Control of innate immune response by biomaterial surface topography, energy, and stiffness

As the focus of implantable biomaterials has shifted from bioinert implants to bioactive designs, recent research has highlighted the complex interactions between cell physiologic systems and material properties, particularly physical cues. From the cells known to interact with implanted biomaterials, the response of the immune system has been a critical target of study recently. Here, we review studies characterizing the response of innate immune cells to various material cues, particularly of those at the surface of implanted materials.The innate immune system consists of cell types with various roles in inflammation. Neutrophils and macrophages serve both phagocytic and signaling roles, especially early in the inflammatory phase of biomaterial implantation. These cell types ultimately dictate the outcome of implants as chronic inflammation, fibrosis, or integration. Other cell types like dendritic cells, mast cells, natural killer cells, and innate lymphoid cells may also serve an immunomodulatory role in the biomaterial context. This review highlights recent advances in our understanding of the role of innate immunity in the response to implantable biomaterials as well as key mechanobiological findings in innate immune cells underpinning these advances. STATEMENT OF SIGNIFICANCE: This review highlights recent advances in the understanding of the role of innate immunity in the response to implantable biomaterials, especially in neutrophils and macrophages, as well as key mechanobiological findings in innate immune cells underpinning these advances. Here we discuss how physicochemical properties of biomaterials control innate immune cell behavior.

Wnt signaling modulates macrophage polarization and is regulated by biomaterial surface properties

Macrophages are among the first cells to interact with biomaterials and ultimately determine their integrative fate. Biomaterial surface characteristics like roughness and hydrophilicity can activate macrophages to an anti-inflammatory phenotype. Wnt signaling, a key cell proliferation and differentiation pathway, has been associated with dysregulated macrophage activity in disease. However, the role Wnt signaling plays in macrophage activation and response to biomaterials is unknown. The aim of this study was to characterize the regulation of Wnt signaling in macrophages during classical pro- and anti-inflammatory polarization and in their response to smooth, rough, and rough-hydrophilic titanium (Ti) surfaces. Peri-implant Wnt signaling in macrophage-ablated (MaFIA) mice instrumented with intramedullary Ti rods was significantly attenuated compared to untreated controls. Wnt ligand mRNA were upregulated in a surface modification-dependent manner in macrophages isolated from the surface of Ti implanted in C57Bl/6 mice. In vitro, Wnt mRNAs were regulated in primary murine bone-marrow-derived macrophages cultured on Ti in a surface modification-dependent manner. When macrophageal Wnt secretion was inhibited, macrophage sensitivity to both physical and biological stimuli was abrogated. Loss of macrophage-derived Wnts also impaired recruitment of mesenchymal stem cells and T-cells to Ti implants in vivo. Finally, inhibition of integrin signaling decreased surface-dependent upregulation of Wnt genes. These results suggest that Wnt signaling regulates macrophage response to biomaterials and that macrophages are an important source of Wnt ligands during inflammation and healing.

Substrate stiffness induces neutrophil extracellular trap (NET) formation through focal adhesion kinase activation

Neutrophils predominate the early inflammatory response to tissue injury and implantation of biomaterials. Recent studies have shown that neutrophil activation can be regulated by mechanical cues such as stiffness or surface wettability; however, it is not known how neutrophils sense and respond to physical cues, particularly how they form neutrophil extracellular traps (NET formation). To examine this, we used polydimethylsiloxane (PDMS) substrates of varying physiologically relevant stiffness (0.2-32 kPa) and examined the response of murine neutrophils to untreated surfaces or to surfaces coated with various extracellular matrix proteins recognized by integrin heterodimers (collagen, fibronectin, laminin, vitronectin, synthetic RGD). Neutrophils on higher stiffness PDMS substrates had increased NET formation and higher secretion of pro-inflammatory cytokines and chemokines. Extracellular matrix protein coatings showed that fibronectin induced the most NET formation and this effect was stiffness dependent. Synthetic RGD peptides induced similar levels of NET formation and pro-inflammatory cytokine release than the full-length fibronectin protein. To determine if the observed NET formation in response to substrate stiffness required focal adhesion kinase (FAK) activity, which is down stream of integrin activation, FAK inhibitor PF-573228 was used. Inhibition of FAK using PF-573228 ablated the stiffness-dependent increase in NET formation and pro-inflammatory molecule secretion. These findings demonstrate that neutrophils regulate NET formation in response to physical and mechanical biomaterial cues and this process is regulated through integrin/FAK signaling.

Hydrophilic titanium surfaces reduce neutrophil inflammatory response and NETosis

Neutrophils are sensitive to biomaterial surface properties, controlling activation and inflammatory microenvironment, revealing a novel target for enhancing biomaterial integration.

The Effect of Hospital Visitor Policies on Patients, Their Visitors, and Health Care Providers During the COVID-19 Pandemic: A Systematic Review

Health care policymaking during the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has questioned the precedent of restricting hospital visitors. We aimed to synthesize available data describing the resulting impact on patient, family/visitor, and health care provider well-being. We systematically reviewed articles from the World Health Organization COVID-19 Global Literature on Coronavirus Disease Database published between December 2019 through April 2021. Included studies focused on hospitalized patients and reported 1 or more prespecified main or secondary outcome (coronavirus disease 2019 [COVID-19] disease transmission, global well-being, mortality, morbidity, or health care resource utilization). Two authors independently extracted data into a standardized form with a third author resolving discrepancies. A total of 1153 abstracts were screened, and 26 final full-text articles were included. Ten studies were qualitative, with 7 cohort studies, and no randomized controlled trials. Critically ill patients were the most represented (12 out of 26 studies). Blanket hospital visitor policies were associated with failure to address the unique needs of patients, their visitors, and health care providers in various clinical environments. Overall, a patient-centered, thoughtful, and nuanced approach to hospital visitor policies is likely to benefit all stakeholders while minimizing potential harms.

Surface characteristics on commercial dental implants differentially activate macrophages in vitro and in vivo

OBJECTIVES

Biomaterial implantation provokes an inflammatory response that controls integrative fate. M2 macrophages regulate the response to implants by resolving the inflammatory phase and recruiting progenitor cells to aid healing. We have previously shown that modified titanium (Ti) disks directly induce M2 macrophage polarization. The aim of this study was to examine macrophage response to commercially available Ti or Ti alloy implants with comparable roughness and varying hydrophilicity.

MATERIAL AND METHODS

Eleven commercially available Ti (A-F) or Ti alloy (G-K) dental implants were examined in this study. Surface topography, chemistry, and hydrophilicity were characterized for each implant. To compare the immune response in vitro, human monocyte-derived macrophages were seeded on implants and secreted pro- and anti-inflammatory proteins measured. To evaluate the inflammatory response in vivo, mice were subcutaneously instrumented with clinical implants, and implant adherent macrophage populations were characterized by flow cytometry.

RESULTS

Macrophages on hydrophobic Implant C produced the highest level of pro-inflammatory proteins in vitro. In contrast, hydrophilic Implant E produced the second-highest pro-inflammatory response. Implants F and K, both hydrophilics, produced the highest anti-inflammatory protein secretions. Likewise, pro-inflammatory CD80hi macrophages predominated in vivo on implants C and E, and M2 CD206 + macrophages predominated on implants F and K.

CONCLUSIONS

These findings show that hydrophilicity alone is insufficient to predict the anti-inflammatory effect on macrophage polarization and that other properties-surface composition or topography-determine immune modulation. This in vivo model may be a useful screening method to compare the immunomodulatory response to clinical implants of disparate geometry or size.

Canonical Wnt signaling enhances pro-inflammatory response to titanium by macrophages

Biomaterial characteristics like surface roughness and wettability can determine the phenotype of macrophages following implantation. We have demonstrated that inhibiting Wnt ligand secretion abolishes macrophage polarization in vitro and in vivo; however, the role of canonical Wnt signaling in macrophage activation in response to physical and chemical biomaterial cues is unknown. The aim of this study was to understand whether canonical Wnt signaling affects the response of macrophages to titanium (Ti) surface roughness or wettability in vitro and in vivo. Activating canonical Wnt signaling increased expression of toll-like receptors and interleukin receptors and secreted pro-inflammatory cytokines and reduced anti-inflammatory cytokines on Ti, regardless of surface properties. Inhibiting canonical Wnt signaling reduced pro-inflammatory cytokines on all Ti surfaces and increased anti-inflammatory cytokines on rough or rough-hydrophilic Ti. In vivo, activating canonical Wnt signaling increased total macrophages, pro-inflammatory macrophages, and T cells and decreased anti-inflammatory macrophages on both smooth and rough-hydrophilic implants. Functionally, canonical Wnt activation increases pro-inflammatory macrophage response to cell and cell-extracellular matrix lysates. These results demonstrate that activating canonical Wnt signaling primes macrophages to a pro-inflammatory phenotype that affects their response to Ti implants in vitro and in vivo.

E-cigarette Aerosol Mixtures Inhibit Biomaterial-Induced Osseointegrative Cell Phenotypes

OBJECTIVES

Smoking is a known contributor to the failure of dental implants. Despite a decline in cigarette use, the popularity of e-cigarettes has exploded. However, little is known about how e-cigarettes affect the biologic response to implants. This study examines the effect of e-cigarette aerosol mixtures (ecig-AM) on macrophage activation and osteoblastogenesis of mesenchymal stem cells (MSCs) in response to titanium (Ti) implant surfaces.

METHODS

Ecig-AMs were prepared by bubbling aerosol through PBS. Human-derived MSCs or murine-derived macrophages were plated on smooth, rough-hydrophobic, or rough-hydrophilic Ti surfaces in media supplemented with ecig-AM. In macrophages, expression of inflammatory markers was measured by qPCR and macrophage immunophenotype characterized by flow cytometry after 24 hours of exposure. In MSCs, expression of osteogenic markers and inflammatory cytokines was measured by qPCR and ELISA, while alkaline phosphatase activity (ALP) was determined by colorimetric assay.

RESULTS

Ecig-AM polarized primary macrophages into a pro-inflammatory state with higher effect on ecig-AM with flavorants and nicotine. Metabolic activity of MSCs decreased in a concentration dependent fashion and was stronger in ecig-AM containing nicotine. MSCs reduced expression of osteogenic markers in response to ecig-AM, but increased RANKL secretion, particularly at the highest ecig-AM concentrations. The effect of ecig-AM exposure was lessened when macrophages or MSCs were cultured on rough-hydrophilic substrates.

SIGNIFICANCE

Ecig-AM activated macrophages into a pro-inflammatory phenotype and impaired MSC-to-osteoblast differentiation in response to Ti implant surfaces. These effects were potentiated by flavorants and nicotine, suggesting that e-cigarette use may compromise the osseointegration of dental implants.

EPID-13. CHARACTERIZATION OF PEDIATRIC RADIATION-INDUCED MENINGIOMA: A SEER ANALYSIS

OBJECTIVE

Radiation-induced meningiomas (RIM) are the most common secondary neoplasm arising from radiation therapy. RIM have not been characterized in pediatric populations on a national scale despite displaying shorter latency and higher malignancy rates in institutional studies. The objective of this study was to characterize pediatric RIM and compare latency and malignancy rates to those of adult RIM using the National Cancer Institute’s Surveillance, Epidemiology and End Results Program (SEER) database.

METHODS

From the SEER Research Plus Nov 2020 (1975-2018) dataset, 56161 patients treated with EBRT for ocular/orbital tumors, brain/nervous system tumors, and leukemia were identified. 185 patients meeting criteria for RIM were selected: cranial/spinal EBRT (presumed from diagnostic indication), histologically distinct precedent tumor treated with EBRT, and a minimum 5-year latency from EBRT to meningioma diagnosis. This sub-population was divided into 2 groups – pediatric (ages 0-19, n = 10) and adult (ages > 20, n = 175) RIM – and latency, recurrence rate and multiplicity were compared for each group. The number of tumors classified as malignant (as opposed to benign or borderline malignant) was also compared between groups. Additionally, demographic data were compared for each group.

RESULTS

Of the pediatric RIM patients, 70% were male, 70% were Caucasian, and 10% were African American. No pediatric RIM patients experienced a recurrence or presented with multiple RIMs. The pediatric group showed lower latency (11.00 ± 1.94 years, p < 0.001) and a higher malignancy rate (30%, p = 0.002) than the adult group (latency of 23.38 ± 8.69 years; malignancy rate 5.1%).

CONCLUSION

These data represent the first characterization of pediatric RIM from a national database and support prior findings of shorter latency and higher malignancy rates in pediatric vs adult RIM, as well as lay the groundwork for future nationwide monitoring of this rare yet highly significant complication.

EPID-14. EPIDEMIOLOGICAL SURVEY OF RADIATION-INDUCED MENINGIOMA: A SEER ANALYSIS

OBJECTIVE

Radiation-induced meningioma (RIM) is a rare but serious consequence of cranial and cranio-spinal external beam radiation therapy (EBRT). While recent studies have characterized the epidemiological features of RIM in small populations or systematic reviews, none have studied RIM within a national database for a more generalizable description of this disease entity. The objective of this study was to identify and characterize the population with RIMs within a large national database.

METHODS

From the SEER Research Plus Nov 2020 (1975-2018) dataset, 56161 patients treated with EBRT for the following indications were identified: ocular/orbital tumors, brain/nervous system tumors, and leukemias. Next, a sub-population of 185 RIM patients, defined by histologically distinct precedent tumor treated with EBRT and a minimum 5-year latency from EBRT to meningioma, was identified. RIM prevalence, latency, pathologic behavior, and multiplicity were determined, and comparisons were made by sex, race, and original indication for EBRT.

RESULTS

The prevalence of RIM among the EBRT population was 0.33%. Among RIM patients, 41.62% were male and 84.32% were Caucasian. Average latency to RIM development was 23.39 ± 8.65 years, with no significant difference between sexes or races. Fourteen patients had multiple RIMs at diagnosis, while four patients experienced recurrent RIM. RIMs classified as “malignant” had a shorter latency (16.30 years) than “borderline” (26.11 years) or “benign” (23.36 years) RIMs. Of the most common original EBRT indications, precursor lymphoblastic leukemia (29.89 years) had longer latency to RIM than medulloblastoma (21.57 years) or astrocytoma (22.67 years); this may be explained by lower doses of radiation used for lymphoblastic leukemia treatment.

CONCLUSION

These data provide novel epidemiological information—most importantly, prevalence—of RIM in a nationwide population, and they suggest that RIM occurs in patients independent of sex or race. These findings will aid clinicians in explaining the risk of RIM development to patients undergoing EBRT.

A systematic review of focused ultrasound for psychiatric disorders: current applications, opportunities, and challenges

OBJECTIVE

Advancements in MRI-guided focused ultrasound (MRgFUS) technology have led to the successful treatment of select movement disorders. Based on the comparative success between ablation and deep brain stimulation, interest arises in focused ultrasound (FUS) as a promising treatment modality for psychiatric illnesses. In this systematic review, the authors examined current applications of FUS for psychiatric conditions and explored its potential opportunities and challenges.

METHODS

The authors performed a comprehensive review using the PRISMA guidelines of studies investigating psychiatric applications for FUS. Articles indexed on PubMed between 2014 to 2024 were included. The authors synthesized the psychiatric conditions treated, neural targets, outcomes, study design, and sonication parameters, and they reviewed important considerations for the treatment of psychiatric disorders with FUS. They also discussed active clinical trials in this research domain.

RESULTS

Of 250 articles, 10 met the inclusion criteria. Eight articles investigated the clinical, safety, and imaging correlates of MRgFUS in obsessive-compulsive disorder (OCD), whereas 3 examined treatment-resistant depression. Bilateral anterior capsulotomy resulted in a full responder rate of 67% (≥ 35% reduction in the Yale-Brown Obsessive-Compulsive Scale score) and 33% (≥ 50% reduction in the score on the Hamilton Rating Scale for Depression) in OCD and treatment-resistant depression, respectively. Sonications ranged from 8 to 36 with targeted lesional temperatures of 51°C-56°C. Lesions in the anterodorsal aspect of the anterior limb of the internal capsule (ALIC) and increased functional connectivity to the left dorsolateral prefrontal cortex and dorsal anterior cingulate cortex significantly predicted reduction in symptoms among patients with OCD, with decreases in beta-band activity in the frontocentral and temporal regions associated with reductions in depression and anxiety. Treatment of the nucleus accumbens with low-intensity FUS (LIFU) in patients with opioid-use disorders resulted in significant reductions in cue-reactive cravings, lasting up to 90 days. No serious adverse events were reported, including cognitive decline. Side effects were generally mild and transient, consisting of headaches, pin-site swelling, and nausea. Fourteen active clinical trials were identified, primarily targeting depression with LIFU.

CONCLUSIONS

Currently, FUS for psychiatric conditions is centered on OCD, with early pilot studies demonstrating promising safety and efficacy. Further research expanding on defining optimal patient selection, study design, intensity, and sonication parameters is warranted, particularly as FUS expands to other psychiatric illnesses and incorporates LIFU paradigms. Ethical considerations such as patient consent and equitable access also remain paramount.