Interconnected Pore Morphology Research Articles

REVITALIZATION OF CRITICAL-SIZED CALVARIAL DEFECTS IN RATS USING HEPARIN-CONJUGATED FIBRIN HYDROGEL WITH BMP-2 AND ADIPOSE-DERIVED PERICYTES

Massive bone defects present challenges in orthopedic surgery, requiring innovative solutions. Hydrogels offer promise due to their resemblance to the extracellular matrix. Adipose tissue-derived pericytes (ADPs) and osteoinductive proteins like BMP-2 show potential for bone tissue engineering. Combining them via heparin-conjugated fibrin hydrogel aims to enhance healing in critical-sized calvarial defects. The study investigated the use of a heparin-conjugated fibrin (HCF) hydrogel containing BMP-2 and adipose-derived pericytes for repairing critical-sized calvarial defects in rats. ADPs were cultured from rat adipose tissue, and the HCF hydrogel was prepared accordingly. In vitro experiments assessed BMP-2 release kinetics and bioactivity, while mineralization assays were conducted on cultured ADPs. In vivo experiments involved surgically creating calvarial defects in rats and implanting HCF gel alone or with BMP-2, pericytes, or both. Micro-CT imaging and histological analysis were performed post-implantation to evaluate bone formation. In our study, we prepared the HCF hydrogel by combining heparin-conjugated fibrinogen, human fibrinogen, human thrombin, aprotinin, and calcium chloride. Gelation occurred within 3 minutes at room temperature. SEM analysis revealed an open interconnected pore morphology and macroporous structure, facilitating cell attachment and proliferation. ELISA showed sustained release of BMP-2 from the HCF hydrogel over 28 days. Bioactivity assays demonstrated the ability of released BMP-2 to enhance ALP activity in rat neonatal calvarial osteoblasts. Additionally, BMP-2 induced osteogenic differentiation of rat ADPs, as evidenced by increased ALP activity, osteocalcin expression, and calcium deposition. Implantation of HCF hydrogels containing BMP-2 and/or ADPs into rat calvarial defects significantly promoted bone tissue regeneration compared to controls, with the greatest effect observed in the group receiving both BMP-2 and ADPs. Micro-CT and histological analysis confirmed substantial bone formation and defect closure after three months. In conclusion, our in vitro findings demonstrated that the HCF hydrogel provided sustained release of BMP-2, retaining its bioactivity and promoting osteogenesis in rat calvarial osteoblasts and ADPs. In vivo results showed that combining allogeneic ADPs with BMP-2 enhanced bone regeneration in critical-sized calvarial defects, indicating the potential of this approach for large bone defect restoration.

Phyllanthus emblica‐Loaded Cryogels for Improved Wound Care: Characterization and In Vitro Studies

AbstractWound dressings developed by combining plant extracts with polymers have made a great progress in wound care treatment. One plant with remarkable healing properties is Phyllanthus emblica Linn (P. emblica), which is described as having potent antioxidant, antimicrobial and anti‐inflammatory properties. The aim of this study is to evaluate the biocompatibility of P. emblica‐loaded polyvinyl alcohol/gelatin‐based cryogels (PVA/Gel/P.emblica) through cytotoxicity and proliferation tests in HaCaT cells and examine their potential in wound dressing applications. Accordingly, PVA/Gel/P.emblica cryogels are successfully synthesized and characterization studies and in vitro cell culture studies are performed. The swelling tests and Brunauer–Emmett–Teller analysis results show that swelling and surface area properties of cryogels increase with increasing P. emblica amounts. Morphological results display that the cryogels have a dense, interconnected pore morphology and a macroporous structure. 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide, trypan blue exclusion, and live–dead assay results reveal that P. emblica enhances cell proliferation, increases cell number, and improves cell viability. Based on the scanning electron microscope, immunofluorescence, and Giemsa staining images, it is observed that P. emblica promotes cell attachment, proliferation, and penetration. These findings confirm that PVA/Gel/P.emblica cryogels are suitable for use as wound dressing materials and can be developed with further studies.

In Vitro and In Vivo Biocompatible and Controlled Resveratrol Release Performances of HEMA/Alginate and HEMA/Gelatin IPN Hydrogel Scaffolds.

Scaffold hydrogel biomaterials designed to have advantageous biofunctional properties, which can be applied for controlled bioactive agent release, represent an important concept in biomedical tissue engineering. Our goal was to create scaffolding materials that mimic living tissue for biomedical utilization. In this study, two novel series of interpenetrating hydrogel networks (IPNs) based on 2-hydroxyethyl methacrylate/gelatin and 2-hydroxyethyl methacrylate/alginate were crosslinked using N-ethyl-N′-(3-dimethyl aminopropyl)carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS). Characterization included examining the effects of crosslinker type and concentration on structure, morphological and mechanical properties, in vitro swelling, hydrophilicity as well as on the in vitro cell viability (fibroblast cells) and in vivo (Caenorhabditis elegans) interactions of novel biomaterials. The engineered IPN hydrogel scaffolds show an interconnected pore morphology and porosity range of 62.36 to 85.20%, favorable in vitro swelling capacity, full hydrophilicity, and Young’s modulus values in the range of 1.40 to 7.50 MPa. In vitro assay on healthy human fibroblast (MRC5 cells) by MTT test and in vivo (Caenorhabditis elegans) survival assays show the advantageous biocompatible properties of novel IPN hydrogel scaffolds. Furthermore, in vitro controlled release study of the therapeutic agent resveratrol showed that these novel scaffolding systems are suitable controlled release platforms. The results revealed that the use of EDC and the combination of EDC/NHS crosslinkers can be applied to prepare and tune the properties of the IPN 2-hydroxyethyl methacrylate/alginate and 2-hydroxyethyl methacrylate/gelatin hydrogel scaffolds series, which have shown great potential for biomedical engineering applications.

Controllable surficial and internal hierarchical structures of porous poly (L-lactic acid) membranes for hydrophobicity and potential application in oil-water separation

Focused on the design and construction of controllable surface microtopographyand interconnected pore morphologyof porous poly (L-lactic acid) membrane. Asimple solvent evaporation-induced precipitation methodis proposed to regulate microstructures by one-step method without any additive. Controllable microstructures (fibrous networks, interconnected pores, and crystallized PLLA protrusions) and interconnected pore morphology were facilely achieved by adjusting the PLLA concentration and/or precipitation temperature. In view of the shortcomings of previous foam preparation, the contact area between solvent and non-solvent was broadenedto realize the improvement of porosity and the construction of surface micro-nano structure. The results show that the crystallinity of prepared PLLA membranes is kept in a high range between 61.8% and 75.8% and the maximum watercontact angle (WCA) is largely increased to 142.3°. Surprisingly, surface wettability of PLLA membranes possess the wonderful mechanical damage resistance, and the porosity and oil-absorption capacity are increased to 90.8% and 24.1 g/grespectively. Predictably, the porous PLLA membrane has great application potential as a biodegradable oil-water separation material.

Investigation on preparation porous titanium through calciothermic reduction of porous TiO precursors

A route is present for preparing porous titanium scaffolds with open and interconnected pore morphology through calcium thermal in-situ reduction of TiO precursor. Titanium and dioxide titanium powders, with ammonium carbonate as the space holder, were used to prepare porous precursor whose main phase is TiO by a sintering process. Then calcium vapor was conduced to reduce the precursor and CaO was removed by leaching to obtain porous titanium structures. The morphology, pore structure, phase analysis of porous titanium precursor and porous titanium scaffolds were investigated by means of XRD, SEM and EDS. The porosity was observed by Archimedes method. By this route, the porous titanium with multi-gradient pore sizes ranging from a few microns to several hundred microns was formed. The porous titanium is of multi-gradient pore size distribution of 100 μm bigger, 10 μm∼100 μm and 10 μm smaller. The micro-pores on the pore walls increases connectivity between the macro-pores throughout the porous titanium interior. The porous titanium obtained by this method has a porosity of 50–65% and a titanium content more than 99%.

Modeling and Simulation of Cu Drift in Porous Low-k Dielectrics

Integrating nanometer sized pores into low-k ILD films is one of the approaches to lower the RC signal delay and thus help sustain the continued scaling of micro-electronic devices. While increasing porosity of porous dielectrics lowers the dielectric constant (k), it also creates many reliability and implementation issues. One of the problems is the little understood metal ion drift in porous media. Here, we extend the rigorous simulation method of Cu diffusion in porous dielectrics based on elementary jump probabilities (presented at 231st ECS Spring Meeting 2017 [1]) to include the ion drift in electric fields and explore the conditions for metal filament formation in porous media. The present atomistic approach allows a consistent co-implementation of Cu diffusion and Cu ion drift in electric field by lowering and raising of the diffusion activation energy Ea along the electric field Eel direction as exp(-(Ea ±1/2qlEel)/kT), where l is the elementary jump distance, q is the elementary electronic charge, "-" denotes the enhancement factor in the field direction and "+" the retardation factor against the field. Our analysis of resistive switching behavior in porous dielectrics [2] shows that electric fields responsible for Cu filament formation are in excess of 106 V/cm. At such high fields, the drift transport based mobility (m) concept where drift velocity v=m´Eel is no longer valid since the required inequality Eel<< kT/(ql) = 1.2´105 V/cm for T=300K and l=21 A, does not hold, and, consequentially, all modeling methods based on drift-diffusion continuum equations fail to describe ion drift adequately. As described in [1] as a numerical method the diffusion tensor technique (4th rank tensor in 2D, 9th rank in 3D) has been used with elementary diffusion/drift jump probabilities at each lattice site. Simulation shows that the Cu drift transport across porous materials depends more on the type of morphology than on the level of porosity. Three different basic pore morphologies are considered: 1) columnar pores laterally oriented to the Cu transport, 2) Columnar pores vertically oriented to the Cu transport, and 3) Uniform distribution of pores of the same size across the dielectric. For all morphologies, the porosity is varied between 0% and 47%. We find that, for spherical pores distributed more or less uniformly, the effective drift transport of Cu across dielectric at a room temperature comes to a stop at a porosity of around 40%. At room temperature, uniform spherical pore morphologies at certain porosity levels will block the drift transport of Cu across the dielectric entirely. However, for the same pore morphology at elevated temperatures, the relative jump frequency enhancement factor caused by the electric field is considerably reduced and now the increased lateral jump frequencies, owing to pure diffusion, help circumnavigate the pores causing a significant surge of drift transport of Cu ions. This is important technologically in CMOS back-end Cu lines when those are operated at high currents or at high switching frequencies. Under such circumstances, the local temperature of the dielectric may rise significantly over the room temperature. We have performed atomistic drift-diffusion simulations in the temperature interval between 27 oC and 400 oC. We find that although the relative electric field enhancement factor has been substantially reduced, the increased lateral jump frequencies give rise to a significant drift transport of Cu ions across the porous dielectric. One consequence of this is that resistive switching in porous media is facilitated by rising temperature which may pose a reliability issue. In case of columnar pore morphology, when the electric field is aligned to the main pore orientation, the so called “channeling effect” [1] is simply enhanced by the drift component. However, the drift enhancement factor is decreasing with increasing temperature. In most of morphologies, the increasing temperature makes the drift-diffusion transport more efficient. However, in the case of the columnar morphology with its main orientation perpendicular to the electric field, the effective drift-transport may decrease with the increasing temperature. The reason for this unusual transport retardation at elevated temperatures is the deflection of the Cu ions due to increase of lateral movement into the quasi-trapping regions between the columnar pores which weakens the overall perpendicular drift diffusion transport from the Cu electrode to the counter-electrode. In our simulation grain boundary diffusion can be accommodated as a particular embodiment of interconnected pore morphology. [1] R. Ali et al, “Modeling and Simulation of Cu Diffusion in Porous low-k Dielectrics’ 231stECS Spring MTG, 2017 [2] Y. Fan et al, “Characterization of Porous BEOL Dielectrics for Resistive Switching”, 229th ECS Spring MTG, 2016

Fabrication of porous chitin with continuous substructure by regeneration from gel with CaBr2·2H2O/methanol

In this study, we investigated the fabrication of porous chitins with continuous channel substructure by regeneration from gels with CaBr2·2H2O/methanol solution. After rapidly removing methanol from the gels, the products were immersed in methanol, followed by washing out CaBr2 with water and lyophilization to obtain regenerated chitins with inter-connected continuous pore morphology. Scanning electron microscopic results supported that the materials were consisted of continuous substructures of porous channels. The materials were further characterized by SEM-EDX and XRD measurements. The mechanical property and water absorbability were also evaluated. The plausible mechanism for the formation of the inter-connected pore morphology during the regeneration procedure was discussed.

Preparation, Characterization and Mechanical Assessment of Poly (Lactide-Co-Glycolide)/ Hyaluronic Acid/ Fibrin/ Bioactive Glass Nano-composite Scaffolds for Cartilage Tissue Engineering Applications

The purpose of this study was to evaluate the microstructural and mechanical properties of poly (Lactide-co-Glycolide) (PLGA) and PLGA/ Hyaluronic acid (Ha)/ Fibrin (F)/ Bioactive glass (BG) nanocomposite scaffolds for cartilage tissue engineering. Nanocomposite scaffolds composed of PLGA/ Ha/ F/ BG, containing different amounts of Ha, F, and BG nanoparticles were prepared via solvent casting and particulate leaching (SC/PL) techniques. Characterization techniques such as Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and X-ray diffraction (XRD), were performed. Furthermore, mechanical properties of the PLGA and nanocomposite scaffolds were determined. The results revealed that the scaffolds contain sufficient porosity with highly interconnected pore morphology. Desired distribution of BG nanoparticles with a few agglomerates was observed in the nanocomposite scaffolds by microscopic techniques. Increase the amount of fibrin enhanced compressive modulus and compressive strength of the nanocomposite scaffolds.

A bioactive “self-fitting” shape memory polymer scaffold with potential to treat cranio-maxillo facial bone defects

While tissue engineering is a promising alternative for treating critical-sized cranio-maxillofacial bone defects, improvements in scaffold design are needed. In particular, scaffolds that can precisely match the irregular boundaries of bone defects as well as exhibit an interconnected pore morphology and bioactivity would enhance tissue regeneration. In this study, a shape memory polymer (SMP) scaffold was developed exhibiting an open porous structure and the capacity to conformally “self-fit” into irregular defects. The SMP scaffold was prepared via photocrosslinking of poly(ε-caprolactone) (PCL) diacrylate using a SCPL method, which included a fused salt template. A bioactive polydopamine coating was applied to coat the pore walls. Following exposure to warm saline at T>Ttrans (Ttrans=Tm of PCL), the scaffold became malleable and could be pressed into an irregular model defect. Cooling caused the scaffold to lock in its temporary shape within the defect. The polydopamine coating did not alter the physical properties of the scaffold. However, polydopamine-coated scaffolds exhibited superior bioactivity (i.e. formation of hydroxyapatite in vitro), osteoblast adhesion, proliferation, osteogenic gene expression and extracellular matrix deposition.

Synthesis of composite gelatin-hyaluronic acid-alginate porous scaffold and evaluation for in vitro stem cell growth and in vivo tissue integration

Engineering three-dimensional (3-D) porous scaffolds with precise bio-functional properties is one of the most important issues in tissue engineering. In the present study, a three-dimensional gelatin-hyaluronic acid-alginate (GHA) polymeric composite was synthesized by freeze-drying, which was followed by ionic crosslinking using CaCl2, and evaluated for its suitability in bone tissue engineering applications. The obtained matrix showed high porosity (85%), an interconnected pore morphology and a rapid swelling behavior. The rheological analysis of GHA showed a viscoelastic characteristic, which suggested a high load bearing capacity without fractural deformation. The influence of the GHA matrix on cell growth and on modulating the differentiation ability of mesenchymal stem cells was evaluated by different biochemical and immunostaining assays. The monitoring of cells over a period of four weeks showed increased cellular proliferation and osteogenic differentiation without external growth factors, compared with control (supplemented with osteogenic differentiation medium). The in vivo matrix implantation showed higher matrix-tissue integration and cell infiltration as the duration of the implant increased. These results suggest that a porous GHA matrix with suitable mechanical integrity and tissue compatibility is a promising substrate for the osteogenic differentiation of stem cells for bone tissue engineering applications.

Effects of processing parameters in thermally induced phase separation technique on porous architecture of scaffolds for bone tissue engineering

Tissue engineering makes use of 3D scaffolds to sustain three-dimensional growth of cells and guide new tissue formation. To meet the multiple requirements for regeneration of biological tissues and organs, a wide range of scaffold fabrication techniques have been developed, aiming to produce porous constructs with the desired pore size range and pore morphology. Among different scaffold fabrication techniques, thermally induced phase separation (TIPS) method has been widely used in recent years because of its potential to produce highly porous scaffolds with interconnected pore morphology. The scaffold architecture can be closely controlled by adjusting the process parameters, including polymer type and concentration, solvent composition, quenching temperature and time, coarsening process, and incorporation of inorganic particles. The objective of this review is to provide information pertaining to the effect of these parameters on the architecture and properties of the scaffolds fabricated by the TIPS technique.

Reactive thiol-ene emulsion-templated porous polymers incorporating pentafluorophenyl acrylate

Highly porous polymers (polyHIPEs) incorporating activated esters have been prepared by photopolymerisation of high internal phase emulsions (HIPEs) containing pentafluorophenyl acrylate (PFPA) in the monomer phase. The resulting materials have nominal porosity of 80% and a well-defined, interconnected pore morphology with average pore diameters ranging from 30 to 50 μm. PFPA could be added at up to 50 wt% of the monomer phase without destabilising the HIPE noticeably, however analysis of the polyHIPE materials revealed that only around half of this was incorporated into the final porous materials. The pentafluorophenyl groups were shown to be reactive towards a range of amines (tris-(2-aminoethyl)amine, benzylamine and Rhodamine 123), giving near complete loss of fluorine over the period of the reaction. The extent of functionalisation was however determined to be around 50% by elemental analysis, suggesting some loss of fluorine by hydrolysis of activated esters. We believe that this represents a facile method for the preparation of a variety of well-defined functional porous polymers by a post-polymerisation functionalisation route.

Ion-responsive alginate based macroporous injectable hydrogel scaffolds prepared by emulsion templating.

Ion-responsive biocompatible macroporous hydrogels with a well-defined highly interconnected open porous structure were synthesised using oil-in-water (o/w) high internal phase emulsion (HIPE) templating. Methacrylate-modified alginate was crosslinked in the continuous minority water phase and the oil internal phase removed to produce macroporous hydrogel monoliths. The physical dimensions, pore and pore throat size as well as water uptake of the alginate polyHIPE hydrogel can be controllably tuned by ion-responsive behaviour towards Ca2+ ions. The ionic crosslinks formed are fully reversible and be dissolved using sodium citrate to remove Ca2+ ions through chelation. The polyHIPE hydrogels possess mechanical properties with storage moduli up to 20 kPa and are biocompatible as shown by cytotoxicity assays. The hydrogel can be extruded through a hypodermic needle causing it to break into small pieces (about 1 to 3 mm in diameter) while retaining the interconnected pore morphology after injection. Furthermore, these hydrogel fragments can be reformed into a coherent scaffold under mild conditions using an alginate solution containing Ca2+ ions.

Fabrication of porous titanium implants with biomechanical compatibility

By using H 2O 2 as foaming reagent, porous titanium with open and interconnected pore morphology was obtained. The morphology, pore structure and elemental composition were observed by SEM–EDX. The mechanical property was determined by compressive test. The results show that the compressive strength and Young's modulus of porous titanium with 64% porosity were 102 ± 10 MPa and 3.3 ± 0.8 GPa, respectively, and for 76% porosity porous titanium, the values were 23 ± 10 MPa and 2.1 ± 0.5 GPa. These results suggest that the former has sufficient mechanical properties for clinical use under load-bearing conditions and the latter has the potential application for tissue engineering scaffolds.

Preparation of Porous Titanium by a Novel Foaming Process and MG63 Cell Behavior &lt;i&gt;In Vitro&lt;/i&gt;

A novel two-step foaming process has been developed to prepare the porous titanium implant. By using H2O2 and stearic acid as foaming reagent ordinally, a foamed structure with an open, interconnected pore morphology was obtained. The mechanical property was determined by compressive test. In vitro study was conducted to evaluate the ability of the porous titanium to support the growth and differentiation of Human osteosarcoma cell line MG63. The results show that the porous titanium has better interconnection compared to that obtained by traditional slurry foaming and its compressive strength and Young’s modulus were approximate 23.6 MPa and 2.1 GPa, respectively. Cell culture experiment results indicate that the porous titanium has good biocompatibility and acid-alkali treatment facilitates the adherence and proliferation of cells.

Preparation and characterisation of poly(lactide-co-glycolide) (PLGA) and PLGA/Bioglass® composite tubular foam scaffolds for tissue engineering applications

Polylactide-co-glycolide (PLGA) and PLGA/Bioglass® foams of tubular shape have been prepared with a 1 wt.% 45S5 Bioglass® content. Porous membranes with varying thickness and porosity were fabricated via a thermally induced phase separation process, from which tubes of controlled diameter and wall thickness in the range 1.5–3 mm were produced. Scanning electron microscopy (SEM) revealed that the structure of the tubular foams consisted of radially oriented and highly interconnected pores with two distinct pore sizes, i.e. macropores ∼100-μm average diameter and interconnected micropores of 10–50-μm diameter. Foams with Bioglass® inclusions showed similarly well-defined tubular and interconnected pore morphology. Cell culture studies using mouse fibroblasts (L929) were conducted to assess the biocompatibility of the scaffolds in vitro. L929 fibroblasts cultured in medium that was pre-conditioned by incubating with PLGA tubes containing Bioglass® had a significant reduction in cell proliferation compared with fibroblasts grown in unconditioned medium ( p<0.0001). The PLGA and PLGA/Bioglass® tubular foams developed here are candidate materials for soft-tissue engineering scaffolds, holding promise for the regeneration of tissues requiring a tubular shape scaffold, such as intestine, trachea and blood vessels.

The influence of pore morphology on corrosion

Porous titanium parts fabricated powder-metallurgically are known to have pore morphologies that range from large, open, interconnected pores to small, isolated pores. Although the latter geometry is synonymous with highly dense and mechanically strong materials, it conceivably encourages stagnation of electrolyte and prevents its free flow crucial to the ion incorporation/titanium release process of passivation. In this case, the depletion of oxygen leads to crevice corrosion which further increases the corrosion rate of these large-surfacearea systems. To investigate the localised corrosion resistance of porous titanium (porosity 10–30%, pore size 50–100μm), cyclic polarisation tests were performed in saline solution at 37 °C, on porous pure titanium compacts with varying porosities and pore sizes, solid titanium and 316L stainless steel. As expected, 316L stainless steel exhibited poor corrosion resistance compared to titanium. A distinct hysteresis was observed in the reverse scan of the former which indicates the weak resistance to crevice and pitting corrosion of this well-established metallic biomaterial. The main reason for the excellent corrosion resistance of the solid and porous titanium compacts is the strong affinity of the metal to even a slight trace of oxygen in an aqueous environment, resulting in a highly resistant and self-regenerating passive film. However, the cyclic polarisation studies also showed that the final E corr value reduces with decreasing porosity. This is due to the small, isolated pore morphology that traps ionic species and exhausts the supply of oxygen. In highly porous compacts with an open, interconnected pore morphology, the free flow of species resulted in a material with much higher resistance to pitting.