Incorporation of tripolyphosphate nanoparticles into fibrous poly(lactide-co-glycolide) scaffolds for tissue engineering

COLLOID–CELL INTERACTION ANALYSIS WITH ATOMIC FORCE MICROSCOPY — ζ CALCULATION AND ADHESION ANALYSIS

The interaction between cells and colloids is an important characteristic that influences cell behavior. Theoretically, much information could be revealed by analyzing the interactions in colloid–cell contact. In this study, in order to explore the interaction between cells and colloids, we developed a novel computational method able to obtain a zeta potential directly calculated from the force distance curve and apply to adhesion analysis, which used atomic force microscope (AFM), based on DLVO (Deryaguin–Landau–Verwey–Overbeek) theory and Mann Whitney U test, and combined with Zetasizer measurement. The calculation and analysis of [Formula: see text] of the cell surfaces of ncyc-1324 yeast, ncyc-1681 yeast and Pseudomonas fluorescens showed that pH affected the electrostatic distribution on the cell surface. Compared with the previous research methods, this method significantly reduces the computation and manual control, which is an effective method for multi-element surface analysis and comparison. For example, the reverse calculation and curve fitting method will significantly request more computation and manual control to set up the reference force curve that simulated with set zeta potential, while this method only need to calculate on one force curve. The deconvolution of different adhesion events from force curves showed that the heterogeneity of cell surface can be significantly displayed. This provides a method for determining the complexity of the cell surface. Furthermore, this method was used to study the effect of amoxicillin on cell surface interaction, which showed that the cells surface forces were influenced even the medicine concentration is not enough to make significant influence on microbials optical observation appearance. Thus, AFM force analysis is a more sensitive method to research the medicine influence compared to the traditional method.

Local and Sustained Delivery of Rifampicin from a Bioactive Ceramic Carrier Treats Bone Infection in Rat Tibia

Next-generation treatment strategies to treat osteomyelitis with complete eradication of pathogen at the bone nidus and prevention of emergence of drug resistance is a real challenge in orthopedics. Conventional treatment strategies including long-term adherence of patients to systemic antibiotic delivery, local delivery using nondegradable vehicles, and surgical debridement are not completely effective in achieving successful results. In this study, a broad-spectrum antibiotic, rifampicin (RFP), was incorporated into a biphasic nanohydroxyapatite (nHAP)/calcium sulfate ceramic carrier (NC) system. In vivo release and distribution of rifampicin was evaluated for a period of one month by implanting NC and NC + RFP in a subcutaneous pouch in a rat model. We detected the RFP in bone and implanted NC scaffolds even after day 28 and the concentration was still higher than the minimal inhibitory concentration of RFP when it was implanted with NC in an abdominal subcutaneous pouch. Moreover, we also observed the accumulation of RFP in bone and NC when administered orally, showing strong binding between RFP and nHAP. Additionally, we generated an osteomyelitis bone infection model in the rat tibia using Staphylococcus aureus as an infective agent to evaluate the antibacterial and osteogenic efficiency of RFP containing NC as a delivery system. S. aureus mediated implant infection is a major problem in orthopedics. The results suggested that NC loaded with RFP could eradicate the pathogen completely in the bone nidus. Further, defect healing and bone formation were also evaluated by micro-CT and histological analysis demonstrating proper trabecular-type bone formation at the debridement site and complete healing of the defect when NC + RFP was implanted. Our findings provide an insight into the use of an nHAP based ceramic matrix as a carrier of rifampicin to eradicate the bone infection and simultaneously promote bone healing at the bone nidus.

Electrospun acid-neutralizing fibers for the amelioration of inflammatory response

Biodegradable aliphatic polyesters, especially polylactide (PLA), polyglycolide (PGA), and their copolymer poly(lactide-co-glycolide) (PLGA), are the most representative and widely used synthetic polymers in the field of tissue engineering and regenerative medicine. However, these polyesters often give rise to aseptic inflammation because of their acidic degradation products after implantation. Here, unidirectional shell-core structured fibers of chitosan/poly(lactide-co-glycolide) (i.e., CTS/PLGA) with acid-neutralizing capability were developed for addressing the noted issue by coating the PLGA fiber surfaces with a layer of the alkaline chitosan by coaxial electrospinning. Our results showed that during a period of 8-week degradation, the shell-layer of chitosan with its unique alkaline nature for acid-neutralization obviously hindered the pH decrease as a result of the degradation of PLGA-core. In a mocked acidic environment testing of the human dermal fibroblasts, chitosan-enabled acidity neutralization could significantly reduce in vitro the secretion of inflammatory factors and downregulate the expression of related inflammatory genes. Thereafter, biocompatibility assessment in vitro showed that the CTS/PLGA fibers had poorer cell adhesion capacity than the PLGA fibers but were cytocompatible and promoted cell migration and secretion of collagen. Moreover, subcutaneous embedding for two and four weeks in vivo revealed that the CTS/PLGA fibers significantly reduced the recruitment of inflammatory cells and the formation of foreign body giant cells (FBGCs). This study thereby demonstrated the evident acid-neutralizing effect of the chitosan-coating layer on alleviating the inflammatory responses caused by the acidic degradation products of the PLGA-core. Our highly aligned CTS/PLGA fibers, as a kind of quasi "pH-neutral fibers" with the acid-neutralizing capability, could be potentially applied for engineering those architecturally anisotropic tissues (e.g., tendon/ligament) toward improved efficacy of regeneration. STATEMENT OF SIGNIFICANCE: It is well known that acidic degradation products from representative aliphatic polyesters (e.g., PLA, PGA, and PLGA) give rise to the problem of aseptic inflammation. Various alkaline components acting as neutralizing agents have been used to address the noted issue. However, rather less attention has been paid to engineer these polyesters into a fibrous form with acid-neutralizing functionality. The present study proposes the concept of "pH-neutral fibers" and develops shell-core structured unidirectional fibers of chitosan/poly(lactide-co-glycolide) with acid-neutralizing capability for ameliorating inflammatory responses caused by the acidic degradation products of PLGA. It provides a comprehensive study encompassing fiber characterization and in vitro and in vivo evaluation, which would pave the way for developing sophisticated pH-neutral fibers for functional tissue regeneration.

Monomer sequence in PLGA microparticles: Effects on acidic microclimates and in vivo inflammatory response

Controlling the backbone architecture of poly(lactic-co-glycolic acid)s (PLGAs) is demonstrated to have a strong influence on the production and release of acidic degradation by-products in microparticle matrices. Previous efforts for controlling the internal and external accumulation of acidity for PLGA microparticles have focused on the addition of excipients including neutralization and anti-inflammatory agents. In this report, we utilize a sequence-control strategy to tailor the microstructure of PLGA. The internal acidic microclimate distributions within sequence-defined and random PLGA microparticles were monitored in vitro using a non-invasive ratiometric two-photon microscopy (TPM) methodology. Sequence-defined PLGAs were found to have minimal changes in pH distribution and lower amounts of percolating acidic by-products. A parallel scanning electron microscopy study further linked external morphological events to internal degradation-induced structural changes. The properties of the sequenced and random copolymers characterized in vitro translated to differences in in vivo behavior. The sequence alternating copolymer, poly LG, had lower granulomatous foreign-body reactions compared to random racemic PLGA with a 50:50 ratio of lactic to glycolic acid.

STATEMENT OF SIGNIFICANCE

This paper demonstrates that changing the monomer sequence in poly(lactic-co-glycolic acid)s (PLGAs) leads to dramatic differences in the rate of degradation and the internal acidic microclimate of microparticles degrading in vitro. We note that the acidic microclimates within these particles were imaged for the first time with two-photon microscopy, which gives an extremely clear and detailed picture of the degradation process. Importantly, we also document that the observed sequence-controlled in vitro processes translate into differences in the in vivo behavior of polymers which have the same L to G composition but differing microstructures. These data, placed in the context of our prior studies on swelling, erosion, and MW loss (Biomaterials2017, 117, 66 and other references cited within the manuscript), provide significant insight not only about sequence effects in PLGAs but into the underlying mechanisms of PLGA degradation in general.

Antibacterial and anti-encrustation biodegradable polymer coating for urinary catheter

Bacterial biofilm and crystalline deposits are the common causes of failure of long-term indwelling urinary catheter. Bacteria colonise the catheter surface causing serious infections in the urinary tract and encrustations that can block the catheter and induce trauma in patients. In this study, the strategy used to resist bacterial adhesion and encrustation represents a combination of the antibacterial effects of norfloxacin and silver nanoparticles and the PLGA-based neutralisation of alkali products of urea hydrolysis gained through the degradation of the polymer in an aqueous milieu. Silver nanoparticles were coated with tetraether lipids (TEL) to avoid aggregation when dispersed in acetone and during the film formation. The polymer films loaded with the two antibacterial agents were applied on Polyurethane (PUR) and Silicon sheets. We demonstrated the antibacterial and anti-adhesion effectiveness of the coatings whereby commercially available biocompatible polymers PUR and Silicon were used as controls. Using artificial urine and an in vitro encrustation model, it was shown that the coatings resist the encrustation for at least 2 weeks. This combination of a biodegradable polymer and wide-range antibacterial agents represents a potentially attractive biocompatible coating for urinary catheters.

Controlled release of strontium through neutralization reaction within a methoxy(polyethylene glycol)-polyester hydrogel

BACKGROUND

The aim of this study was to develop a minimally invasive hydrogel system that can release strontium ions, an element that has been shown to increase osteoblast proliferation and prohibit bone resorption, in a controlled manner.

METHODS

SrCO3 was selected as the salt of choice due to potential acid neutralization reaction between SrCO3 and degradation by-products of methoxy(polyethylene glycol)-co-poly(lactic-co-glycolic acid) (mPEG-PLGA): namely, lactic acid and glycolic acid. SrCO3 was incorporated into mPEG-PLGA hydrogel, and the system was assessed for gelation properties, drug release and biocompatibility.

RESULTS

SrCO3 incorporation at hydrogel to SrCO3 ratios of 5:1, 3:1 and 1:1 (wt%) did not compromise the thermosensitivity of mPEG-PLGA hydrogels. Furthermore, incorporation of SrCO3 at 1:1 ratio prevented copolymer self-catalysis and decreased hydrogel weight loss from 85% to 61% in vitro after 30 days. During the 30-day time frame, zero-order strontium release was observed and was correlated to hydrogel degradation and acidity. The addition of SrCO3 also improved in vivo hydrogel biocompatibility, due to moderation of acidic microenvironment and amelioration of inflammatory response.

CONCLUSIONS

These results showed that the described system is suitable for the extended release of strontium and exhibits potential for localized treatment for osteoporosis or as a bone void filler.

In Vivo Host Response and Degradation of Copolymer Scaffolds Functionalized with Nanodiamonds and Bone Morphogenetic Protein 2

The aim is to evaluate the effect of modifying poly[(l-lactide)-co-(ε-caprolactone)] scaffolds (PLCL) with nanodiamonds (nDP) or with nDP+physisorbed BMP-2 (nDP+BMP-2) on in vivo host tissue response and degradation. The scaffolds are implanted subcutaneously in Balb/c mice and retrieved after 1, 8, and 27 weeks. Molecular weight analysis shows that modified scaffolds degrade faster than the unmodified. Gene analysis at week 1 shows highest expression of proinflammatory markers around nDP scaffolds; although the presence of inflammatory cells and foreign body giant cells is more prominent around the PLCL. Tissue regeneration markers are highly expressed in the nDP+BMP-2 scaffolds at week 8. A fibrous capsule is detectable by week 8, thinnest around nDP scaffolds and at week 27 thickest around PLCL scaffolds. mRNA levels of ALP, COL1α2, and ANGPT1 are significantly upregulating in the nDP+BMP-2 scaffolds at week 1 with ectopic bone seen at week 8. Even when almost 90% of the scaffold is degraded at week 27, nDP are observable at implantation areas without adverse effects. In conclusion, modifying PLCL scaffolds with nDP does not aggravate the host response and physisorbed BMP-2 delivery attenuates inflammation while lowering the dose of BMP-2 to a relatively safe and economical level.

Reconstructing spinal dura-like tissue using electrospun poly(lactide-co-glycolide) membranes and dermal fibroblasts to seamlessly repair spinal dural defects in goats

Many neuro- and spinal surgeries involving access to the underlying nervous tissue will cause defect of spinal dural mater, further resulting in cerebrospinal fluid leakage. The current work was thus aimed to develop a package which included two layers of novel electrospun membranes, dermal fibroblasts and mussel adhesive protein for repairing spinal dural defect. The inner layer is electrospun fibrous poly(lactide-co-glycolide) membrane with oriented microstructure (O-poly(lactide-co-glycolide)), which was used as a substrate to anchor dermal fibroblasts as seed cells to reconstitute dura-like tissue via tissue engineering technique. The outer layer is chitosan-coated electrospun nonwoven poly(lactide-co-glycolide) membrane (poly(lactide-co-glycolide)-chitosan). During surgery, the inner reconstituted tissue layer was first used to directly cover dura defects, while the outer layer was placed onwards with its marginal area tightly immobilized to the surrounding normal spinal dura aided by mussel adhesive protein. Efficacy of the current design was verified in goats with spinal dural defects (0.6 cm × 0.5 cm) in lumbar. It was shown that seamless and quick sealing of the defect area with the implants was realized by mussel adhesive protein. Guided tissue growth and regeneration in the defects of goats were observed when they were repaired by the current package. Effective cerebrospinal fluid containment and anti-adhesion of the regenerated tissue to the surrounding tissue could be achieved in the current animal model. Hence, it could be ascertained that the current package could be a favorite choice for surgeries involving spinal dural defects.

Current Uses of Poly(lactic-co-glycolic acid) in the Dental Field: A Comprehensive Review

Poly(lactic-co-glycolic acid) or PLGA is a biodegradable polymer used in a wide range of medical applications. Specifically PLGA materials are also developed for the dental field in the form of scaffolds, films, membranes, microparticles, or nanoparticles. PLGA membranes have been studied with promising results, either alone or combined with other materials in bone healing procedures. PLGA scaffolds have been used to regenerate damaged tissues together with stem cell-based therapy. There is solid evidence that the development of PLGA microparticles and nanoparticles may be beneficial to a wide range of dental fields such as endodontic therapy, dental caries, dental surgery, dental implants, or periodontology. The aim of the current paper was to review the recent advances in PLGA materials and their potential uses in the dental field.

Adjustable degradation properties and biocompatibility of amorphous and functional poly(ester-acrylate)-based materials

Tuning the properties of materials toward a special application is crucial in the area of tissue engineering. The design of materials with predetermined degradation rates and controlled release of degradation products is therefore vital. Providing a material with various functional groups is one of the best ways to address this issue because alterations and modifications of the polymer backbone can be performed easily. Two different 2-methylene-1,3-dioxepane/glycidyl methacrylate-based (MDO/GMA) copolymers were synthesized with different feed ratios and immersed into a phosphate buffer solution at pH 7.4 and in deionized water at 37 °C for up to 133 days. After different time intervals, the molecular weight changes, mass loss, pH, and degradation products were determined. By increasing the amount of GMA functional groups in the material, the degradation rate and the amount of acidic degradation products released from the material were decreased. As a result, the composition of the copolymers greatly affected the degradation rate. A rapid release of acidic degradation products during the degradation process could be an important issue for biomedical applications because it might affect the biocompatibility of the material. The cytotoxicity of the materials was evaluated using a MTT assay. These tests indicated that none of the materials demonstrated any obvious cytotoxicity, and the materials could therefore be considered biocompatible.

Biocompatibility and degradation characteristics of PLGA-based electrospun nanofibrous scaffolds with nanoapatite incorporation

The aim of current study was to evaluate the effect of nano-apatitic particles (nAp) incorporation on the degradation characteristics and biocompatibility of poly(lactide-co-glycolide) (PLGA)-based nanofibrous scaffolds. Composite PLGA/poly(ɛ-caprolactone) (PCL) blended (w/w = 3/1) polymeric electrospun scaffolds with 0-30 wt% of nAp incorporation (n0-n30) were prepared. The obtained scaffolds were firstly evaluated by morphological, physical and chemical characterization, followed by an in vitro degradation study. Further, n0 and n30 in both virgin and 3-week pre-degraded status were subcutaneously implanted in rats, either directly or in stainless steel mesh cages, to evaluate in vivo tissue response. The results showed that the incorporation of nAp yields an nAp amount-dependent buffering effect on pH-levels during degradation and delayed polymer degradation based on molecular weight analysis. Regarding biocompatibility, nAp incorporation significantly improved the tissue response during a 4-week subcutaneous implantation, showing less infiltration of inflammatory cells (monocyte/macrophages) as well as less foreign body giant cells (FBGCs) formation surrounding the scaffolds. Similar cytokine expression (gene and protein level) was observed for all groups of implanted scaffolds, although marginal differences were found for TNF-α and TGF-β at gene level as well as GRO-KC at protein level after 1 week of implantation. The results of the current study indicate that hybridization of the weak alkaline salt nAp is effective to control the in vivo adverse tissue reaction of PLGA materials, which is beneficial for optimizing final clinical application of different PLGA-based biomedical devices.

Novel gradient casting method provides high-throughput assessment of blended polyester poly(lactic-co-glycolic acid) thin films for parameter optimization

Pure polymer films cannot meet the diverse range of controlled release and material properties demanded for the fabrication of medical implants or other devices. Additives are added to modulate and optimize thin films for the desired qualities. To characterize the property trends that depend on additive concentration, an assay was designed which involved casting a single polyester poly(lactic-co-glycolic acid) (PLGA) film that blends a linear gradient of any PLGA-soluble additive desired. Four gradient PLGA films were produced by blending polyethylene glycol or the more hydrophobic polypropylene glycol. The films were made using a custom glass gradient maker in conjunction with a 180 cm film applicator. These films were characterized in terms of thickness, percent additive, total polymer (PLGA+additive), and controlled drug release using drug-like fluorescent molecules such as coumarin 6 (COU) or fluorescein diacetate (FDAc). Material properties of elongation and modulus were also accessed. Linear gradients of additives were readily generated, with phase separation being the limiting factor. Additive concentration had a Pearson's correlation factor (R) of >0.93 with respect to the per cent total release after 30 days for all gradients characterized. Release of COU had a near zero-order release over the same time period, suggesting that coumarin analogs may be suitable for use in PLGA/polyethylene glycol or PLGA/polypropylene glycol matrices, with each having unique material properties while allowing tuneable drug release. The gradient casting method described has considerable potential in offering higher throughput for optimizing film or coating material properties for medical implants or other devices.

Bioactive polymer scaffold for fabrication of vascularized engineering tissue

Tissue engineering seeks strategies to design polymeric scaffolds that allow high-cell-density cultures with signaling molecules and suitable vascular supply. One major obstacle in tissue engineering is the inability to create thick engineered-tissue constructs. A pre-vascularized tissue scaffold appears to be the most favorable approach to avoid nutrient and oxygen supply limitations as well as to allow waste removal, factors that are often hurdles in developing thick engineered tissues. Vascularization can be achieved using strategies in which cells are cultured in bioactive polymer scaffolds that can mimic extracellular matrix environments. This review addresses recent advances and future challenges in developing and using bioactive polymer scaffolds to promote tissue construct vascularization.

Poly(lactide-co-glycolide) porous scaffolds for tissue engineering and regenerative medicine

Porous scaffolds fabricated from biocompatible and biodegradable polymers play vital roles in tissue engineering and regenerative medicine. Among various scaffold matrix materials, poly(lactide-co-glycolide) (PLGA) is a very popular and an important biodegradable polyester owing to its tunable degradation rates, good mechanical properties and processibility, etc. This review highlights the progress on PLGA scaffolds. In the latest decade, some facile fabrication approaches at room temperature were put forward; more appropriate pore structures were designed and achieved; the mechanical properties were investigated both for dry and wet scaffolds; a long time biodegradation of the PLGA scaffold was observed and a three-stage model was established; even the effects of pore size and porosity on in vitro biodegradation were revealed; the PLGA scaffolds have also been implanted into animals, and some tissues have been regenerated in vivo after loading cells including stem cells.

Surface characterisation of bioadhesive PLGA/chitosan microparticles produced by supercritical fluid technology

PURPOSE

Novel biodegradable and mucoadhesive PLGA/chitosan microparticles with the potential for use as a controlled release gastroretentive system were manufactured using supercritical CO(2) (scCO(2)) by the Particle Gas Saturated System (PGSS) technique (also called CriticalMix(TM)).

METHODS

Microparticles were produced from PLGA with the addition of mPEG and chitosan in the absence of organic solvents, surfactants and crosslinkers using the PGSS technique. Microparticle formulations were morphologically characterized by scanning electron microscope; particle size distribution was measured using laser diffraction. Microparticle surface was analyzed using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) to evaluate the presence of chitosan on the surface. Mucoadhesiveness of the microparticles was evaluated in vitro using a mucin assay employing two different kinds of mucin (Mucin type III and I-S) with different degrees of sialic acid contents, 0.5-1.5% and 9-17%, respectively.

RESULTS

The two analytical surface techniques (XPS and ToF-SIMS) demonstrated the presence of the chitosan on the surface of the particles (<100 μm), dependent on the polymer composition of the microparticles. The interaction between the mucin solutions and the PLGA/chitosan microparticles increased significantly with an increasing concentration of mucin and chitosan.

CONCLUSIONS

The strong interaction of mucin with the chitosan present on the surface of the particles suggests a potential use of the mucoadhesive carriers for gastroretentive and oral controlled drug release.