Investigation of the early healing response to dicationic imidazolium-based ionic liquids: a biocompatible coating for titanium implants

Revolutionizing fracture fixation in diabetic and non-diabetic rats: High mobility group box 1-based coating for enhanced osseointegration

Chronic inflammation and hyperglycemia in diabetic patients increase the risk of implant failure and impaired fracture healing. We previously developed and characterized a titanium (Ti) coating strategy using an imidazolium-based ionic liquid (IonL) with a fully reduced, non-oxidizable High Mobility Group Box 1 (HMGB1) isoform (Ti-IonL-HMGB1) to immunomodulate tissue healing. In this study, we used an open reduction fracture fixation (ORIF) model in non-diabetic (ND) and diabetic (D) rats to further investigate the effectiveness of this Ti-IonL-HMGB1 coating on orthopedic applications. Ninety male Lewis rats (12-15 weeks) were divided into D (n = 45) and ND (n = 45) groups that were distributed into three subgroups based on the type of local treatment received: Ti (uncoated Ti), Ti-IonL, and Ti-IonL-HMGB1 implants. Fracture healing and osseointegration were evaluated using microtomographic, histological, and immunohistochemical analysis of proliferating cell nuclear antigen (PCNA), Runt-related transcription factor 2 (RUNX2), and HMGB1 markers at 2, 10, and 21 days post-ORIF. Scanning Electron Microscopy verified the coating stability after placement. Microtomographic and histological analysis demonstrated increased fracture healing and osseointegration for ND rats in all treatment groups at 10 days, with impaired healing for D rats. Immunohistochemical analysis exhibited elevated PCNA+ and RUNX2+ cells for D animals treated with Ti-IonL-HMGB1 at 21 days compared to all other groups. The immunohistochemical marker HMGB1 was elevated at all time points for D animals in comparison to ND animals, yet was lowered for D tissues near the Ti-IonL-HMGB1 treated implant. Improved osseous healing was demonstrated in D animals with Ti-IonL-HMGB1 treatment by 21 days, compared to D animals with other treatments. To the best of our knowledge, this is the first study analyzing Ti-IonL-HMGB1 implantation in an injury site through ORIF procedures in ND and D rats. This surface approach has potential for improving implanted biomaterials in diabetic environments.

The Potential Role of Ionic Liquid as a Multifunctional Dental Biomaterial

In craniofacial research and routine dental clinical procedures, multifunctional materials with antimicrobial properties are in constant demand. Ionic liquids (ILs) are one such multifunctional intelligent material. Over the last three decades, ILs have been explored for different biomedical applications due to their unique physical and chemical properties, high task specificity, and sustainability. Their stable physical and chemical characteristics and extremely low vapor pressure make them suitable for various applications. Their unique properties, such as density, viscosity, and hydrophilicity/hydrophobicity, may provide higher performance as a potential dental material. ILs have functionalities for optimizing dental implants, infiltrate materials, oral hygiene maintenance products, and restorative materials. They also serve as sensors for dental chairside usage to detect oral cancer, periodontal lesions, breath-based sobriety, and dental hard tissue defects. With further optimization, ILs might also make vital contributions to craniofacial regeneration, oral hygiene maintenance, oral disease prevention, and antimicrobial materials. This review explores the different advantages and properties of ILs as possible dental material.

A Model Study to Evaluate Osseointegration and Fracture Healing Following Open Reduction and Internal Fixation (ORIF) in Diabetic Lewis Rats

There is a higher risk of implant osseointegration failure after open reduction and internal fixation (ORIF) in patients with diabetes due to increased inflammatory conditions, associated metallic corrosion and infection. While it is possible to avoid elective osseous surgery in patients with diabetes, it may not be the case in nonelective cases, such as ORIF ankle fractures. A total of 30 male Lewis rats (12-15 weeks old) were distributed into diabetic (D) and nondiabetic (ND) groups. Fracture healing and osseointegration were evaluated at 2-, 10-, and 21-day time points. Microtomographic and histological analysis depicted distinct differences in fracture healing and osseointegration between D and ND animals. Immunohistochemical analysis exhibited elevated proliferation (PCNA) and osteogenic (Runx2) cells for ND animals, while HMGB1 (inflammatory marker) was elevated for D animals during healing. Bone resorption marker CTX-1 was elevated in the plasma of D animals at 2 days, while bone formation marker P1NP was higher for ND animals at 10 days. Overall, this model resulted in delayed implant osseointegration and fracture healing in diabetic animals, highlighting the importance of developing new biomaterials or implant coatings that can improve bone healing outcomes in this patient population.

Biological Effects of New Titanium Surface Coatings Based on Ionic Liquids and HMGB1: A Cellular and Molecular Characterization in Lewis Rats

High Mobility Group Box 1 (HMGB1) is a redox-sensitive molecule that plays dual roles in tissue healing and inflammation. We previously demonstrated that HMGB1 is stable when anchored by a well-characterized imidazolium-based ionic liquid (IonL), which serves as a delivery vehicle for exogenous HMGB1 to the site of injury and prevents denaturation from surface adherence. However, HMGB1 exists in different isoforms [fully reduced HMGB1 (FR), a recombinant version of FR resistant to oxidation (3S), disulfide HMGB1 (DS), and inactive sulfonyl HMGB1(SO)] that have distinct biological functions in health and disease. Thus, the goal of this study was to evaluate the effects of different recombinant HMGB1 isoforms on the host response using a rat subcutaneous implantation model. A total of 12 male Lewis rats (12-15 weeks) were implanted with titanium discs containing different treatments (n = 3/time point; Ti, Ti-IonL, Ti-IonL-DS, Ti-IonL-FR, and Ti-IonL-3S) and assessed at 2 and 14 days. Histological (H&E and Goldner trichrome staining), immunohistochemistry, and molecular analyses (qPCR) of surrounding implant tissues were employed for analysis of inflammatory cells, HMGB1 receptors, and healing markers. Ti-IonL-DS samples resulted in the thickest capsule formation, increased pro-inflammatory, and decreased anti-inflammatory cells, while Ti-IonL-3S samples demonstrated suitable tissue healing similar to uncoated Ti discs, as well as an upregulation of anti-inflammatory cells at 14 days compared to all other treatments. Thus, results from this study demonstrated that Ti-IonL-3S are safe alternatives for Ti biomaterials. Future studies are necessary to investigate the healing potential of Ti-IonL-3S in osseointegration scenarios.

Choline ester based ionic liquid: A multi-functional system to enhance nucleic acid stability, drug solubilization and cell penetration

Ionic liquids (ILs) are emerging systems with applications in varying areas of biomedical research. This study aims at developing a biocompatible, dual function choline ester-based IL with chloride as anion ([Ch] IL) for stabilizing nucleic acids (DNA) and enhancing cellular uptake of drugs. The ability of IL to complex with DNA was characterized using electrophoresis, dye displacement and UV absorbance. The effect of pH on complex stability and protection of DNA from nuclease were also studied. Even though [Ch] IL had positive zeta potential and showed effective complex formation, at physiological pH the zeta potential of the complex decreased and became negative, thereby, destabilizing the complex. To address this, citric acid (CA) was added to [Ch] IL which facilitated strong complexation. Further, DNA could be retrieved from these complexes without compromising its purity and integrity. Additionally, [Ch] IL was found to improve the cellular uptake of doxorubicin by improving its solubility in water. Thus, we demonstrate that the [Ch] IL developed here can enhance nucleic acid stability, drug solubilization and cell penetration. Our results show that the developed [Ch] IL can be used for long term storage of nucleic acids as well as for enhancing permeation of drugs in vivo.

Exogenous Protein Delivery of Ionic Liquid-Mediated HMGB1 Coating on Titanium Implants

Strategies for modifying titanium (Ti) implant surfaces are becoming increasingly popular to enhance osseointegration during acute and inflammatory healing stages. In this study, two dicationic imidazolium-based ionic liquids (IonLs) containing phenylalanine and methionine anions (IonL-Phe(1,10-bis(3-methylimidazolium-1-yl)decane diphenylalanine) and IonL-Met(1,10-bis(3-methylimidazolium-1-yl)decane dimethionine)) were investigated to stably deliver exogenous proteins on Ti to promote osseointegration. The protein selected for this study is High-Mobility Group Box 1 (HMGB1), which recruits inflammatory and mesenchymal stem cells to the implantation site, contributing to healing. To explore IonL-Ti interactions and HMGB1 stability on the IonL-coated surface, experimental characterization techniques including X-ray photoelectron spectroscopy, scanning electron microscopy, dynamic scanning calorimetry (DSC), and liquid chromatography mass spectrometry (LC-MS) were used along with molecular dynamics (MD) computer simulations to provide a detailed molecular level description. Results show well-structured IonL molecules on the Ti surface that impact protein crystallization and coating morphology. IonL cations and anions were found to bind strongly to oppositely charged residues of the protein. LC-MS/MS reveals that HMGB1 B-box lysine residues bind strongly to the IonLs. Stronger interactions of HMGB1 with Ion-Phe in contrast to IonL-Met results in greater retention capacity of HMGB1 in the IonL-Phe coating. Overall, this study provides evidence that the selected IonLs strongly interact with HMGB1, which can be a potential surface treatment for bone-implantable Ti devices.

Effects of Dicationic Imidazolium-Based Ionic Liquid Coatings on Oral Osseointegration of Titanium Implants: A Biocompatibility Study in Multiple Rat Demographics

Dicationic imidazolium-based ionic liquids with amino acid anions, such as IonL-phenylalanine (IonL-Phe), have been proposed as a multifunctional coating for titanium (Ti) dental implants. However, there has been no evaluation of the biocompatibility of these Ti coatings in the oral environment. This study aims to evaluate the effects of IonL-Phe on early healing and osseointegration of Ti in multiple rat demographics. IonL-Phe-coated and uncoated Ti screws were implanted into four demographic groups of rats to represent biological variations that could affect healing: young males (YMs) and females (YFs), ovariectomized (OVXFs) females, and old males (OMs). Samples underwent histopathological and histomorphometric analysis to evaluate healing at 7 and 30 days around IonL-coated and uncoated Ti. The real-time quantitative polymerase chain reaction was also conducted at the 2- and 7-day YM groups to evaluate molecular dynamics of healing while the IonL-Phe was present on the surface. IonL-coated and uncoated implants demonstrated similar histological signs of healing, while coated samples’ differential gene expression of immunological and bone markers was compared with uncoated implants at 2 and 7 days in YMs. While YMs presented suitable osseointegration for both uncoated and IonL-Phe-coated groups, decreased success rate in other demographics resulted from lack of supporting bone in YFs and poor bone quality in OVXFs and OMs. Overall, it was found that IonL-coated samples had increased bone-to-implant contact across all demographic groups. IonL-Phe coating led to successful osseointegration across all animal demographics and presented the potential to prevent failures in scenarios known to be challenged by bacteria.

Biobanked human foreskin epithelial cell sheets reduce inflammation and promote wound healing in a nude mouse model

BACKGROUND

Human epithelial cell sheets (ECSs) are used to clinically treat epithelial conditions such as burns, corneal blindness, middle ear cholesteatoma and vitiligo. As a widely used material in clinic, there is little information on the biobanking of ECSs and its repair effect after storage.

RESULTS

Two methods for biobanking foreskin ECSs were compared in a short term (7 days): 4-degree storage and programmed cryopreservation. Cell sheet integrity, viability, apoptosis, immunogenicity, mechanical properties and function were evaluated. In vivo, ECSs were directly transplanted to skin defect models and histological examination was performed at 1 week postoperatively. We successfully extracted human foreskin-derived primary epithelial cells and fabricated them into ECSs. Compared with 4-degree storage, programmed cryopreservation preserved the ECS structural integrity, enhanced the mechanical properties, decreased HLA-I expression, and increased cell viability and survival. An increased proportion of melanocytes with proliferative capacity remained in the cryopreserved sheets, and the undifferentiated epithelial cells were comparable to those of the fresh sheets. In vivo, cryopreserved ECSs could reduce inflammatory cell infiltration and promote connective tissue remodeling, epithelial cell proliferation and vascular regeneration.

CONCLUSIONS

Programmed cryopreservation of ECSs was superior and more feasible than 4-degree storage and the cryopreserved ECSs achieved satisfying skin wound healing in vivo. We anticipate that the off-the-shelf ECSs could be quickly used, such as, to repair human epithelial defect in future.

Development of Nanoscale Hybrids from Ionic Liquid-Peptide Amphiphile Assemblies as New Functional Materials

Over the years, ionic liquids (ILs) have gained tremendous importance because of their unique properties and plethora of applications. In this work, we have developed a new nanoscale hybrid gel consisting of 1-ethyl-3-methylimidazolium dimethyl phosphate, [C2mim][dmp], and self-assembled peptide nanoassemblies. The peptide nanoassemblies were formed by self-assembly of a newly synthesized peptide bolaamphiphile bis(N-α-amido-threonine) 1,7 heptane dicarboxylate (ThrC7). Upon mild heating and sonication of the IL and ThrC7 nanoassemblies, ThrC7-IL nanocomposites were formed. We explored the formation of nanohybrids by varying the ratio of IL to ThrC7 assemblies. While at lower IL ratios, a gelatinous matrix was formed, at higher IL ratios, highly ordered multilayered structures were observed by atomic force microscopy (AFM) imaging. The interactions between the ThrC7 nanofibers and [C2mim][dmp] IL were probed by Fourier transform infrared spectroscopy, transmission electron microscopy, and AFM imaging. Differential scanning calorimetry and thermogravimetric analysis showed that the nanohybrids illustrated distinct thermal phase changes due to changes in hydrogen bonding interactions and unfolding of the nanoassemblies. The viscoelastic behavior of the nanohybrids indicated that the materials displayed higher storage modulus upon incorporation of the ThrC7 nanoassemblies when compared to the IL. Furthermore, the nanohybrids were found to adhere to and promote proliferation of human dermal fibroblasts, while cytotoxicity was observed toward MCF-7 breast cancer cells. Thus, for the first time, we have developed peptide-based nanohybrids with an imidazolium-based IL with unique structural properties that may open new avenues for exploring potential biological applications.