Preparation and characterization of chitosan microspheres for doxycycline delivery

Development strategy of novel drug formulations for the delivery of doxycycline in the treatment of wounds of various etiologies

Doxycycline hyclate (DOXH) is a broad-spectrum antibiotic derived synthetically from tetracycline. Despite its use in clinical practice for more than 40 years, DOXH remains an effective antibiotic with retained activity. The potential advantages of DOXH for wound healing therapy include its mechanisms of action, such as anti-inflammatory effects, antioxidant properties, modulation of cellular processes, stimulation of collagen synthesis, and antimicrobial activity. As current standards of care aim to improve wound healing by promoting rapid closure, a relevant direction is the development of novel DOXH formulations for parenteral delivery that enhance both skin regeneration and control of infectious conditions. Oral delivery is the most common and commercially available route for administering DOXH therapeutic agents. However, parenteral delivery of DOXH, where the antibiotic substance is not in a solid state (as in powdered or compressed solid form) but rather dissolved in any carrier, presents challenges regarding DOX solubility and the stability of DOXH solutions, which are major factors complicating the development of new formulations for parenteral administration. This review discusses the achievements in research strategies and the development of new pharmaceutical formulations for the delivery of doxycycline in the treatment of wounds of various etiologies.

A polyglutamic acid/tannic acid-based nano drug delivery system: Antibacterial, immunoregulation and sustained therapeutic strategies for oral ulcers

Oral ulcers are a common inflammatory mucosal ulcer, and the moist and dynamic environment in the oral cavity makes topical pharmacological treatment of oral ulcers challenging. Herein, oral ulcer tissue adhesion nanoparticles were prepared by using esterification reaction between polyglutamic acid and tannic acid, and at the same time doxycycline hydrochloride was loaded into the nanoparticles. The obtained slow drug release effect of the drug-loaded nanoparticles reduced the toxicity of the drug, and by penetrating into the fine crevice region of the wound tissue and adhering to it, they could in-situ release the carried drug more effectively and thus have shown significant antibacterial effects. In addition, tannic acid in the system conferred adhesion, antioxidant and immune regulation activities to the nanocarriers. A rat oral ulcer model based on fluorescent labeling was established to investigate the retention of nanoparticles at the ulcer, and the results showed that the retention rate of drug-loaded nanoparticles at the ulcer was 17 times higher than that of pure drug. Due to the antibacterial and immune regulation effects of the drug-loaded nanoparticles, the healing of oral ulcer wounds was greatly accelerated. Such application of doxycycline hydrochloride loaded polyglutamic acid/tannic acid nanoparticles is a novel and effective treatment strategy for oral ulcer.

Collagen membrane loaded with doxycycline through hydroxypropyl chitosan microspheres for the early reconstruction of alkali-burned cornea

Corneal alkali burn is one of the most devastating ophthalmic emergencies correlated with remarkable morbidity resulting in severe visual impairment. Appropriate intervention in the acute phase determines the eventual outcome for later corneal restoration treatment. Since the epithelium plays an essential role in inhibiting inflammation and promoting tissue repair, sustained anti-matrix metalloproteinases (MMPs) and pro-epithelialization are the prior remedies during the first week. In this study, a drug-loaded collagen membrane (Dox-HCM/Col) that could be sutured to overlay the burned cornea was developed to accelerate the early reconstruction. Doxycycline (Dox), a specific inhibitor of MMPs, was encapsulated in collagen membrane (Col) through hydroxypropyl chitosan microspheres (HCM) to develop Dox-HCM/Col, affording a preferable pro-epithelialization microenvironment and an in-situ controlled release. Results showed that loading HCM into Col prolonged the release time to 7 days, and Dox-HCM/Col could significantly suppress the expression of MMP-9 and -13 in vitro and in vivo. Furthermore, the membrane accelerated the corneal complete re-epithelialization and promoted early reconstruction within the first week. Overall, Dox-HCM/Col was a promising biomaterial membrane for treating alkali-burned cornea in the early stage, and our attempt may provide a clinically feasible method for the ocular surface reconstruction.

Drug-Loaded Chitosan Scaffolds for Periodontal Tissue Regeneration

Chitosan is a natural anionic polysaccharide with a changeable architecture and an abundance of functional groups; in addition, it can be converted into various shapes and sizes, making it appropriate for a variety of applications. This article examined and summarized current developments in chitosan-based materials, with a focus on the modification of chitosan, and presented an abundance of information about the fabrication and use of chitosan-derived products in periodontal regeneration. Numerous preparation and modification techniques for enhancing chitosan performance, as well as the uses of chitosan and its metabolites, were reviewed critically and discussed in depth in this study. Chitosan-based products may be formed into different shapes and sizes, considering fibers, nanostructures, gels, membranes, and hydrogels. Various drug-loaded chitosan devices were discussed regarding periodontal regeneration.

Mupirocin-Loaded Chitosan Microspheres Embedded in Piper betle Extract Containing Collagen Scaffold Accelerate Wound Healing Activity

This study reports the formulation of mupirocin-loaded chitosan microspheres embedded in Piper betle extract containing collagen scaffold as combinational drug delivery for improved wound healing. Selection of chitosan type (molecular weight and degree of deacetylation) was carried out based on their antibacterial efficacy. The low molecular weight chitosan was selected owing to the highest antibacterial action against gram-positive as well as gram-negative bacteria. Low molecular weight chitosan-microspheres showed spherical shape with largely smooth surface morphology, 11.81% of mupirocin loading, and its controlled release profile. The XRD, DSC thermograms, and FT-IR spectral analysis revealed the mupirocin loaded in molecularly dispersed or in amorphous form, and having no chemical interactions with the chitosan matrix, respectively. The in vivo study indicates potential effect of the mupirocin, Piper betle, and chitosan in the collagen scaffold in the wound healing efficiency with approximately 90% wound healing observed at the end of 15 days of study for combinational drug-loaded chitosan microspheres-collagen scaffold-treated group. The histopathology examination further revealed tissue lined by stratified squamous epithelium, collagen deposition, fibroblastic proliferation, and absence of inflammation indicating relatively efficient wound healing once treated with combinational drug-loaded chitosan microspheres containing scaffold.

Electrophoretic deposition of novel semi-permeable coatings on 3D-printed Ti-Nb alloy meshes for guided alveolar bone regeneration

OBJECTIVE

Guided bone regeneration (GBR) techniques use barrier membranes to augment the alveolar ridge for the site-specific growth of bone defects. However, current approaches using cast metal substructures exhibit poor adaptation to the surgical site and increased risk of infection. This study aimed to fabricate multi-functional coatings with 3D-printed porous titanium-niobium (Ti-Nb) alloy meshes to maintain space, prevent the ingrowth of fibroblasts and inhibit the colonization of bacteria for GBR.

METHODS

Ti-Nb alloy meshes were prepared by selective laser melting (SLM) and used as substrates for novel surface coatings. Porous chitosan (CS)/ gelatin (G)/ doxycycline (Dox) coatings were formed on the meshes using electrophoretic deposition (EPD) and freeze-drying. The process of EPD was characterized through Fourier transform infrared spectroscopy (FT-IR), zeta potential, and particle size analysis. The cytotoxicity of the coatings was evaluated through the culture of osteoblasts and immunostaining. The antibacterial activity of the coatings was tested using inhibition zone tests against Staphylococcus aureus (S. aureus) and scanning electron microscope (SEM). The inhibition of fibroblasts infiltration and nutrients transfer properties were analyzed using immunostaining and permeability tests.

RESULTS

High yield strength (567.5 ± 3.5 MPa) and low elastic modulus (65.5 ± 0.2 GPa) were achieved in Ti-Nb alloy bulk samples. The data of zeta potential, FT-IR and SEM indicated that porous spongy coatings were chemically bonded following EPD. In vitro analysis of CSGDox1 (containing Dox at 1 mg·mL^-1) coating revealed its antibacterial effect and biocompatibility. Moreover, the CSGDox1 coating was proved to be effective for preventing the ingrowth of fibroblasts, whilst allowing the infiltration of nutrients.

SIGNIFICANCE

This study verified that the EPD of CSGDox coatings on the 3D-printed Ti-Nb meshes can maintain space, provide antibiotic release whilst maintaining a barrier against soft-tissue growth, which is essential for the success of GBR treatment.

Modulation of Entrapment Efficiency and In Vitro Release Properties of BSA-Loaded Chitosan Microparticles Cross-Linked with Citric Acid as a Potential Protein-Drug Delivery System

Microparticles, aimed for oral protein and peptide drug delivery, were prepared via emulsion cross-linking using citric acid as cross-linker and polyglycerol polyricinoleate as surfactant. A comparative study of the interaction between chitosan and citric acid and its effect on the resulting microparticle properties was performed using different chitosan-to-cross-linker mass ratios and pH-values during fabrication of the microparticles. Non-cross-linked and cross-linked microparticles were studied in terms of size (4-12 μm), zeta potential (-15.7 to 12.8 mV), erosion (39.7-75.6%), a model protein encapsulation efficiency (bovine serum albumin) (6.8-27.6%), and loading capacity (10.4-40%). Fourier transform infrared spectroscopy and X-ray diffraction confirmed the ionic interaction between the protonated amine groups of chitosan and the carboxylate ions of the cross-linking agent. Scanning electron microscopy revealed that the non-cross-linked microparticles had an uneven shape with wrinkled surfaces, while the cross-linked formulations were spherical in shape with smooth surfaces. On the basis of these data, the role of the surfactant and microparticle structure on the release mechanism was proposed. Control of the microparticle shape and release mechanisms is expected to be crucial in developing carriers for the controlled delivery of proteins and peptides.

Enhanced efficiency in isolation and expansion of hAMSCs via dual enzyme digestion and micro-carrier

A two-stage method of obtaining viable human amniotic stem cells (hAMSCs) in large-scale is described. First, human amniotic stem cells are isolated via dual enzyme (collagenase II and DNAase I) digestion. Next, relying on a culture of the cells from porous chitosan-based microspheres in vitro, high purity hAMSCs are obtained in large-scale. Dual enzymatic (collagenase II and DNase I) digestion provides a primary cell culture and first subculture with a lower contamination rate, higher purity and a larger number of isolated cells. The obtained hAMSCs were seeded onto chitosan microspheres (CM), gelatin-chitosan microspheres (GCM) and collagen-chitosan microspheres (CCM) to produce large numbers of hAMSCs for clinical trials. Growth activity measurement and differentiation essays of hAMSCs were realized. Within 2 weeks of culturing, GCMs achieved over 1.28 ± 0.06 × 107 hAMSCs whereas CCMs and CMs achieved 7.86 ± 0.11 × 106 and 1.98 ± 0.86 × 106 respectively within this time. In conclusion, hAMSCs showed excellent attachment and viability on GCM-chitosan microspheres, matching the hAMSCs' normal culture medium. Therefore, dual enzyme (collagenase II and DNAase I) digestion may be a more useful isolation process and culture of hAMSCs on porous GCM in vitro as an ideal environment for the large-scale expansion of highly functional hAMSCs for eventual use in stem cell-based therapy.

Advances in Biomaterials and Technologies for Vascular Embolization

Minimally invasive transcatheter embolization is a common nonsurgical procedure in interventional radiology used for the deliberate occlusion of blood vessels for the treatment of diseased or injured vasculature. A wide variety of embolic agents including metallic coils, calibrated microspheres, and liquids are available for clinical practice. Additionally, advances in biomaterials, such as shape-memory foams, biodegradable polymers, and in situ gelling solutions have led to the development of novel preclinical embolic agents. The aim here is to provide a comprehensive overview of current and emerging technologies in endovascular embolization with respect to devices, materials, mechanisms, and design guidelines. Limitations and challenges in embolic materials are also discussed to promote advancement in the field.

Delivery of silver sulfadiazine and adipose derived stem cells using fibrin hydrogel improves infected burn wound regeneration

Infection control is necessary for improved burn wound regeneration. In this study contact burn wounds were induced on the dorsum of the rats and were infected with Pseudomonas aeruginosa (107cfu/ml of saline) and left overnight (12-14 hours) to establish the infection. After 12 hours, the wounds were treated with PEGylated fibrin hydrogel containing 50 mgs of silver sulfadiazine (SSD) loaded chitosan microsphere (SSD-CSM-FPEG). On day 9, SSD-CSM-FPEG treated burn wounds further received adipose derived stem cell (5×104 ASCs cells/ml) embedded in PEGylated fibrin hydrogel. Wounds were assessed for the healing outcomes such as neovascularization, granulation tissue formation, wound closure and collagen maturation. Analysis of bacterial load in the burn wound biopsies, demonstrated that SSD-CSM-FPEG significantly reduced bacterial infection, while overt infection was still observed in the untreated groups on day 14. Sequential treatment of infected wounds with SSD-CSM-FPEG followed by ASC-FPEGs (SSD-CSM-ASC-FPEG) significantly reduced bacterial colonization (9 log reduction) and pro-inflammatory cytokine (TNF-α) expression. A significant increase in neovascularization markers; NG2 and vWF was also observed. Histological analysis indicated the wounds treated with SSD-CSM-ASC-FPEG increased amount of dermal collagen matrix deposition, a thicker granulation tissue on day 21 and more mature collagen on day 28. This work demonstrates that the sequential treatment of infected burn wounds with SSD-CSM-FPEG followed by ASC-FPEG reduces bacterial infection as well as promotes neo-vascularization with improved matrix remodeling.

Potential of chitosan-based carrier for periodontal drug delivery

Periodontal diseases are chronic infectious diseases and are a major oral health burden. With the progress in the understanding of etiology, epidemiology and pathogenesis of periodontal diseases coupled with the understanding of the polymicrobial synergy in the dysbiotic oral microbial flora, several new therapeutic targets have been identified. The strategies to curb bacterial growth and production of factors that gradually destroy the tissue surrounding and supporting the teeth have been the cornerstone for inhibiting periodontitis. Systemic administration of antibiotics for the treatment of periodontitis have shown several drawbacks including: inadequate antibiotic concentration at the site of the periodontal pocket, a rapid decline of the plasma antibiotic concentration to sub-therapeutic levels, the development of microbial resistance due to sub-therapeutic drug levels and peak-plasma antibiotic concentrations which may be associated with various side effects. These obvious disadvantages have evoked an interest in the development of localized drug delivery systems that can provide an effective concentration of antibiotic at the periodontal site for the duration of the treatment with minimal side effects. A targeted sustained release device which could be inserted in the periodontal pocket and prolong the therapeutic levels at the site of action at a much lower dose is the need of the hour. Chitosan, a deacetylated derivative of chitin has attracted considerable attention owing to its special properties including antimicrobial efficacy, biodegradability, biocompatibility and non-toxicity. It also has the propensity to act as hydrating agent and display tissue healing and osteoinducting effect. The aim of this review is to shine a spotlight on the chitosan based devices developed for drug delivery application in the effective treatment of various periodontal disorders. The chitosan based carriers like fibers, films, sponge, microparticles, nanoparticles, gels that have been designed for sustained release of drug into the periodontal pocket are highlighted.

Controlled Release of Doxycycline by Magnetized Microporous MIL53(Fe); Focus on Magnetization and Drug Loading

Background:

In this research, MIL-53(Fe) was magnetized and the performance of the magnetized material as a drug delivery system for doxycycline was studied.

Objectives:

The experiments were designed to load the magnetic delivery compounds with different amount of the drug.

Methods:

The in vitro release rate of doxycycline from magnetic MIL-53(Fe) with different drug content into saline buffered fluid (SBF, pH=7.4) and phosphate buffered saline (PBS, pH=3) was then studied.

Results:

The results showed that the releasing process of the drug in PBS media achieved the equilibration within 48h with 98% of releasing efficiency, while the releasing process in SBF media (pH=7.4) was slower and the equilibrium was established within 264 h with the releasing efficiency of 95%. The amount of the released doxycycline from the samples with different drug content was measured at various time intervals.

Conclusion:

It was concluded that in PBS media after 75 h, 85, 95 and 98% of loaded doxycycline released, respectively, from the sample containing 22, 32 and 35% of the drug. In SBF media, the release was slower and after 350 h, 82, 91 and 95% of loaded doxycycline released from the samples, respectively, containing 22, 32 and 35 % of the drug. The results of this study indicated that by use of drugreleasing profile and selecting appropriate carrier dose, the released amount of the drug into the patient body can be controlled.

MBG scaffolds containing chitosan microspheres for binary delivery of IL-8 and BMP-2 for bone regeneration

Biomimetic delivery of chemokines and growth factors based on stem cell recruitment and endochondral ossification, as the key steps in natural regenerative process, has been an area of intense research in recent years. An inflammatory chemokine, interleukin-8 (IL-8), was recently reported with high recruitment efficiency of bone marrow stem cells, chondrogenic inductivity and immune regulatory functions. In this study, the effect of IL-8 action duration on bone morphogenetic protein-2 (BMP-2)-induced bone regeneration was studied to achieve an optimal synergism of these two proteins. Herein, a mesoporous bioactive glass (MBG)-based scaffold with BMP-2 entrapment and IL-8-loaded chitosan microspheres (CMs) was developed. The MBG scaffold with size-matched mesopores was adopted for the long-term sustained delivery of BMP-2; and CMs with different sizes, prepared using a modified ionotropic gelation method, were customized to match the optimal action time of IL-8. The results indicated that CMs of 100 μm diameter and medium crosslinking density exhibited an 85% release of IL-8 in 7 days and the MBG substrate exhibited a long-term sustained release of BMP-2. Furthermore, the binary delivery system exhibited excellent biocompatibility and synergistically enhanced osteoinductivity. In an in situ bone regeneration model of a rabbit radius large segmental defect, the system efficiently accelerated the whole regenerative process, with the highest bone formation amount from an early stage and the highest degree of regenerative completion. Since delivery systems for multiple cytokines have been in great demand due to the requirement of complicated biological processes, we believe that this new binary delivery system could be customized to design other dual delivery systems for improving bone-repairing biomaterials with higher regenerative efficiency.

Design and biological response of doxycycline loaded chitosan microparticles for periodontal disease treatment

The aim of this study was to develop chitosan (CS) microparticulated mucoadhesive drug delivery system (DDS) with improved therapeutic performance and biological responce. Ionotropic gelation/spray drying process was used for preparation of doxycycline hyclate (DOXY) loaded low and medium molecular weight (LMw and MMw) CS/sodium tripolyphosphate microparticles (CS/TPP MPs), further coated with ethyl cellulose (EC) using coacervation/solvent displacement technique. The relevant physico-chemical and biopharmaceutical properties were optimized using experimental design approach. Both coated and uncoated CS/TPP MPs showed high mucoadhesive potential and did not affect the viability of the tested epithelial cell line. The MPs induced slow and gradual apoptotic response in murine macrophage cell line RAW 264.7 and the observed effect depended upon formulation type and MP concentration. Biological effect of the CS-based MPs observed in our experiments point to synergism of the biological response of the carrier with the anti-inflammatory effect of DOXY.

Electrospun nanofibers comprising of silk fibroin/gelatin for drug delivery applications: Thyme essential oil and doxycycline monohydrate release study

In this study, a nanofibrous electrospun substrate based on the silk fibroin (SF) and gelatin (GT) polymers were prepared and evaluated. The SF/GT blended solutions were prepared with various ratios of GT in formic acid and electrospun to obtain bead-free fibers. Results showed that addition of GT to SF increased nanofiber's diameter, bulk hydrophilicity, surface wettability, mass loss percentage, but decreased Young's modulus, tensile strength, and porosity of the SF/GT mats. According to the obtained results, the mat containing 10% of GT was selected as the optimized mat for further studies and loaded with thyme essential oil (TEO) and doxycycline monohydrate (DCMH) as the antibacterial agents. Release studies showed a burst release of TEO from the mat within the first 3 h, while the DCMH had a sustained release during 48 h. In comparison to the TEO-loaded mat, the DCMH-loaded one showed larger inhibition zones against Staphylococcus aureus and Klebsiella pneumoniae bacteria. Meanwhile, cellular studies using mouse fibroblast L929 cells showed excellent cell-compatibility of TEO- and DCMH-loaded mats. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1092-1103, 2018.

Chitosan-doxycycline hydrogel: An MMP inhibitor/sclerosing embolizing agent as a new approach to endoleak prevention and treatment after endovascular aneurysm repair

The success of endovascular repair of abdominal aortic aneurysms remains limited due to the development of endoleaks. Sac embolization has been proposed to manage endoleaks, but current embolizing materials are associated with frequent recurrence. An injectable agent that combines vascular occlusion and sclerosing properties has demonstrated promise for the treatment of endoleaks. Moreover, the inhibition of aneurysmal wall degradation via matrix metalloproteinases (MMPs) may further prevent aneurysm progression. Thus, an embolization agent that promotes occlusion, MMP inhibition and endothelial ablation was hypothesized to provide a multi-faceted approach for endoleak treatment. In this study, an injectable, occlusive chitosan (CH) hydrogel containing doxycycline (DOX)-a sclerosant and MMP inhibitor-was developed. Several CH-DOX hydrogel formulations were characterized for their mechanical and sclerosing properties, injectability, DOX release rate, and MMP inhibition. An optimized formulation was assessed for its short-term ability to occlude blood vessels in vivo. All formulations were injectable and gelled rapidly at body temperature. Only hydrogels prepared with 0.075M sodium bicarbonate and 0.08M phosphate buffer as the gelling agent presented sufficient mechanical properties to immediately impede physiological flow. DOX release from this gel was in a two-stage pattern: a burst release followed by a slow continuous release. Released DOX was bioactive and able to inhibit MMP-2 activity in human glioblastoma cells. Preliminary in vivo testing in pig renal arteries showed immediate and delayed embolization success of 96% and 86%, respectively. Altogether, CH-DOX hydrogels appear to be promising new multifunctional embolic agents for the treatment of endoleaks.

STATEMENT OF SIGNIFICANCE

An injectable embolizing chitosan hydrogel releasing doxycycline (DOX) was developed as the first multi-faceted approach for the occlusion of blood vessels. It combines occlusive properties with DOX sclerosing and MMP inhibition properties, respectively known to prevent recanalization process and to counteract the underlying pathophysiology of vessel wall degradation and aneurysm progression. After drug release, the biocompatible scaffold can be invaded by cells and slowly degrade. Local DOX delivery requires lower drug amount and decreases risks of side effects compared to systemic administration. This new gel could be used for the prevention or treatment of endoleaks after endovascular aneurysm repair, but also for the embolization of other blood vessels such as venous or vascular malformations.

Asymmetric Collagen/chitosan Membrane Containing Minocycline-loaded Chitosan Nanoparticles for Guided Bone Regeneration

Infections caused by pathogens colonization at wound sites in the process of bone healing are considered as one of the major reasons for the failure of guided bone regeneration (GBR). The objective of this study was to prepare a novel asymmetric collagen/chitosan GBR membrane containing minocycline-loaded chitosan nanoparticles. The morphologies of the membranes and nanoparticles were observed by SEM and TEM, respectively. The characterization and biocompatibility of the membranes was evaluated. The effect of the membrane on bone regeneration was assessed using the critical-size at cranial defect model. TEM images showed the spherical morphology of the nanoparticles. The results of SEM indicated that the asymmetric membrane contained a dense collagen layer and a loose chitosan layer. An in vitro experiment showed that the membrane can inhibit bacterial growth and promote osteoblasts and fibroblasts growth. The membrane showed the ability to promote angiogenesis and enhance bone regeneration in vivo. An asymmetric collagen/chitosan GBR membrane can be fabricated by loading minocycline encapsulated chitosan nanoparticles, and shows satisfactory biocompatibility and barrier function, which enhances bone regeneration. Therefore, this antibacterial GBR membrane is a promising therapeutic approach to prevent infection and guide bone regeneration.

Effective release of a broad spectrum antibiotic from elastin-like polypeptide-collagen composite

Preparation of hydrogels that possess an effective antibiotic release profile and better mechanical properties compared to the traditionally used collagen hydrogels has the potential to minimize post-surgical infections and support wound healing. Toward this goal, we prepared elastin-like polypeptide (ELP)-collagen composite hydrogels that displayed a significantly higher elastic modulus compared to the collagen hydrogels. We then characterized the release behavior of the collagen and ELP-collagen hydrogels loaded with varying dosages (1-5% w/w) of a commonly used broad spectrum antibiotic, doxycycline hyclate. Both collagen and ELP-collagen hydrogels showed a gradual time dependent doxycycline release over a period of 5 days. The ELP-collagen hydrogels, in general, showed a slower release of the doxycycline compared to the collagen hydrogels. The released doxycycline was found to be effective against four bacterial strains (Escherichia coli, Pseudomonas aeruginosa, Streptococcus sanguinis, and methicillin-resistant Staphylococcus aureus) in a dose dependent manner. Combined with their improved mechanical properties, the gradual and effective drug release from the biocompatible ELP-collagen hydrogels shown here may be beneficial for drug delivery and tissue engineering applications.

Drug-loaded nanoparticles induce gene expression in human pluripotent stem cell derivatives

Tissue engineering and advanced manufacturing of human stem cells requires a suite of tools to control gene expression spatiotemporally in culture. Inducible gene expression systems offer cell-extrinsic control, typically through addition of small molecules, but small molecule inducers typically contain few functional groups for further chemical modification. Doxycycline (DXC), a potent small molecule inducer of tetracycline (Tet) transgene systems, was conjugated to a hyperbranched dendritic polymer (Boltorn H40) and subsequently reacted with polyethylene glycol (PEG). The resulting PEG-H40-DXC nanoparticle exhibited pH-sensitive drug release behavior and successfully controlled gene expression in stem-cell-derived fibroblasts with a Tet-On system. While free DXC inhibited fibroblast proliferation and matrix metalloproteinase (MMP) activity, PEG-H40-DXC nanoparticles maintained higher fibroblast proliferation levels and MMP activity. The results demonstrate that the PEG-H40-DXC nanoparticle system provides an effective tool to controlling gene expression in human stem cell derivatives.

A PEGylated fibrin-based wound dressing with antimicrobial and angiogenic activity

Wounds sustained under battlefield conditions are considered to be contaminated and their initial treatment should focus on decreasing this contamination and thus reducing the possibility of infection. The early and aggressive administration of antimicrobial treatment starting with intervention on the battlefield has resulted in improved patient outcomes and is considered the standard of care. Chitosan microspheres (CSM) loaded with silver sulfadiazine (SSD) were developed via a novel water-in-oil emulsion technique to address this problem. The SSD-loaded spheres were porous with needle-like structures (attributed to SSD) that were evenly distributed over the spheres. The average particle size of the SSD-CSM was 125-180 μm with 76.50 ± 2.8% drug entrapment. As a potential new wound dressing with angiogenic activity SSD-CSM particles were impregnated in polyethylene glycol (PEGylated) fibrin gels. In vitro drug release studies showed that a burst release of 27.02% in 6h was achieved, with controlled release for 72 h, with an equilibrium concentration of 27.7% (70 μg). SSD-CSM-PEGylated fibrin gels were able to exhibit microbicidal activity at 125 and 100 μg ml(-1) against Staphylococcus aureus and Pseudomonas aeruginosa, respectively. The in vitro vasculogenic activity of this composite dressing was shown by seeding adipose-derived stem cells (ASC) in SSD-CSM-PEGylated fibrin gels. The ASC spontaneously formed microvascular tube-like structures without the addition of any exogenous factors. This provides a method for the extended release of an antimicrobial drug in a matrix that may provide an excellent cellular environment for revascularization of infected wounds.

Active wound coverings: bioengineered skin and dermal substitutes

Extensive skin loss and chronic wounds present a significant challenge to the clinician. With increased understanding of wound healing, cell biology, and cell culture techniques, various synthetic dressings and bioengineered skin substitutes have been developed. These materials can protect the wound, increase healing, provide overall wound coverage, and improve patient care. The ideal skin substitute may soon become a reality.

Adipose-derived stem cell delivery into collagen gels using chitosan microspheres

Integration of stem cells to injured tissues requires an appropriate delivery device and scaffolding system. In the present study we have developed an in vitro strategy to load and release adipose-derived mesenchymal stem cells (ASC) from chitosan microspheres (CSM) into a collagen gel scaffold. Porous CSM of uniform size and composition were prepared and used as a stem cell carrier. ASC were allowed to attach to the microspheres and infiltrate through the microsphere pores. The number of viable cells was counted in vitro, using MTT and Calcein acetoxymethyl ester (AM) assays, and it showed a proportional increase with seeding density and reached a maximum cell number by 24 h. The cells inside the microspheres remained metabolically active and viable, could be retrieved from the spheres, and maintained expression of stem-cell-specific markers. Electron microscopic evaluation of the cell-microsphere complex showed that the CSM were able to support cell attachment and that the cells had infiltrated into the pores of the microspheres. The ability of the cells to proliferate and differentiate into adipogenic- and osteogenic-like precursors indicates that the cells have maintained their multipotency after migration out of the microspheres. To mimic cell delivery into a tissue, ASC-loaded CSM were embedded in type-1 collagen scaffold by mixing them with type-1 collagen solution while inducing gelation. By 14 days the cells released into the collagen gel and were able to populate the entire scaffold. When observed through transmission electron microscopy, the cells align along the collagen fibrils with a characteristic fibroblast-like morphology. This study provides a model to capture pluripotent stem cells, expand their cell number within a biomaterial scaffold in vitro, and deliver within an appropriate matrix to repair damaged tissue.