In vivo evaluation of a novel alginate dressing

Bioarchitectural Design of Bioactive Biopolymers: Structure-Function Paradigm for Diabetic Wound Healing

Chronic wounds such as diabetic ulcers are a major complication in diabetes caused by hyperglycemia, prolonged inflammation, high oxidative stress, and bacterial bioburden. Bioactive biopolymers have been found to have a biological response in wound tissue microenvironments and are used for developing advanced tissue engineering strategies to enhance wound healing. These biopolymers possess innate bioactivity and are biodegradable, with favourable mechanical properties. However, their bioactivity is highly dependent on their structural properties, which need to be carefully considered while developing wound healing strategies. Biopolymers such as alginate, chitosan, hyaluronic acid, and collagen have previously been used in wound healing solutions but the modulation of structural/physico-chemical properties for differential bioactivity have not been the prime focus. Factors such as molecular weight, degree of polymerization, amino acid sequences, and hierarchical structures can have a spectrum of immunomodulatory, anti-bacterial, and anti-oxidant properties that could determine the fate of the wound. The current narrative review addresses the structure-function relationship in bioactive biopolymers for promoting healing in chronic wounds with emphasis on diabetic ulcers. This review highlights the need for characterization of the biopolymers under research while designing biomaterials to maximize the inherent bioactive potency for better tissue regeneration outcomes, especially in the context of diabetic ulcers.

Fabrication, Property and Application of Calcium Alginate Fiber: A Review

As a natural linear polysaccharide, alginate can be gelled into calcium alginate fiber and exploited for functional material applications. Owing to its high hygroscopicity, biocompatibility, nontoxicity and non-flammability, calcium alginate fiber has found a variety of potential applications. This article gives a comprehensive overview of research on calcium alginate fiber, starting from the fabrication technique of wet spinning and microfluidic spinning, followed by a detailed description of the moisture absorption ability, biocompatibility and intrinsic fire-resistant performance of calcium alginate fiber, and briefly introduces its corresponding applications in biomaterials, fire-retardant and other advanced materials that have been extensively studied over the past decade. This review assists in better design and preparation of the alginate bio-based fiber and puts forward new perspectives for further study on alginate fiber, which can benefit the future development of the booming eco-friendly marine biomass polysaccharide fiber.

Fundamentals and Current Strategies for Peripheral Nerve Repair and Regeneration

A body of evidence indicates that peripheral nerves have an extraordinary yet limited capacity to regenerate after an injury. Peripheral nerve injuries have confounded professionals in this field, from neuroscientists to neurologists, plastic surgeons, and the scientific community. Despite all the efforts, full functional recovery is still seldom. The inadequate results attained with the "gold standard" autograft procedure still encourage a dynamic and energetic research around the world for establishing good performing tissue-engineered alternative grafts. Resourcing to nerve guidance conduits, a variety of methods have been experimentally used to bridge peripheral nerve gaps of limited size, up to 30-40 mm in length, in humans. Herein, we aim to summarize the fundamentals related to peripheral nerve anatomy and overview the challenges and scientific evidences related to peripheral nerve injury and repair mechanisms. The most relevant reports dealing with the use of both synthetic and natural-based biomaterials used in tissue engineering strategies when treatment of nerve injuries is envisioned are also discussed in depth, along with the state-of-the-art approaches in this field.

Alginate Hydrogels with Embedded ZnO Nanoparticles for Wound Healing Therapy

INTRODUCTION

In this in-vitro study, we designed a 3D printed composite of zinc oxide (ZnO) nanoparticles (NPs) with photocatalytic activities encapsulated within hydrogel (alginate) constructs, for antibacterial purposes applicable towards wound healing. We primarily sought to confirm the mechanical properties and cell compatibility of these ZnO NP infused scaffolds.

METHODS

The antibacterial property of the ZnO NPs was confirmed by hydroxyl radical generation using ultraviolet (U.V.) photocatalysis. Titanium dioxide (TiO2), a well-known antibacterial compound, was used as a positive control (1% w/v) for the ZnO NP-based alginate constructs and their antibacterial efficacies compared. Among the ZnO group, 3D printed gels containing 0.5% and 1% w/v of ZnO were analyzed and compared with manually casted samples via SEM, swelling evaluation, and rheological analysis. Envisioning an in-vivo application for the 3D printed ZnO NP-based alginates, we studied their antibacterial properties by bacterial broth testing, cytocompatibility via live/dead assay, and moisture retention capabilities utilizing a humidity sensor.

RESULTS

3D printed constructs revealed significantly greater pore sizes and enhanced structural stability compared to manually casted samples. For all samples, the addition of ZnO or TiO2 resulted in significantly stiffer gels in comparison with the alginate control. Bacterial resistance testing on Staphylococcus epidermidis indicated the addition of ZnO NPs to the gels decreased bacterial growth when compared to the alginate only gels. Cell viability of STO-fibroblasts was not adversely affected by the addition of ZnO NPs to the alginate gels. Furthermore, the addition of increasing doses of ZnO NPs to the alginate demonstrated increased humidity retention in gels.

DISCUSSION

The customization of 3D printed alginates containing antibacterial ZnO NPs leads to an alternative that allows accessible mobility of molecular exchange required for improving chronic wound healing. This scaffold can provide a cost-effective and durable antibacterial treatment option.

Accelerating healing of excisional wound with alginate hydrogel containing naringenin in rat model

Wounds have always been considered as one of the most common physical damages. Therefore, various researches have been conducted to find an appropriate method to improve wound healing process. Among various materials, since hydrogels have appropriate properties for wound healing, they are widely used for this purpose. In this study, to develop a potential wound dressing, different concentrations of naringenin (0%, 1%, 10% and 20%) were incorporated in alginate hydrogel followed by evaluating its characters such as morphology, swelling properties, weight loss, antibacterial activity, releasing profile of the naringenin, hemo-, and cytocompatibility. Finally, to evaluate the effect of developed hydrogels on wound healing, the full-thickness dermal wound model in rat was used. Our results provided that the prepared hydrogels have appropriate porosity (86.7 ± 5.3%) with the interconnected pores. Moreover, weight loss assessment confirmed that fabricated hydrogels have suitable biodegradability (about 89% after 14 days). MTT assay also revealed the positive effect of hydrogels on cell viabilities, and they have no toxicity effect on cells. In vivo study indicated that the prepared hydrogels had better wound closure than the gauze-treated wound (the control), and alginate/20% naringenin group had the best wound closure among other groups. All in all, this study concluded that alginate/naringenin hydrogel has positive effect on wound healing process, and it can be used to treat skin injuries in the clinic. Graphical abstract.

Recent advances on biomedical applications of scaffolds in wound healing and dermal tissue engineering

The tissue engineering field has developed in response to the shortcomings related to the replacement of the tissues lost to disease or trauma: donor tissue rejection, chronic inflammation and donor tissue shortages. The driving force behind the tissue engineering is to avoid the mentioned issues by creating the biological substitutes capable of replacing the damaged tissue. This is done by combining the scaffolds, cells and signals in order to create the living, physiological, three-dimensional tissues. A wide variety of skin substitutes are used in the treatment of full-thickness injuries. Substitutes made from skin can harbour the latent viruses, and artificial skin grafts can heal with the extensive scarring, failing to regenerate structures such as glands, nerves and hair follicles. New and practical skin scaffold materials remain to be developed. The current article describes the important information about wound healing scaffolds. The scaffold types which were used in these fields were classified according to the accepted guideline of the biological medicine. Moreover, the present article gave the brief overview on the fundamentals of the tissue engineering, biodegradable polymer properties and their application in skin wound healing. Also, the present review discusses the type of the tissue engineered skin substitutes and modern wound dressings which promote the wound healing.

Regeneration of rat corpora cavernosa tissue by transplantation of CD133+ cells derived from human bone marrow and placement of biodegradable gel sponge sheet

The objective is to develop an easier technique for regenerating corpora cavernosa tissue through transplantation of human bone marrow-derived CD133 + cells into a rat corpora cavernosa defect model. We excised 2 mm × 2 mm squares of the right corpora cavernosa of twenty-three 8-week-old male nude rats. Alginate gel sponge sheets supplemented with 1 × 10 4 CD133 + cells were then placed over the excised area of nine rats. Functional and histological evaluations were carried out 8 weeks later. The mean intracavernous pressure/mean arterial pressure ratio for the nine rats (0.34258 ± 0.0831) was significantly higher than that for eight rats with only the excision (0.0580 ± 0.0831, P = 0.0238) and similar to that for five rats for which the penis was exposed, and there was no excision (0.37228 ± 0.1051, P = 0.8266). Immunohistochemical analysis revealed that the nine fully treated rats had venous sinus-like structures and quantitative reverse transcription polymerase chain reaction analysis of extracts from their alginate gel sponge sheets revealed that the amounts of mRNA encoding the nerve growth factor (NGF), and vascular endothelial growth factor (VEGF) were significantly higher than those for rats treated with alginate gel sheets without cell supplementation (NGF: P = 0.0309; VEGF: P < 0.0001). These findings show that transplantation of CD133 + cells accelerates functional and histological recovery in the corpora cavernosa defect model.

Preparation and characterization of gatifloxacin-loaded sodium alginate hydrogel membranes supplemented with hydroxypropyl methylcellulose and hydroxypropyl cellulose polymers for wound dressing

Introduction:

The aim of this study is to evaluate gatifloxacin-loaded sodium alginate hydrogel membranes, supplemented with glycerol (a plasticizer), glutaraldehyde (a cross-linking agent), and hydroxypropyl methylcellulose (HPMC) or hydroxypropyl cellulose (HPC) polymers, as potential wound dressing materials based on their physicochemical properties and the sustain-release phenomenon.

Materials and Methods:

The physicochemical properties of the prepared hydrogel membranes were evaluated by several methods including Fourier transform infrared and differential scanning calorimetry. Different techniques were used to assess the swelling behavior, tensile strength and elongation, % moisture absorption, % moisture loss, water vapor transmission rate (WVTR), and microbial penetration for the hydrogel membranes. In vitro gatifloxacin release from the hydrogel membranes was examined using the United States Pharmacopeia XXIII dissolution apparatus. Four kinetics models (zero-order, first-order, Higuchi equation, and Korsmeyer-Peppas equation) were applied to study drug release kinetics.

Results:

The addition of glycerol, glutaraldehyde, HPMC, and HPC polymers resulted in a considerable increase in the tensile strength and flexibility/elasticity of the hydrogel membranes. WVTR results suggest that hydrated hydrogel membranes can facilitate water vapor transfer. None of the hydrogel membranes supported microbial growth. HPMC-treated and HPC-treated hydrogel membranes allow slow, but sustained, release of gatifloxacin for 48 h. Drug release kinetics revealed that both diffusion and dissolution play an important role in gatifloxacin release.

Conclusions:

Given their physicochemical properties and gatifloxacin release pattern, HPMC-treated and HPC-treated hydrogel membranes exhibit effective and sustained drug release. Furthermore, HPMC-treated and HPC-treated hydrogel membranes possess physiochemical properties that make them effective and safe wound dressing materials.

Evaluation of skin regeneration after burns in vivo and rescue of cells after thermal stress in vitro following treatment with a keratin biomaterial

Thermal burns typically display an injury pattern dictated by the transfer of the thermal energy into the skin and underlying tissues and creation of three zones of injury represented by a necrotic zone of disrupted cells and tissue, an intermediate zone of injured and dying cells, and a distant zone of stressed cells that will recover with proper treatment. The wound healing capabilities of a keratin biomaterial hydrogel were studied in two pilot studies, one using a chemical burn model in mice and the other a thermal burn model in swine. In both studies, keratin was shown to prevent enlargement of the initial wound area and promote faster wound closure. Interestingly, treating thermally stressed dermal fibroblast in culture demonstrated that soluble keratin was able to maintain cell viability and promote proliferation. Separation of so-called alpha and gamma fractions of the keratin biomaterial had differential effects, with the gamma fraction producing more pronounced cell survival and recovery. These results suggest that the gamma fraction, composed essentially of degraded alpha keratin proteins, may facilitate cell rescue after thermal injury. Treatment of burns with gamma keratin may therefore represent a potential therapy for wounds with an intermediate zone of damaged tissue that has the potential to contribute to spontaneous healing.

Recent advances in topical wound care

There are a wide variety of dressing techniques and materials available for management of both acute wounds and chronic non-healing wounds. The primary objective in both the cases is to achieve a healed closed wound. However, in a chronic wound the dressing may be required for preparing the wound bed for further operative procedures such as skin grafting. An ideal dressing material should not only accelerate wound healing but also reduce loss of protein, electrolytes and fluid from the wound, and help to minimize pain and infection. The present dictum is to promote the concept of moist wound healing. This is in sharp contrast to the earlier practice of exposure method of wound management wherein the wound was allowed to dry. It can be quite a challenge for any physician to choose an appropriate dressing material when faced with a wound. Since wound care is undergoing a constant change and new products are being introduced into the market frequently, one needs to keep abreast of their effect on wound healing. This article emphasizes on the importance of assessment of the wound bed, the amount of drainage, depth of damage, presence of infection and location of wound. These characteristics will help any clinician decide on which product to use and where,in order to get optimal wound healing. However, there are no ‘magical dressings’. Dressings are one important aspect that promotes wound healing apart from treating the underlying cause and other supportive measures like nutrition and systemic antibiotics need to be given equal attention.

Electrospun zwitterionic poly(sulfobetaine methacrylate) for nonadherent, superabsorbent, and antimicrobial wound dressing applications

Zwitterionic poly(sulfobetaine methacrylate) (PSBMA) has been well studied for its superhydrophilic and ultralow biofouling properties, making it a promising material for superabsorbent and nonadherent wound dressings. Electrospinning provides multiple desirable features for wound dressings, including high absorptivity due to high surface-area-to-volume ratio, high gas permeation, and conformability to contour of the wound bed. The goal of this work is to develop a fibrous membrane of PSBMA via electrospinning and evaluate its properties related to wound dressing applications. Being superhydrophilic, PSBMA fibers fabricated by a conventional electrospinning method would readily dissolve in water, whereas if cross-linker is added, the formation of hydrogel would prevent electrospinning. A three-step polymerization-electrospinning-photo-cross-linking process was developed in this work to fabricate the cross-linked electrospun PSBMA fibrous membrane. Such electrospun membrane was stable in water and exhibited high water absorption of 353% (w/w), whereas the PSBMA hydrogel only absorbed 81% water. The electrospun membrane showed strong resistance to protein adsorption and cell attachment. Bacterial adhesion studies using Gram negative P. aeruginosa and Gram positive S. epidermidis showed that the PSBMA electrospun membrane was also highly resistant to bacterial adhesion. The Ag(+)-impregnated electrospun PSBMA membrane was shown microbicidal, against both S. epidermidis and P. aeruginosa. Such electrospun PSBMA membrane is ideal for a novel type of nonadherent, superabsorbent, and antimicrobial wound dressing. The superior water absorption aids in fluid removal from highly exudating wounds while keeping the wound hydrated to support healing. Because of the resistance to protein, cell, and bacterial adhesion, the dressing removal will neither cause patients' pain nor disturb the newly formed tissues. The dressing also prevents the attachment of environmental bacteria and offers broad-spectrum antimicrobial activity. It is the first work to develop the water-stable electrospun PSBMA membrane, which has great potential for wound dressing and other applications.

Alginates: Existing and Potential Biotechnological and Medical Applications

The present chapter on alginates in biotechnology and medicine comprises a description of traditional uses where alginates have been used as devices in e.g. wound dressings, as well as an in-depth introduction to possible future applications. The latter area is based on new scientific information on the immunostimulating properties of certain alginate sequences, as well as on the popularity gained by the alginate as immobilization matrix for cells. The latter opens up the use of alginate encapsulated cells for specific cell transplantation provided that the properties of the capsules are properly understood and controlled.

Biological activity of laminin peptide-conjugated alginate and chitosan matrices

Laminin active peptide-conjugated chitosan mambranes have been previously demonstrated as a useful biomaterial for tissue engineering. Here, three laminin active peptides, A99 (AGTFALRGDNPQG), AG73 (RKRLQVQLSIRT), and EF1zz (ATLQLQEGRLHFXFDLGKGR, X: Nle), which interact with integrin αvβ3, syndecans, and integrin α2β1, respectively, were conjugated to alginate and evaluated the biological activities. A99-alginate (3-3000 ng/mm(2)) promoted cell attachment depending on the amount of alginate. More than 300 ng/mm(2) of the A99-alginate matrices effectively promoted cell attachment, cell spreading with well-organized actin stress fibers, and neurite outgrowth. AG73- and EF1zz-alginates promoted strong cell attachment at the all amounts (3-3000 ng/mm(2)). A99-alginate (30-3000 ng/mm(2)) promoted strong neurite outgrowth but lower amounts of A99-alginate (3 ng/mm(2)) showed weak activity. In contrast, AG73-alginates (3-30 ng/mm(2)) showed strong neurite outgrowth activity but higher amounts of AG73-alginate (300-3000 ng/mm(2)) decreased the activity. These data indicate that neurite outgrowth activity of peptide-alginate matrices is peptide specific and the activity is dependent on the amount of alginate. Further, biological activities of the peptides on alginate and chitosan matrices were different, suggesting that the integrin- and syndecan-mediated cellular functions on the peptide-matrices are highly influenced by the scaffold structure including polysaccharide types and amounts. The laminin active peptide-conjugated alginate and chitosan matrices can control receptor type specific functions and are useful for tissue engineering.

In vitro microbial inhibition and cellular response to novel biodegradable composite wound dressings with controlled release of antibiotics

About 70% of all people with severe burns die from related infections, despite advances in treatment regimens and the best efforts of nurses and doctors. Although silver-eluting wound dressings are available for addressing this problem, there is growing evidence of the deleterious effects of such dressings in delaying the healing process owing to cellular toxicity. A new concept of antibiotic-eluting composite wound dressings is described here. These dressings are based on a polyglyconate mesh coated with a porous poly-(dl-lactic-co-glycolic acid) matrix loaded with antibiotic drugs. The effect of antibiotic release on bacterial inhibition was studied, and cell cytotoxicity was examined. The dressings resulted in a 99.99% decrease in the viable counts of Pseudomonas aeruginosa and Staphylococcus albus at very high initial inoculations of 10⁷-10⁸ CFU ml⁻¹ after only 1 day, while such a decrease in Staphylococcus aureus was obtained within 3 days. Bacterial inhibition zones around the dressing material were found to persist for 2 weeks, indicating a long-lasting antimicrobial effect. Despite severe toxicity to bacteria, the dressing material was found to have no toxic effect on cultured fibroblasts, indicating that the new antibiotic-eluting wound dressings represent an effective option for selective treatment of bacterial infections.

Synthetic alginate is a carrier of OP-1 for bone induction

Bone morphogenetic proteins (BMPs) can induce bone formation in vivo when combined with appropriate carriers. Several materials, including animal collagens and synthetic polymers, have been evaluated as carriers for BMPs. We examined alginate, an approved biomaterial for human use, as a carrier for BMP-7. In a mouse model of ectopic bone formation, the following four carriers for recombinant human OP-1 (BMP-7) were tested: alginate crosslinked by divalent cations (DC alginate), alginate crosslinked by covalent bonds (CB alginate), Type I atelocollagen, and poly-D,L-lactic acid-polyethyleneglycol block copolymer (PLA-PEG). Discs of carrier materials (5-mm diameter) containing OP-1 (3-30 microg) were implanted beneath the fascia of the back muscles in six mice per group. These discs were recovered 3 weeks after implantation and subjected to radiographic and histologic studies. Ectopic bone formation occurred in a dose-dependent manner after the implantation of DC alginate, atelocollagen, and PLA-PEG, but occurred only at the highest dose implanted with CB alginate. Bone formation with DC alginate/OP-1 composites was equivalent to that with atelocollagen/OP-1 composites. Our data suggest DC alginate, a material free of animal products that is already approved by the FDA and other authorities, is a safe and potent carrier for OP-1. This carrier may also be applicable to various other situations in the orthopaedic field.

Hydrogels in regenerative medicine

Hydrogels, due to their unique biocompatibility, flexible methods of synthesis, range of constituents, and desirable physical characteristics, have been the material of choice for many applications in regenerative medicine. They can serve as scaffolds that provide structural integrity to tissue constructs, control drug and protein delivery to tissues and cultures, and serve as adhesives or barriers between tissue and material surfaces. In this work, the properties of hydrogels that are important for tissue engineering applications and the inherent material design constraints and challenges are discussed. Recent research involving several different hydrogels polymerized from a variety of synthetic and natural monomers using typical and novel synthetic methods are highlighted. Finally, special attention is given to the microfabrication techniques that are currently resulting in important advances in the field.

The biodegradability of poly(Pro-Hyp-Gly) synthetic polypeptide and the promotion of a dermal wound epithelialization using a poly(Pro-Hyp-Gly) sponge

Collagens are widely used in medical applications, but animal-derived collagens have several drawbacks, such as low thermal stability, nonspecific cell attachment, and susceptibility to contamination by infectious pathogens, such as prions, which may transfect humans. We have previously reported the chemical synthesis of polypeptides consisting of a Pro-Hyp-Gly sequence and the high thermostability of their triple-helical structure. To clarify the biomaterial characteristics of the poly(Pro-Hyp-Gly) polypeptide, we assessed its biodegradability and its capability for skin regeneration. Eight weeks after implantation, a poly(Pro-Hyp-Gly) freeze-dried sponge embedded subcutaneously into a rat dorsal area degraded at the same rate as Terudermis, which is made from bovine type I atelocollagen and is used as an artificial dermis. Surprisingly, compared with Terudermis, the poly(Pro-Hyp-Gly) sponge significantly promoted epithelialization of a full-thickness wound on a rabbit's ear pad. This chemically synthesized polypeptide may be useful as a scaffold for tissue engineering and tissue regeneration.

Treating the chronic wound: A practical approach to the care of nonhealing wounds and wound care dressings

Chronic wounds are a major healthcare problem costing the United States billions of dollars a year. The American Academy of Dermatology has underscored the significance of wound care in dermatological practice. It is critical for all dermatologists to understand the elements of diagnosis and therapy. We emphasize major aspects of diagnosis and present a simple classification of wound dressings with guidelines for usage and relative cost data.

LEARNING OBJECTIVE

After completing this learning activity, participants should be able to diagnose common types of chronic wounds, formulate a therapeutic plan, and describe the major classes of topical therapies and dressings for the chronic wound.

Stabilized hemocompatible coating of nitinol devices based on photo-cross-linked alginate/heparin multilayer

A novel stabilized hemocompatible multicomponent coating was engineered by consecutive alternating adsorption of two polysaccharides, alginate (Alg) and heparin (Hep), onto a Nitinol surface via electrostatic interaction in combination with photoreaction in situ. For this purpose, a photosensitive cross-linker, p-diazonium diphenyl amine polymer (PA), was used as an interlayer between alginate and heparin. The optical intensity of UV/vis spectra increased linearly with the number of layers, indicating the buildup of a multilayer structure and uniform coating. Photo-cross-linking resulted in higher stability without compromising its catalytic capacity to promote antithrombin III (ATIII)-mediated thrombin inactivation. Chromogenic assays for heparin activity proved definitively that anticoagulation activity really comes from surface-bound heparin in multilayer film, not from solution-phase free heparin that has leaked from multilayer film. The activated partial thromboplastin time (aPTT) assay showed that both (PA/Hep)8- and (PA/Alg/PA/Hep)4-coated Nitinol were less thrombogenic than the uncoated one. Yet, the latter was found to be more stable under a continuous shaken wash. In addition, (PA/Alg/PA/Hep)4 film exhibited lower surface roughness and higher hydrophilicity than (PA/Hep)8. As a result, hemolysis of (PA/Alg/PA/Hep)4 (0.34 +/- 0.064%) was lower than (PA/Hep)8 (0.52 +/- 0.241%). The naked Nitinol and (PA/Hep)8-coated Nitinol showed relatively strong platelet adhesion. On the contrary, no sign of any cellular matter was seen on the (PA/Alg/PA/Hep)4 surface. It is believed that the phenomenon of interlayer diffusion resulted in blended structures, hence, the enhanced wettability and antifouling properties after the incorporation of alginate layers. It is likely that the cooperative effect of alginate and heparin led to the excellent blood compatibility of the (PA/Alg/PA/Hep)4 coating. To simplify, there is greater advantage in utilizing cross-linked alginate/heparin surfaces rather than merely the heparin surface for improving blood- and tissue-compatible devices.

Injectable gel with synthetic collagen-binding peptide for enhanced osteogenesis in vitro and in vivo

A synthetic peptide denoted as collagen-binding motif (CBM) was identified from osteopontin (OPN), a multisubunit extracellular matrix (ECM) protein, by enzymatic digestion with chymotrypsin. The aim of this study was to examine the feasibility of identified CBM peptide as an active component of gel type scaffold material in osteogenesis. The binding of CBM peptide to collagen was specific and presented high affinity. Cell adhesion and growth on CBM peptide-immobilized gel were significantly increased as compared with those on gel with control peptide or without peptide. The CBM peptide-immobilized gel increased osteoblastic differentiation, followed by marked bone formation in the rabbit calvarial defect sites at 4 weeks. Taken together, the injectable gel with synthetic CBM peptide has a potential to induce osteogenesis in vitro and in vivo, suggesting its clinical application in bone regeneration procedure.

Preparation of carbon nanotube-alginate nanocomposite gel for tissue engineering

A novel scaffold material based on an alginate hydrogel which contained carbon nanotubes (CNTs) was prepared, and its mechanical property and biocompatibility evaluated. Soluble CNTs were prepared with acid treatment and dispersed in sodium alginate solution as a cross-linker. After which, the mechanical property (elastic deformation), saline sorption, histological reaction, and cell viability of the resultant nanocomposite gel (CNT-Alg gel) were evaluated. The CNT-Alg gel showed faster gelling and higher mechanical strength than the conventional alginate gel. Saline sorption amount of freeze-dried CNT-Alg gel was equal to that of the alginate gel. In terms of histological evaluation and cell viability assay, CNT-Alg gel exhibited a mild inflammatory response and non-cytotoxicity. These results thus suggested that CNT-Alg gel could be useful as a scaffold material in tissue engineering with the sidewalls of CNTs acting as active sites for chemical functionalization.

Cavernous nerve regeneration by biodegradable alginate gel sponge sheet placement without sutures

OBJECTIVES

Alginate, a biodegradable polysaccharide, may be applied to facilitate nerve regeneration. We attempted to regenerate excised cavernous nerves by filling the gap with a biodegradable alginate gel sponge sheet without sutures.

METHODS

Bilateral cavernous nerves of male Wistar rats were excised to make an approximately 2-mm gap. A piece of freeze-dried alginate sheet was then placed over the gap to cover each stump without suturing (alginate group). We also performed sham operations (sham group) and bilateral nerve excision alone (excision group).

RESULTS

Erection was confirmed visually by mating behavior in 9%, 36% and 73% of alginate rats at 2, 4, and 12 weeks, respectively. In contrast, no excision rats had an erection. At 12 weeks postoperatively, electrical stimulation of the pelvic plexus increased intracavernous pressure in the sham group and alginate rats with restored erectile function. However, no increase occurred in the excision group. In a retrograde neural tracing study with FluoroGold at 12 weeks, rich FluoroGold-positive cells were observed in the sham group and alginate rats with restoration, but very few were found in the excision group. Double-labeled immunochemistry with anti-S-100 and beta-tubulin III antibodies showed that the neural gap was connected with the regenerated nerve fibers at 12 weeks.

CONCLUSIONS

The results of our animal study have demonstrated that by simply filling the nerve gap using an alginate sheet, the cavernous nerve can be regenerated and erectile function may be restored.

Repair of 20-mm long rabbit radial bone defects using BMP-derived peptide combined with an α-tricalcium phosphate scaffold

In previous studies, we have reported that the BMP-2-derived peptide KIPKASSVPTELSAISTLYL, corresponding to BMP-2 residues 73-92, binds to a BMP-2-specific receptor, and elevates both alkaline phosphatase activity and osteocalcin mRNA in the murine mesenchymal cell line, C3H10T1/2. This 73-92 peptide conjugated to a covalently crosslinked alginate gel induced ectopic bone formation in rat calf muscle, and activated osteoblasts to promote the repair of rat tibial bone defects. Here, we report repair of 20-mm long rabbit radial bone defects using the 73-92 peptide combined with a porous alpha-tricalcium phosphate (TCP) scaffold. In vitro, the 73-92 peptide was released from the porous alpha-TCP scaffold over more than one week. In vivo, radiomorphometric analysis showed that the 73-92 peptide combined with the porous alpha-TCP scaffold promoted calcification in the implanted area in a dose-dependent manner, and that 5 mg of the 73-92 peptide induced connection of 20-mm long defects, defects of critical size, 12 weeks after implantation. Histological examination revealed newly formed bone and a marrow cavity in the implanted area. The area of bone denser than 690 mg/cm(3) induced by the 73-92 peptide was nearly equal to that of the contralateral radius.

Effect of Viscous Injectable Pure Alginate Sol on Cultured Fibroblasts

BACKGROUND

Alginates have a wide variety of potential clinical applications, including use in cell encapsulation, drug delivery, and tissue engineering. Although the compounds are typically used in the form of a calcium hydrogel, alginates in this form possess several disadvantages, including low biodegradability, induction of foreign body reactions, and cytotoxicity secondary to Ca2+ efflux and contamination with bioincompatible substances. Thus, the goal of the present study was to develop a new method of obtaining sterilized, pure, highly viscous alginate sol from seaweed alginates and to determine its utility as an injectable antiadhesion drug.

METHODS

Viscous injectable pure alginate sol was produced from a commercially available sodium alginate, and its molecular and physical characteristics were analyzed. The biological properties of the viscous injectable pure alginate sol were analyzed using cultured fibroblasts prepared from the dorsal skin of neonatal rats to determine its biocompatibility and its effects on cell proliferation, cell migration, and collagen lattice contraction.

RESULTS

The mannuronic acid-to-glucuronic acid ratio of viscous injectable pure alginate sol, as determined by nuclear magnetic resonance studies, was 1.2, and its viscosity at 5 percent was 17,800 mPa. Purification used to produce viscous injectable pure alginate sol decreased contamination by insoluble particles by 20 percent and decreased polyphenol concentration by 17 percent. In vitro analyses with cultured fibroblasts demonstrated that viscous injectable pure alginate sol had excellent biodegradability and biocompatibility and that viscous injectable pure alginate sol inhibited fibroblast proliferation and migration. Furthermore, assessment of collagen contraction with floating fibroblast-loaded collagen lattices indicated that viscous injectable pure alginate sol enhanced wound healing in surrounding connective tissues.

CONCLUSIONS

The authors conclude that viscous injectable pure alginate sol can inhibit scar formation by presenting a physical barrier to invading fibroblasts and by enhancing wound healing of surrounding tissues.

Accelerated bone repair with the use of a synthetic BMP-2-derived peptide and bone-marrow stromal cells

A novel synthetic peptide corresponding to BMP-2 residues 73-92 that can induce bone formation and can form a conjugate with a carrier to localize its effect has been reported previously. The synthetic peptide was bound to a BMP-2-specific receptor, and it elevated both the alkaline phosphatase activity and the osteocalcin mRNA in the murine multipotent mesenchymal cell line, C3H10T1/2. The 73-92 peptide also induced ectopic bone formation when conjugated to a covalently crosslinked alginate gel and implanted into a rat's calf muscle. Here, it is reported that the 73-92 peptide-conjugated alginate gel particles significantly promoted the repair of rat tibial bone defects, whereas the alginate gel sponge that the peptide was conjugated with was less effective. Further acceleration and denser bone regeneration was achieved when the 73-92 peptide-conjugated alginate gel particles were coimplanted with syngeneic rat bone-marrow stromal cells. Therefore, the 73-92 peptide can induce differentiation of osteoblast precursor cells into osteoblasts, and can activate osteoblasts to promote the repair of bone defects.

Novel heparin/alginate gel combined with basic fibroblast growth factor promotes nerve regeneration in rat sciatic nerve

We have developed an alginate gel crosslinked with covalent bonds for regeneration of dermis, nerve, and bone. Recently, a novel matrix (H/A gel) which consists of heparin and alginate covalently crosslinked with ethylenediamine, was designed. It can stabilize and release biologically active basic fibroblast growth factor (bFGF) for 1 month, which is one of the heparin-binding growth factors. In the present report, we examined the effect of this novel H/A gel on nerve regeneration in the rat sciatic nerve. In this study, regenerated axons in H/A gel with bFGF grew faster than in ordinary alginate gel with bFGF in the early stage. Myelinated fibers showed a tendency to increase in diameter toward the normal size in the later stage. Nerve bundles in the implantation exhibited minimal fibrosis and good vascularization. H/A gel with bFGF exhibited better-developed vascularization than ordinary alginate gel with bFGF. These findings suggested that H/A gel with bFGF could serve not only as an efficient cellular scaffold, but also as a stabilizing matrix for bFGF for peripheral nerve regeneration.

Use of porcine renal capsule matrix as a full-thickness dermal wound-healing material in rats

OBJECTIVE

To compare the utility of porcine renal capsule matrix (RCM) with porcine small intestinal mucosa (SIS) in a rat full-thickness skin wound model.

METHOD

Groups of rats had surgically-created wounds filled with either SIS or RCM. On each rat a contralateral wound was left unfilled (RCM-U or SIS-U). Wound diameter was measured 3, 7, 12, 17, 26 and 30 days after creation. Wound sites sampled 3, 7, 14, 28, 42 and 56 days after wound creation were numerically graded for degree of histologic change and for collagen content, based on intensity of trichrome staining.

RESULTS

Wounds in all groups rapidly contracted to less than 50% of the original diameter within 12 days. There were no differences in wound diameter between RCM- and SIS-treated wounds at any time point, but these wounds had significantly greater (p < 0.001) diameters than their unfilled counterparts on days 7, 12 and 17. There were no differences in histologic scores or trichrome-staining scores between RCM- and SIS-treated wounds and their unfilled counterparts at any time point, except for a greater (p < 0.05) histologic score in SIS-treated wounds compared with unfilled controls on day 14. In both treatment groups an acute inflammatory response at the wound site was soon replaced by an influx of macrophages and fibroblasts.

CONCLUSION

The results show that RCM is equivalent to SIS for the treatment of full-thickness wounds and that these materials may enhance wound healing in terms of wound-tissue collagenisation and maturation. These materials therefore merit further study in other wound-care models.

Prolonged ectopic calcification induced by BMP-2-derived synthetic peptide

Bone morphogenetic protein-2 (BMP-2) promotes the formation and regeneration of bone and cartilage, and therefore constitutes the most promising candidate for a bone repair material. However, it also has a wide range of functions, such as in organogenesis and apoptosis. Therefore, we investigated a novel synthetic peptide corresponding to residues 73-92 of BMP-2. This peptide bound to a BMP-2-specific receptor and elevated both alkaline phosphatase activity and osteocalcin mRNA in the murine cell line, C3H10T1/2. The 73-92 peptide also induced ectopic calcification when conjugated to a covalently crosslinked alginate gel. Here we report that the 73-92 peptide-conjugated alginate gel showed prolonged ectopic calcification for up to 7 weeks in rat calf muscle. In contrast, rhBMP-2-impregnated collagen gel showed maximum ectopic calcification at 3 weeks, and the calcified products that had formed disappeared after 5 weeks. Histological examination showed that the 73-92 peptide-conjugated alginate gel induced many osteoblast-like cells and few osteoclasts. In contrast, rhBMP-2-impregnated collagen gel induced many osteoclasts. These results suggest that the 73-92 peptide on alginate gel remains active at the implanted site, continuously induces differentiation of osteoblast precursor cells into osteoblasts, and activates osteoblasts to promote ectopic calcification.

Alginate Enhances Elongation of Early Regenerating Axons in Spinal Cord of Young Rats

Freeze-dried alginate sponge cross-linked with covalent bonds has been demonstrated to enhance nerve regeneration in peripheral nerves and spinal cords. The present study examined, at early stages after surgery, the outgrowth of regenerating axons and reactions of astrocytes at the stump of transected spinal cord in young rats. Two segments (Th7-8) were resected, and alginate was implanted in the lesion. As controls, collagen gel was implanted in place of alginate or the lesion was left without implantation. Two and 4 weeks after surgery, nerve outgrowth and astrocyte reactions were examined. Many regenerating axons, some of which were accompanied by astrocytic processes, were found to extend from the stump into the alginate-implanted lesion. In the all nonimplanted animals, large cystic cavities were formed at both interfaces with no definite axonal outgrowth into the lesion. In collagen-implanted animals, cavity formation was found in some rats, and regenerating axons once formed at the stumps did not extend further into the lesion. Astrocytic processes extending into alginate-implanted lesion had no basal laminae, whereas those found in control experiments were covered by basal laminae. These findings suggest that alginate contributed to reducing the barrier composed of connective tissues and reactive astrocytic processes, and served as a scaffold for the outgrowth of regenerating axons and elongation of astrocytic processes.