Biocomposites of non-crosslinked natural and synthetic polymers

Biocompatible and Thermoresistant Hydrogels Based on Collagen and Chitosan

Hydrogels are considered good biomaterials for soft tissue regeneration. In this sense, collagen is the most used raw material to develop hydrogels, due to its high biocompatibility. However, its low mechanical resistance, thermal stability and pH instability have generated the need to look for alternatives to its use. In this sense, the combination of collagen with another raw material (i.e., polysaccharides) can improve the final properties of hydrogels. For this reason, the main objective of this work was the development of hydrogels based on collagen and chitosan. The mechanical, thermal and microstructural properties of the hydrogels formed with different ratios of collagen/chitosan (100/0, 75/25, 50/50, 25/75 and 0/100) were evaluated after being processed by two variants of a protocol consisting in two stages: a pH change towards pH 7 and a temperature drop towards 4 °C. The main results showed that depending on the protocol, the physicochemical and microstructural properties of the hybrid hydrogels were similar to the unitary system depending on the stage carried out in first place, obtaining FTIR peaks with similar intensity or a more porous structure when chitosan was first gelled, instead of collagen. As a conclusion, the synergy between collagen and chitosan improved the properties of the hydrogels, showing good thermomechanical properties and cell viability to be used as potential biomaterials for Tissue Engineering.

Bioactive Agent-Loaded Electrospun Nanofiber Membranes for Accelerating Healing Process: A Review

Despite the advances that have been achieved in developing wound dressings to date, wound healing still remains a challenge in the healthcare system. None of the wound dressings currently used clinically can mimic all the properties of normal and healthy skin. Electrospinning has gained remarkable attention in wound healing applications because of its excellent ability to form nanostructures similar to natural extracellular matrix (ECM). Electrospun dressing accelerates the wound healing process by transferring drugs or active agents to the wound site sooner. This review provides a concise overview of the recent developments in bioactive electrospun dressings, which are effective in treating acute and chronic wounds and can successfully heal the wound. We also discuss bioactive agents used to incorporate electrospun wound dressings to improve their therapeutic potential in wound healing. In addition, here we present commercial dressings loaded with bioactive agents with a comparison between their features and capabilities. Furthermore, we discuss challenges and promises and offer suggestions for future research on bioactive agent-loaded nanofiber membranes to guide future researchers in designing more effective dressing for wound healing and skin regeneration.

Viscous and Failure Mechanisms in Polymer Networks: A Theoretical Micromechanical Approach

Polymeric materials typically present a complex response to mechanical actions; in fact, their behavior is often characterized by viscous time-dependent phenomena due to the network rearrangement and damage induced by chains' bond scission, chains sliding, chains uncoiling, etc. A simple yet reliable model-possibly formulated on the basis of few physically-based parameters-accounting for the main micro-scale micromechanisms taking place in such a class of materials is required to properly describe their response. In the present paper, we propose a theoretical micromechanical approach rooted in the network's chains statistics which allows us to account for the time-dependent response and for the chains failure of polymer networks through a micromechanics formulation. The model is up-scaled to the mesoscale level by integrating the main field quantities over the so-called 'chains configuration space'. After presenting the relevant theory, its reliability is verified through the analysis of some representative tests, and some final considerations are drawn.

A gelatin/collagen/polycaprolactone scaffold for skin regeneration

Background

A tissue-engineered skin substitute, based on gelatin (“G”), collagen (“C”), and poly(ε-caprolactone) (PCL; “P”), was developed.

Method

G/C/P biocomposites were fabricated by impregnation of lyophilized gelatin/collagen (GC) mats with PCL solutions, followed by solvent evaporation. Two different GC:PCL ratios (1:8 and 1:20) were used.

Results

Differential scanning calorimetry revealed that all G/C/P biocomposites had characteristic melting point of PCL at around 60 °C. Scanning electron microscopy showed that all biocomposites had similar fibrous structures. Good cytocompatibility was present in all G/C/P biocomposites when incubated with primary human epidermal keratinocytes (PHEK), human dermal fibroblasts (PHDF) and human adipose-derived stem cells (ASCs) in vitro. All G/C/P biocomposites exhibited similar cell growth and mechanical characteristics in comparison with C/P biocomposites. G/C/P biocomposites with a lower collagen content showed better cell proliferation than those with a higher collagen content in vitro. Due to reasonable mechanical strength and biocompatibility in vitro, G/C/P with a lower content of collagen and a higher content of PCL (GC_LP_H) was selected for animal wound healing studies. According to our data, a significant promotion in wound healing and skin regeneration could be observed in GC_LP_H seeded with adipose-derived stem cells by Gomori’s trichrome staining.

Conclusion

This study may provide an effective and low-cost wound dressings to assist skin regeneration for clinical use.

Recent Overviews in Functional Polymer Composites for Biomedical Applications

Composite materials are considered as an essential part of our daily life due to their outstanding properties and diverse applications. Polymer composites are a widespread class of composites, characterized by low cost, facile processing methods, and varied applications ranging from daily-use issues to highly complicated electronics and advanced medical combinations. In this review, we focus on the most important fabrication techniques for bioapplied polymer composites such as electrospinning, melt-extrusion, solution mixing, and latex technology, as well as in situ methods. Additionally, significant and recent advances in biomedical applications are spotlighted, such as tissue engineering (including bone, blood vessels, oral tissues, and skin), dental resin-based composites, and wound dressing.

Polymer-Based Electrospun Nanofibers for Biomedical Applications

Electrospinning has been considered a promising and novel procedure to fabricate polymer nanofibers due to its simplicity, cost effectiveness, and high production rate, making this technique highly relevant for both industry and academia. It is used to fabricate non-woven fibers with unique characteristics such as high permeability, stability, porosity, surface area to volume ratio, ease of functionalization, and excellent mechanical performance. Nanofibers can be synthesized and tailored to suit a wide range of applications including energy, biotechnology, healthcare, and environmental engineering. A comprehensive outlook on the recent developments, and the influence of electrospinning on biomedical uses such as wound dressing, drug release, and tissue engineering, has been presented. Concerns regarding the procedural restrictions and research contests are addressed, in addition to providing insights about the future of this fabrication technique in the biomedical field.

Fundamentals of protein and cell interactions in biomaterials

The extracellular matrix (ECM) is an active and complex microenvironment with outstanding biomechanical, biophysical, and biochemical characteristics, which can indirectly or directly controls cell adhesion, migration, proliferation, and differentiation, as well as partaking in regeneration and homeostasis of organs and tissues. The ECM has captivated a great deal of attention with the rapid progress of tissue engineering (TE) in the field of regenerative medicine (RM). Approaches to TE, RM and cancer therapy center on the necessity to deliver cell signals to direct cell proliferation and differentiation. These "external signals" are induced from cell-cell, and cell-ECM, interactions, as well as from physico-chemical, mechanical stimuli and growth factors. With the advent of new biomaterials such as casein, we gave a general insight into cell-ECM protein interactions in biomaterials and their applications in TE, RM and cancer therapy. An account of the main ECM molecules and cellular receptors with emphasis on integrins and its ligands was given, their effect on the induction of particular signal transduction pathways is also elucidated.

Colloidal β-Tricalcium Phosphate Prepared by Discharge in a Modified Body Fluid Facilitates Synthesis of Collagen Composites

The development of hydroxyapatite/collagen composites that are naturally synthesized and need no additional treatment is required for use in bone repair. Since reducing the diameter can increase the specific surface area of calcium phosphate particles that can conjugate collagen molecules, we expected colloidal calcium phosphates of submicron diameter obtained by discharge to be effective in formulating these composites. Additionally, since biodegradable β-tricalcium phosphate has better osteoconductivity than hydroxyapatite, this study aimed to investigate the synthesis of colloidal hydroxyapatite and β-tricalcium phosphate/collagen composites. Collagen molecules were tightly polymerized in the β-tricalcium phosphate/collagen composite by catalysis of the generated -P-O-P- polyphosphate chain. Bonding strength between collagen NH+ amino groups and -P-O-P-, and cross-linking of the Ca++-RCOO− in the collagen were increased compared with those in the hydroxyapatite/collagen composite. These chemical reactions due to colloidal β-tricalcium phosphate might play a key role in the synthesis of collagen composites.

Tailoring the in vitro characteristics of poly(vinyl alcohol)-nanohydroxyapatite composite scaffolds for bone tissue engineering

Poly(vinyl alcohol) reinforced with nanohydroxyapatite (PVA-nHA) composite scaffolds were developed by varying the nHA (1%, 2%, 3%, 4%, and 5%, w/v) composition in the PVA matrix by solvent casting technique. The developed composite scaffolds were characterized using scanning electron microscopy (SEM), X-ray powder diffraction (XRD), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, and contact angle measurement. The stability of the composite scaffolds in physiological environment was evaluated by swelling and degradation studies. Further, these composite scaffolds were tested for in vitro bioactivity, hemolysis, biocompatibility, and mechanical strength. SEM micrographs showed a homogenous distribution of nHA (3%, w/v) in the PVA matrix. XRD and ATR-FTIR analysis confirmed no phase contamination and the existence of the chemical bond between PVA-nHA at approximately 2474 cm-1. PVA-nHA composite scaffolds with 3% (w/v) concentration of nHA showed nominal swelling and degradation behavior with good mechanical strength. The mechanical strength and degradation properties of the scaffold above 3% (w/v) of nHA was found to deteriorate, which is due to the agglomeration of nHA. The in vitro bioactivity and hemolysis studies showed improved apatite formation and hemocompatibility of the developed scaffolds. In vitro cell adhesion, proliferation, alkaline phosphatase activity, and Alizarin red S staining confirmed the biocompatibility of the composite scaffolds.

Graphite Oxide to Graphene. Biomaterials to Bionics

The advent of implantable biomaterials has revolutionized medical treatment, allowing the development of the fields of tissue engineering and medical bionic devices (e.g., cochlea implants to restore hearing, vagus nerve stimulators to control Parkinson's disease, and cardiac pace makers). Similarly, future materials developments are likely to continue to drive development in treatment of disease and disability, or even enhancing human potential. The material requirements for implantable devices are stringent. In all cases they must be nontoxic and provide appropriate mechanical integrity for the application at hand. In the case of scaffolds for tissue regeneration, biodegradability in an appropriate time frame may be required, and for medical bionics electronic conductivity is essential. The emergence of graphene and graphene-family composites has resulted in materials and structures highly relevant to the expansion of the biomaterials inventory available for implantable medical devices. The rich chemistries available are able to ensure properties uncovered in the nanodomain are conveyed into the world of macroscopic devices. Here, the inherent properties of graphene, along with how graphene or structures containing it interface with living cells and the effect of electrical stimulation on nerves and cells, are reviewed.

Challenges and strategies in the repair of ruptured annulus fibrosus

Lumbar discectomy is the surgical procedure most frequently performed for patients suffering from low back pain and sciatica. Disc herniation as a consequence of degenerative or traumatic processes is commonly encountered as the underlying cause for the painful condition. While discectomy provides favourable outcome in a majority of cases, there are conditions where unmet requirements exist in terms of treatment, such as large disc protrusions with minimal disc degeneration; in these cases, the high rate of recurrent disc herniation after discectomy is a prevalent problem. An effective biological annular repair could improve the surgical outcome in patients with contained disc herniations but otherwise minor degenerative changes. An attractive approach is a tissue-engineered implant that will enable/stimulate the repair of the ruptured annulus. The strategy is to develop three-dimensional scaffolds and activate them by seeding cells or by incorporating molecular signals that enable new matrix synthesis at the defect site, while the biomaterial provides immediate closure of the defect and maintains the mechanical properties of the disc. This review is structured into (1) introduction, (2) clinical problems, current treatment options and needs, (3) biomechanical demands, (4) cellular and extracellular components, (5) biomaterials for delivery, scaffolding and support, (6) pre-clinical models for evaluation of newly developed cell- and material-based therapies, and (7) conclusions. This article highlights that an interdisciplinary approach is necessary for successful development of new clinical methods for annulus fibrosus repair. This will benefit from a close collaboration between research groups with expertise in all areas addressed in this review.

Development of a recombinant yeast assay to detect ah-receptor ligands

Endocrine systems of humans and animals are disturbed by dioxin-like compounds, which are ligands of the aryl hydrocarbon receptor (AhR). It is important to determine the accumulation of dioxin-like compounds in the environment for maintenance of human health. In this study, we developed a new method for screening ligands of the AhR using a yeast hybrid system. Reporter genes constructed by the insertion of dioxin response elements were integrated into HIS and lacZ yeast genomes. Then yeast was transformed with GAL4-activated domain-fused AhR and aryl hydrocarbon receptor nuclear translocator expression constructs. At 10(-4) M of beta-naphthoflavone, which is an AhR ligand, the absorbance of optical density at 600 nm (OD 600) and beta-galactosidase activity was significantly increased. beta-galactosidase activity was increased when the concentration of 3-methylcholanthrene (MC) was increased. ATP concentration increased as concentration of MC increased up to 10(-10) M but decreased at higher concentrations. The concentration of ATP in the cell suspensions increased linearly with OD 600, used as an index of cell density (r(2) = 0.8366, F = 209.9, p < 0.0001, n = 44). The established yeast assay could possibly be used in the future to detect dioxin-like compounds in environmental samples.

Preparation and characterization of collagen-nanohydroxyapatite biocomposite scaffolds by cryogelation method for bone tissue engineering applications

Recent efforts of bone repair focus on development of porous scaffolds for cell adhesion and proliferation. Collagen-nanohydroxyapatite (HA) scaffolds (70:30; 50:50; and 30:70 mass percentage) were produced by cryogelation technique using 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide hydrochloride/N-hydroxysuccinimide as crosslinking agents. A pure collagen scaffold was used as control. Morphology analysis revealed that all cryogels had highly porous structure with interconnective porosity and the nanoHA aggregates were randomly dispersed throughout the scaffold structure. Chemical analysis showed the presence of all major peaks related to collagen and HA in the biocomposites and indicated possible interaction between nanoHA aggregates and collagen molecules. Porosity analysis revealed an enhancement in the surface area as the nanoHA percentage increased in the collagen structure. The biocomposites showed improved mechanical properties as the nanoHA content increased in the scaffold. As expected, the swelling capacity decreased with the increase of nanoHA content. In vitro studies with osteoblasts cells showed that they were able to attach and spread in all cryogels surfaces. The presence of collagen-nanoHA biocomposites resulted in higher overall cellular proliferation compared to pure collagen scaffold. A statistically significant difference between collagen and collagen-nanoHA cryogels was observed after 21 day of cell culture. These innovative collagen-nanoHA cryogels could have potentially appealing application as scaffolds for bone regeneration.

Electrospun composite polycaprolactone scaffolds for optimized tissue regeneration

There is evidence to suggest that the development of a stable microvasculature at the site of a critical-sized bone defect or fracture aids in repairing or regenerating bone. Identifying a tissue engineering scaffold that optimizes bone tissue and blood vessel development could improve regenerative capabilities. In this paper we study the proliferation and directed differentiation potentials of endothelial colony forming cells and mesenchymal stem cells cultured on electrospun polycaprolactone matrices and compare them with data obtained for composite polycaprolactone–hydroxyapatite, polycaprolactone–hydroxyapatite/β-tricalcium phosphate and polycaprolactone–small intestine submucosa electrospun matrices. Polycaprolactone–hydroxyapatite and polycaprolactone–hydroxyapatite/β-tricalcium phosphate fibers on average displayed a two-fold increase in fiber diameter and average pore-size area as compared with polycaprolactone or polycaprolactone–small intestine submucosa scaffolds. X-ray diffraction showed that significant additions of hydroxyapatite, hydroxyapatite/β-tricalcium phosphate and small intestine submucosa were present in the composite scaffolds. Incorporating hydroxyapatite or hydroxyapatite/β-tricalcium phosphate into the polycaprolactone fiber increased the modulus and ultimate tensile strength significantly. Both endothelial colony forming cell and mesenchymal stem cell proliferation was two-fold greater on polycaprolactone–small intestine submucosa scaffolds; whereas on polycaprolactone–hydroxyapatite and polycaprolactone–hydroxyapatite/β-tricalcium phosphate scaffolds only endothelial colony forming cell proliferation was observed to be significant. Alkaline phosphatase analysis for mesenchymal stem cell-seeded scaffolds indicated that only polycaprolactone–small intestine submucosa scaffolds displayed significant increases after 10 days of culture, suggesting an osteoblast phenotype. Electrospun polycaprolactone–small intestine submucosa scaffolds stimulated proliferation of both cell types and directed mesenchymal stem cell differentiation, providing a stable platform to investigate the potential of endothelial colony forming cell in directing bone tissue repair or regeneration.

In vitro and in vivo degradation of non-woven materials made of poly(ε-caprolactone) nanofibers prepared by electrospinning under different conditions

The aim of this study was to prepare non-woven materials from a biodegradable polymer, poly(epsilon-caprolactone) (PCL) by electrospinning. PCL was synthesized by ring-opening polymerization of epsilon-caprolactone in bulk using stannous octoate as the catalyst under nitrogen atmosphere. PCL was then processed into non-woven matrices composed of nanofibers by electrospinning of the polymer from its solution using a high voltage power supply. The effects of PCL concentration, composition of the solvent (a mixture of chloroform and DMF with different DMF content), applied voltage and tip-collector distance on fiber diameter and morphology were investigated. The diameter of fibers increased with the increase in the polymer concentration and decrease in the DMF content significantly. Applied voltage and tip-collector distance were found critical to control 'bead' formation. Elongation-at-break, ultimate strength and Young's modulus were obtained from the mechanical tests, which were all increased by increasing fiber diameter. The fiber diameter significantly influenced both in vitro degradation (performed in Ringer solution) and in vivo biodegradation (conducted in rats) rates. In vivo degradation was found to be faster than in vitro. Electrospun membranes were more hydrophobic than PCL solvent-casted ones; therefore, their degradation was a much slower process.

A composite polyelectrolytic matrix for controlled oral drug delivery

The purpose of this study was to formulate drug-loaded polyelectrolyte matrices constituting blends of pectin, chitosan (CHT) and hydrolyzed polyacrylamide (HPAAm) for controlling the premature solvation of the polymers and modulating drug release. The model drug employed was the highly water-soluble antihistamine, diphenhydramine HCl (DPH). Polyelectrolyte complex formation was validated by infrared spectroscopy. Matrices were characterized by textural profiling, porositometry and SEM. Drug release studies were performed under simulated gastrointestinal conditions using USP apparatus 3. FTIR spectra revealed distinctive peaks indicating the presence of -COO(-) symmetrical stretching (1,425-1,390 cm(-1)) and -NH (3) (+) deformation (1,535 cm(-1)) with evidence of electrostatic interaction between the cationic CHT and anionic HPAAm corroborated by molecular mechanics simulations of the complexes. Pectin-HPAAm matrices showed electrostatic attraction due to residual -NH(2) and -COO(-) groups of HPAAm and pectin, respectively. Textural profiling demonstrated that CHT-HPAAm matrices were most resilient at 6.1% and pectin-CHT-HPAAm matrices were the least (3.9%). Matrix hardness and deformation energy followed similar behavior. Pectin-CHT-HPAAm and CHT-HPAAm matrices produced type IV isotherms with H3 hysteresis and mesopores (22.46 nm) while pectin-HPAAm matrices were atypical with hysteresis at a low P/P(0) and pore sizes of 5.15 nm and a large surface area. At t (2 h), no DPH was released from CHT-HPAAm matrices, whereas 28.2% and 82.2% was released from pectin-HPAAm and pectin-CHT-HPAAm matrices, respectively. At t (4 h), complete DPH release was achieved from pectin-CHT-HPAAm matrices in contrast to only 35% from CHT-HPAAm matrices. This revealed the release-modulating capability of each matrix signifying their applicability in controlled oral drug delivery applications.

The Use of Electrospun Polycaprolactone as a Dermal Scaffold for Skin Tissue Engineering

Rapid healing of acute and chronic skin defects is an important objective. In the present work, we report on the design and feasibility of a co-culture system for fibroblasts and keratinocytes by using electrospun polycaprolactone (PCL) scaffolds. Specifically, we quantified the effect of scaffold fiber diameter on keratinocyte attachment, proliferation and differentiation along with collagen secretion by fibroblasts post vacuum seeding with fibroblasts at various depths. The results show that fibroblasts secrete more collagen and keratinocytes differentiate more on 400 nm scaffolds than on 1000 nm scaffolds. Also, fibroblasts co-cultured with keratinocytes provide increased collagen secretion and keratinocyte differentiation. These results suggest that the fiber architecture can be a useful parameter in skin tissue engineering.

The effect of elastin on chondrocyte adhesion and proliferation on poly (ɛ-caprolactone)/elastin composites

The aim of this study was to demonstrate the effect of elastin on chondrocyte adhesion and proliferation within the structure of poly (ɛ-caprolactone) (PCL)/elastin composites. The homogenous 3D structure composites were constructed by using high pressure CO(2) in two stages. Porous PCL structures with average pore sizes of 540 ± 21 μm and a high degree of interconnectivity were produced using gas foaming/salt leaching. The PCL scaffolds were then impregnated with elastin and cross-linked with glutaraldehyde (GA) under high pressure CO(2). The effects of elastin and cross-linker concentrations on the characteristics of composites were investigated. Increasing the elastin concentration from 25mg/ml to 100mg/ml elevated the amount of cross-linked elastin inside the macropores of PCL. Fourier transform infrared (FTIR) analysis showed that elastin was homogeneously distributed throughout the 3D structure of all composites. The weight gain of composites increased 2-fold from 15.8 ± 0.3 to 38.3 ± 0.7 (w/w) % by increasing the elastin concentration from 25mg/ml to 50mg/ml and approached a plateau above this concentration. The presence of elastin within the pores of PCL improved the water uptake properties of PCL scaffolds; the water uptake ratio of PCL was enhanced 100-fold from 0.030 ± 0.005g liquid/g polymer to 11.80 ± 0.01g liquid/g polymer, when the elastin solution concentration was 50mg/ml. These composites exhibited lower compressive modulus and energy loss compared to pure PCL scaffolds due to their higher water content and elasticity. In vitro studies show that these composites can support primary articular cartilage chondrocyte adhesion and proliferation within the 3D structures. These results demonstrate the potential of using PCL/elastin composites for cartilage repair.

Clay Aerogel Composite Materials

A simple, inexpensive, and environmentally-friendly process for converting mixtures of clays and polymers has been developed. Polymer and clay are combined in water, and the mixtures are freeze dried to produce materials which have bulk densities typically in the range of 0.03 – 0.15 g/cm3. These low density polymer/clay aerogel materials possess good mechanical properties similar to those of traditional polymer foams, can be reinforced with fibers, modified with nanoparticles, biomineralized, or converted into porous ceramics.

Poly-epsilon-caprolactone/gel hybrid scaffolds for cartilage tissue engineering

The aim of this study was to determine the suitability of hybrid scaffolds composed of naturally derived biopolymer gels and macroporous poly-epsilon-caprolactone (PCL) scaffolds for neocartilage formation in vitro. Rabbit articular chondrocytes were seeded into PCL/HA (1 wt % hyaluronan), PCL/CS (0.5 wt % chitosan), PCL/F (1:3 fibrin sealant plus aprotinin), and PCL/COL1 (0.24% type I collagen) hybrids and cultured statically for up to 50 days. Growth characteristics were evaluated by histological analysis, scanning electron microscopy, and confocal laser scanning microscopy. Neocartilage was quantified using a dimethyl-methylene blue assay for sulfated glycosaminoglycans (sGAG) and an enzyme-linked immunosorbent assay for type II collagen (COL2), normalized to dsDNA content by fluorescent PicoGreen assay. Chondrocytes were homogenously distributed throughout the entire scaffold and exhibited a predominantly spheroidal shape 1 h after being seeded into scaffolds. Immunofluorescence depicted expanding proteoglycan deposition with time. The sGAG per dsDNA increased in all hybrids between days 25 and 50. PCL/HA scaffolds consistently promoted highest yields. In contrast, total sGAG and total COL2 decreased in all hybrids except PCL/CS, which favored increasing values and a significantly higher total COL2 at day 50. Overall, dsDNA content decreased significantly with time, and particularly between days 3 and 6. The PCL/HA hybrid displayed two proliferation peaks at days 3 and 25, and PCL/COL1 displayed one proliferation peak at day 12. The developed hybrids provided distinct short-term environments for implanted chondrocytes, with not all of them being explicitly beneficial (PCL/F, PCL/COL1). The PCL/HA and PCL/CS hybrids, however, promoted specific neocartilage formation and initial cell retention and are thus promising for cartilage tissue engineering.

Visualization of the nanoscale assembly of type I collagen on PLA by AFM

Collagen adsorption and the morphology of its assemblies at polymer surface play an important role in improving the biocompatibility of materials. In this study, the nanoscale organization of type I collagen on Polylactide (PLA) was observed directly by high-resolution atomic force microscopy. The results show that the supramolecular structure of adsorbed collagen was affected by the concentration of collagen solution, appropriate pH and electrolyte composition of the buffer. On PLA substrate, network structures formed in high humidity atmosphere. In addition, collagen formed well-oriented nano-patterns at nearly neutral pH and appropriate electrolyte composition. Particularly, the typical 65 nm D-periodicity of collagen fibers was observed in the presence of potassium ions. Our investigation provides useful insights into the regulation of collagen assembly by substrates and environmental conditions, which is important for understanding the mechanism of collagen adsorption and assembly on polymer surfaces. It also offers a potential way to create surfaces of bio-functioned and nano-patterned materials for biotechnological and biomedical applications.

Electrical stimulation of nerve cells using conductive nanofibrous scaffolds for nerve tissue engineering

Fabrication of scaffolds with suitable chemical, mechanical, and electrical properties is critical for the success of nerve tissue engineering. Electrical stimulation was directly applied to electrospun conductive nanofibrous scaffolds to enhance the nerve regeneration process. In the present study, electrospun conductive nanofibers were prepared by mixing 10 and 15 wt% doped polyaniline (PANI) with poly (epsilon-caprolactone)/gelatin (PG) (70:30) solution (PANI/PG) by electrospinning. The fiber diameter, pore size, hydrophilicity, tensile properties, conductivity, Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy spectra of nanofibers were determined, and the in vitro biodegradability of the different nanofibrous scaffolds was also evaluated. Nanofibrous scaffolds containing 15% PANI was found to exhibit the most balanced properties to meet all the required specifications for electrical stimulation for its enhanced conductivity and is used for in vitro culture and electrical stimulation of nerve stem cells. 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay and scanning electron microscopy results showed that conductive nanofibrous scaffolds are suitable substrates for the attachment and proliferation of nerve stem cells. Electrical stimulation through conductive nanofibrous PANI/PG scaffolds showed enhanced cell proliferation and neurite outgrowth compared to the PANI/PG scaffolds that were not subjected to electrical stimulation.

Development of porous PEG hydrogels that enable efficient, uniform cell-seeding and permit early neural process extension

Three-dimensional polymer scaffolds are useful culture systems for neural cell growth and can provide permissive substrates that support neural processes as they extend across lesions in the brain and spinal cord. Degradable poly(ethylene) glycol (PEG) gels have been identified as a particularly promising scaffold material for this purpose; however, process extension within PEG gels is limited to late stages of hydrogel degradation. Here we demonstrate that earlier process extension can be achieved from primary neural cells encapsulated within PEG gels by creating a network of interconnected pores throughout the gel. Our method of incorporating these pores involves co-encapsulating a cell solution and a fibrin network within a PEG gel. The fibrin is subsequently enzymatically degraded under cytocompatible conditions, leaving behind a network of interconnected pores within the PEG gel. The primary neural cell population encapsulated in the gel is of mixed composition, containing differentiated neurons, and multipotent neuronal and glial precursor cells. We demonstrate that the initial presence of fibrin does not influence the cell-fate decisions of the encapsulated precursor cells. We also demonstrate that this fabrication approach enables simple, efficient and uniform seeding of viable cells throughout the entire porous scaffold.

Immobilization of biomolecules on the surface of electrospun polycaprolactone fibrous scaffolds for tissue engineering

To make polycaprolactone (PCL) more suitable for tissue engineering, PCL in the form of electrospun fibrous scaffolds was first modified with 1,6-hexamethylenediamine to introduce amino groups on their surface. Various biomolecules, i.e., collagen, chitosan, and Gly-Arg-Gly-Asp-Ser (GRGDS) peptide, were then immobilized on their surface, with N,N'-disuccinimidylcarbonate being used as the coupling agent. Dynamic water contact angle measurement indicated that the scaffold surface became more hydrophilic after the aminolytic treatment and the subsequent immobilization of the biomolecules. The appropriateness of these PCL fibrous scaffolds for the tissue/cell culture was evaluated in vitro with three different cell lines, e.g., mouse fibroblasts (L929), human epidermal keratinocytes (HEK001), and mouse calvaria-derived preosteoblastic cells (MC3T3-E1). Both the neat and the modified PCL fibrous scaffolds released no substances in the levels that were harmful to these cells. Among the various biomolecule-immobilized PCL fibrous scaffolds, the ones that had been immobilized with type I collagen, a Arg-Gly-Asp-containing protein, showed the greatest ability to support both the attachment and the proliferation of all of the investigated cell types, followed by those that had been immobilized with GRGDS peptide.

Immobilization of peptides by ozone activation to promote the osteoconductivity of PLLA substrates

In this study, ozone treatment was applied to modify poly(L-lactic acid) (PLLA) with the intermediate reagent acryl-N-succinimide (ASI). Then, P15, the peptide related to the attachment and differentiation of osteoblastic cells, was reacted with ASI. Ozone activation successfully created peroxides on the surface of PLLA, which was quantitatively determined by the iodide method. By changing the activation temperature, oxygen flow rate, reaction bath, reaction temperature or addition of ferrous ions, the amount of peroxides was controlled and the effects of these variables were explored in this research. The immobilizations of ASI and P15 were confirmed and quantitative analyzed by FT-IR spectroscopy, elementary analysis and amino-acid analysis. Also, the optimization for ozone activation and ASI grafting were performed. From in vitro experiments, the cultured ROS cells expressed significantly higher ALPase activity and calcium deposition after P15 immobilization. The results demonstrated that the ROS cells expressed osteoblastic phenotypes more significantly when cultured with the substrate modified with P15. In this study, PLLA was successfully modified with P15 by ozone activation and the modification promoted the osteoconductivity of PLLA substrates, which could be helpful in bone tissue engineering.

Three-dimensional ingrowth of bone cells within biodegradable cryogel scaffolds in bioreactors at different regimes

Three-dimensional cell ingrowth within biodegradable cryogel scaffolds made of cross-linked 2-hydroxyethyl methacrylate (HEMA)-lactate-dextran with interconnected macropores was studied in bioreactors at different regimes (static, perfusion, and compression-perfusion). An osteoblast-like cell line (MG63) was used in these studies. The samples taken after selected times from the bioreactors were examined by microscopy techniques (light, SEM, TEM, and laser scanning confocal). The cell culture conditions were found to have a significant impact not only on the cell morphology, such as the extent of cell attachment and ingrowth, but also on cellular activities. Dynamic conditions (perfusion and/or compression) greatly improved cell ingrowth and extracellular matrix (ECM) synthesis. Alkaline phosphatase activity results confirmed the positive effect of dynamic conditions on bone cells.