), nitrosation of cysteines of proteins, lipid peroxidation, DNA unwinding and modulation of metabolic pathways. For the treatment of chronic wounds, extensive research is ongoing to explore a variety of nanoplatforms, including metallic and nonmetallic NPs, nanofibers and self-accumulating nanocarriers. As the use of the magnetic nanoparticle (MNP)-entrenched pre-designed hydrogel sheet (MPS) is found to enhance wound healing, the bio-nanocomposites consisting of bacterial cellulose and magnetic nanoparticles (magnetite) are now successfully used for the healing of chronic wounds. With the objective of precise targeting, some kinds of "intelligent" nanoparticles are constructed to react according to the required environment, which are later incorporated in the dressings, so that the wound can be treated with nano-impregnated dressing material in situ. For the effective healing of skin wounds, high-expressing, transiently modified stem cells, controlled by nano 3D architectures, have been developed to encourage angiogenesis and tissue regeneration. In order to overcome the challenge of time and dose constraints during drug administration, the approach of combinatorial nano therapy is adopted, whereby AI will help to exploit the full potential of nanomedicine to treat chronic wounds.

Microfluidic Surgery in Single Cells and Multicellular Systems

Microscale surgery on single cells and small organisms has enabled major advances in fundamental biology and in engineering biological systems. Examples of applications range from wound healing and regeneration studies to the generation of hybridoma to produce monoclonal antibodies. Even today, these surgical operations are often performed manually, but they are labor intensive and lack reproducibility. Microfluidics has emerged as a powerful technology to control and manipulate cells and multicellular systems at the micro- and nanoscale with high precision. Here, we review the physical and chemical mechanisms of microscale surgery and the corresponding design principles, applications, and implementations in microfluidic systems. We consider four types of surgical operations: (1) sectioning, which splits a biological entity into multiple parts, (2) ablation, which destroys part of an entity, (3) biopsy, which extracts materials from within a living cell, and (4) fusion, which joins multiple entities into one. For each type of surgery, we summarize the motivating applications and the microfluidic devices developed. Throughout this review, we highlight existing challenges and opportunities. We hope that this review will inspire scientists and engineers to continue to explore and improve microfluidic surgical methods.

Microfluidic and Lab-on-a-Chip Systems for Cutaneous Wound Healing Studies

Cutaneous wound healing is a complex, multi-stage process involving direct and indirect cell communication events with the aim of efficiently restoring the barrier function of the skin. One key aspect in cutaneous wound healing is associated with cell movement and migration into the physically, chemically, and biologically injured area, resulting in wound closure. Understanding the conditions under which cell migration is impaired and elucidating the cellular and molecular mechanisms that improve healing dynamics are therefore crucial in devising novel therapeutic strategies to elevate patient suffering, reduce scaring, and eliminate chronic wounds. Following the global trend towards the automation, miniaturization, and integration of cell-based assays into microphysiological systems, conventional wound healing assays such as the scratch assay and cell exclusion assay have recently been translated and improved using microfluidics and lab-on-a-chip technologies. These miniaturized cell analysis systems allow for precise spatial and temporal control over a range of dynamic microenvironmental factors including shear stress, biochemical and oxygen gradients to create more reliable in vitro models that resemble the in vivo microenvironment of a wound more closely on a molecular, cellular, and tissue level. The current review provides (a) an overview on the main molecular and cellular processes that take place during wound healing, (b) a brief introduction into conventional in vitro wound healing assays, and (c) a perspective on future cutaneous and vascular wound healing research using microfluidic technology.

Microphysiological systems for the modeling of wound healing and evaluation of pro-healing therapies

Wound healing is a multivariate process involving the coordinated response of numerous proteins and cell types. Accordingly, biomedical research has seen an increased adoption of the use of in vitro wound healing assays with complexity beyond that offered by traditional well-plate constructs. These microphysiological systems (MPS) seek to recapitulate one or more physiological features of the in vivo microenvironment, while retaining the analytical capacity of more reductionist assays. Design efforts to achieve relevant wound healing physiology include the use of dynamic perfusion over static culture, the incorporation of multiple cell types, the arrangement of cells in three dimensions, the addition of biomechanically and biochemically relevant hydrogels, and combinations thereof. This review provides a brief overview of the wound healing process and in vivo assays, and we critically review the current state of MPS and supporting technologies for modelling and studying wound healing. We distinguish between MPS that seek to inform a particular phase of wound healing, and constructs that have the potential to inform multiple phases of wound healing. This distinction is a product of whether analysis of a particular process is prioritized, or a particular physiology is prioritized, during design. Material selection is emphasized throughout, and relevant fabrication techniques discussed.

Lipoconstruct surface topography grating size influences vascularization onset in the dorsal skinfold chamber model

After skin tissue injury or pathological removal, vascularization timing is paramount in graft survival. As full thickness skin grafts often fail to become perfused over larger surfaces, split-thickness grafts are preferred and can be used together with biomaterials, which themselves are non-angiogenic. One way of promoting vascular ingrowth is to "pre-vascularize" an engineered substitute by introducing endothelial cells (ECs). Since it has been previously demonstrated that surface structured biomaterials have an effect on wound healing, skin regeneration, and fibrosis reduction, we proposed that a microvascular-rich lipoconstruct with anisotropic topographical cues could be a clinically translatable vascularization approach. Murine lipofragments were formed with three polydimethylsiloxane molds (flat, 5 µm, and 50 µm parallel gratings) and implanted into the dorsal skinfold chamber of male C57BL/6 mice. Vascular ingrowth was observed through intravital microscopy over 21 days and further assessed by histology and protein identification. Our investigation revealed that topographical feature size influenced the commencement of neovascular ingrowth, with 5 µm gratings exhibiting early construct perfusion at 3 days post-operation, and 50 µm being delayed until day 5. We therefore postulate that surface structured lipoconstructs may serve as an easily obtained and produced construct suitable for providing soft tissue and ECs to tissue defects. STATEMENT OF SIGNIFICANCE: Skin graft failures due to inadequate or uneven perfusion frequently occur and can be even more complicated in deep, difficult to heal wounds, or bone coverage. In complex injuries, biomaterials are often used to cover bone structures with a standard split thickness graft; however, perfusion can take up to 3 weeks. Thus, any means to promote faster and uniform vascularization could significantly reduce healing time, as well as lower patient down-time. As pre-vascularized constructs have reported success in research, we created a cost-efficient, translatable method with no additional laboratory time as adipose tissue can be harvested and used immediately. We further used surface topography as an aspect to modulate construct perfusion, which has been reported for the first time here.