Accelerated wound closure of pressure ulcers in aged mice by chitosan scaffolds with and without bFGF

Composite material consisting of microporous β-TCP ceramic and alginate for delayed release of antibiotics

OBJECTIVE

The aim of this study was to produce a novel composite of microporous β-TCP filled with alginate and Vancomycin (VAN) to prolong the release behavior of the antibiotic for up to 28days.

MATERIAL AND METHODS

Using the flow chamber developed by the group, porous ceramics in a directional flow were filled with alginates of different composition containing 50mg/mL of antibiotics. After cross-linking the alginate with calcium ions, incubation took place in 10mL double-distilled water for 4weeks at 37°C. At defined times (1, 2, 3, 6, 9, 14, 20 and 28days), the liquid was completely exchanged and analyzed by capillary zone electrophoresis and microtiter trials. For statistical purposes, the mean and standard deviation were calculated and analyzed by ANOVA.

RESULTS

The release of VAN from alginate was carried out via an external calcium source over the entire period with concentrations above the minimal inhibitory concentration (MIC). The burst release measured 35.2±1.5%. The release of VAN from alginate with an internal calcium source could only be observed over 14days. The burst release here was 61.9±4.3%. The native alginate's burst release was 54.1±7.8%; that of the sterile alginate 40.5±6.4%. The microtiter experiments revealed efficacy over the entire study period for VAN. The MIC value was determined in the release experiments as well in a range of 0.5-2.0μg/mL against Staphylococcus aureus.

STATEMENT OF SIGNIFICANCE

Drug release systems based on β-TCP and hydrogels are well documented in literature. However, in all described systems the ceramic, as granule or powder, is inserted into a hydrogel. In our work, we do the opposite, a hydrogel which acts as reservoir for antibiotics is placed into a porous biodegradable ceramic. Eventually, this system should be applied as treatment of bone infections. Contrary to the "granule in hydrogel" composites it has the advantage of mechanical stability. Thus, it can take over functions of the bone during the healing process. For a quicker translation from our scientific research into clinical use, only FDA approved materials were used in this work.

Delivery of growth factor-based therapeutics in vascular diseases: Challenges and strategies

Either cardiovascular or peripheral vascular diseases have become the major cause of morbidity and mortality worldwide. Recently, growth factors therapeutics, whatever administrated in form of exogenous growth factors or their relevant genes have been discovered to be an effective strategy for the prevention and therapy of vascular diseases, because of their promoting angiogenesis. Besides, as an alternative, stem cell-based therapy has been also developed in view of their paracrine-mediated effect or ability of differentiation toward angiogenesis-related cells under assistance of growth factors. Despite of being specific and potent, no matter growth factors or stem cells-based therapy, their full clinical transformation is limited from bench to bedside. In this review, the potential choices of therapeutic modes based on types of different growth factors or stem cells were firstly summarized for vascular diseases. The confronted various challenges such as lack of non-invasive delivery method, the physiochemical challenge, the short half-life time, and poor cell survival, were carefully analyzed for these therapeutic modes. Various strategies to overcome these limitations are put forward from the perspective of drug delivery. The expertised design of a suitable delivery form will undoubtedly provide valuable insight into their clinical application in the regenerative medicine.

An overview of the therapeutic potential of regenerative medicine in cutaneous wound healing

The global burden of disease associated with wounds is an increasingly significant public health concern. Current treatments are often expensive, time-consuming and limited in their efficacy in chronic wounds. The challenge of overcoming current barriers associated with wound care requires innovative management techniques. Regenerative medicine is an emerging field of research that focuses on the repair, replacement or regeneration of cells, tissues or organs to restore impaired function. This article provides an overview of the pathophysiology of wound healing and reviews the latest evidence on the application of the principal components of regenerative medicine (growth factors, stem cell transplantation, biomaterials and tissue engineering) as therapeutic targets. Improved knowledge and understanding of the pathophysiology of wound healing has pointed to new therapeutic targets. Regenerative medicine has the potential to underpin the design of specific target therapies in acute and chronic wound healing. This personalised approach could eventually reduce the burden of disease associated with wound healing. Further evidence is required in the form of large animal studies and clinical trials to assess long-term efficacy and safety of these new treatments.

Polysaccharide Fabrication Platforms and Biocompatibility Assessment as Candidate Wound Dressing Materials

Wound dressings are critical for wound care because they provide a physical barrier between the injury site and outside environment, preventing further damage or infection. Wound dressings also manage and even encourage the wound healing process for proper recovery. Polysaccharide biopolymers are slowly becoming popular as modern wound dressings materials because they are naturally derived, highly abundant, inexpensive, absorbent, non-toxic and non-immunogenic. Polysaccharide biopolymers have also been processed into biomimetic platforms that offer a bioactive component in wound dressings that aid the healing process. This review primarily focuses on the fabrication and biocompatibility assessment of polysaccharide materials. Specifically, fabrication platforms such as electrospun fibers and hydrogels, their fabrication considerations and popular polysaccharides such as chitosan, alginate, and hyaluronic acid among emerging options such as arabinoxylan are discussed. A survey of biocompatibility and bioactive molecule release studies, leveraging polysaccharide's naturally derived properties, is highlighted in the text, while challenges and future directions for wound dressing development using emerging fabrication techniques such as 3D bioprinting are outlined in the conclusion. This paper aims to encourage further investigation and open up new, disruptive avenues for polysaccharides in wound dressing material development.

Morphological study on the pressure ulcer-like dermal lesions formed in the rat heel skin after transection of the sciatic nerves

Due to transection of bilateral sciatic nerves, pressure ulcer-like dermal lesion occurred in the hairy skin covering of the heel skin in almost all rats. In the present study, chronological changes of the rat heel skin after the transection were morphologically and immunohistochemically examined. In the heel skin, redness and swelling began by 3days after the operation, and open wound formed by 17days. At the redness and swelling stage, edema extensively occurred in the dermis. At the thickening stage, the epidermis at the pressed site became transiently thicker, and at the whitening stage, rapidly thinner. At these stages, the epidermis in the skin surrounding the pressed site became gradually thicker. At the yellow scar stage, the skin was covered only by necrotic tissues and horny layer. These layers were scratched during walking and turning, and the yellow scar stage became the open wound stage. Inflammatory reaction began at the thickening stage, and at the yellow scar and open wound stages, necrosis, infiltration of inflammatory cells and dilation of small blood vessels were observed. These morphological features are quite similar to those in the human pressure ulcer. These findings suggest that these dermal injuries could compare the human pressure ulcer for medical treatment and depressurization in future study.

Chitosan as a starting material for wound healing applications

Chitosan and its derivatives have attracted great attention due to their properties beneficial for application to wound healing. The main focus of the present review is to summarize studies involving chitosan and its derivatives, especially N,N,N-trimethyl-chitosan (TMC), N,O-carboxymethyl-chitosan (CMC) and O-carboxymethyl-N,N,N-trimethyl-chitosan (CMTMC), used to accelerate wound healing. Moreover, formulation strategies for chitosan and its derivatives, as well as their in vitro, in vivo and clinical applications in wound healing are described.

Prospects of chitosan-based scaffolds for growth factor release in tissue engineering

Tissue engineering is concerned about the rejuvenation and restoration of diseased and damages tissues/organs using man-made scaffolds that mimic the native environment of the cells. In recent years, a variety of biocompatible and biodegradable natural materials is employed for the fabrication of such scaffolds. Of these natural materials, chitosan is the most preferred one as it imitates the extracellular matrix (ECM) of the cells. Moreover, chitosan-based materials are pro-angiogenic and have antibacterial activity. These materials can be easily fabricated into the desired shape of the scaffolds that are suitable for tissue support and regeneration. Growth factors are small proteins/peptides that support and enhance the growth and differentiation of cells into a specific lineage. It has been observed that scaffolds capable of delivering growth factor promote tissue repair and regeneration at a faster rate when compared to scaffolds without growth factor. The present review focuses on the recent developments on chitosan-based scaffolds for the delivery of growth factors thereby improving and enhancing tissue regeneration.

Adipose stromal cells repair pressure ulcers in both young and elderly mice: potential role of adipogenesis in skin repair

More than 2.5 million patients in the U.S. require treatment for pressure ulcers annually, and the elderly are at particularly high risk for pressure ulcer development. Current therapy for pressure ulcers consists of conservative medical management for shallow lesions and aggressive debridement and surgery for deeper lesions. The current study uses a murine model to address the hypothesis that adipose-derived stromal/stem cell (ASC) treatment would accelerate and enhance pressure ulcer repair. The dorsal skin of both young (2 months old [mo]) and old (20 mo) C57BL/6J female mice was sandwiched between external magnets for 12 hours over 2 consecutive days to initiate a pressure ulcer. One day following the induction, mice were injected with ASCs isolated from congenic mice transgenic for the green fluorescent protein under a ubiquitous promoter. Relative to phosphate-buffered saline-treated controls, ASC-treated mice displayed a cell concentration-dependent acceleration of wound closure, improved epidermal/dermal architecture, increased adipogenesis, and reduced inflammatory cell infiltration. The ASC-induced improvements occurred in both young and elderly recipients, although the expression profile of angiogenic, immunomodulatory, and reparative mRNAs differed as a function of age. The results are consistent with clinical reports that fat grafting improved skin architecture in thermal injuries; the authors of this published study have invoked ASC-based mechanisms to account for their clinical outcomes. Thus, the current proof-of-principle study sets the stage for clinical translation of autologous and/or allogeneic ASC treatment of pressure ulcers.

SIGNIFICANCE

Adipose-derived stromal/stem cells (ASCs) promote the healing of pressure ulcer wounds in both young and old mice. ASCs enhance wound healing rates through adipogenic differentiation and regeneration of the underlying architecture of the skin.

Characterization of a Murine Pressure Ulcer Model to Assess Efficacy of Adipose-derived Stromal Cells

BACKGROUND

As the world's population lives longer, the number of individuals at risk for pressure ulcers will increase considerably in the coming decades. In developed countries, up to 18% of nursing home residents suffer from pressure ulcers and the resulting hospital costs can account for up to 4% of a nation's health care budget. Although full-thickness surgical skin wounds have been used as a model, preclinical rodent studies have demonstrated that repeated cycles of ischemia and reperfusion created by exposure to magnets most closely mimic the human pressure ulcer condition.

METHODS

This study uses in vivo and in vitro quantitative parameters to characterize the temporal kinetics and histology of pressure ulcers in young, female C57BL/6 mice exposed to 2 or 3 ischemia-reperfusion cycles. This pressure ulcer model was validated further in studies examining the efficacy of adipose-derived stromal/stem cell administration.

RESULTS

Optimal results were obtained with the 2-cycle model based on the wound size, histology, and gene expression profile of representative angiogenic and reparative messenger RNAs. When treated with adipose-derived stromal/stem cells, pressure ulcer wounds displayed a dose-dependent and significant acceleration in wound closure rates and improved tissue histology.

CONCLUSION

These findings document the utility of this simplified preclinical model for the evaluation of novel tissue engineering and medical approaches to treat pressure ulcers in humans.

Current wound healing procedures and potential care

In this review, we describe current and future potential wound healing treatments for acute and chronic wounds. The current wound healing approaches are based on autografts, allografts, and cultured epithelial autografts, and wound dressings based on biocompatible and biodegradable polymers. The Food and Drug Administration approved wound healing dressings based on several polymers including collagen, silicon, chitosan, and hyaluronic acid. The new potential therapeutic intervention for wound healing includes sustained delivery of growth factors, and siRNA delivery, targeting microRNA, and stem cell therapy. In addition, environment sensors can also potentially utilize to monitor and manage microenvironment at wound site. Sensors use optical, odor, pH, and hydration sensors to detect such characteristics as uric acid level, pH, protease level, and infection - all in the hopes of early detection of complications.

Design and characterization of a chitosan physical gel promoting wound healing in mice

In this study, a sterile and biocompatible chitosan (CHI) gel for wound healing applications was formulated. CHI powder was treated in autoclave (ttCHI) to prepare sterile formulations. The heat treatment modified the CHI molecular weight, as evidenced by GPC analysis, and its physical-chemical features. Differential scanning calorimetry studies indicated that the macromolecules, before and after thermal treatment, differ in the strength of water-polymer interaction leading to different viscoelastic and flow properties. Thermally treated CHI exhibited the following effects: (i) increased the proliferation and migration of human foreskin foetal fibroblasts at 24 h; (ii) accelerated wound healing (measured as area of lesion) at 3 and 10 days in an in vivo model of pressure ulcers. These effects were linked to the increase of the hydroxyproline and haemoglobin content as well as Wnt protein expression. Moreover, we found a reduction of myeloperoxidase activity and TNF-α mRNA expression. These observations suggest the potential of this novel CHI gel in wound healing and other therapeutic applications.

Chitosan-based dressings loaded with neurotensin--an efficient strategy to improve early diabetic wound healing

One important complication of diabetes mellitus is chronic, non-healing diabetic foot ulcers (DFUs). This study aims to develop and use dressings based on chitosan derivatives for the sustained delivery of neurotensin (NT), a neuropeptide that acts as an inflammatory modulator in wound healing. Three different derivatives, namely N-carboxymethyl chitosan, 5-methyl pyrrolidinone chitosan (MPC) and N-succinyl chitosan, are presented as potential biomaterials for wound healing applications. Our results show that MPC has the best fluid handling capacity and delivery profile, also being non-toxic to Raw 264.7 and HaCaT cells. NT-loaded and non-loaded MPC dressings were applied to control/diabetic wounds to evaluate their in vitro/in vivo performance. The results show that the former induced more rapid healing (50% wound area reduction) in the early phases of wound healing in diabetic mice. A NT-loaded MPC foam also reduced expression of the inflammatory cytokine TNF-α (P<0.001) and decreased the amount of inflammatory infiltrate on day 3. On day 10 MMP-9 was reduced in diabetic skin (P<0.001), significantly increasing fibroblast migration and collagen (COL1A1, COL1A2 and COL3A1) expression and deposition. These results suggest that MPC-based dressings may work as an effective support for sustained NT release to reduce DFUs.

Polymicrobial wound infections: pathophysiology and current therapeutic approaches

Acute and chronic wounds represent a very common health problem in the entire world. The dermal wounds are colonized by aerobic and anaerobic bacterial and fungal strains, most of them belonging to the resident microbiota of the surrounding skin, oral cavity and gut, or from the external environment, forming polymicrobial communities called biofilms, which are prevalent especially in chronic wounds. A better understanding of the precise mechanisms by which microbial biofilms delay repair processes together with optimizing methods for biofilm detection and prevention may enhance opportunities for chronic wounds healing. The purpose of this minireview is to assess the role of polymicrobial biofilms in the occurrence and evolution of wound infections, as well as the current and future preventive and therapeutic strategies used for the management of polymicrobial wound infections.

Exogenous bFGF or TGFβ1 accelerates healing of reconstructed dura by CO2 laser soldering in minipigs

This study aims to explore the probable mechanism of better result of dural reconstruction by CO2 laser soldering and the effect of exogenous basic fibroblast growth factor (bFGF) or transforming growth factor-beta1(TGFβ1) on wound healing. In part I of the study, ten minipigs were randomized into two equal groups, and the dural defects were reconstructed by conventional fibrin glue (FG) bonding (group I a) or by CO2 laser soldering (group Ib). In part II, 36 minipigs were randomized into three equal groups, and the dural defect was reconstructed by CO2 laser soldering; then exogenous bFGF or TGFβ1 was administered in group IIb and group IIc, respectively, while group IIa served as control group. The dural specimens were harvested at 1st week postoperatively in part I; and at 1st, 2nd, 3rd, and 4th week postoperatively in part II, they were examined for healing condition and subjected to hematoxylin-eosin (HE) staining and immunohistochemical (IHC) staining with antibodies against bFGF and TGFβ1. In part I, group Ib showed higher fibroblast cell density than group Ia (P < 0.05). The optical density (OD) for IHC staining with antibodies against bFGF of group Ib was significantly higher than that of group Ia (P < 0.05), and for IHC staining with antibodies against TGFβ1, group Ib showed positive staining while group Ia was negative. In part II, administering exogenous bFGF or TGFβ1 made a left shift of fibroblast cell number-time curve compared with control group. For specimens' IHC staining with antibodies against bFGF, the OD of group IIb was higher than that of group IIa in the corresponding time. For specimens' IHC staining with antibodies against TGFβ1, the OD of groups IIb and IIc was both higher than that of group IIa (P < 0.05 and P < 0.01, respectively). In conclusion, CO2 laser may trigger fibroblast proliferation through stimulating the secretion of bFGF and TGFβ1. Topically administering exogenous bFGF or TGFβ1 could accelerate the healing of the reconstructed dura by enhancing secretion of bFGF and/or TGFβ1 and promoting the process of fibroblast gathering-degrading.

Effects of VEGF-loaded chitosan coatings

Vascular endothelial growth factor (VEGF) is a powerful growth factor that promotes vascularization as well as osteoblastic differentiation and bone regeneration, all of which are key processes in the osseointegration of dental implants. Strategies to increase vascularization through delivery of VEGF may improve osseointegration, especially in patients with reduced bone healing potential. The aim of this study was to determine the potential of chitosan coatings on titanium to deliver VEGF and to support growth and matrix production of osteoblastic cells in vitro. Chitosan was chemically bonded to titanium coupons via silane-glutaraldehyde linker molecules and loaded with 0, 20, 50, or 100 ng of VEGF. Protein was released during a three day period with around 75% of VEGF (4.44, 11.37, and 22.10 ng/mL/cm(2) from the 20, 50, and 100 ng loaded levels, respectively) released during the first 12 h, and 90-95% of the VEGF released from the coatings by day 3. Saos-2 bone cells continued to proliferate over the 28-day period on the VEGF-loaded chitosan coatings in contrast to cells seeded on uncoated titanium, which plateaued after 14 days. Cells on uncoated titanium exhibited a peak in alkaline phosphatase expression at approximately 14 days, concomitant with the plateau in growth. While osteoblast-like cells on all chitosan coatings exhibited up to a 2-fold enhancement of the alkaline phosphatase activity and 10-fold increase in calcium deposition compared to uncoated controls, the incorporation of VEGF into the coatings did not enhance osteoblast matrix production over plain chitosan coatings throughout this study.

In vitro characterization of a chitosan skin regenerating template as a scaffold for cells cultivation

Chitosan is a marine-derived product that has been widely used in clinical applications, especially in skin reconstruction. The mammalian scaffolds derived from bovine and porcine material have many limitations, for example, prion transmission and religious concerns. Therefore, we created a chitosan skin regenerating template (SRT) and investigated the behavior of fibroblast cell-scaffold constructs. Primary human dermal fibroblasts (HDF) were isolated and then characterized using vimentin and versican. HDF were seeded into chitosan SRT at a density of 3×10⁶ cells/cm² for fourteen days. Histological analysis and live cells imaging revealed that the cell-chitosan constructs within interconnected porous chitosan showed significant interaction between the cells as well as between the cells and the chitosan. Scanning electron microscopy (SEM) analysis revealed cells spreading and covering the pores. As the pore sizes of the chitosan SRT range between 40–140 μm, an average porosity is about 93 ± 12.57% and water uptake ratio of chitosan SRT is 536.02 ± 14.29%, it is a supportive template for fibroblast attachment and has potential in applications as a dermal substitute.

Zmpste24-/- mouse model for senescent wound healing research

BACKGROUND

The graying of our population has motivated the authors to better understand age-related impairments in wound healing. To increase research throughput, the authors hypothesized that the Hutchinson-Gilford progeria syndrome Zmpste24-deficient (Zmpste24(-/-)) mouse could serve as a model of senescent wound healing.

METHODS

Using a stented excisional wound closure model, the authors tested this hypothesis on 8-week-old male Zmpste24(-/-) mice (n = 25) and age-matched male C57BL/6J wild-type mice (n = 25). Wounds were measured photogrammetrically and harvested for immunohistochemistry, enzyme-linked immunosorbent assay, and quantitative real-time polymerase chain reaction, and circulating vasculogenic progenitor cells were measured by flow cytometry.

RESULTS

Zmpste24(-/-) mice had a significant delay in wound closure compared with wild-type mice during the proliferative/vasculogenic phase. Zmpste24(-/-) wounds had decreased proliferation, increased 8-hydroxy-2'-deoxyguanosine levels, increased proapoptotic signaling (i.e., p53, PUMA, BAX), decreased antiapoptotic signaling (i.e., Bcl-2), and increased DNA fragmentation. These changes correlated with decreased local vasculogenic growth factor expression, decreased mobilization of bone marrow-derived vasculogenic progenitor cells, and decreased new blood vessel formation. Age-related impairments in wound closure are multifactorial.

CONCLUSIONS

The authors' data suggest that the Hutchinson-Gilford progeria syndrome Zmpste24(-/-) progeroid syndrome shares mechanistic overlap with normal aging and therefore might provide a uniquely informative model with which to study age-associated impairments in wound closure.

Acute and impaired wound healing: pathophysiology and current methods for drug delivery, part 2: role of growth factors in normal and pathological wound healing: therapeutic potential and methods of delivery

This is the second of 2 articles that discuss the biology and pathophysiology of wound healing, reviewing the role that growth factors play in this process and describing the current methods for growth factor delivery into the wound bed.

Controlled gentamicin release from multi-layered electrospun nanofibrous structures of various thicknesses

Polyvinyl alcohol nanofibers incorporating the wide spectrum antibiotic gentamicin were prepared by Nanospider™ needleless technology. A polyvinyl alcohol layer, serving as a drug reservoir, was covered from both sides by polyurethane layers of various thicknesses. The multilayered structure of the nanofibers was observed using scanning electron microscopy, the porosity was characterized by mercury porosimetry, and nitrogen adsorption/desorption measurements were used to determine specific surface areas. The stability of the gentamicin released from the electrospun layers was proved by high-performance liquid chromatography (HPLC) and inhibition of bacterial growth. Drug release was investigated using in vitro experiments with HPLC/MS quantification, while the antimicrobial efficacy was evaluated on Gram-positive Staphylococcus aureus and Gram-negative Pseudomonas aeruginosa. Both experiments proved that the released gentamicin retained its activity and showed that the retention of the drug in the nanofibers was prolonged with the increasing thickness of the covering layers.

Chitosan dressing promotes healing in third degree burns in mice: gene expression analysis shows biphasic effects for rapid tissue regeneration and decreased fibrotic signaling

Burns are a significant health challenge and healing can result in scar formation. Chitosan, a derivative of chitin, has been used to promote wound healing. In this study we used gene expression profiling in a mouse model of full thickness cutaneous burn to assess the benefits of treating with a chitosan lactate dressing. Three days after wounding mice treated with chitosan showed increased expression of genes associated with formation of granulation tissue. At a later time point, seven days after wounding, genes that initially showed increased expression were now down-regulated, and there was increased expression of genes involved in remodeling suggesting that the chitosan treatment results in accelerated healing. Quantitative RT-PCR showed modulated mRNA levels for TGFβ1 by the chitosan dressing. TGFβ1 initially promotes healing but extended activity can result in scarring. Importantly we found that expression was elevated at day three, but decreased at day seven suggesting that chitosan treatment will not result in scar formation, and may even be beneficial in preventing scar formation. Additionally, the biphasic regulation of expression of TGFβ1 could be a powerful biomarker for future studies of the wound-healing potential of chitosan based and other treatments for burn wounds.

Nanofibers prepared by needleless electrospinning technology as scaffolds for wound healing

Electrospun gelatin and poly-ε-caprolactone (PCL) nanofibers were prepared using needleless technology and their biocompatibility and therapeutic efficacy have been characterized in vitro in cell cultures and in an experimental model of a skin wound. Human dermal fibroblasts, keratinocytes and mesenchymal stem cells seeded on the nanofibers revealed that both nanofibers promoted cell adhesion and proliferation. The effect of nanofibers on wound healing was examined using a full thickness wound model in rats and compared with a standard control treatment with gauze. Significantly faster wound closure was found with gelatin after 5 and 10 days of treatment, but no enhancement with PCL nanofibers was observed. Histological analysis revealed enhanced epithelialisation, increased depth of granulation tissue and increased density of myofibroblasts in the wound area with gelatin nanofibers. The results show that gelatin nanofibers produced by needleless technology accelerate wound healing and may be suitable as a scaffold for cell transfer and skin regeneration.

Chitosan preparations for wounds and burns: antimicrobial and wound-healing effects

Since its discovery approximately 200 years ago, chitosan, as a cationic natural polymer, has been widely used as a topical dressing in wound management owing to its hemostatic, stimulation of healing, antimicrobial, nontoxic, biocompatible and biodegradable properties. This article covers the antimicrobial and wound-healing effects of chitosan, as well as its derivatives and complexes, and its use as a vehicle to deliver biopharmaceuticals, antimicrobials and growth factors into tissue. Studies covering applications of chitosan in wounds and burns can be classified into in vitro, animal and clinical studies. Chitosan preparations are classified into native chitosan, chitosan formulations, complexes and derivatives with other substances. Chitosan can be used to prevent or treat wound and burn infections not only because of its intrinsic antimicrobial properties, but also by virtue of its ability to deliver extrinsic antimicrobial agents to wounds and burns. It can also be used as a slow-release drug-delivery vehicle for growth factors to improve wound healing. The large number of publications in this area suggests that chitosan will continue to be an important agent in the management of wounds and burns.

Human endothelial colony forming cells undergo vasculogenesis within biphasic calcium phosphate bone tissue engineering constructs

An important consideration in bone regeneration is the need for expedited neovascularization within the defect site. Formation of a vascular network is critical for cell viability and normal function leading to tissue regeneration, but spontaneous angiogenesis is too slow to yield sufficient vessel formation. In this pilot study, human umbilical cord blood (hUCB)-derived endothelial colony forming cells (ECFCs) were evaluated for in vivo vasculogenesis in the macropores of biphasic calcium phosphate (BCP)/bone morphogenetic protein-2 (BMP-2) bone tissue engineering constructs. Constructs were implanted on the abdominal wall of NOD/SCID mice for 4 weeks. This study demonstrated in vivo vasculogenesis by human ECFCs within the macropore space of BCP/BMP-2 constructs. The human ECFC-derived vessels anastomosed with the host vasculature and perfused vessels were visible in the very center of the 5mm diameter, 2.5mm tall scaffolds. Additionally, the vessels were evenly distributed throughout the construct. This study suggests that scaffolds containing ECFCs have significant potential for expedited neovascularization in bony defects.

Pressure ulcers: description of a new model and use of mesenchymal stem cells for repair

BACKGROUND

Pressure ulcers (PUs) still represent a heavy burden on many patients and nursing institutions. Our understanding of the pathophysiology and development of new treatments are hampered by the scarcity of suitable animal models.

OBJECTIVE

Evaluation of the translational value of an easily accessible mouse model.

METHODS

PUs were induced by application of magnetic devices on the dorsal skin of mice, which causes localized ischemia. The extent of the lesions and healing rate were quantified. Variations in ischemic exposure time were compared in hairless and normal mice. A detailed histological analysis of regeneration is presented. The influence of streptozotocin-induced diabetes, skin X-irradiation and treatment of the ulcers with human mesenchymal stem cells (MSCs) was investigated using immunodeficient NOD/SCID mice.

RESULTS

Ulcers induced by this form of ischemia have many features in common with decubitus ulcers in humans. No difference between hairy and hairless mice was observed in the rate of healing of the PUs. Unexpectedly, healing was not delayed in diabetic mice, but skin X-irradiation prior to ischemia resulted in a doubling of the time to complete closure of the PUs, and delayed repair of the dermis and panniculus carnosus muscle. Intradermal transplantation of human MSCs did not accelerate healing. The grafted MSCs were short-lived and only marginally participated in regeneration by differentiating into tissue-specific cells.

CONCLUSION

The results emphasize the difference in the characteristics of PUs as compared to surgical wounds. This experimental model is recommended for preclinical research on decubitus ulcers because of its mechanistic similarity with clinical PUs and its simplicity.

Controlled release of chitosan/heparin nanoparticle-delivered VEGF enhances regeneration of decellularized tissue-engineered scaffolds

Regeneration deficiency is one of the main obstacles limiting the effectiveness of tissue-engineered scaffolds. To develop scaffolds that are capable of accelerating regeneration, we created a heparin/chitosan nanoparticle-immobilized decellularized bovine jugular vein scaffold to increase the loading capacity and allow for controlled release of vascular endothelial growth factor (VEGF). The vascularization of the scaffold was evaluated in vitro and in vivo. The functional nanoparticles were prepared by physical self-assembly with a diameter of 67–132 nm, positive charge, and a zeta potential of ∼30 mV and then the nanoparticles were successfully immobilized to the nanofibers of scaffolds by ethylcarbodiimide hydrochloride/hydroxysulfosuccinimide modification. The scaffolds immobilized with heparin/chitosan nanoparticles exhibited highly effective localization and sustained release of VEGF for several weeks in vitro. This modified scaffold significantly stimulated endothelial cells’ proliferation in vitro. Importantly, utilization of heparin/chitosan nanoparticles to localize VEGF significantly increased fibroblast infiltration, extracellular matrix production, and accelerated vascularization in mouse subcutaneous implantation model in vivo. This study provided a novel and promising system for accelerated regeneration of tissue-engineering scaffolds.

Analysis of the roles of microporosity and BMP-2 on multiple measures of bone regeneration and healing in calcium phosphate scaffolds

Osteoinductive agents, such as BMP-2, are known to improve bone formation when combined with scaffolds. Microporosity (<20 μm) has also been shown to influence bone regeneration in calcium phosphate (CaP) scaffolds. However, many studies use only the term "osteoconductive" to describe the effects of BMP-2 and microporosity on bone formation, and do not assess the degree of healing that occurred. The objective of this study was to quantify the influence of BMP-2 and microporosity on bone regeneration and healing in biphasic calcium phosphate scaffolds using multiple measures including bone volume fraction, radial distribution, and specific surface area. These measures were quantitatively compared by analyzing microcomputed tomography data and used to formally define and assess healing. A custom image segmentation program was used to segment >100 samples, with 900 images each, that were implanted in porcine mandibular defects for 3, 6, 12 and 24 weeks. The assessment of healing presented in this work demonstrates the level of detail possible in evaluating scaffold-guided bone regeneration. The analysis shows that BMP-2 and microporosity accelerate healing up to 4-fold. BMP-2 and microporosity were shown to have different and complementary roles in bone formation that effect the time needed for a defect to heal.

Treatment of skin injury due to vinorelbine extravasation using bFGF and rhGM-CSF: an experimental study in a murine model

BACKGROUND AND OBJECTIVE

A murine model of skin injury from vinorelbine extravasation was established to evaluate the treatment efficacy of basic fibroblast growth factor (bFGF) and recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF).

MATERIALS AND METHOD

Experimental models were divided into bFGF, rhGM-CSF, and control (saline) groups, with 40 mice in each group. Edema and ulceration were measured on Days 1, 3, 5, 7, 10, 14, and 18 after the onset of extravasation; injuries were examined pathomorphologically in three mice/group/time point.

RESULTS

Edema reached maximum size on Day 3 in the bFGF and rhGM-CSF groups and Day 5 in the control group. The difference between the two experimental groups was not significant; differences between the control group and the experimental groups were statistically significant at all time points. Edema and ulceration began to improve on Day 10 in the bFGF and rhGM-CSF groups and Day 18 in the control group. Healing duration was 14-18 days in the experimental groups, with a (not significantly) shorter duration in the bFGF group. Healing was completed by Day 27.5 in the control group. Pathomorphological evaluation showed regular re-epithelization and newly formed granulation tissue in the bFGF and rhGM-CSF groups on Day 13. In the control group, wounds were partially healed, edema and shallow ulcers existed, and epithelization was fragile and disorganized on Day 18.

CONCLUSIONS

bFGF and rhGM-CSF are useful for the treatment of skin injury due to vinorelbine extravasation, but bFGF may be slightly more effective in decreasing time and improving quality of healing.

The effect of BMP-2 on micro- and macroscale osteointegration of biphasic calcium phosphate scaffolds with multiscale porosity

It is well established that scaffolds for applications in bone tissue engineering require interconnected pores on the order of 100 microm for bone in growth and nutrient and waste transport. As a result, most studies have focused on scaffold macroporosity (>100 microm). More recently researchers have investigated the role of microporosity in calcium phosphate -based scaffolds. Osteointegration into macropores improves when scaffold rods or struts contain micropores, typically defined as pores less than approximately 50 microm. We recently demonstrated multiscale osteointegration, or growth into both macropores and intra-red micropores (<10 microm), of biphasic calcium phosphate (BCP) scaffolds. The combined effect of BMP-2, a potent osteoinductive growth factor, and multiscale porosity has yet to be investigated. In this study we implanted BCP scaffolds into porcine mandibular defects for 3, 6, 12 and 24 weeks and evaluated the effect of BMP-2 on multiscale osteointegration. The results showed that given this in vivo model BMP-2 influences osteointegration at the microscale, but not at the macroscale, but not at the macroscale. Cell density was higher in the rod micropores for scaffolds containing BMP-2 compared with controls at all time points, but BMP-2 was not required for bone formation in micropores. In contrast, there was essentially no difference in the fraction of bone in macropores for scaffolds with BMP-2 compared with controls. Additionally, bone in macropores seemed to have reached steady-state by 3 weeks. Multiscale osteointegration results in bone-scaffold composites that are fully osteointegrated, with no 'dead space'. These composites are likely to contain a continuous cell network as well as the potential for enhanced load transfer and improved mechanical properties.

Chitosan-based hydrogels for controlled, localized drug delivery

Hydrogels are high-water content materials prepared from cross-linked polymers that are able to provide sustained, local delivery of a variety of therapeutic agents. Use of the natural polymer, chitosan, as the scaffold material in hydrogels has been highly pursued thanks to the polymer's biocompatibility, low toxicity, and biodegradability. The advanced development of chitosan hydrogels has led to new drug delivery systems that release their payloads under varying environmental stimuli. In addition, thermosensitive hydrogel variants have been developed to form a chitosan hydrogel in situ, precluding the need for surgical implantation. The development of these intelligent drug delivery devices requires a foundation in the chemical and physical characteristics of chitosan-based hydrogels, as well as the therapeutics to be delivered. In this review, we investigate the newest developments in chitosan hydrogel preparation and define the design parameters in the development of physically and chemically cross-linked hydrogels.

Naturally derived materials-based cell and drug delivery systems in skin regeneration

The objective of regenerative medicine is to provide cells with a local environment of artificial extracellular matrix where they can proliferate and differentiate efficiently and therefore, induce the repair of defective tissues according to the natural healing potential of patients. For this purpose, naturally derived materials are being widely used because of their similarities to the extracellular matrix, typically good biocharacteristics and inherent cellular interaction. Also, natural polymers can be engineered to release growth factors and related agents in response to physiologic signals to imitate the natural healing process and to promote fast tissue regeneration and reduce scarring in wounds. Although synthetic materials have been used extensively in tissue engineering fields, this review illustrates the contribution of natural materials and natural materials-based protein delivery systems to regenerative medicine research, with emphasis on the application of multifunctional vehicles for cell and growth factor delivery in skin regeneration research.