Ammonium bicarbonate as porogen to make tetracycline-loaded porous bioresorbable membranes for dental guided tissue regeneration: failure due to tetracycline instability

Antibiotic-Loaded Polymeric Barrier Membranes for Guided Bone/Tissue Regeneration: A Mini-Review

Polymeric membranes are frequently used for bone regeneration in oral and periodontal surgery. Polymers provide adequate mechanical properties (i.e., Young’s modulus) to support oral function and also pose some porosity with interconnectivity to permit for cell proliferation and migration. Bacterial contamination of the membrane is an event that may lead to infection at the bone site, hindering the clinical outcomes of the regeneration procedure. Therefore, polymeric membranes have been proposed as carriers for local antibiotic therapy. A literature search was performed for papers, including peer-reviewed publications. Among the different membranes, collagen is the most employed biomaterial. Collagen membranes and expanded polytetrafluoroethylene loaded with tetracyclines, and polycaprolactone with metronidazole are the combinations that have been assayed the most. Antibiotic liberation is produced in two phases. A first burst release is sometimes followed by a sustained liberation lasting from 7 to 28 days. All tested combinations of membranes and antibiotics provoke an antibacterial effect, but most of the time, they were measured against single bacteria cultures and usually non-specific pathogenic bacteria were employed, limiting the clinical relevance of the attained results. The majority of the studies on animal models state a beneficial effect of these antibiotic functionalized membranes, but human clinical assays are scarce and controversial.

New biodegradable nanoparticles-in-nanofibers based membranes for guided periodontal tissue and bone regeneration with enhanced antibacterial activity

Introduction

Guided tissue regeneration (GTR) and guided bone regeneration (GBR) are commonly used surgical procedures for the repair of damaged periodontal tissues. These procedures include the use of a membrane as barrier to prevent soft tissue ingrowth and to create space for slowly regenerating periodontium and bone. Recent approaches involve the use of membranes/scaffolds based on resorbable materials. These materials provide the advantage of dissolving by time without the need of surgical intervention to remove the scaffolds.

Objectives

This study aimed at preparing a new series of nanofibrous scaffolds for GTR/GBR applications with enhanced mechanical properties, cell adhesion, biocompatibility and antibacterial properties.

Methods

Electrospun nanofibrous scaffolds based on polylactic acid/cellulose acetate (PLA/CA) or poly(caprolactone) (PCL) polymers were prepared and characterized. Different concentrations of green-synthesized silver nanoparticles, AgNPs (1-2% w/v) and hydroxyapatite nanoparticles, HANPs (10-20% w/v) were incorporated into the scaffolds to enhance the antibacterial and bone regeneration activity.

Results

In-vitro studies showed that addition of HANPs improved the cell viability by around 50% for both types of nanofibrous scaffolds. The tensile properties were also improved through addition of 10% HANPs but deteriorated upon increasing the concentration to 20%. AgNPs significantly improved the antibacterial activity with 40 mm inhibition zone after 32 days. Additionally, the nanofibrous scaffolds showed a desirable degradation profile with losing around 40-70% of its mass in 8 weeks.

Conclusions

The obtained results show that the developed nanofibrous membranes are promising scaffolds for both GTR and GBR applications.

Selectively enrichment of antibiotics and ARGs by microplastics in river, estuary and marine waters

The partition of antibiotics and antibiotic resistant genes (ARGs) between the microplastics (MPs) and the surrounding water with various salinity are still unclear. In this study, we hypothesized that adsorption of antibiotics on MPs might cause a significant change of the structure of microbial communities, diversity and abundance of ARGs on MPs and this might be further affected by change of salinity. In this study, we investigated adsorption of four common antibiotics (sulfamerazine, tetracycline, chloramphenicol and tylosin) to polyethylene (PE) MPs in river, estuary and marine waters, and the differences of antibiotic resistant genes (ARGs) and bacterial communities on MPs and in the three waters. The results showed that MPs can enrich antibiotics, ARGs and microbes from the surrounding water. Elevated salinity could reduce adsorption of antibiotics to MPs and the abundance of ARGs. For example, MPs can concentrate more antibiotics and ARGs in the fresh river water than in the estuary and the marine waters. In addition, ARGs and bacterial communities on MPs at various salinity were significantly different under the pressure of four antibiotics. On MPs, sul1, sulA/folP-01, tetA, tetC, tetX and ermE increased significantly but a few new ARGs such as sulA/folP-01 and tetA appeared. The structure of the bacterial communities on MPs was different from the surrounding water since some bacteria species found on MPs were barely detected in the surrounding water while some genera on MPs vanished after exposure to antibiotics. As the antibiotics adsorbed and the ARGs on MPs decreased with the water salinity, the structure of the communities on MPs thus varied with salinity change. These findings are important to understand the effects of MPs on the transport, fate and ecological risk of antibiotics and ARGs in different aquatic environments.

* Engineering Membranes for Bone Regeneration

This review is focused on the use of membranes for the specific application of bone regeneration. The first section focuses on the relevance of membranes in this context and what are the specifications that they should possess to improve the regeneration of bone. Afterward, several techniques to engineer bone membranes by using "bulk"-like methods are discussed, where different parameters to induce bone formation are disclosed in a way to have desirable structural and functional properties. Subsequently, the production of nanostructured membranes using a bottom-up approach is discussed by highlighting the main advances in the field of bone regeneration. Primordial importance is given to the promotion of osteoconductive and osteoinductive capability during the membrane design. Whenever possible, the films prepared using different techniques are compared in terms of handability, bone guiding ability, osteoinductivity, adequate mechanical properties, or biodegradability. A last chapter contemplates membranes only composed by cells, disclosing their potential to regenerate bone.

Fabrication of porous synthetic polymer scaffolds for tissue engineering

Tissue engineering provides a novel and promising approach to replace damaged tissue with an artificial substitute. Porous synthetic biodegradable polymers are the preferred materials for this substitution due to their microstructure, biocompatibility, biodegradability, and low cost. As a crucial element in tissue engineering, a scaffold acts as an artificial extracellular matrix (ECM) and provides support for cell migration, differentiation, and reproduction. The fabrication of viable scaffolds, however, has been a challenge in both clinical and academic settings. Methods such as solvent casting/particle leaching, thermally induced phase separation (TIPS), electrospinning, gas foaming, and rapid prototyping (additive manufacturing) have been developed or introduced for scaffold fabrication. Each method has its own advantages and disadvantages. In this review, the commonly used synthetic polymer scaffold fabrication methods will be introduced and discussed in detail, and recent progress regarding scaffold fabrication—such as combining different scaffold fabrication methods, combining various materials, and improving current scaffold fabrication methods—will be reviewed as well.

Fabrication of interpenetrate chitosan: bioactive glass, using dense gas CO2

Success of bone tissue engineering relies on using bioactive scaffolds with ideal pore morphology which can mimic the properties of the natural extracellular matrix (ECM). The objective of this study was to interpenetrate bioactive glass components throughout the three dimensional (3D) structure of the chitosan scaffold to increase the average pore size of the scaffold and also the osteoconductivity and osteoinductivity of the fabricated scaffold. Scanning electron microscopy was used to observe the microsturcture of the hydrogel. The results of this study demonstrated that the average pore size in the hydrogel was increased significantly (p<0.05) from 97 ± 44 μm to 150 ± 24 μm by increasing the BG concentration from 0 wt% to 40 wt%. This effect might be due to the interaction between ceramic and chitosan. The composite hydrogel fabricated swell in water and has high potential to be used for bone tissue engineering applications; bioactive glass can substantially improve bioactivity of the bone tissue engineering scaffolds However, further studies are required to investigate the effect of BG on the biocompatibility of the scaffolds. In addition, in vitro cell studies are also required to confirm the suitability of the fabricated scaffold for bone tissue engineering.

Development of an electrospun nano-apatite/PCL composite membrane for GTR/GBR application

In dental practice, membranes are used as a barrier to prevent soft tissue ingrowth and create space for slowly regenerating periodontal and bony tissues. The aim of this study was to develop a biodegradable membrane system which can be used for guided tissue or bone regeneration. Three types of composite fibrous membranes based on nano-apatite (nAp) and poly(epsilon-caprolactone) (PCL) were made by electrospinning, i.e. n0 (nAp:PCL=0:100), n25 (nAp:PCL=25:100) and n50 (nAp:PCL=50:100) with average fiber diameters ranging from 320 to 430 nm. Their structural, mechanical, chemical and biological properties were evaluated. Tensile test revealed that n25 had the highest strength and toughness, indicating there is an optimal ratio of nAp to polymer for mechanical reinforcement. Subsequently, a simulated body fluid immersion test confirmed that the presence of nAp enhanced the bioactive behavior of the membranes. Finally, an in vitro osteoblast cell study showed that all membranes supported proliferation, but the presence of nAp facilitated an early cell differentiation. This study demonstrated that an electrospun membrane incorporating nAp is strong, enhances bioactivity and supports osteoblast-like cell proliferation and differentiation. The membrane system can be used as a prototype for the further development of an optimal membrane for clinical use.