Fixation of biological tissues with a naturally occurring crosslinking agent: fixation rate and effects of pH, temperature, and initial fixative concentration

Contact-Active Layer-by-Layer Grafted TPU/PDMS Blends as an Antiencrustation and Antibacterial Platform for Next-Generation Urological Biomaterials: Validation in Artificial and Human Urine

Urinary tract infections and urinary encrustation impede the long-term clinical performance of urological implants and medical devices. Together, biofilm formation and encrustation constitute serious complications, driving the development of next-generation urological biomaterials. The currently available bioengineered solutions have limited success during long-term usage in the urinary environment. In addressing this unmet clinical challenge, contact-active, antiencrustation surface grafting were conceived onto a dynamically cross-linked polydimethylsiloxane (PDMS) modified thermoplastic polyurethane (TPU) blend using the layer-by-layer (LbL) assembly route. To the best of the authors' knowledge, the present study is the first to investigate the LbL grafting in developing an antiencrustation platform. These multilayered assemblies strategically employed covalent cross-linking and electrostatic interaction-assisted progressive depositions of branched polyethyleneimine and poly(2-ethyl-2-oxazoline). While polyethyleneimine conferred the contact-killing bactericidal activity, the much-coveted antiencrustation properties were rendered by incorporating a partially hydrolyzed derivative of poly(2-ethyl-2-oxazoline). The performance of the resultant surface-modified TPU/PDMS blends was benchmarked against the conventional urological alloplasts, in a customized lab-scale bioreactor-based dynamic encrustation study and in human urine. After 6 weeks of exposure to an artificial urine medium, simulating urease-positive bacterial infection, the surface-modified blends exhibited a remarkable ability to suppress Ca and Mg encrustation. In addition, these blends also displayed superior grafting stability and antibacterial efficacy against common uropathogens. As high as 4-fold log reduction in the planktonic growth of Gram-negative P. mirabilis and Gram-positive MRSA was recorded with the LbL platform vis-à-vis medical-grade TPU. In conjunction, the in vitro cellular assessment with human keratinocytes (HaCaT) and human embryonic kidney cells (HEK) established the uncompromised cytocompatibility of the multilayered grafted blends. Finally, the physiologically relevant functionality of the LbL grafting has been validated using clinical samples of human urine collected from 129 patients with a broad spectrum of disease conditions. The phase-I pre-clinical study, entailing 6 week-long incubation in human urine, demonstrated significantly improved encrustation resistance of the blends. The collective findings of the present work clearly establish the success of LbL strategies in the development of stable, multifunctional new-generation urological biomaterials.

Crosslinking Efficacy and Cytotoxicity of Genipin and Its Activated Form Prepared by Warming It in a Phosphate Buffer: A Comparative Study

The aim of the present study was to compare the acute and cumulative cytotoxicity of intact (n-GE) and warmed genipin (w-GE), while investigating the differences in crosslinking capabilities of these two genipins by rheological and mechanical tests. The n-GE solution was prepared by dissolving genipin powder in a sodium phosphate buffer solution. The w-GE solution was prepared by warming the n-GE solution at 37 °C for 24 h. The mechanical tests for chitosan (CH)/genipin gels showed the crosslinking rate of w-GE was much greater than that of n-GE up until 6 h after preparation, whereas the degree of crosslinking of CH/n-GE gels became higher at 12 h. The ISO 10993-5 standard method, which is established specifically for evaluating cumulative cytotoxicity, determined equivalent IC50 for w-GE (0.173 mM) and n-GE (0.166 mM). On the other hand, custom-made cytotoxicity tests using a WST-8 assay after 1 h of cultivation showed that the acute cytotoxicity of w-GE was significantly higher than that of n-GE at concentrations between 0.1–5 mM. The acute cytotoxicity of w-GE should be taken into consideration in its practical uses, despite the fact that the much faster crosslinking of w-GE is useful as an effective cross linker for in-situ forming gels.

Efficient fabrication of stretching hydrogels with programmable strain gradients as cell sheet delivery vehicles

Fabricating functional cell sheets with excellent mechanical strength for tissue regeneration remains challenging. Therefore, we devised a novel 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide/N-hydroxy-succinimide crosslinked hydrogel carrier composed of gelatin (Ge) and beta-cyclodextrin (β-CD) that promoted the adhesion and proliferation of keratinocytes (Kcs) compared with those cultured on a Ge hydrogel due to significantly higher pore size, porosity, and stiffness, as confirmed using field emission scanning electron microscopy (FE-SEM) and shear wave elastography (SWE). Upon exposure to a programmable gradient microenvironment, cells displayed a stress/strain-dependent spatial-temporal distribution of extended cellular phenotypes and cytoskeletons. The promoted proliferation of Kcs and the increased retention of the undifferentiated cell phenotype on Ge-β-CD composite hydrogels under a 15% strain led to the accelerated detachment of cell sheets with retained cell-cell junctions. Moreover, the stretch-triggered upregulated expression of phosphorylated yes-associated protein (YAP) 1 suggested that this effect might be associated with the mechanical stimulation-induced activation of the YAP pathway.

Decellularized Extracellular Matrix-based Bioinks for Engineering Tissue- and Organ-specific Microenvironments

Biomaterials-based biofabrication methods have gained much attention in recent years. Among them, 3D cell printing is a pioneering technology to facilitate the recapitulation of unique features of complex human tissues and organs with high process flexibility and versatility. Bioinks, combinations of printable hydrogel and cells, can be utilized to create 3D cell-printed constructs. The bioactive cues of bioinks directly trigger cells to induce tissue morphogenesis. Among the various printable hydrogels, the tissue- and organ-specific decellularized extracellular matrix (dECM) can exert synergistic effects in supporting various cells at any component by facilitating specific physiological properties. In this review, we aim to discuss a new paradigm of dECM-based bioinks able to recapitulate the inherent microenvironmental niche in 3D cell-printed constructs. This review can serve as a toolbox for biomedical engineers who want to understand the beneficial characteristics of the dECM-based bioinks and a basic set of fundamental criteria for printing functional human tissues and organs.

Evaluation of effect of two different functionalized nanoparticle photodynamic therapy on nanohardness of root dentin-An in vitro study

INTRODUCTION

The aim of this study was to evaluate the effect of functionalized nanoparticle photodynamic therapy on Nano hardness of root dentin METHODOLOGY: Fifty single rooted lower premolars were decoronated and sectioned into two halves. Then the samples were embedded horizontally in to the acrylic resin to expose the dentin surface. Baseline nanohardness was done at midroot level using a Nanohardness tester. Exposed dentin surfaces were immersed in the following irrigating solutions Post treatment nanohardness testing was done and results were analyzed statistically RESULTS: In general, all the samples in their respective groups had significant change in nanohardness following immersion in irrigant solutions except in NaOCl + EDTA and saline group. CSRB-np and PLGA-MBnp showed increased nanohardness (P = 0.005 and P = 0.007 respectively). Whereas NaOCl + EDTA + CHX showed decrease in nanohardness (P = 0.04). With regards to Modulus of elasticity (MOE), CSRB-np showed significant difference (P = 0.002) compared to the other groups. MOE increased in CSRB-np and PLGA-MBnp while it decreased in all the other groups.

CONCLUSION

In this study, the improvement of nanohardness and modulus of elasticity following the immersion of root dentin in CSRB-np solution was demonstrated.

Selection of biological prosthesis for abdominal wall repair on the basis of in vitro biocompatibility determination

Research on prostheses for repairing abdominal wall defects has progressed through past decades for developing an ideal prosthesis. The study was designed to compare different extracellular matrix (ECM) derived biological prostheses as alternate to conventional synthetic polymeric prostheses for the repair of full thickness abdominal wall defects. Five biological scaffolds derived from bovine diaphragm, bovine aorta, bovine gall bladder, porcine gall bladder, and rabbit skin were prepared and screened for their in vitro biocompatibility. Decellularized ECMs were subjected to various biocompatibility analyses, namely, water absorption potential, matrix degradation analysis, biomechanical testing, and cytocompatibility analysis. Though the rabbit skin displayed maximum biomechanical strength, due to its rapid degradation, it failed to fulfill the criteria of an ideal prosthesis. ECMs derived from bovine diaphragm and aorta were found to be superior than others based upon hydration and matrix degradation analysis, with best scores for bovine diaphragm followed by bovine aorta. The bovine diaphragm and aorta also displayed sufficient biomechanical strength, with diaphragm being the second highest (next to rabbit skin), in biomechanical strength followed by aorta. None of the biological prosthesis revealed any cytotoxicity. Thus, bovine diaphragm and aorta derived ECM fulfill the necessary criteria for their use as biological prosthesis. Because these prostheses are biocompatible, apart from their low cost, ease of availability, and simple preparation, they present a potential alternative to synthetic prosthesis for repair of abdominal wall defects, especially in veterinary patients.

Wound healing and antimicrobial effect of active secondary metabolites in chitosan-based wound dressings: A review

Wound healing can lead to complex clinical problems, hence finding an efficient approach to enhance the healing process is necessary. An ideal wound dressing should treat wounds at reasonable costs, with minimal inconveniences for the patient. Chitosan is one of the most investigated biopolymers for wound healing applications due to its biocompatibility, biodegradability, non-toxicity, and antimicrobial activity. Moreover, chitosan and its derivative have attracted numerous attentions because of the accelerating wound healing, and easy processability into different forms (gels, foams, membranes, and beads). All these properties make chitosan-based materials particularly versatile and promising for wound dressings. Besides, secondary natural metabolites could potentially act like the antimicrobial and anti-inflammatory agents and accelerate the healing process. This review collected almost all studies regarding natural compounds applications in wound healing by focusing on the chitosan-based bioactive wound dressing systems. An accurate analysis of different chitosan formulations and the influence of bioactive compounds on their wound healing properties are reported.

Genipin as An Emergent Tool in the Design of Biocatalysts: Mechanism of Reaction and Applications

Genipin is a reagent isolated from the Gardenia jasminoides fruit extract, and whose low toxicity and good crosslinking properties have converted it into a reactive whose popularity is increasing by the day. These properties have made it widely used in many medical applications, mainly in the production of chitosan materials (crosslinked by this reactive), biological scaffolds for tissue engineering, and nanoparticles of chitosan and nanogels of proteins for controlled drug delivery, the genipin crosslinking being a key point to strengthen the stability of these materials. This review is focused on the mechanism of reaction of this reagent and its use in the design of biocatalysts, where genipin plays a double role, as a support activating agent and as inter- or intramolecular crosslinker. Its low toxicity makes this compound an ideal alterative to glutaraldehyde in these processes. Moreover, in some cases the features of the biocatalysts prepared using genipin surpassed those of the biocatalysts prepared using other standard crosslinkers, even disregarding toxicity. In this way, genipin is a very promising reagent in the design of biocatalysts.

The inhibitory effect of carboxyl-terminated polyamidoamine dendrimers on dentine host-derived matrix metalloproteinases in vitro in an etch-and-rinse adhesive system

The biomimetic remineralization of collagen fibrils has increased interest in restoring the demineralized dentine generated by dental caries. Carboxyl-terminated polyamidoamine dendrimers (PAMAM-COOH), hyperbranched polymeric macromolecules, can act as non-collagenous proteins to induce biomimetic remineralization on a dentine organic matrix. However, in vivo remineralization is an extremely time-consuming process; before complete remineralization, demineralized dentine collagen fibrils are susceptible to degradation by host-derived matrix metalloproteinases (MMPs). Therefore, we examined the effect of fourth-generation PAMAM-COOH (G4-PAMAM-COOH) on the collagenolytic activities of endogenous MMPs, the interaction between G4-PAMAM-COOH and demineralized dentine collagen and the influence of G4-PAMAM-COOH pre-treatment on resin-dentine bonding. G4-PAMAN-COOH not only inhibited exogenous soluble rhMMP9 but also hampered the proteolytic activities of dentine collagen-bound MMPs. Cooperated with the results of G4-PAMAM-COOH absorption and desorption, FTIR spectroscopy provided evidence for the exclusive electrostatic interaction rather than hydrogen or covalent bonding between G4-PAMAM-COOH and dentine collagen. Furthermore, G4-PAMAM-COOH pre-treatment showed no damage to resin-dentine bonding because it did not significantly decrease the elastic modulus of the demineralized dentine, degree of conversion, penetration of the adhesive into the dentinal tubules or ultimate tensile strength. Thus, G4-PAMAM-COOH can effectively inactivate MMPs, retard the enzymolysis of collagen by MMPs and scarcely influence the application of resin-dentine bonding.

Electrospun polycaprolactone/collagen nanofibers cross-linked with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide and genipin facilitate endothelial cell regeneration and may be a promising candidate for vascular scaffolds

Purpose

A promising vascular scaffold must possess satisfying mechanical properties, great hemocompatibility, and favorable tissue regeneration. Combining natural with synthetic materials is a popular method of creating/enhancing such scaffolds. However, the effect of additional modification on the materials requires further exploration.

Materials and methods

We selected polycaprolactone (PCL), which has excellent mechanical properties and biocompatibility and can be combined with collagen. Electrospun fibers created using a PCL/collagen solution were used to fashion mixed nanofibers, while separate syringes of PCL and collagen were used to create separated nanofibers, resulting in different pore sizes. Mixed and separated nanofibers were cross-linked with glutaraldehyde (GA), 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), and genipin; hence, we named them as mixed GA, mixed EDC (ME), mixed genipin (MG), separated GA, separated EDC (SE), and separated genipin (SG).

Results

Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction showed that cross-linking did not affect the main functional groups of fibers in all groups. ME, MG, SE, and SG met the requisite mechanical properties, and they also resisted collagenase degradation. In hemocompatibility assays, only ME and MG demonstrated ideal safety. Furthermore, ME and MG presented the greatest cytocompatibility. For vascular scaffolds, rapid endothelialization helps to prevent thrombosis. According to human umbilical vein endothelial cell migration on different nanofibers, ME and MG are also successful in promoting cell migration.

Conclusion

ME and MG may be promising candidates for vascular tissue engineering. The study suggests that collagen cross-linked by EDC/N-hydroxysuccinimide or genipin facilitates endothelial cell regeneration, which could be of great benefit in tissue engineering of vascular scaffolds.

Processing of collagen based biomaterials and the resulting materials properties

Collagen, the most abundant extracellular matrix protein in animal kingdom belongs to a family of fibrous proteins, which transfer load in tissues and which provide a highly biocompatible environment for cells. This high biocompatibility makes collagen a perfect biomaterial for implantable medical products and scaffolds for in vitro testing systems. To manufacture collagen based solutions, porous sponges, membranes and threads for surgical and dental purposes or cell culture matrices, collagen rich tissues as skin and tendon of mammals are intensively processed by physical and chemical means. Other tissues such as pericardium and intestine are more gently decellularized while maintaining their complex collagenous architectures. Tissue processing technologies are organized as a series of steps, which are combined in different ways to manufacture structurally versatile materials with varying properties in strength, stability against temperature and enzymatic degradation and cellular response. Complex structures are achieved by combined technologies. Different drying techniques are performed with sterilisation steps and the preparation of porous structures simultaneously. Chemical crosslinking is combined with casting steps as spinning, moulding or additive manufacturing techniques. Important progress is expected by using collagen based bio-inks, which can be formed into 3D structures and combined with live cells. This review will give an overview of the technological principles of processing collagen rich tissues down to collagen hydrolysates and the methods to rebuild differently shaped products. The effects of the processing steps on the final materials properties are discussed especially with regard to the thermal and the physical properties and the susceptibility to enzymatic degradation. These properties are key features for biological and clinical application, handling and metabolization.

Therapeutic Potential and Effective Components of the Chinese Herb Gardeniae Fructus in the Treatment of Senile Disease

Gardeniae fructus (GF), an evergreen Rubiaceae shrub, is one of the most commonly used Chinese herbs in traditional Chinese medicine (TCM) and has been used for over a thousand years. It is usually prescribed for the treatment of brain aging, vascular aging, bone and joint aging, and other age-related diseases. It has been demonstrated that several effective compounds of GF, such as geniposide, genipin and crocin, have neuroprotective or related activities which are involved in senile disease treatment. These bioactivities include the mitochondrion dysfunction, antioxidative activity, apoptosis regulation and an anti-inflammatory activity, which related to multiple signaling pathways such as the nuclear factor-κB pathway, AMP-activated protein kinase signaling pathway, and the mitogen-activated protein kinase pathway. To lay the ground for fully elucidating the potential mechanisms of GF in treating age-related pathologies, we summarized the available research conducted in the last fifteen years about GF and its effective components, which have been studied in vivo and in vitro

Novel decellularized animal conchal cartilage graft for application in human patient

Restoration of the external ear and nose in human patients, in either congenital deformity or acquired defects, is a challenge in reconstructive surgery. Optimization of the currently available materials is necessary for rhinoplasty and microtia correction to avoid intraoperative manoeuvring and early rejection. The aim of this study was to develop cross-linked decellularized caprine conchal cartilages as biocompatible, robust, and non-toxic matrix template. The characterization of the decellularized tissue encompasses in vitro lymphoproliferation assay, cytotoxicity test, agar gel precipitation test, in vivo immunocompatibility study, histology, and determination of pro-inflammatory cytokines in animal model. Decellularized cartilage was implanted in human volunteer at R. G. Kar Medical College and Hospital, Kolkata, India, and samples were assessed histologically by retrieving those after 4 months. The processed cartilages were implanted in rhinoplasty (nine) and microtia patients (six) keeping autogenous cartilage graft as control up to 18 months after surgery. Primary outcomes were viability and safety of the material, both in animal model and human pre-application in actual site. Secondary outcomes included self-assessed clinical findings on gross examination. This study is under the ethical approval no. RKC/14 dated January 27, 2012. The in vitro cellular reactivity was less in processed cartilage protein than control. Histology of retrieved tissues in animal model and human volunteer showed no adverse reactions. Production of IL-2, IL-6, and TNF-α cytokines was lower at 4 weeks. The rhinoplasty and microtia operation in clinical patients utilizing the processed cartilage showed satisfactory recovery with improved facial look. These low cost, easily available, biocompatible, safe xenocartilage biomatrices of caprine conchal cartilage origin are very flexible in shape and size, enabling them as potential bioimplant for repair of nasal and auricular structure without any rejection or diverse biomedical applications.

Biomedical analysis of formalin-fixed, paraffin-embedded tissue samples: The Holy Grail for molecular diagnostics

More than a century ago in 1893, a revolutionary idea about fixing biological tissue specimens was introduced by Ferdinand Blum, a German physician. Since then, a plethora of fixation methods have been investigated and used. Formalin fixation with paraffin embedment became the most widely used types of fixation and preservation method, due to its proper architectural conservation of tissue structures and cellular shape. The huge collection of formalin-fixed, paraffin-embedded (FFPE) sample archives worldwide holds a large amount of unearthed information about diseases that could be the Holy Grail in contemporary biomarker research utilizing analytical omics based molecular diagnostics. The aim of this review is to critically evaluate the omics options for FFPE tissue sample analysis in the molecular diagnostics field.

Accelerating effects of genipin-crosslinked small intestinal submucosa for defected gastric mucosa repair

Slow healing of gastric mucosa defects caused by endoscopic surgery is a common but severe clinical problem for lack of an effective treatment. Small intestinal submucosa (SIS) is a bio-derived extracellular matrix scaffold with remarkable repairing ability for soft tissue, but its rapid degradation and poor mechanical properties in the stomach environment limit its application for gastric mucosa regeneration. Herein, we modified SIS by genipin, a natural crosslinking agent, to improve its resistance against degradation in gastric juice and to promote the healing of gastric mucosa defects. The crosslinking characteristics of genipin-crosslinked SIS (GP-CR SIS) were evaluated by crosslinking degree, swelling ratio and FITR, respectively. GP-CR SIS was highly resistant to gastric juice digestion and had a great improvement in mechanical properties. Additionally, GP-CR SIS maintained excellent biocompatibility according to a cytotoxicity test, hemolysis test, and rat subcutaneous implant assay. In an in vivo study, we treated defected gastric mucosa with GP-CR SIS in a rabbit endoscopic submucosal dissection (ESD)-related ulcer model. After two weeks of surgical treatment, GP-CR SIS significantly expedited wound closure and ameliorated newly constructed tissue by providing a protective microenvironment for rapid granulation tissue formation and accelerating angiogenesis/re-epithelialization. In conclusion, this study demonstrates the huge therapeutic potential of GP-CR SIS scaffolds for accelerating defected gastric mucosa regeneration.

Development of bioresorbable bilayered systems for application as affordable wound dressings

The objective of this work was the preparation and evaluation of a bioresorbable bilayered system for application in the treatment of dermal lesions. The system was based on a polyesterurethane as the external layer and a gelatin membrane as the internal layer. The polyesterurethane was synthesized from poly(ε-caprolactone), polyethylene glycol of 1 or 10 kDa as a hydrophilic component or Pluronic F127 as an amphiphilic component and l-lysine ethyl ester diisocyanate as an urethane precursor. Gelatin membrane was obtained by crosslinking with the naturally occurring crosslinker genipin. Three important points were addressed in this study: the physicochemical characterization of the system, the in vitro behaviour and the in vivo performance on a full-thickness wound defect of rat. The polyesterurethane containing polyethylene glycol of 10 kDa presented the optimum properties for the designed application as to be tested in animal experiments. The in vivo results showed good healing of the lesion with the formation of epidermis similar to normal rat skin. These promising results suggest the potential of this system to be used as an affordable wound dressing in the treatment of different dermal lesions.

Genipin-cross-linked electrospun collagen fibers

The fabrication of a fibrous collagen scaffold using electrospinning is desirable for tissue-engineering applications. Previously, electrospun collagen fibers were shown to be unstable in aqueous environments and, therefore, cross-linking is essential to stabilize these fibers. In this study genipin, a significantly less cytotoxic cross-linking agent compared to glutaraldehyde, was used to cross-link electrospun collagen fibers. The significance of this research lies in the use of four alcohol/water solvent systems to carry out the crosslinking reaction to maintain fibrous morphology during cross-linking. The four cross-linking conditions established were: (1) ethanol, 5% water and 3 days, (2) ethanol, 3% water and 5 days, (3) ethanol, 5% water and 5 days, and (4) isopropanol, 5% water and 5 days at a genipin concentration of 0.03 M. Results illustrated that genipin-cross-linking was effective in maintaining collagen fiber integrity in aqueous and cell culture media environments for up to 7 days. In addition, it was shown that fiber swelling could be controlled by using different cross-linking conditions. Swelling of cross-linked fibers immersed in Dulbecco's modified eagle medium for 7 days ranged from 0 to 59 ± 4%. The cross-linked fibers were analyzed using scanning electron microscopy, Fourier transform infrared spectroscopy and ninhydrin assay. Finally, studies using primary human fibroblasts indicated good cell adhesion to these scaffolds. Overall, our data suggest that these stabilized fibrous collagen scaffolds provide a promising environment for tissue-regeneration applications.

Fabrication and characterization of Eri silk fibers-based sponges for biomedical application

Cocoon-derived semi-domesticated Eri silk fibers still lack exploitation for tissue engineering applications due to their poor solubility using conventional methods. The present work explores the ability to process cocoon fibers of non-mulberry Eri silk (Samia/Philosamia ricini) into sponges through a green approach using ionic liquid (IL)--1-buthyl-imidazolium acetate as a solvent. The formation of β-sheet structures during Eri silk/IL gelation was acquired by exposing the Eri silk/IL gels to a saturated atmosphere composed of two different solvents: (i) isopropanol/ethanol (physical stabilization) and (ii) genipin, a natural crosslinker, dissolved in ethanol (chemical crosslinking). The sponges were then obtained by freeze-drying. This approach promotes the formation of both stable and ordered non-crosslinked Eri silk fibroin matrices. Moreover, genipin-crosslinked silk fibroin sponges presenting high height recovery capacity after compression, high swelling degree and suitable mechanical properties for tissue engineering applications were produced. The incorporation of a model drug--ibuprofen--and the corresponding release study from the loaded sponges demonstrated the potential of using these matrices as effective drug delivery systems. The assessment of the biological performance of ATDC5 chondrocyte-like cells in contact with the developed sponges showed the promotion of cell adhesion and proliferation, as well as extracellular matrix production within 2 weeks of culture. Sponges' intrinsic properties and biological findings open up their potential use for biomedical applications.

STATEMENT OF SIGNIFICANCE

This work addresses the preparation and characterization of non-mulberry cocoon-derived Eri silk sponges. The insolubility of cocoons-derived non-mulberry silkworms impairs their processability and applications in the healthcare field. We used a green approach with ionic liquids to overcome the lack solubility of such silk fibers. The formation of beta-sheet structures into Eri-based sponges was physically and chemically induced. The sponges were obtained by freeze-drying. The developed structures exhibited flexibility to adapt and recover their shapes upon application and subsequent removal of load, high swelling degree, ability to load an anti-inflammatory drug and to promote its sustained release. They promoted in vitro cellular adhesion, proliferation and extracellular matrix production of a chondrocyte-like cell line, opening up their potential application for biomedical applications.

Hybrid cross-linked hydrogels based on fibrous protein/block copolymers and layered silicate nanoparticles: tunable thermosensitivity, biodegradability and mechanical durability

Schematic representation of LAPONITE® reinforced pluronic/chitosan/keratin nanocomposite hydrogel crosslinked with Genipin.

Ex vivo proof-of-concept of end-to-end scaffold-enhanced laser-assisted vascular anastomosis of porcine arteries

OBJECTIVE

The low welding strength of laser-assisted vascular anastomosis (LAVA) has hampered the clinical application of LAVA as an alternative to suture anastomosis. To improve welding strength, LAVA in combination with solder and polymeric scaffolds (ssLAVA) has been optimized in vitro. Currently, ssLAVA requires proof-of-concept in a physiologically representative ex vivo model before advancing to in vivo studies. This study therefore investigated the feasibility of ex vivo ssLAVA in medium-sized porcine arteries.

METHODS

Scaffolds composed of poly(ε-caprolactone) (PCL) or poly(lactic-co-glycolic acid) (PLGA) were impregnated with semisolid solder and placed over coapted aortic segments. ssLAVA was performed with a 670-nm diode laser. In the first substudy, the optimum number of laser spots was determined by bursting pressure analysis. The second substudy investigated the resilience of the welds in a Langendorf-type pulsatile pressure setup, monitoring the number of failed vessels. The type of failure (cohesive vs adhesive) was confirmed by electron microscopy, and thermal damage was assessed histologically. The third substudy compared breaking strength of aortic repairs made with PLGA and semisolid genipin solder (ssLAVR) to repairs made with BioGlue.

RESULTS

ssLAVA with 11 lasing spots and PLGA scaffold yielded the highest bursting pressure (923 ± 56 mm Hg vs 703 ± 96 mm Hg with PCL ssLAVA; P = .0002) and exhibited the fewest failures (20% vs 70% for PCL ssLAVA; P = .0218). The two failed PLGA ssLAVA arteries leaked at 19 and 22 hours, whereas the seven failed PCL ssLAVA arteries burst between 12 and 23 hours. PLGA anastomoses broke adhesively, whereas PCL welds failed cohesively. Both modalities exhibited full-thickness thermal damage. Repairs with PLGA scaffold yielded higher breaking strength than BioGlue repairs (323 ± 28 N/cm(2) vs 25 ± 4 N/cm(2), respectively; P = .0003).

CONCLUSIONS

PLGA ssLAVA yields greater anastomotic strength and fewer anastomotic failures than PCL ssLAVA. Aortic repairs with BioGlue were inferior to those produced with PLGA ssLAVR. The results demonstrate the feasibility of ssLAVA/R as an alternative method to suture anastomosis or tissue sealant. Further studies should focus on reducing thermal damage.

Activity of MMP-9 after repair of abdominal wall defects with acellular and crosslinked bovine pericardium in rabbit

This study was undertaken for the identification of matrix metalloproteinases (MMPs) in extracts obtained from native, acellular and crosslinked bovine pericardium (in vitro), as well as in the plasma after implantation of these biomaterials in rabbits (in vivo). Native pericardium (NP) expressed a 72 kDa (MMP-2) band; whereas, in acellular pericardium (AP) two bands (10 kDa and 92 kDa) of MMPs were observed of which, 92 kDa band was very faint. AP crosslinked with glutaraldehyde did not show any gelatinase activity and thus reflects the creation of new additional chemical bonds between the collagen molecules which has been effectively removed. Gelatin zymography showed only one major band of 92 kDa in all the implanted and untreated rabbit plasma, but the relative amount of 92 kDa was 1-2 times higher in acellular bovine pericardium implanted rabbits as compared to crosslinked and native groups. In NP group, the 92 kDa band was the dullest among the three groups. This indicated that the level of MMP-9 corresponds to the degree of collagen degradation.

The effects of different crossing-linking conditions of genipin on type I collagen scaffolds: an in vitro evaluation

The purpose of this paper is to analyze the properties of fabricating rat tail type I collagen scaffolds cross-linked with genipin under different conditions. The porous genipin cross-linked scaffolds are obtained through a two step freeze-drying process. To find out the optimal cross-link condition, we used different genipin concentrations and various cross-linked temperatures to prepare the scaffolds in this study. The morphologies of the scaffolds were characterized by scanning electron microscope, and the mechanical properties of the scaffolds were evaluated under dynamic compression. Additionally, the cross-linking degree was assessed by ninhydrin assay. To investigate the swelling ratio and the in vitro degradation of the collagen scaffold, the tests were also carried out by immersion of the scaffolds in a PBS solution or digestion in a type I collagenase respectively. The morphologies of the non-cross-linked scaffolds presented a lattice-like structure while the cross-linked ones displayed a sheet-like framework. The morphology of the genipin cross-linked scaffolds could be significantly changed by either increasing genipin concentration or the temperature. The swelling ratio of each cross-linked scaffold was much lower than that of the control (non-cross-linked).The ninhydrin assay demonstrated that the higher temperature and genipin concentration could obviously increase the cross-linking efficiency. The in vitro degradation studies indicated that genipin cross-linking can effectively elevate the biostability of the scaffolds. The biocompatibility and cytotoxicity of the scaffolds was evaluated by culturing rat chondrocytes on the scaffold in vitro and by MTT. The results of MTT and the fact that the chondrocytes adhered well to the scaffolds demonstrated that genipin cross-linked scaffolds possessed an excellent biocompatibility and low cytotoxicity. Based on these results, 0.3 % genipin concentrations and 37 °C cross-linked temperatures are recommended.

Synthesis and characterization of protected oligourethanes as crosslinkers of collagen-based scaffolds

This paper describes the preparation and characterization of water-soluble urethane oligomers bearing protected isocyanate groups. It also points out its ability to crosslink decellularized pericardium.

Nanohybrid structure analysis and biomolecule release behavior of polysaccharide-CDHA drug carriers

Nanoscaled polymer composites were prepared from polysaccharide chitosan (CS) and Ca-deficient hydroxyapatite (CDHA). CS-CDHA nanocomposites were synthesized by in situ precipitation at pH 9, and the CS-CDHA carriers were then fabricated by ionic cross-linking methods using tripolyphosphate and chemical cross-linking methods by glutaraldehyde and genipin. Certain biomolecules such as vitamin B12, cytochrome c, and bovine serum albumin were loaded into the CS-CDHA carriers, and their release behaviors were investigated. Furthermore, these CS-CDHA carriers were examined by transmission electron microscopy, electron spectroscopy for chemical analysis, and X-ray diffraction. The release behavior of the biomolecules was controlled by the CS/CDHA ratios and cross-linked agents. By increasing the concentration of CS and the concentration of the cross-linking agents, cross-linking within carriers increases, and the release rate of the biomolecules is decreased. Moreover, the release rate of the biomolecules from the CS-CDHA carriers at pH 4 was higher than that at pH 10, displaying a pH-sensitive behavior. Therefore, these CS-CDHA hydrogel beads may be useful for intelligent drug release and accelerate bone reconstruction.

Temperature-responsive gelation of type I collagen solutions involving fibril formation and genipin crosslinking as a potential injectable hydrogel

We investigated the temperature-responsive gelation of collagen/genipin solutions using pepsin-solubilized collagen (PSC) and acid-solubilized collagen (ASC) as substrates. Gelation occurred in the PSC/genipin solutions at genipin concentrations 0-2 mM under moderate change in temperature from 25 to 37°C. The PSC/genipin solutions exhibited fluidity at room temperature for at least 30 min, whereas the ASC/genipin solutions rapidly reached gel points. In specific cases PSC would be preferred over ASC as an injectable gel system. The temperature-responsive gelation of PSC/genipin solutions was due to temperature responses to genipin crosslinking and collagen fibril formation. The elastic modulus of the 0.5% PSC/genipin gel system could be adjusted in a range of 2.5 to 50 kPa by the PSC and genipin concentrations, suggesting that a PSC/genipin solution is a potential injectable gel system for drug and cell carriers, with mechanical properties matching those of living tissues.

Preparation and characterization of genipin-crosslinked rat acellular spinal cord scaffolds

The feasibility of rat acellular spinal cord scaffolds for tissue engineering applications was investigated. Fresh rat spinal cords were decellularized and crosslinked with genipin (GP) to improve their structural stability and mechanical properties. The GP-crosslinked spinal cord scaffolds possessed a porous structure with an average pore diameter of 31.1 μm and a porosity of 81.5%. The resultant scaffolds exhibited a water uptake ratio of 229%, and moderate in vitro degradation rates of less than 5% in phosphate-buffered saline (PBS) and slightly more than 20% in trypsin-containing buffer, within 14 days. The ultimate tensile strength and elastic modulus of GP-crosslinked spinal cord scaffolds were determined to be 0.193±0.064 MPa and 1.541±0.082 MPa, respectively. Compared with glutaraldehyde (GA)-crosslinked acellular spinal cord scaffolds, GP-crosslinked scaffolds demonstrated similar microstructure and mechanical properties but superior biocompatibility as indicated by cytotoxicity evaluation and rat mesenchymal stem cell (MSC) adhesion behavior. Cells were able to penetrate throughout the crosslinked scaffold due to the presence of an interconnected porous structure. The low cytotoxicity of GP facilitated cell proliferation and extracellular matrix (ECM) secretion in vitro on the crosslinked scaffolds over 7 days. Thus, these GP-crosslinked spinal cord scaffolds show great promise for tissue engineering applications.

Modulation of the proliferation and matrix synthesis of chondrocytes by dynamic compression on genipin-crosslinked chitosan/collagen scaffolds

Dynamic compression is an important physical stimulus for the physiology of chondrocyte and articular cartilage tissue engineering. In this study, modulation of chondrocyte behaviors in chitosan/collagen scaffolds with different mechanical properties under free-swelling or dynamic compression conditions was investigated. Rabbit chondrocytes were seeded in chitosan/collagen scaffolds crosslinked by genipin (GP) with different concentrations, and then cultured for 3 days prior to cyclic compression of 40% strain, 0.1 Hz, and 30 min/day for 2 weeks. The results showed that the cell proliferation was increased with increasing genipin concentrations and dynamic compression. On the other hand, although total glycosaminoglycans (GAGs) deposition was enhanced by dynamic compression under certain conditions, e.g. the GP0.5 chitosan/collagen scaffolds for 1 week of compression culture, normalized GAGs deposition per cell was decreased by dynamic compression. Our results suggest that while several studies suggest that dynamic compression benefits articular cartilage tissue engineering, many factors including scaffold types and compression conditions determine the outcome of dynamic compression culture.

Sporicidal efficacy of genipin: a potential theoretical alternative for biomaterial and tissue graft sterilization

Terminal sterilization of musculoskeletal allografts by gamma radiation minimizes the risk of disease transmission but impairs allograft mechanical properties. Commonly employed crosslinking agents can sterilize tissues without affecting mechanical properties adversely; however, these agents are toxic. Genipin is reported to be a benign crosslinking agent that strengthens mechanical properties of tissues; however, the antimicrobial capacity of genipin is largely unknown. The present study's aims were: (1) to assess the sporicidal potential of genipin, (2) to improve antimicrobial capacity by changing chemical and physical treatment conditions. To establish genipin's sterilization potential Bacillus subtilis var. niger spore strips were treated with 0-10% genipin in PBS or in 1:1 DMSO:PBS up to 72 h at room temperature (RT). Sterilizing doses and concentrations of genipin were used to treat B. pumilus and Geobacillus stearothermophilus spores to assess broader spectrum sporicidal activity of genipin. Scanning electron microscopy (SEM) was performed to evaluate gross morphological changes after genipin treatment. Optimal sterilization conditions were determined by evaluating the effects of temperature (RT-50 °C), DMSO:PBS ratio (0:100-100:0), and treatment duration (24-72 h) on B. subtilis. Genipin penetration of full thickness bovine patellar tendon and cortical bone specimens was observed to assess the feasibility of the agent for treating grafts. Initial studies showed that after 72 h of treatment at RT with 0.63-10% genipin/DMSO:PBS B. subtilis spore strips were sterilized; 0.63% genipin/PBS did not sterilize spore strips at 72 h at RT. Genipin doses and concentrations that sterilized B. subtilis spore strips sterilized B. pumilus and G. stearothermophilus spore strips. SEM revealed no gross morphological differences between untreated and treated spores. Treatment optimization resulted in sterilization within 24 h with 100% PBS, and DMSO facilitated sporicidal activity. Genipin penetrated full thickness patellar tendon specimens and 3.72 ± 0.58 mm in cortical bone specimens. Genipin sterilizes B. subtilis, B. pumilus, and G. stearothermophilus spore strips. It penetrates soft and hard tissues at doses previously shown to be non-toxic and to improve mechanical strength in collagen-rich soft tissues. Further studies are indicated to assess genipin's effects on the mechanical properties of genipin-sterilized grafts, the ability of genipin to eradicate infectious species other than spores, and to assess whether sterilant activity persists after penetrating tissues and biomaterials.

Novel silk fibroin/elastin wound dressings

Silk fibroin (SF) and elastin (EL) scaffolds were successfully produced for the first time for the treatment of burn wounds. The self-assembly properties of SF, together with the excellent chemical and mechanical stability and biocompatibility, were combined with elastin protein to produce scaffolds with the ability to mimic the extracellular matrix (ECM). Porous scaffolds were obtained by lyophilization and were further crosslinked with genipin (GE). Genipin crosslinking induces the conformational transition from random coil to β-sheet of SF chains, yielding scaffolds with smaller pore size and reduced swelling ratios, degradation and release rates. All results indicated that the composition of the scaffolds had a significant effect on their physical properties, and that can easily be tuned to obtain scaffolds suitable for biological applications. Wound healing was assessed through the use of human full-thickness skin equivalents (EpidermFT). Standardized burn wounds were induced by a cautery and the best re-epithelialization and the fastest wound closure was obtained in wounds treated with 50SF scaffolds; these contain the highest amount of elastin after 6 days of healing in comparison with other dressings and controls. The cytocompatibility demonstrated with human skin fibroblasts together with the healing improvement make these SF/EL scaffolds suitable for wound dressing applications.

Genipin crosslinking elevates the strength of electrochemically aligned collagen to the level of tendons

Collagen-based tissue mimics are important in clinical research because collagen is the main structural element in tendons. The current study aimed to improve the mechanical strength of Electronically Aligned Collagen (ELAC) threads by optimizing several crosslinking parameters. The results indicated that elevating the concentration of genipin to 2% and the solvent to 90% ethanol significantly enhanced the wet ultimate tensile stress of ELAC threads to 109 MPa with a crosslinking degree of 65%. Furthermore, significantly higher adhesion and proliferation of hMSCs was observed in ELAC threads crosslinked with 2% genipin in 90% ethanol compared to 0.625% genipin in 1X PBS. In conclusion, ELAC threads with mechanical strength on par with native tendon have significant potential to be used as scaffolds in tendon tissue engineering applications.

Characterization of a conjugate between Rose Bengal and chitosan for targeted antibiofilm and tissue stabilization effects as a potential treatment of infected dentin

Bacterial biofilms and dentin structural changes are some of the major challenges in the management of infected dentin tissue. This study characterized a photosensitizer-conjugated chitosan with enhanced photodynamic efficacy against dental biofilms, as well as the ability to reinforce the postinfected dentin matrix in order to improve its mechanical and chemical stability. Rose Bengal-conjugated chitosan (CSRB) was synthesized using a chemical cross-linking method and characterized for photophysical, photobiological, and cytotoxicity properties. Its potential as an antibacterial and matrix-reinforcing agent on dentin collagen was also evaluated. Enterococcus faecalis as planktonic and in vitro biofilms was treated with CSRB and photodynamically activated with 5 to 60 J/cm(2) green light. Dentin collagen was used for the CSRB cross-linking experiments and evaluated for chemical changes, resistance to enzymatic degradation, and mechanical properties. CSRB was a photosensitizer with efficient singlet oxygen yield. In vitro photoactivation gave higher fibroblast cell survival than did RB alone. CSRB showed significant antibiofilm photoinactivation (P < 0.01). The CSRB-cross-linked dentin collagen showed higher resistance to collagenase degradation and superior mechanical properties (P < 0.05). In summary, the photoactivated CSRB particles synthesized in this study may be a synergistic multifunctional treatment approach with lower cytotoxicity and effective antibiofilm activity as well as the ability to reinforce the dentin collagen to enhance resistance to degradation and improve mechanical properties. This may be a targeted treatment strategy to deal with infected dentin hard tissues in a clinical scenario, where both disinfection and structural integrity need to be addressed concomitantly.

EVALUATION OF CROSS-LINKING TIME FOR POROUS GELATIN HYDROGELS ON CELL SHEET DELIVERY PERFORMANCE

To overcome the drawbacks posed by surgical manipulation of bioengineered corneal endothelial cell (CEC) sheets, a simple stirring process combined with freeze-drying method was recently developed for the production of cross-linked porous gelatin hydrogels that can provide the support structure and improve the aqueous humor circulation. In this study, we further evaluated the influence of cross-linking time (0–48 h) on the delivery performance of carbodiimide modified gelatin carriers. It was found that smaller pore size, lower porosity, and larger superficial area were associated with increasing extent of cross-linking of the carrier discs. Although the hydrogels treated for short reaction time (i.e., below 6 h) had low resistance to initial nutrient permeation, these materials exhibited rapid swelling, implying a potential anterior segment tissue squeezing effect for use as intraocular implants. In addition, the delivery carriers with limited extent of cross-linking degraded too fast to be effective for retention of cell sheet grafts at the site of injury. By contrast, the gelatin samples with cross-linking degrees greater than 50% showed slower degradation rates and smaller porous structure, thereby possibly causing a significant inhibition of CEC proliferation. Cell sheet transfer studies demonstrated that the carrier discs with a high cross-linking degree (59.4 ± 1.3%) were more difficult to achieve stable cell attachment than their counterparts with a low cross-linking degree (48.3 ± 1.5%). Our findings suggest that among the cross-linked porous samples studied, 12 h is the best cross-linking reaction time for preparation of cell sheet carriers with suitable delivery performance.