Understanding biomaterial-tissue interface quality: combined in vitro evaluation

Ultrastructural and immunohistochemical evaluation of hyperplastic soft tissues surrounding dental implants in fibular jaws

In reconstructive surgery, complications post-fibula free flap (FFF) reconstruction, notably peri-implant hyperplasia, are significant yet understudied. This study analyzed peri-implant hyperplastic tissue surrounding FFF, alongside peri-implantitis and foreign body granulation (FBG) tissues from patients treated at the Department of Oral and Maxillofacial Surgery, Seoul National University Dental Hospital. Using light microscopy, pseudoepitheliomatous hyperplasia, anucleate and pyknotic prickle cells, and excessive collagen deposition were observed in FFF hyperplastic tissue. Ultrastructural analyses revealed abnormal structures, including hemidesmosome dilation, bacterial invasion, and endoplasmic reticulum (ER) swelling. In immunohistochemical analysis, unfolded protein-response markers ATF6, PERK, XBP1, inflammatory marker NFκB, necroptosis marker MLKL, apoptosis marker GADD153, autophagy marker LC3, epithelial-mesenchymal transition, and angiogenesis markers were expressed variably in hyperplastic tissue surrounding FFF implants, peri-implantitis, and FBG tissues. NFκB expression was higher in peri-implantitis and FBG tissues compared to hyperplastic tissue surrounding FFF implants. PERK expression exceeded XBP1 significantly in FFF hyperplastic tissue, while expression levels of PERK, XBP1, and ATF6 were not significantly different in peri-implantitis and FBG tissues. These findings provide valuable insights into the interconnected roles of ER stress, necroptosis, apoptosis, and angiogenesis in the pathogenesis of oral pathologies, offering a foundation for innovative strategies in dental implant rehabilitation management and prevention.

Mechanical stimulation devices for mechanobiology studies: a market, literature, and patents review

Significant advancements in various research and technological fields have contributed to remarkable findings on the physiological dynamics of the human body. To more closely mimic the complex physiological environment, research has moved from two-dimensional (2D) culture systems to more sophisticated three-dimensional (3D) dynamic cultures. Unlike bioreactors or microfluidic-based culture models, cells are typically seeded on polymeric substrates or incorporated into 3D constructs which are mechanically stimulated to investigate cell response to mechanical stresses, such as tensile or compressive. This review focuses on the working principles of mechanical stimulation devices currently available on the market or custom-built by research groups or protected by patents and highlights the main features still open to improvement. These are the features which could be focused on to perform, in the future, more reliable and accurate mechanobiology studies.

Graphic abstract

Optimization of Lactoferrin-Derived Amyloid Coating for Enhancing Soft Tissue Seal and Antibacterial Activity of Titanium Implants

A poor seal of the titanium implant-soft tissue interface provokes bacterial invasion, aggravates inflammation, and ultimately results in implant failure. To ensure the long-term success of titanium implants, lactoferrin-derived amyloid is coated on the titanium surface to increase the expression of cell integrins and hemidesmosomes, with the goal of promoting soft tissue seal and imparting antibacterial activity to the implants. The lactoferrin-derived amyloid coated titanium structures contain a large number of amino and carboxyl groups on their surfaces, and promote proliferation and adhesion of epithelial cells and fibroblasts via the PI3K/AKT pathway. The amyloid coating also has a strong positive charge and possesses potent antibacterial activities against Staphylococcus aureus and Porphyromonas gingivalis. In a rat immediate implantation model, the amyloid-coated titanium implants form gingival junctional epithelium at the transmucosal region that resembles the junctional epithelium in natural teeth. This provides a strong soft tissue seal to wall off infection. Taken together, lactoferrin-derived amyloid is a dual-function transparent coating that promotes soft tissue seal and possesses antibacterial activity. These unique properties enable the synthesized amyloid to be used as potential biological implant coatings.

Development of an Ingestible Expandable Capsule for Weight Loss

Obesity has grown to epidemic proportions with 2.1 billion people being overweight worldwide. A food-grade expandable capsule named EndoXpand for the treatment of overweight people was designed and developed in this study. EndoXpand consists of an inner expandable material (core), an embracing membrane, and a gelatin capsule shell. It is designed to occupy volume in the stomach and reduce hunger sensation. The occupied volume is changeable over time, dependent on the number of ingested capsules and their degradation time. This will avoid gastric accommodation to constant volume devices as seen in the use of intragastric balloons. Several materials were tested. Collagen casing was selected as the membrane and corn silk was used to tie the membrane. Dried black fungus (Auricularia auricula) was the biological material that expanded most. However, synthesized cellulose-based hydrogel expanded more and was chosen as the optimal expandable core material. The hydrogel-based EndoXpand expanded 72 times after soaking in an acidic environment for 80 min. The corn silk ligations weakened and broke after 3 h. This resulted in release of the expanded material that was designed to easily pass the pylorus and travel down the intestine for digestion or excretion. In conclusion, this study provides design and in vitro proof-of-technology data for a potential groundbreaking approach. Further studies are needed in animal models and human phase I studies.

Antimicrobial effects of hydroxyapatite mosaicked polyvinyl alcohol-alginate semi-interpenetrating hydrogel-loaded with ethanolic extract of Glycyrrhiza glabra against oral pathogens

Glycyrrhiza glabra (GG) elicits protective effects against periodontal diseases. However, the sustained bioavailability of GG extract at therapeutic concentration warrants ideal delivery vehicles. Present study has focused on the design, fabrication, and evaluations of ethanolic-crude extract of GG-loaded semi-interpenetrating network (semi-IPN) hydrogel (HAAPS-GG) using alginic acid and polyvinyl alcohol (PVA) hydrogel mosaicked with HA for periodontal regeneration. The study has examined the performance of the hydrogel against the selected oral pathogens S. mutans, E. faecalis, L. acidophilus and C. albicans. HAAPS-GG was successfully fabricated and the surface functional groups were confirmed by attenuated total reflectance-infrared (ATR-IR) spectroscopy. HAAPS-GG displayed interconnecting pores, hydrophilicity and excellent water profile contributing to the biocompatibility as evident from direct contact and MTT assay in L929 fibroblasts. The hydrogel was mechanically stable and was immunocompatible owing to the relatively decreased levels of pro-inflammatory mediators COX2, 5LPO, iNOS and MPO in RAW 264.7 macrophages. In addition, the transcript analysis on RAW 264.7 revealed the down-regulation of inflammatory transcription factor NF-κβ and the pro-inflammatory cytokine TNF-α. Importantly, HAAPS-GG arrested the progression of periodontal pathogens predominantly S. mutans, and C. albicans as evident by disc diffusion assay, MTT assay and confocal microscopy. Overall, the HAAPS-GG system offers promising translational avenues in periodontal regeneration.

Additive Manufacturing: An Opportunity for the Fabrication of Near-Net-Shape NiTi Implants

Nickel–titanium (NiTi) is a shape-memory alloy, a type of material whose name is derived from its ability to recover its original shape upon heating to a certain temperature. NiTi falls under the umbrella of metallic materials, offering high superelasticity, acceptable corrosion resistance, a relatively low elastic modulus, and desirable biocompatibility. There are several challenges regarding the processing and machinability of NiTi, originating from its high ductility and reactivity. Additive manufacturing (AM), commonly known as 3D printing, is a promising candidate for solving problems in the fabrication of near-net-shape NiTi biomaterials with controlled porosity. Powder-bed fusion and directed energy deposition are AM approaches employed to produce synthetic NiTi implants. A short summary of the principles and the pros and cons of these approaches is provided. The influence of the operating parameters, which can change the microstructural features, including the porosity content and orientation of the crystals, on the mechanical properties is addressed. Surface-modification techniques are recommended for suppressing the Ni ion leaching from the surface of AM-fabricated NiTi, which is a technical challenge faced by the long-term in vivo application of NiTi.

The Role of Interstitial Fluid Pressure in Cerebral Porous Biomaterial Integration

Recent advances in biomaterials offer new possibilities for brain tissue reconstruction. Biocompatibility, provision of cell adhesion motives and mechanical properties are among the present main design criteria. We here propose a radically new and potentially major element determining biointegration of porous biomaterials: the favorable effect of interstitial fluid pressure (IFP). The force applied by the lymphatic system through the interstitial fluid pressure on biomaterial integration has mostly been neglected so far. We hypothesize it has the potential to force 3D biointegration of porous biomaterials. In this study, we develop a capillary hydrostatic device to apply controlled in vitro interstitial fluid pressure and study its effect during 3D tissue culture. We find that the IFP is a key player in porous biomaterial tissue integration, at physiological IFP levels, surpassing the known effect of cell adhesion motives. Spontaneous electrical activity indicates that the culture conditions are not harmful for the cells. Our work identifies interstitial fluid pressure at physiological negative values as a potential main driver for tissue integration into porous biomaterials. We anticipate that controlling the IFP level could narrow the gap between in vivo and in vitro and therefore decrease the need for animal screening in biomaterial design.

Benefits of Residual Aluminum Oxide for Sand Blasting Titanium Dental Implants: Osseointegration and Bactericidal Effects

OBJECTIVES

The purpose of this work was to determine the influence of residual alumina after sand blasting treatment in titanium dental implants. This paper studied the effect of alumina on physico-chemical surface properties, such as: surface wettability, surface energy. Osseointegration and bacteria adhesion were determined in order to determine the effect of the abrasive particles.

MATERIALS AND METHODS

Three surfaces were studied: (1) as-received, (2) rough surface with residual alumina from sand blasting on the surface and (3) with the same roughness but without residual alumina. Roughness was determined by white light interferometer microscopy. Surface wettability was evaluated with a contact angle video-based system and the surface free energy by means of Owens and Wendt equation. Scanning electron microscopy equipped with microanalysis was used to study the morphology and determine the chemical composition of the surfaces. Bacteria (Lactobacillus salivarius and Streptococcus sanguinis) were cultured in each surface. In total, 110 dental implants were placed into the bone of eight minipigs in order to compare the osseointegration. The percentage of bone-to-implant contact was determined after 4 and 6 weeks of implantation with histometric analysis.

RESULTS

The surfaces with residual alumina presented a lower surface free energy than clean surfaces. The in vivo studies demonstrated that the residual alumina accelerated bone tissue growth at different implantation times, in relation to clean dental implants. In addition, residual alumina showed a bactericidal effect by decreasing the quantity of bacteria adhering to the titanium.

CONCLUSIONS

It is possible to verify the benefits that the alumina (percentages around 8% in weight) produces on the surface of titanium dental implants.

CLINICAL RELEVANCE

Clinicians should be aware of the benefits of sand-blasted alumina due to the physico-chemical surface changes demonstrated in in vivo tests.

The Antibacterial Effectiveness of Propolis on Medical Screws

Background

Medical screws are widely used in orthopedic surgery for fracture fixation. The antibacterial effectiveness of propolis is well known. In this study, we aimed to demonstrate the antibacterial effectiveness of medical screws coated with propolis.

Methodology

Between March 2019 and April 2020, we formed five experimental groups and investigated the antibacterial activities of different amounts of propolis and polymer-coated screws. Staphylococcus aureus was used to determine the antibacterial activity. Carbopol, chosen as the model polymer, was used to improve the adhesion of propolis to the screws. Agar diffusion test of surface-coated screws was used to evaluate the antibacterial effect.

Results

The mean zone diameters were 24.3 ± 1.1, 23.0 ± 0.8, 21.8 ± 1.6, 19.3 ± 0.6, and 20.2 ± 0.8 mm for IS-7.5, IS-5.0, IS-2.5, IS-P, and IS-P-7.5, respectively. The IS-7.5 group had the most antibacterial activities. The antibacterial activities of the medical screws determined using the agar diffusion method were significantly increased by the propolis coating on the screws. Our results showed that the propolis-coated screws had antibacterial activity against S. aureus.

Conclusions

As a result, we believe that the combination of gel and propolis is an effective method in increasing the antibacterial resistance of medical screws and preventing the formation of a biofilm layer of microorganisms.

Biomechanical and functional comparison of moulded and 3D printed medical silicones

Modern 3D printing of implantable devices provides an important opportunity for the development of personalized implants with good anatomical fit. Nevertheless, 3D printing of silicone has been challenging and the recent advances in technology are provided by the systems which can print medical grade silicone via extrusion. However, the potential impacts of the 3D printing process of silicone on its biomechanical properties has not been studied in sufficient detail. Therefore, the present study compares 3D printed and moulded silicone structures for their cytotoxicity, surface roughness, biomechanical properties, and in vivo tissue reaction. The 3D printing process creates increased nanoscale roughness and noticeably changes microscale topography. Neither the presence of these features nor the differences in processes were found to result in an increase in cytotoxicity or tissue reaction for 3D printed structures, exhibiting limited inflammatory reaction and cell viability above the threshold values. On the contrary, the biomechanical properties have demonstrated significant differences in static and dynamic conditions, and in thermal expansion. Our results demonstrate that 3D printing can be used for establishing a better biomechanical microenvironment for the surrounding tissue of the implant particularly for fragile soft tissue like epithelial mucosa without having any negative effect on the cytotoxicity or in vivo reaction to silicone. For engineering of the implants, however, one must consider the differences in mechanical properties to result in correct and personalized geometry and proper physical interaction with tissues.

Biomechanical Properties of Bone and Mucosa for Design and Application of Dental Implants

Dental implants’ success comprises their proper stability and adherence to different oral tissues (integration). The implant is exposed to different mechanical stresses from swallowing, mastication and parafunctions for a normal tooth, leading to the simultaneous mechanical movement and deformation of the whole structure. The knowledge of the mechanical properties of the bone and gingival tissues in normal and pathological conditions is very important for the successful conception of dental implants and for clinical practice to access and prevent potential failures and complications originating from incorrect mechanical factors’ combinations. The challenge is that many reported biomechanical properties of these tissues are substantially scattered. This study carries out a critical analysis of known data on mechanical properties of bone and oral soft tissues, suggests more convenient computation methods incorporating invariant parameters and non-linearity with tissues anisotropy, and applies a consistent use of these properties for in silico design and the application of dental implants. Results show the advantages of this approach in analysis and visualization of stress and strain components with potential translation to dental implantology.

Enhancement of Gingival Tissue Adherence of Zirconia Implant Posts: In Vitro Study

Prevention of bacterial inflammation around dental implants (peri-implantitis) is one of the keys to success of the implantation and can be achieved by securing the gingival tissue-abutment interface preventing penetration of bacteria. Modern dental practice has adopted zirconia abutments in place of titanium, but the adhesion of gingival tissue to zirconia is inferior to titanium. The aim of this study was to assess and improve the adhesion of mucosal tissues to zirconia posts using sol-gel derived TiO₂ coating following dynamic mechanical testing. The posts were cultivated with porcine bone-gingival tissue specimens in vitro for 7 and 14 days and then subjected to dynamic mechanical analysis simulating physiological loading at 1 Hz up to 50 μm amplitude. In parallel in silico analysis of stresses and strains have been made simulating "the worst case" when the fixture fails in osseointegration while the abutment still holds. Results show treatment of zirconia can lead to double interface stiffness (static shear stiffness values from 5-10 to 17-23 kPa and dynamic from 20-50 to 60-125 kPa), invariant viscostiffness (from 5-35 to 45-90 kPa·s^α) and material memory values (increased from 0.06-0.10 to 0.17-0.25), which is beneficial in preventing bacterial contamination in dental implants. This suggests TiO₂-coated zirconia abutments may have a significant clinical benefit for prevention of the bacterial contamination.

Biomechanical Features of Graphene-Augmented Inorganic Nanofibrous Scaffolds and Their Physical Interaction with Viruses

Nanofibrous substrates and scaffolds are widely being studied as matrices for 3D cell cultures, and disease models as well as for analytics and diagnostic purposes. These scaffolds usually comprise randomly oriented fibers. Much less common are nanofibrous scaffolds made of stiff inorganic materials such as alumina. Well-aligned matrices are a promising tool for evaluation of behavior of biological objects affected by micro/nano-topologies as well as anisotropy. In this work, for the first time, we report a joint analysis of biomechanical properties of new ultra-anisotropic, self-aligned ceramic nanofibers augmented with two modifications of graphene shells (GAIN scaffolds) and their interaction of three different viral types (influenza virus A, picornavirus (human parechovirus) and potato virus). It was discovered that nano-topology and structure of the graphene layers have a significant implication on mechanical properties of GAIN scaffolds resulting in non-linear behavior. It was demonstrated that the viral adhesion to GAIN scaffolds is likely to be guided by physical cues in dependence on mutual steric factors, as the scaffolds lack common cell membrane proteins and receptors which viruses usually deploy for transfection. The study may have implications for selective viral adsorption, infected cells analysis, and potentially opening new tools for anti-viral drugs development.

Carbon nanostructures as a scaffold for human embryonic stem cell differentiation toward photoreceptor precursors

Carbon nanomaterials have been introduced as a scaffold for various biological applications due to their unique physical and electrical properties. Here we studied carbon nanotubes (CNTs) and carbon nanofibers (CNFs) as scaffold materials for the differentiation of human embryonic stem cells (hESCs) towards photoreceptor precursor cells (PRPs). We report on their cytoxicity, their effect on cell morphology, cell-surface interface and the differentiation process. To this end, hESCs were differentiated into PRPs on carbon nanofibers (CNFs), long horizontal CNTs (LHCNTs), vertically aligned CNTs (VACNTs) or glass (control) surfaces. The differentiated cells were investigated by immunohistochemistry, fluorescence imaging and electron microscopy. Our results revealed that the investigated nanomaterials were not cytotoxic to the cells during the differentiation process. The surface interface effect on the cells was apparent, affecting cell directionality, migration and morphology. Interestingly, cell fate was not dependent on the substrate type, as inferred from the similar dynamics of the loss of pluripotency and the comparable expression levels of the photoreceptor marker Crx for all investigated substrates. These results are important for better understanding the effect of nanomaterial surface interaction with differentiating neural cells in general, and for future use of these materials as scaffolds for differentiating photoreceptors for vision restoration in particular.

Strategies for Using Polydopamine to Induce Biomineralization of Hydroxyapatite on Implant Materials for Bone Tissue Engineering

In the field of tissue engineering, there are several issues to consider when designing biomaterials for implants, including cellular interaction, good biocompatibility, and biochemical activity. Biomimetic mineralization has gained considerable attention as an emerging approach for the synthesis of biocompatible materials with complex shapes, categorized organization, controlled shape, and size in aqueous environments. Understanding biomineralization strategies could enhance opportunities for novel biomimetic mineralization approaches. In this regard, mussel-inspired biomaterials have recently attracted many researchers due to appealing features, such as strong adhesive properties on moist surfaces, improved cell adhesion, and immobilization of bioactive molecules via catechol chemistry. This molecular designed approach has been a key point in combining new functionalities into accessible biomaterials for biomedical applications. Polydopamine (PDA) has emerged as a promising material for biomaterial functionalization, considering its simple molecular structure, independence of target materials, cell interactions for adhesion, and robust reactivity for resulting functionalization. In this review, we highlight the strategies for using PDA to induce the biomineralization of hydroxyapatite (HA) on the surface of various implant materials with good mechanical strength and corrosion resistance. We also discuss the interactions between the PDA-HA coating, and several cell types that are intricate in many biomedical applications, involving bone defect repair, bone regeneration, cell attachment, and antibacterial activity.

Effects of statherin on the biological properties of titanium metals subjected to different surface modification

The failure of dental implants is usually caused by bacteria infection, poor bioactivity and biocompatibility. It is a common phenomenon clinically. Statherin, a salivary protein, plays a crucial role of mediator between materials and cells/bacteria. However, the conformation of statherin might be changed by the implants in vivo. In this study, we investigated the effects of statherin on the bioactivities, antibacterial abilities and biocompatibilities of the titanium metals and the reaction mechanism. We found that the conformation of statherin was mainly influenced by surface composition, surface structure, surface roughness, surface hydrophilia and Ti-OH groups of materials. Statherin could decrease the cell biocompatibility of the titanium metals including pure titanium (PT), anodic oxidation (AO), sandblasting and etching (SLA) and plasma spraying hydroxyapatite (HA) coating in HGF cell experiments, regulate the bio-mineralization ability of HA coating in SBF, and enhance the antibacterial properties of PT and HA coating. This study revealed that surface properties of materials could change the conformation of statherin, which influenced the bioactivities, antibacterial properties and biocompatibilities of the materials in return.

Elucidating structure–function relationships governing the interfacial response of human mesenchymal stem cells to polydopamine coatings

Deposition of mussel-inspired polydopamine (PDA) has rapidly emerged as a simple yet effective strategy to functionalize the surface of biomaterials.

The Importance of Controlled Mismatch of Biomechanical Compliances of Implantable Scaffolds and Native Tissue for Articular Cartilage Regeneration

Scaffolds for articular cartilage repair have to be optimally biodegradable with simultaneous promotion of hyaline cartilage formation under rather complex biomechanical and physiological conditions. It has been generally accepted that scaffold structure and composition would be the best when it mimics the structure of native cartilage. However, a reparative construct mimicking the mature native tissue in a healing tissue site presents a biological mismatch of reparative stimuli. In this work, we studied a new recombinant human type III collagen-polylactide (rhCol-PLA) scaffolds. The rhCol-PLA scaffolds were assessed for their relative performance in simulated synovial fluids of 1 and 4 mg/mL sodium hyaluronate with application of model-free analysis with Biomaterials Enhanced Simulation Test (BEST). Pure PLA scaffold was used as a control. The BEST results were compared to the results of a prior in vivo study with rhCol-PLA. Collectively the data indicated that a successful articular cartilage repair require lower stiffness of the scaffold compared to surrounding cartilage yet matching the strain compliance both in static and dynamic conditions. This ensures an optimal combination of load transfer and effective oscillatory nutrients supply to the cells. The results encourage further development of intelligent scaffold structures for optimal articular cartilage repair rather than simply trying to imitate the respective original tissue.

Tissue repair in neonatal and paediatric surgery: Analysis of infection in surgical implantation of synthetic resorbable biomaterials

BACKGROUND

There has been increased interest in the use of biomaterials that resorb completely leaving only the patient's native tissue. Synthetic materials are advantageous for tissue repair because they are highly customisable. The infection rate of using resorbable natural materials in paediatric surgery has recently been outlined, but there has not yet been a review of the use of synthetic resorbable materials in paediatric surgery.

OBJECTIVES

This systematic review analyses the risk of infection after implantation of fully resorbable synthetic biomaterials in paediatric cases.

METHODS

The literature was searched from January 1970 to January 2018 (inclusive), specifically searching for paediatric cases (0-18 years old), use of synthetic resorbable materials and infection.

RESULTS

The infection rate in 3573 cases of synthetic resorbable material implantation was 1.1% (41 cases). A Chi-squared test for independence found infection rate to vary among materials. Of the many biomaterials identified in this review, the highest infection rates were seen in Suprathel's use in burns injuries (12.1%).

CONCLUSIONS

This review found a low infection rate in synthetic resorbable materials used in paediatric surgery, with particularly strong evidence for low infection risk in LactoSorb® use.

Graphene-Augmented Nanofiber Scaffolds Trigger Gene Expression Switching of Four Cancer Cell Types

Three-dimensional (3D) customized scaffolds are anticipated to provide new frontiers in cell manipulation and advanced therapy methods. Here, we demonstrate the application of hybrid 3D porous scaffolds, representing networks of highly aligned self-assembled ceramic nanofibers, for culturing four types of cancer cells. Ultrahigh aspect ratio (∼10⁷) of graphene augmented fibers of tailored nanotopology is shown as an alternative tool to substantially affect cancerous gene expression, eventually due to differences in local biomechanical features of the cell–matrix interactions. Here, we report a clear selective up- and down-regulation of groups of markers for breast cancer (MDA-MB231), colorectal cancer (CaCO2), melanoma (WM239A), and neuroblastoma (Kelly) depending on only fiber orientation and morphology without application of any other stimulus. Changes in gene expression are also revealed for Mitomycin C treatment of MDA-MB231, making the scaffold a suitable platform for testing of anticancer agents. This allows an opportunity for selective “clean” guidance to a deep understanding of mechanisms of cancer cells progressive growth and tumor formation without possible side effects by manipulation with the specific markers.