The physiological relevance of wet versus dry differential scanning calorimetry for biomaterial evaluation: a technical note

Effect of collagen denaturation degree on mechanical properties and biological activity of nanofibrous scaffolds

Further progress in regenerative medicine and bioengineering highly depends on the development of 3D polymeric scaffolds with active biological properties. The most attention is paid to natural extracellular matrix components, primarily collagen. Herein, nonwoven nanofiber materials with various degrees of collagen denaturation and fiber diameters 250-500 nm were produced by electrospinning, stabilized by genipin, and characterized in detail. Collagen denaturation has been confirmed using DSC and FTIR analysis. The comparative study of collagen and gelatin nonwoven materials (NWM) revealed only minor differences in their biocompatibility with skin fibroblasts and keratinocytes in vitro. In long-term subcutaneous implantation study, the inflammation was less evident on collagen than on gelatin NWM. Remarkably, the pronounced calcification was revealed in the collagen NWM only. The results obtained can be useful in terms of improving the electrospinning technology of collagen from aqueous solutions, as well as emphasize the importance of long-term study to ensure proper implementation of the material, taking into account the ability of collagen to provoke calcification.

Characterization of Collagen from Jellyfish Aurelia aurita and Investigation of Biomaterials Potentials

Marine collagen sources are potent alternatives due to abundant yield, low pathogen infection risk, high biocompatibility, and any religious and ethical restrictions compared to terrestrial collagen sources. In this research, we aim to investigate the biomaterials potential of the collagen from Aurelia aurita, which is a native jellyfish species in the Marmara Sea. Spectroscopic techniques were used to investigate the structure of jellyfish collagen (JCol) from acid-soluble fraction and compared to Jellagen® from Rhizostoma pulmo. MALDI-TOF showed the main peak of Jellagen® at 276,765.161 Da and jellyfish collagen at 276,761.687 Da. SDS-PAGE indicated α1 and α2 bands at about 122 kDa and 140 kDa, respectively. In FTIR and Raman spectra, the locations of amide bands of both species were almost the same. The pI of JCol was determined as 4.46. The particle size decreased abruptly at 43 oC from 890 to 290 nm. Water, organic and inorganic ratios of collagen were determined at 7.14%, 63.59, and 29.27 respectively. In DSC, the denaturation temperature (Td) of JCol was found at 43.7 oC and found to be higher than that of the collagens from jellyfishes that have been reported so far in the literature. Biocompatibility testing by metabolic assay revealed significantly higher fibroblast proliferation on collagen film than on the Tissue Culture Plate. To conclude, Aurelia aurita collagen would be a suitable source of collagen when biomaterials are needed to have high biocompatibility and unique macromolecular properties such as high denaturation temperatures.

The influence of animal species, gender and tissue on the structural, biophysical, biochemical and biological properties of collagen sponges

Although collagen type I is extensively used in biomedicine, no study to-date has assessed how the properties of the produced scaffolds are affected as a function of species, gender and tissue from which the collagen was extracted. Herein, we extracted and characterised collagen from porcine and bovine, male and female and skin and tendon tissues and we subsequently fabricated and assessed the structural, biophysical, biochemical and biological properties of collagen sponges. All collagen preparations were of similar purity and free-amine content (p > 0.05). In general, the porcine groups yielded more collagen; had higher (p < 0.05) denaturation temperature and resistance to enzymatic degradation; and lower (p < 0.05) swelling ratio and compression stress and modulus than the bovine groups of the same gender and tissue. All collagen preparations supported growth of human dermal fibroblasts and exhibited similar biological response to human THP-1 monocytes. These results further illustrate the need for standardisation of collagen preparations for the development of reproducible collagen-based devices. Assessment of the physicochemical and biological properties of collagen sponges as a function of animal species (bovine versus porcine), gender (male versus female) and tissue (skin versus tendon).

Development of chitosan, gelatin and liposome film and analysis of its biocompatibility in vitro

A film of chitosan, gelatin and liposome has been designed for dermatological applications. Several adaptations were required throughout development to facilitate in vitro analysis, physicochemical characterization and biocompatibility evaluation. The final version of the film was characterized by differential scanning calorimetry, evaluation of swelling and scanning electron microscopy. The biocompatibility of the film was assessed by investigating cellular parameters of three types of human cells by direct contact or through films extracts: I) primary culture of adipose-derived mesenchymal stromal cells (ADCSs) and melanoma cell lines were used to test cell adhesion and morphology by direct cell culture on the material; II) ADSCs and immortalized keratinocytes were used in cell viability assay using different films extracts. The film showed physicochemical characteristics that favored cellular input, being suitable for in vitro analysis, which allowed its biocompatible characteristics such as the absence of toxicity to be verified without causing significant morphological changes in ADSCs and melanoma cell line. Altogether, these results suggest that the material has a potential application for drug delivery and promotion of skin tissue repair and is therefore worthwhile for further investigations using preclinical models to cover dermal lesions.

In vivo degradation behavior of enzyme-degradable poly(trimethylene carbonate)-based biohybrid networks of varying water content

Polymeric biohybrid networks have significant potential as supportive materials for soft connective tissue regeneration. Their success in this regard is determined by their initial mechanical properties, which are dependent on their water content, as well as the rate at which these properties change with time due to cell mediated degradation. In this study the in vivo degradation and tissue response following implantation of matrix metalloproteinase (MMP)-degradable poly(trimethylene carbonate) (PTMC)-based biohybrid networks were assessed in a Wistar rat model. The networks examined varied in equilibrium water content from circa 20% to 70% w/w. The networks degraded through MMP secretion by inflammatory cells at the tissue-material interface, generating a mass loss profile consistent with surface erosion but modulus and sol content changes consistent with a bulk erosion process. This degradation profile was explained in terms of a population gradient in MMP concentration from the surface to the bulk of the networks due to diffusion restrictions. A histological analysis of the tissue surrounding the implants confirmed a moderate tissue response comparable to that observed towards a Vicryl^TM suture, suggesting that these new materials can be considered biocompatible.

Light-Activated Tissue-Integrating Sutures as Surgical Nanodevices

Sutures are typically the primary means of soft tissue repair in surgery and trauma. Despite their widespread use, sutures do not result in immediate sealing of approximated tissues, which can result in bacterial infection and leakage. Nonabsorbable sutures and staples can be traumatic to tissue, and the trauma can be exacerbated by their subsequent removal. Use of cyanoacrylate glues is limited because of their brittleness and toxicity. In this work, laser-activated tissue-integrating sutures (LATIS) are described as novel nanodevices for soft tissue approximation and repair. Incorporation of gold nanorods within fibers generated from collagen result in LATIS fibers which demonstrate robust photothermal responses following irradiation with near infrared laser light. Compared to conventional sutures, LATIS fibers result in greater biomechanical recovery of incised skin in a mouse model of skin closure after spine surgeries. Histopathology analyses show improved repair of the epidermal gap in skin, which indicate faster tissue recovery using LATIS. The studies indicate that LATIS-facilitated approximation of skin in live mice synergizes the benefits of conventional suturing and laser-activated tissue integration, resulting in new approaches for faster sealing, tissue repair, and healing.

Production and Characterization of Chemically Cross-Linked Collagen Scaffolds

Chemical cross-linking of collagen-based devices is used as a means of increasing the mechanical stability and control the degradation rate upon implantation. Herein, we describe techniques to produce cross-linked with glutaraldehyde (GTA; amine terminal cross-linker), 4-arm polyethylene glycol succinimidyl glutarate (4SP; amine terminal cross-linker), diphenyl phosphoryl azide (DPPA; carboxyl terminal cross-linker), and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC; carboxyl terminal cross-linker) collagen films. In addition, we provide protocols to characterize the biophysical (swelling), biomechanical (tensile), and biological (metabolic activity, proliferation and viability using human dermal fibroblasts and THP-1 macrophages) properties of the cross-linked collagen scaffolds.

The Collagen Suprafamily: From Biosynthesis to Advanced Biomaterial Development

Collagen is the oldest and most abundant extracellular matrix protein that has found many applications in food, cosmetic, pharmaceutical, and biomedical industries. First, an overview of the family of collagens and their respective structures, conformation, and biosynthesis is provided. The advances and shortfalls of various collagen preparations (e.g., mammalian/marine extracted collagen, cell-produced collagens, recombinant collagens, and collagen-like peptides) and crosslinking technologies (e.g., chemical, physical, and biological) are then critically discussed. Subsequently, an array of structural, thermal, mechanical, biochemical, and biological assays is examined, which are developed to analyze and characterize collagenous structures. Lastly, a comprehensive review is provided on how advances in engineering, chemistry, and biology have enabled the development of bioactive, 3D structures (e.g., tissue grafts, biomaterials, cell-assembled tissue equivalents) that closely imitate native supramolecular assemblies and have the capacity to deliver in a localized and sustained manner viable cell populations and/or bioactive/therapeutic molecules. Clearly, collagens have a long history in both evolution and biotechnology and continue to offer both challenges and exciting opportunities in regenerative medicine as nature's biomaterial of choice.

An experimental toolbox for characterization of mammalian collagen type I in biological specimens

Collagen type I is the most abundant extracellular matrix protein, and collagen type I supramolecular assemblies (e.g., tissue grafts, biomaterials and cell-assembled systems) are used extensively in tissue engineering and regenerative medicine. Many studies, for convenience or economic reasons, do not accurately determine collagen type I purity, concentration, solubility and extent of cross-linking in biological specimens, frequently resulting in erroneous conclusions. In this protocol, we describe solubility; normal, reduced and delayed (interrupted) SDS-PAGE; hydroxyproline; Sircol collagen and Pierce BCA protein; denaturation temperature; ninhydrin/trinitrobenzene sulfonic acid; and collagenase assays and assess them in a diverse range of biological samples (e.g., tissue samples; purified solutions or lyophilized materials; 3D scaffolds, such as sponges and hydrogels; and cell media and layers). Collectively, the described protocols provide a comprehensive, yet fast and readily implemented, toolbox for collagen type I characterization in any biological specimen.

Acetic acid and pepsin result in high yield, high purity and low macrophage response collagen for biomedical applications

Collagen based devices are frequently associated with foreign body response. Although several pre- (e.g. species, state of animal, tissue) and post- (e.g. cross-linking, scaffold architecture) extraction method factors have a profound effect on foreign body response, little is known about which and how during the extraction process factors mediate foreign body response. In this study, we assessed the influence of acetic acid and hydrochloric acid and the utilisation or not of pepsin or salt precipitation during collagen extraction on the yield, purity, free amines, denaturation temperature, resistance to collagenase degradation and macrophage response. Acetic acid/pepsin extracted collagen exhibited the highest yield, purity and free amine content and the lowest denaturation temperature. No differences in resistance to collagenase digestion were detected between the groups. Although all treatments exhibited similar macrophage morphology comprised of round cells (M1 phenotype), elongated cells (M2 phenotype) and cell aggregates (foreign body response), significantly more elongated cells were observed on HC films. Although no differences in metabolic activity were observed between the groups, the DNA concentration was significantly lower for the hydrochloric acid treatments. Further, cytokine analysis revealed that hydrochloric acid treatments induced significantly higher IL-1β and TNF-α release with respect to acetic acid treatments. Salt precipitation did not influence the parameters assessed. Collectively, these data suggest that during the collagen extraction process variables should also be monitored as, evidently, they affect the physicochemical and biological properties of collagen preparations.

Shape memory polymers with visible and near-infrared imaging modalities: Synthesis, characterization and in vitro analysis

Shape memory polymers (SMPs) are promising for non-invasive medical devices and tissue scaffolds, but are limited by a lack of visibility under clinical imaging. Fluorescent dyes are an alternative to radiocontrast agents in medical applications, they can be utilized in chemical sensors and monitors and may be anti-microbial agents. Thus, a fluorescent SMP could be a highly valuable biomaterial system. Here, we show that four fluorescent dyes (phloxine B (PhB), eosin Y (Eos), indocyanine green(IcG), and calcein (Cal)) can be crosslinked into the polymer backbone to enhance material optical properties without alteration of shape memory and thermomechanical properties. Examinations of the emission wavelengths of the materials compared with the dye solutions showed a slight red shift in the peak emissions, indicative of crosslinking of the material. Quantitative analysis revealed that PhB enabled visibility through 1 cm of blood and through soft tissue. We also demonstrate the utility of these methods in combination with radio-opaque microparticle additives and the use of laser-induced shape recovery to allow for rapid shape recovery below the glass transition temperature. The crosslinking of fluorescent dyes into the SMP enables tuning of physical properties and shape memory and independently of the fluorescence functionality. This fluorescent SMP biomaterial system allows for use of multiple imaging modalities with potential application in minimally invasive medical devices.

* Collagen Cross-Linking: Biophysical, Biochemical, and Biological Response Analysis

Extracted forms of collagen are subjected to chemical cross-linking to enhance their stability. However, traditional cross-linking approaches are associated with toxicity and inflammation. This work investigates the stabilization capacity, cytotoxicity and inflammatory response of collagen scaffolds cross-linked with glutaraldehyde (GTA), 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide, 4-arm polyethylene glycol (PEG) succinimidyl glutarate (4SP), genipin (GEN), and oleuropein. Although all cross-linking methods reduced free amine groups, variable data were obtained with respect to denaturation temperature, resistance to collagenase digestion, and mechanical properties. With respect to biological analysis, fibroblast cultures showed no significant difference between the treatments. Although direct cultures with human-derived leukemic monocyte cells (THP-1) clearly demonstrated the cytotoxic effect of GTA, THP-1 cultures supplemented with conditioned medium from the various groups showed no significant difference between the treatments. With respect to cytokine profile, no significant difference in secretion of proinflammatory (e.g., interleukin [IL]-1β, IL-8, tumor necrosis factor-α) and anti-inflammatory (e.g., vascular endothelial growth factor) cytokines was observed between the noncross-linked and the 4SP and GEN cross-linked groups, suggesting the suitability of these agents as collagen cross-linkers.

Feasibility of a Gelatin Temperature Sensor Based on Electrical Capacitance

The innovative use of gelatin as a temperature sensor based on capacitance was studied at a temperature range normally used for meat cooking (20–80 °C). Interdigital electrodes coated by gelatin solution and two sensors of different thicknesses (38 and 125 µm) were studied between 300 MHz and 900 MHz. At 38 µm, the capacitance was adequately measured, but for 125 µm the slope capacitance versus temperature curve decreased before 900 MHz due to the electrothermal breakdown between 60 °C and 80 °C. Thus, for 125 µm, the capacitance was studied applying 600 MHz. Sensitivity at 38 µm at 868 MHz (0.045 pF/°C) was lower than 125 µm at 600 MHz (0.14 pF/°C), influencing the results in the simulation (temperature range versus time) of meat cooking; at 125 µm, the sensitivity was greater, mainly during chilling steps. The potential of gelatin as a temperature sensor was demonstrated, and a balance between thickness and frequency should be considered to increase the sensitivity.

In Vitro Enzymatic Degradation of Tissue Grafts and Collagen Biomaterials by Matrix Metalloproteinases: Improving the Collagenase Assay

Matrix metalloproteinase-1 and -8 are active during the wound healing and remodelling processes, degrading native extracellular matrix and implantable devices. However, traditional in vitro assays utilize primarily matrix metalloproteinase-1 to mimic the in vivo degradation microenvironment. Herein, we assessed the influence of various concentrations of matrix metalloproteinase- 1 and 8 (50, 100, and 200 U/mL) as a function of pH (5.5 and 7.4) and time (3, 6, 9, 12, and 24 h) on the degradation profile of three tissue grafts (chemically cross-linked Permacol, nonchemically cross-linked Permacol and nonchemically cross-linked Strattice) and a collagen biomaterial (nonchemically cross-linked collagen sponge). Chemically cross-linked and nonchemically cross-linked Permacol samples exhibited the highest resistance to enzymatic degradation, while nonchemically cross-linked collagen sponges exhibited the least resistance to enzymatic degradation. Qualitative and quantitative degradation analysis of all samples revealed a similar degradation profile over time, independently of the matrix metalloproteinase used and its respective concentration and pH. These data indicate that matrix metalloproteinase-1 and matrix metalloproteinase-8 exhibit similar degradation profile in vitro, suggesting that matrix metalloproteinase-8 should be used for collagenase assay.

Biocompatibility Assessment of PLCL-Sericin Copolymer Membranes Using Wharton's Jelly Mesenchymal Stem Cells

Stem cells based tissue engineering requires biocompatible materials, which allow the cells to adhere, expand, and differentiate in a large scale. An ideal biomaterial for clinical application should be free from mammalian products which cause immune reactivities and pathogen infections. We invented a novel biodegradable poly(L-lactic-co-ε-caprolactone)-sericin (PLCL-SC) copolymer membrane which was fabricated by electrospinning. Membranes with concentrations of 2.5 or 5% (w/v) SC exhibited qualified texture characteristics with a noncytotoxic release profile. The hydrophilic properties of the membranes were 35–40% higher than those of a standard PLCL and commercial polystyrene (PS). The improved characteristics of the membranes were due to an addition of new functional amide groups, C=O, N–H, and C–N, onto their surfaces. Degradation of the membranes was controllable, depending on the content proportion of SC. Results of thermogram indicated the superior stability and crystallinity of the membranes. These membranes enhanced human Wharton's jelly mesenchymal stem cells (hWJMSC) proliferation by increasing cyclin A and also promoted cell adhesion by upregulating focal adhesion kinase (FAK). On the membranes, hWJMSC differentiated into a neuronal lineage with the occurrence of nestin. These data suggest that PLCL-SC electrospun membrane represents some properties which will be useful for tissue engineering and medical applications.

Examination of radio-opacity enhancing additives in shape memory polyurethane foams

Three microparticle additives, tungsten (W), zirconium oxide (ZrO2), and barium sulfate (BaSO4) were selected to enhance the radio-opacity in shape memory polymer (SMP) foam biomaterials. The addition of filler causes no significant alterations of glass transition temperatures, density of the materials increases, pore diameter decreases, and total volume recovery decreases from approximately 70 times in unfilled foams to 20 times (4% W and 10% ZrO2). The addition of W increases time to recovery; ZrO2 causes little variation in time to shape recovery; BaSO4 increases the time to recovery. On a 2.00 mean X-ray density (mean X.D.) scale, a GDC coil standard has a mean X.D. of 0.62; 4% W enhances the mean X.D. to 1.89, 10% ZrO2 to 1.39 and 4% BaSO4 to 0.74. Radio-opacity enhancing additives could be used to produce SMP foams with controlled shape memory kinetics, low density, and enhanced X-ray opacity for medical materials.

Magnetic bioinspired hybrid nanostructured collagen-hydroxyapatite scaffolds supporting cell proliferation and tuning regenerative process

A bioinspired mineralization process was applied to develop biomimetic hybrid scaffolds made of (Fe(2+)/Fe(3+))-doped hydroxyapatite nanocrystals nucleated on self-assembling collagen fibers and endowed with super-paramagnetic properties, minimizing the formation of potentially cytotoxic magnetic phases such as magnetite or other iron oxide phases. Magnetic composites were prepared at different temperatures, and the effect of this parameter on the reaction yield in terms of mineralization degree, morphology, degradation, and magnetization was investigated. The influence of scaffold properties on cells was evaluated by seeding human osteoblast-like cells on magnetic and nonmagnetic materials, and differences in terms of viability, adhesion, and proliferation were studied. The synthesis temperature affects mainly the chemical-physical features of the mineral phase of the composites influencing the degradation, the microstructure, and the magnetization values of the entire scaffold and its biological performance. In vitro investigations indicated the biocompatibility of the materials and that the magnetization of the super-paramagnetic scaffolds, induced applying an external static magnetic field, improved cell proliferation in comparison to the nonmagnetic scaffold.

Porosity and dielectric properties as tools to predict drug release trends from hydrogels

Conventional studies on hydrogel properties such as viscosity, pH and swelling provide information without treating the components of hydrogel, viz., water and polymer individually. Water and hydrophilic polymers need to be studied individually to understand their relationship with each other to relate their influence on drug release. In this context, we have assigned the combination of porosity and dielectric properties as tools to explore the hydrogels. Porosity and dielectric properties have been analyzed using thermoporometry and alternative current impedance measurements, respectively. A well-known hydrogel genipin cross linked gelatin-chitosan (GC) composite, with catechin as model drug has been studied. The increasing concentration of chitosan in the hydrogel composites led to increase in bound water content and incorporation of charge entrapping moieties. Controlled and medium drug release are observed for GC1 whereas the native hydrogels and composites with lower ratio of chitosan yield immediate release and composites with higher ratio effects in slow release for limited duration (9 hours) of drug delivery process. This trend of drug release is in accordance with the results obtained from porosity and dielectric properties where reduction in pore radii to lower range and increase in relaxation time of polymeric components were observed at higher concentration of chitosan. Thus, these properties can be judiciously used for predicting drug release and designing biomaterials according to it.

Novel biodegradable, biomimetic and functionalised polymer scaffolds to prevent expansion of post-infarct left ventricular remodelling

Over the past decade, a large number of strategies and technologies have been developed to reduce heart failure progression. Among these, cardiac tissue engineering is one of the most promising. Aim of this study is to develop a 3D scaffold to treat cardiac failure. A new three-block copolymer, obtained from δ-valerolactone and polyoxyethylene, was synthesised under high vacuum without catalyst. Copolymer/gelatine blends were microfabricated to obtain a ECM-like geometry. Structures were studied under morphological, mechanical, degradation and biological aspects. To prevent left ventricular remodelling, constructs were biofunctionalises with molecularly imprinted nanoparticles towards the matrix metalloproteinase MMP-9. Results showed that materials are able to reproduce the ECM structure with high resolution, mechanical properties were in the order of MPa similar to those of the native myocardium and cell viability was verified. Nanoparticles showed the capability to rebind MMP-9 (specific rebinding 18.67) and to be permanently immobilised on the scaffold surface.