Influence of diabetes on the foreign body response to nitric oxide-releasing implants

Emerging strategies for nitric oxide production and their topical application as nanodressings to promote diabetic wound healing

The challenges associated with prolonged healing or non-healing of chronic diabetic wounds contribute significantly to the increased incidence of lower limb amputation. A pivotal factor in the impediment of healing is the reduced production of endogenous nitric oxide (NO) due to the hyperglycemic microenvironment typical of chronic diabetes. While both endogenous and exogenous NO have been shown to promote the healing process of diabetic wounds, the direct application of NO in wound management is limited due to its gaseous nature and the risk of explosive release. This review summarizes recent advances of nanodressings incorporating NO donors in the treatment of diabetic wounds, detailing the specific conditions under which these nanodressings facilitate NO release, with a focus on the beneficial effects of NO, strategies for its supplementation, and the challenges encountered in the clinical translation of NO donors as a clinically viable nanomedicine in the context of improving diabetic wound healing.

Investigating Immunomodulatory Biomaterials for Preventing the Foreign Body Response

Implantable biomaterials represent the forefront of regenerative medicine, providing platforms and vessels for delivering a creative range of therapeutic benefits in diverse disease contexts. However, the chronic damage resulting from implant rejection tends to outweigh the intended healing benefits, presenting a considerable challenge when implementing treatment-based biomaterials. In response to implant rejection, proinflammatory macrophages and activated fibroblasts contribute to a synergistically destructive process of uncontrolled inflammation and excessive fibrosis. Understanding the complex biomaterial-host cell interactions that occur within the tissue microenvironment is crucial for the development of therapeutic biomaterials that promote tissue integration and minimize the foreign body response. Recent modifications of specific material properties enhance the immunomodulatory capabilities of the biomaterial and actively aid in taming the immune response by tuning interactions with the surrounding microenvironment either directly or indirectly. By incorporating modifications that amplify anti-inflammatory and pro-regenerative mechanisms, biomaterials can be optimized to maximize their healing benefits in harmony with the host immune system.

In Vivo Study of the Inflammatory Tissue Response Surrounding a Novel Extended-Wear Kink-Resistant Insulin Infusion Set Prototype Compared With a Commercial Control Over Two Weeks of Wear Time

BACKGROUND

Infusion set function remains the limiting factor of insulin pump therapy due to nonmetabolic complications. Here, we tested an investigational extended-wear infusion set prototype with a soft, angled, wire-reinforced cannula with three additional side holes, and compared failure mechanisms and tissue response with a commercial Teflon control.

METHODS

A total of 48 Teflon and 48 prototype infusion sets were inserted subcutaneously every other day for 14 days in 12 swine and infused with dilute insulin. After two weeks, tissue around cannulas was excised, and occlusions, leaks, and kinks were determined. Tissue was processed and stained to assess the total area of inflammation (TAI) and the inflammatory layer thickness (ILT) around the cannulas. Data were analyzed using Fisher's exact, analysis of variance-general linear model, Kruskal-Wallis, and post hoc tests.

RESULTS

On average, the TAI surrounding the investigational cannula was 52.6% smaller than around the commercial control. The ILT was 66.3% smaller around investigational cannulas. Kinks occurred in 2.1% (investigational) vs 32.4% (commercial) cannulas (P < .001). There was no difference in occlusion alarms and leaks onto skin.

CONCLUSIONS

The data suggest that the infusion set prototype elicits less inflammation over an extended wear time and is resistant to kinking, compared with a commercial Teflon device. This is consistent with previously published data on the impact of cannula material/angle on the inflammatory tissue response. We highlight the following important aspects of infusion set design: (1) secure skin adhesion, (2) reliable cannula insertion, (3) automatic removal of the stylet, (4) cannula material/design that resists kinking, and (5) minimization of local tissue inflammation.

Soft robot-mediated autonomous adaptation to fibrotic capsule formation for improved drug delivery

The foreign body response impedes the function and longevity of implantable drug delivery devices. As a dense fibrotic capsule forms, integration of the device with the host tissue becomes compromised, ultimately resulting in device seclusion and treatment failure. We present FibroSensing Dynamic Soft Reservoir (FSDSR), an implantable drug delivery device capable of monitoring fibrotic capsule formation and overcoming its effects via soft robotic actuations. Occlusion of the FSDSR porous membrane was monitored over 7 days in a rodent model using electrochemical impedance spectroscopy. The electrical resistance of the fibrotic capsule correlated to its increase in thickness and volume. Our FibroSensing membrane showed great sensitivity in detecting changes at the abiotic/biotic interface, such as collagen deposition and myofibroblast proliferation. The potential of the FSDSR to overcome fibrotic capsule formation and maintain constant drug dosing over time was demonstrated in silico and in vitro. Controlled closed loop release of methylene blue into agarose gels (with a comparable fold change in permeability relating to 7 and 28 days in vivo) was achieved by adjusting the magnitude and frequency of pneumatic actuations after impedance measurements by the FibroSensing membrane. By sensing fibrotic capsule formation in vivo, the FSDSR will be capable of probing and adapting to the foreign body response through dynamic actuation changes. Informed by real-time sensor signals, this device offers the potential for long-term efficacy and sustained drug dosing, even in the setting of fibrotic capsule formation.

Mechanisms of Foreign Body Response Mitigation by Nitric Oxide Release

Implantable glucose biosensors provide real-time information about blood glucose fluctuations, but their utility and accuracy are time-limited due to the foreign body response (FBR) following their insertion beneath the skin. The slow release of nitric oxide (NO), a gasotransmitter with inflammation regulatory properties, from a sensor surface has been shown to dramatically improve sensors' analytical biocompatibility by reducing the overall FBR response. Indeed, work in a porcine model suggests that as long as the implants (sensors) continue to release NO, even at low levels, the inflammatory cell infiltration and resulting collagen density are lessened. While these studies strongly support the benefits of NO release in mitigating the FBR, the mechanisms through which exogenous NO acts on the surrounding tissue, especially under the condition of hyperglycemia, remain vague. Such knowledge would inform strategies to refine appropriate NO dosage and release kinetics for optimal therapeutic activity. In this study, we evaluated mediator, immune cell, and mRNA expression profiles in the local tissue microenvironment surrounding implanted sensors as a function of NO release, diabetes, and implantation duration. A custom porcine wound healing-centric multiplex gene array was developed for nanoString barcoding analysis. Tissues adjacent to sensors with sustained NO release abrogated the implant-induced acute and chronic FBR through modulation of the tissue-specific immune chemokine and cytokine microenvironment, resulting in decreased cellular recruitment, proliferation, and activation at both the acute (7-d) and chronic (14-d) phases of the FBR. Further, we found that sustained NO release abrogated the implant-induced acute and chronic foreign body response through modulation of mRNA encoding for key immunological signaling molecules and pathways, including STAT1 and multiple STAT1 targets including MAPK14, IRAK4, MMP2, and CXCL10. The condition of diabetes promoted a more robust FBR to the implants, which was also controlled by sustained NO release.

Application of Metal–Organic Framework in Diagnosis and Treatment of Diabetes

Diabetes-related chronic wounds are often accompanied by a poor wound-healing environment such as high glucose, recurrent infections, and inflammation, and standard wound treatments are fairly limited in their ability to heal these wounds. Metal–organic frameworks (MOFs) have been developed to improve therapeutic outcomes due to their ease of engineering, surface functionalization, and therapeutic properties. In this review, we summarize the different synthesis methods of MOFs and conduct a comprehensive review of the latest research progress of MOFs in the treatment of diabetes and its wounds. State-of-the-art in vivo oral hypoglycemic strategies and the in vitro diagnosis of diabetes are enumerated and different antimicrobial strategies (including physical contact, oxidative stress, photothermal, and related ions or ligands) and provascular strategies for the treatment of diabetic wounds are compared. It focuses on the connections and differences between different applications of MOFs as well as possible directions for improvement. Finally, the potential toxicity of MOFs is also an issue that we cannot ignore.

Carboxymethyl chitosan-alginate hydrogel containing GSNO with the ability to nitric oxide release for diabetic wound healing

Today, despite significant progress in developing skin tissue engineering products, the fabrication of an ideal wound dressing that could meet the essential criteria, such as promoting angiogenesis -mainly in a diabetic wound- still remains a challenge. A diabetic wound is a chronic wound in which vascularization is low, and the wound healing process may stop. In this regard, Nitric oxide (NO) enhances the healing of diabetic wounds by promoting angiogenesis and providing antibacterial activity in wound sites. In this study, we produced a NO-releasing wound dressing (CMC-ALg-GSNO) composed of Carboxymethyl chitosan (CMC), sodium alginate (ALg), and Snitrosoglutathione (GSNO). The results obtained from the scanning electron microscopy (SEM) show that wound dressing has a porous structure. The water uptake and water vapor transmission for the wound dressing were obtained 4354.1 ± 179.3 % and 2753.8 ± 54.6 g/m2 per day, respectively. NO release study showed that NO release from CMC-ALg-GSNO continuously occurred within 168 hours. In vivo test, The CMC-ALg-GSNO wound dressing developed wound healing in a rat model of full-thickness diabetic wounds compared to the CMC-ALg and Gauze wound dressings. Thus, this study showed that CMC-ALg-GSNO wound dressing could lead to novel therapeutic invasions to treat diabetic wounds.

Nitric Oxide Delivering Surfaces: An Overview of Functionalization Strategies and Efficiency Progress

An overview on the design of nitric oxide (NO) delivering surfaces for biomedical purposes is provided, with a focus on the advances of the past 5 years. A localized supply of NO is of a particular interest due to the pleiotropic biological effects of this diatomic compound. Depending on the generated NO flux, the surface can mimic a physiological release profile to provide an activity on the vascular endothelium or an antibacterial activity. Three requirements are considered to describe the various strategies leading to a surface delivering NO. Firstly, the coating must be selected in accordance with the properties of the substrate (nature, shape, dimensions…). Secondly, the releasing and/or generating kinetics of NO should match the targeted biological application. Currently, the most promising structures are developed to provide an adaptable NO supply driven by pathophysiological needs. Finally, the biocompatibility and the stability of the surface must also be considered regarding the expected residence time of the device. A critical point of view is proposed to help readers in the design of the NO delivering surface according to its expected requirement and therapeutic purpose.

The Foreign Body Response to an Implantable Therapeutic Reservoir in a Diabetic Rodent Model

Advancements in type 1 diabetes mellitus treatments have vastly improved in recent years. The move toward a bioartificial pancreas and other fully implantable systems could help restore patient's glycemic control. However, the long-term success of implantable medical devices is often hindered by the foreign body response. Fibrous encapsulation "walls off" the implant to the surrounding tissue, impairing its functionality. In this study we aim to examine how streptozotocin-induced diabetes affects fibrous capsule formation and composition surrounding implantable drug delivery devices following subcutaneous implantation in a rodent model. After 2 weeks of implantation, the fibrous capsule surrounding the devices were examined by means of Raman spectroscopy, micro-computed tomography (μCT), and histological analysis. Results revealed no change in mean fibrotic capsule thickness between diabetic and healthy animals as measured by μCT. Macrophage numbers (CCR7 and CD163 positive) remained similar across all groups. True component analysis also showed no quantitative difference in the alpha-smooth muscle actin and extracellular matrix proteins. Although principal component analysis revealed significant secondary structural difference in collagen I in the diabetic group, no evidence indicates an influence on fibrous capsule composition surrounding the device. This study confirms that diabetes did not have an effect on the fibrous capsule thickness or composition surrounding our implantable drug delivery device. Impact Statement Understanding the impact diabetes has on the foreign body response (FBR) to our implanted material is essential for developing an effective drug delivery device. We used several approaches (Raman spectroscopy and micro-computed tomography imaging) to demonstrate a well-rounded understanding of the diabetic impact on the FBR to our devices, which is imperative for its clinical translation.

Biocompatibility Evolves: Phenomenology to Toxicology to Regeneration

The word "biocompatibility," is inconsistent with the observations of healing for so-called biocompatible biomaterials. The vast majority of the millions of medical implants in humans today, presumably "biocompatible," are walled off by a dense, avascular, crosslinked collagen capsule, hardly suggestive of life or compatibility. In contrast, one is now seeing examples of implant biomaterials that lead to a vascularized reconstruction of localized tissue, a biological reaction different from traditional biocompatible materials that generate a foreign body capsule. Both the encapsulated biomaterials and the reconstructive biomaterials qualify as "biocompatible" by present day measurements of biocompatibility. Yet, this new generation of materials would seem to heal "compatibly" with the living organism, where older biomaterials are isolated from the living organism by the dense capsule. This review/perspective article will explore this biocompatibility etymological conundrum by reviewing the history of the concepts around biocompatibility, today's standard methods for assessing biocompatibility, a contemporary view of the foreign body reaction and finally, a compendium of new biomaterials that heal without the foreign body capsule. A new definition of biocompatibility is offered here to address advances in biomaterials design leading to biomaterials that heal into the body in a facile manner.

Early administration of L-arginine in mdx neonatal mice delays the onset of muscular dystrophy in tibialis anterior (TA) muscle

Duchenne muscular dystrophy (DMD) is a genetic disorder that results in the absence of dystrophin, a cytoskeletal protein. Individuals with this disease experience progressive muscle destruction, which leads to muscle weakness. Studies have been conducted to find solutions for the relief of individuals with this disease, several of which have shown that utrophin, a protein closely related to dystrophin, when overexpressed in mdx neonatal mice (the murine model of DMD), is able to prevent the progressive muscle destruction observed in the absence of dystrophin. Furthermore, recent studies have shown that L‐arginine induces utrophin upregulation in adult mdx mice. We hypothesized that L‐arginine treatment also induces utrophin upregulation to prevent the development of muscle weakness in neonatal mdx mice. Hence, L‐arginine should also prevent progressive muscle destruction via utrophin upregulation in mdx neonatal mice. Mdx neonatal mice were injected intraperitoneally daily with 800 mg/kg of L‐arginine for 6 weeks, whereas control mice were injected with a physiological saline. The following experiments were performed on the tibialis anterior (TA) muscle: muscle contractility and resistance to mechanical stress; central nucleation and peripheral nucleation, utrophin, and creatine kinase quantification as well as a nitric oxide (NO) assay. Our findings show that early administration of L‐arginine in mdx neonatal mice prevents the destruction of the tibialis anterior (TA) muscle. However, this improvement was related to nitric oxide (NO) production rather than the expected utrophin upregulation.

Combination of Nitric Oxide Release and Surface Texture for Mitigating the Foreign Body Response

The tissue response to polyurethane (PU)-coated implants employing active and/or passive FBR mitigation techniques was evaluated over a 28 day study in a diabetic swine model. Active FBR mitigation was achieved through the sustained release of nitric oxide (NO) from a mesoporous silica nanoparticle-doped PU coating. Passive FBR mitigation was achieved through the application of a foam- or fiber-based topcoat. These topcoats were designed to possess topographical features known to promote tissue integration with foam-coated implants having pore sizes of approximately 50 μm and fiber-coated implants consisting of fiber diameters of less than 1 μm. Nitric oxide-release profiles were minimally impacted by the presence of either topcoat. Inflammatory cell density and collagen density at the implant-tissue interface were assessed at 7, 14, 21, and 28 days following implantation. Nitric oxide-releasing implants had significantly lower inflammatory cell density and collagen density than non-NO-releasing controls. The presence of a topcoat did not significantly impact inflammatory cell density, though top-coated textured implants resulted in significantly lower collagen density, irrespective of NO release. Overall, coatings that combine NO release with surface texture demonstrated the greatest potential for tissue-based biomedical device applications.

Functionalized GO Nanovehicles with Nitric Oxide Release and Photothermal Activity-Based Hydrogels for Bacteria-Infected Wound Healing

Bacteria-infected wounds are attracting increasing attention, as antibiotic misuse and multidrug-resistant bacteria complicate their treatment. Herein, we reported a photothermal activity-based drug consisting of β-cyclodextrin (βCD)-functionalized graphene oxide (GO) near-infrared light-responsive nanovehicles combined with the nitric oxide donor BNN6, in a methacrylate-modified gelatin (GelMA)/hyaluronic acid graft dopamine (HA-DA) hydrogel. The synergistic effects of photothermal and gas therapies are expected to improve antibacterial efficiency and reduce drug resistance. The results revealed that GelMA/HA-DA/GO-βCD-BNN6 was an ideal antibacterial material that improved collagen deposition and angiogenesis and promoted wound healing in a mouse model of full-thickness skin repair, compared to the commercially available Aquacel Ag dressing. We developed a multifunctional nanocomposite hydrogel that exhibited antibacterial and angiogenic properties, adhesiveness, and mechanical properties that enhance the regeneration of bacteria-infected wounds.

Long-Term Accurate Continuous Glucose Biosensors via Extended Nitric Oxide Release

Analytical performance and tissue interactions of nitric oxide (NO)-releasing continuous glucose sensors were evaluated over a 28 d study in a diabetic swine model. Interstitial glucose was detected using an implanted needle-type amperometric glucose sensor. Two NO-release durations from the sensor surface were achieved by doping the membranes with nonporous (14 d release) or porous (30 d release) S-nitrosothiol-functionalized silica nanoparticles. Numerical and clinical accuracy of the sensors were assessed at time points (1, 7, 14, 21, and 28 d) following implantation. Nitric oxide-releasing sensors demonstrated accurate glucose detection over a time period directly correlated with the active release of NO. Silica particle-doped sensors that released NO for 30 d showed standard-compliant accuracy (i.e., mean absolute relative difference ≤ 15%) for >3 weeks post-implantation. Histological staining for inflammatory biomarkers suggested that the observed performance improvement was the result of decreased inflammatory cell count and a lower density collagen capsule.

Nitric Oxide-Releasing Polymeric Materials for Antimicrobial Applications: A Review

Polymeric materials releasing nitric oxide have attracted significant attention for therapeutic use in recent years. As one of the gaseous signaling agents in eukaryotic cells, endogenously generated nitric oxide (NO) is also capable of regulating the behavior of bacteria as well as biofilm formation in many metabolic pathways. To overcome the drawbacks caused by the radical nature of NO, synthetic or natural polymers bearing NO releasing moiety have been prepared as nano-sized materials, coatings, and hydrogels. To successfully design these materials, the amount of NO released within a certain duration, the targeted pathogens and the trigger mechanisms upon external stimulation with light, temperature, and chemicals should be taken into consideration. Meanwhile, NO donors like S-nitrosothiols (RSNOs) and N-diazeniumdiolates (NONOates) have been widely utilized for developing antimicrobial polymeric agents through polymer-NO donor conjugation or physical encapsulation. In addition, antimicrobial materials with visible light responsive NO donor are also reported as strong and physiological friendly tools for rapid bacterial clearance. This review highlights approaches to delivery NO from different types of polymeric materials for combating diseases caused by pathogenic bacteria, which hopefully can inspire researchers facing common challenges in the coming 'post-antibiotic' era.

An actuatable soft reservoir modulates host foreign body response

The performance of indwelling medical devices that depend on an interface with soft tissue is plagued by complex, unpredictable foreign body responses. Such devices-including breast implants, biosensors, and drug delivery devices-are often subject to a collection of biological host responses, including fibrosis, which can impair device functionality. This work describes a milliscale dynamic soft reservoir (DSR) that actively modulates the biomechanics of the biotic-abiotic interface by altering strain, fluid flow, and cellular activity in the peri-implant tissue. We performed cyclical actuation of the DSR in a preclinical rodent model. Evaluation of the resulting host response showed a significant reduction in fibrous capsule thickness (P = 0.0005) in the actuated DSR compared with non-actuated controls, whereas the collagen density and orientation were not changed. We also show a significant reduction in myofibroblasts (P = 0.0036) in the actuated group and propose that actuation-mediated strain reduces differentiation and proliferation of myofibroblasts and therefore extracellular matrix production. Computational models quantified the effect of actuation on the reservoir and surrounding fluid. By adding a porous membrane and a therapy reservoir to the DSR, we demonstrate that, with actuation, we could (i) increase transport of a therapy analog and (ii) enhance pharmacokinetics and time to functional effect of an inotropic agent. The dynamic reservoirs presented here may act as a versatile tool to further understand, and ultimately to ameliorate, the host response to implantable biomaterials.

Pravastatin regulates host foreign-body reaction to polyetheretherketone implants via miR-29ab1-mediated SLIT3 upregulation

Host rejection to biomaterials can induce uncontrolled foreign-body reactions (FBR), resulting in a dense fibrous encapsulation that blocks mass transport and/or communication between the host and the implant. Adequate angiogenesis between the body and the implant has been implicated as a key regulator for overcoming FBR. Thus, approaches for stimulating neovascularization and/or suppressing FBR are under investigation. In this study, pravastatin (Pra) was loaded onto a 3D network surface of sulfonated polyetheretherketone (SP) to achieve superior local drug effects. The SP loaded with Pra (SP-Pra) promoted angiogenesis and mitigated FBR via miR-29 dependent SLIT3 upregulation in wild-type (WT) mice. miR-29a and miR-29b1 were significantly downregulated in the SP-Pra capsule compared to levels in the SP capsule, while SLIT3 and neovascularization were substantially upregulated in WT mice. However, the above effects presented in the WT mice were not detected in miR-29ab1 knockout mice which was generated by the CRISPR/Cas9 approach. Overall, the results suggest that miR-29 plays a critical role in reducing FBR to these implants by targeting SLIT3. Suppression of FBR by SP-Pra implants offers the potential to improve the performance of current medical devices.

Nitric oxide-releasing semi-crystalline thermoplastic polymers: preparation, characterization and application to devise anti-inflammatory and bactericidal implants

Semi-crystalline thermoplastics are an important class of biomaterials with applications in creating extracorporeal and implantable medical devices. In situ release of nitric oxide (NO) from medical devices can enhance their performance via NO's potent anti-thrombotic, bactericidal, anti-inflammatory, and angiogenic activity. However, NO-releasing semi-crystalline thermoplastic systems are limited and the relationship between polymer crystallinity and NO release profile is unknown. In this paper, the functionalization of poly(ether-block-amide) (PEBA), Nylon 12, and polyurethane tubes, as examples of semi-crystalline polymers, with the NO donor S-nitroso-N-acetylpenicillamine (SNAP) within, is demonstrated via a polymer swelling method. The degree of crystallinity of the polymer plays a crucial role in both SNAP impregnation and NO release. Nylon 12, which has a relatively high degree of crystallinity, exhibits an unprecedented NO release duration of over 5 months at a low NO level, while PEBA tubing exhibits NO release over days to weeks. As a new biomedical application of NO, the NO-releasing PEBA tubing is examined as a cannula for continuous subcutaneous insulin infusion. The released NO is shown to enhance insulin absorption into the bloodstream probably by suppressing the tissue inflammatory response, and thereby could benefit insulin pump therapy for diabetes management.

Photoresponsive Drug/Gene Delivery Systems

Light as an external stimulus can be precisely manipulated in terms of irradiation time, site, wavelength, and density. As such, photoresponsive drug/gene delivery systems have been increasingly pursued and utilized for the spatiotemporal control of drug/gene delivery to enhance their therapeutic efficacy and safety. In this review, we summarized the recent research progress on photoresponsive drug/gene delivery, and two major categories of delivery systems were discussed. The first category is the direct responsive systems that experience photoreactions on the vehicle or drug themselves, and different materials as well as chemical structures responsive to UV, visible, and NIR light are summarized. The second category is the indirect responsive systems that require a light-generated mediator signal, such as heat, ROS, hypoxia, and gas molecules, to cascadingly trigger the structural transformation. The future outlook and challenges are also discussed at the end.

Structural heterogeneity in polymeric nitric oxide donor nanoblended coatings for controlled release behaviors

Controlled nitric oxide (NO) delivery based on the heterogeneity of polymeric coating structures for local NO treatment.