Tissue Scaffold Materials Research Articles

All Biodisintegratable Hydrogel Biohybrid Neural Interfaces with Synergistic Performances of Microelectrode Array Technologies, Tissue Scaffolding, and Cell Therapy

AbstractBiohybrid neural interfaces (BHNIs) are a new class of neuromodulating devices that integrate neural microelectrode arrays (MEAs) and cell transplantation to improve treatment of nerve injuries and disorders. However, current BHNI devices are made from abiotic materials that are usually bio‐passive, non‐biodisintegratable, or rigid, which restricts encapsulated cell activity and host nerve reconstruction and frequently leads to local tissue inflammation. Herein, the first MEA composed of all disintegratable hydrogel tissue scaffold materials with synergistic performances of tissue conformal adhesiveness, MEA technologies, tissue scaffolding and stem cell therapy on a time scale appropriate for nerve tissue repair is proposed. In particular, the MEA conductive tracks are made from extracellular matrix (ECM)‐based double‐cross‐linked dual‐electrically conductive hydrogel (ECH) systems with robust tissue‐mimicking chemical/physical properties, electrical conductivity, and an affinity for neural progenitor stem cells. Meanwhile, the MEA hydrogel substrate prepared from transglutaminase‐incorporated gelatin/silk precursors simultaneously promotes gelation and interfacial adhesion between all MEA stacks, leading to rapid and scalable device integration. When the full hydrogel MEA is subjected to various mechanical stimuli and moisture, it is structurally stable with a low impedance (4 ± 3 kΩ) comparable to a recently reported benchmark. With seamless lamination around peripheral nerve fibers, the device permits successive neural signal monitoring for wound condition evaluation, while demonstrating synergistic effects of spatiotemporally controlled electrical stimulation and cell transplantation to accelerate restoration of motor function. This BHNI is completely degraded by 1 month thus eliminating the need for surgical retrieval to stably remain, interact, and further fuse with host tissues, successfully exhibiting compatible integration of biology and an implanted electrical system.

Antimicrobial PVDF nanofiber composites with the ZnO - vermiculite - chlorhexidine based nanoparticles and their tensile properties

The poly(vinylidene fluoride) (PVDF) nanofiber materials have attracted attention due to their enhanced and exceptional nanostructural characteristics. Electrospinning PVDF based nanofiber is one of the important new materials for the rapidly growing technology development such as nanofiber based conductive tissue engineering, scaffold materials, filters and medical textiles applications. At these areas the risk of microbial contamination is very high, hence in this study the PVDF nanofiber materials with antimicrobial zinc oxide (ZnO), zinc oxide/vermiculite (ZnO/V), zinc oxide/vermiculite-chlorhexidine (ZnO/V_CH) and vermiculite-chlorhexidine (V_CH) nanofillers were prepared by electrospinning, via one-step electrospinning process. The PVDF nanofiber diameters and their orientation were investigated using scanning electron microscope (SEM). The ZnO/V_CH and V/CH nanofillers with positive ζ - potential values were incorporated into PVDF nanofibers with an average diameter of 108 nm for PVDF_ZnO/V_CH and 100 nm for PVDF_V_CH samples. In contrast, ZnO and ZnO/V nanofillers with negative ζ - potential values reacted intensively with PVDF polymer. The slightly hydrophobe character was demonstrated by water contact angle from ∼100°. The chemical interactions were evaluated by the Fourier transform infrared spectroscopy (FTIR). The presence of the β-phase in the original PVDF and the small traces of the α-phase in PVDF_ZnO and PVDF_ZnO/V samples was confirmed. In the PVDF_ZnO/V_CH and PVDF_V/CH samples where the specific interaction of PVDF chains with CH a rapid decrease in the β-phase fraction was evaluated. The mechanical properties based on the Young's modulus (E) and tensile strength (Rm) values were evaluated from the tensile test curves. Antimicrobial activity (longer than 48 h) against S. aureus and E. coli for PVDF_ZnO/V_CH and PVDF_V/CH samples was obtained.

Application and research of nano-biomaterials in ankle sports injury rehabilitation

The ankle joint is an important weight-bearing joint of the lower limbs. It converts the vertical gravity of the human body into an arched structure. When the ankle joint is exposed to external reaction forces and cannot be effectively cushioned, injuries can easily occur. If improper and untimely treatment can cause joint instability, easy to repeatedly sprain in the future, secondary joint adhesions or traumatic arthritis can cause dysfunction. Therefore, strengthening the treatment of ankle joint injury repair is of great significance to improve prognosis and improve clinical effect. Clinically, the treatment of ankle joint injury is mainly based on protection, rest, cold compress, and drug intervention. It is difficult to achieve the expected therapeutic effect. From a large amount of research data, with the development of tissue engineering and bioengineering, currently the use of artificial biological materials to intervene in the healing and rehabilitation of bone injuries has become increasingly mature, but it is relatively rare in rehabilitation measures for ankle sports injuries. Therefore, in this study, 3D printing technology was used to mix PHBV, calcium silicate, and bioactive glass to successfully prepare a bioglass scaffold BG-Si-PHBV. The micromorphology, porosity, water absorption, weight loss analysis and biomechanical characteristics of the biomaterial scaffold were studied. At the same time, this study established an ankle joint sports injury model with Beagle dogs, implanted BG-Si-PHBV biological bone tissue scaffold material into the ankle joint defect area of the affected limb of Beagle dogs, and detected BG-Si-PHBV tissue engineering materials to repair the ankle joint Feasibility of sports injuries. The BG-Si-PHBV biological bone tissue scaffold material prepared in this research has good porosity, hydrophilicity and biomechanical properties, which can meet the conditions of artificial biological materials after ankle injury. Animal experiments show that BG-Si-PHBV biological bone tissue scaffold is ideal for the rehabilitation of ankle joint sports injuries. This helps to improve the biomechanical properties and has broad application prospects.

A Brief Review on Prospective of Polyvinylidene Fluoride as a Tissue Engineered Scaffold Material

This review focuses on the potential of polyvinylidene fluoride (PVDF) as tissue scaffolding materials. PVDF is defined in terms of the synthesis mechanisms and the method of the β phase formation process. General properties are fundamentally discussed in terms of their wettability and electroactive characteristics, which play an essential role in modifying other potential materials for tissue-based applications. The latest technologies for the replacement of artificial tissue scaffolds are evaluated, and the applications of PVDF-based scaffolds are discussed.

Study of a new nano-hydroxyapatite/basic fibroblast growth factor composite promoting periodontal tissue regeneration

Tissue engineering technology provides a new method for periodontal regeneration. Finding or preparing a suitable scaffold is the key to periodontal tissue engineering. Here, we use nano-hydroxyapatite-modified collagen biomimetic material (nHAC) as the packaging material, and carry fibroblast growth factor (bFGF) for the regeneration and repair of periodontal tissue. Due to its low cytotoxicity and high biocompatibility, nHAC shows unique advantages in the construction of periodontal tissue scaffolds. The nHAC periodontal tissue scaffold material has a dense and porous three-dimensional network structure, has a high loading rate of bFGF, and can firmly lock human periodontal ligament cells (HPDLCs), which is easy for cell growth and attachment. In vivo experiments have shown that, in artificial animal periodontal tissue models, the nHAC-loaded bFGF periodontal scaffold covered by Geistlich Bio-Gide (GBG) membrane is better than the simple GBG membrane and the blank group, the nHAC/bFGF-GBG composite membrane It is beneficial to promote the growth of new alveolar bone and cement formation, and realize the regeneration of periodontal tissue.

Preparation of electrospun polycaprolactone nanofiber mats loaded with microalgal extracts.

Sustainable, ecological, and biocompatible materials are emerging for the development of novel components for tissue engineering. Microalgae being one of the unique organisms on Earth to provide various novel compounds with certain bioactivities are also a good source for the development of novel tissue scaffold materials. In this study, electrospinning technique was utilized to fabricate nanofibers from polycaprolactone loaded with microalgal extracts obtained from Haematococcus pluvialis (vegetative and carotenoid producing form) and Chlorella vulgaris. The FTIR results showed that, blending microalgae with polycaprolactone give unique bands rooted from microalgae and polycaprolactone structure. The samples were not diversified from each other, however stable bands were observed. SEM analysis revealed a uniform fiber fabrication with an average diameter of 810±55nm independent from microalgal extracts. MTT assay was done on HUVEC cell lines and results showed that nanofiber mats helped cell proliferation with extended time. Biodegradation resulted with mineral accumulation on the surface of same samples however the fiber degradation was uniform. With slow but stable biodegradation characteristics, microalgal extract loaded nanofiber mats holds great potential to be novel tissue scaffold material.

Direct, Real-Time Detection of Adenosine Triphosphate Release from Astrocytes in Three-Dimensional Culture Using an Integrated Electrochemical Aptamer-Based Sensor.

In this manuscript, we describe the development and application of electrochemical aptamer-based (E-AB) sensors directly interfaced with astrocytes in three-dimensional (3D) cell culture to monitor stimulated release of adenosine triphosphate (ATP). The aptamer-based sensor couples specific detection of ATP, selective performance directly in cell culture media, and seconds time resolution using squarewave voltammetry for quantitative ATP-release measurements. More specifically, we demonstrate the ability to quantitatively monitor ATP release into the extracellular environment after stimulation by the addition of calcium (Ca2+), ionomycin, and glutamate. The sensor response is confirmed to be specific to ATP and requires the presence of astrocytes in culture. For example, PC12 cells do not elicit a sensor response after stimulation with the same stimulants. In addition, we confirmed cell viability in the collagen matrix for all conditions tested. Our hydrogel-sensor interface offers the potential to study the release of small molecule messengers in 3D environments. Given the generality of electrochemical aptamer-based sensors and the demonstrated successful interfacing of sensors with tissue scaffold material, in the long term, we anticipate our sensors will be able to translate from in vitro to in vivo small molecule recordings.

Abstract: A Novel Nanofiber-Hydrogel Tissue Scaffold for Improved Fat Graft Survival

INTRODUCTION: Autologous fat grafting is an important adjunct to soft-tissue reconstruction in patients after oncologic resection of tumors. However, it is associated with multiple complications such as fat necrosis, oil cyst formation, and poor volume retention. There currently exist no tissue scaffold materials that aid in human fat graft retention. The purpose of this study is to demonstrate that our novel nanofiber-hydrogel composite serves as a tissue scaffold that improves fat graft retention and promotes enhanced vascularization within the graft. METHODS: The following groups were studied: 100% lipoaspirate, 50% lipoaspirate/50% composite, 50% lipoaspirate/50% hydrogel, 75% lipoaspirate/25% composite, and 100% composite. 500uL of material was subcutaneously injected into both flanks of Foxn1nu NU/J male mice (2 injections per mouse). Fifteen mice were used per group. Mice were imaged using MRI at post-operative day (POD) 2, 28, 56, and 84 to assess graft volume retention. Grafts were explanted on days 7, 28, and 84. Immunohistochemistry (IHC) was performed on explanted grafts to evaluate graft vascularization and adipocyte morphology. RESULTS: The 50% lipoaspirate/50% composite and 75% lipoaspirate/25% composite groups had the highest volume retention on MRI volumetric analysis (38%, 41% respectively) on POD84. The 100% composite only group had the poorest volume retention (14%) on POD 84. On IHC, groups containing the nanofiber-hydrogel composite demonstrated superior rates of angiogenesis and blood vessel ingrowth into the graft as compared to lipoaspirate and lipoaspirate/hydrogel only groups. Furthermore, adipocyte morphology was better preserved in groups containing the nanofiber-hydrogel composite. CONCLUSION: Both groups containing a combination of lipoaspirate/composite exhibited superior volume retention at POD 84 compared to solely lipoaspirate or lipoaspirate/hydrogel combination. Furthermore, the combination of lipoaspirate and composite results in better volume retention compared to either group alone. As demonstrated through IHC, our nanofiber-hydrogel composite promotes higher degrees of angiogenesis than does 100% lipoaspirate or 50% lipoaspirate/50% hydrogel. The nanofiber-hydrogel composite better preserves adipose cell morphology in fat grafting. This has important clinical implications, as improved fat graft retention would save the patient the additional morbidity of undergoing multiple bouts of anesthesia and multiple surgical procedures.

Scalable method to make tissue scaffold material

To help restore damaged bone, researchers are developing polymer scaffolds that can be implanted in the body to support the growth of new tissue. Poly(propylene fumarate), or PPF, is one of the few...

Pore structures and mechanical properties of porous titanium scaffolds by bidirectional freeze casting

Porous titanium scaffolds with long-range lamellar structure were fabricated using a novel bidirectional freeze casting method. Compared with the ordinarily porous titanium materials made by traditional freeze casting, the titanium walls can offer the structure of ordered arrays with parallel to each other in the transverse cross-sections. And titanium scaffolds with different pore width, wall size and porosity can be synthesized in terms of adjusting the fabrication parameters. As the titanium content was increased from 15vol.% to 25vol.%, the porosity and pore width decreased from 67±3% to 50±2% and 80±10μm to 67±7μm, respectively. On the contrary, as the wall size was increased from 18±2μm to 30±3μm, the compressive strength and stiffness were increased from 58±8MPa to 162±10MPa and from 2.5±0.7GPa to 6.5±0.9GPa, respectively. The porous titanium scaffolds with long-range lamellar structure and controllable pore structure produced in present work will be capable of having potential application as bone tissue scaffold materials.

Synthesis and Characterization of Nanodiamond Reinforced Chitosan for Bone Tissue Engineering.

Multifunctional tissue scaffold material nanodiamond (ND)/chitosan (CS) composites with different diamond concentrations from 1 wt % to 5 wt % were synthesized through a solution casting method. The microstructure and mechanical properties of the composites were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and nanoindentation. Compared with pristine CS, the addition of ND resulted in a significant improvement of mechanical properties, including a 239%, 276%, 321%, 333%, and 343% increase in Young’s modulus and a 68%, 96%, 114%, 118%, and 127% increase in hardness when the ND amount was 1 wt %, 2 wt %, 3 wt %, 4 wt %, and 5 wt %, respectively. The strong interaction between ND surface groups and the chitosan matrix plays an important role in improving mechanical properties.

A novel smart injectable hydrogel prepared by microbial transglutaminase and human-like collagen: Its characterization and biocompatibility

Various tissue scaffold materials are increasingly used to repair skin defects by cross-linking because of the ability to fill and implant in any form via operation. However, crosslinker residues cannot be easily removed from scaffold materials prepared by chemical crosslinking methods, limiting their use for skin tissue engineering. Here, microbial transglutaminase (MTGase), a nontoxic crosslinker with high specific activity and reaction rate under mild conditions, was employed crosslinks in human-like collagen (HLC) to yield novel smart MTGase crosslinked with human-like collagen (MTGH) hydrogels, which are sensitive to temperature and/or enzymes. Various ratios of MTGase/HLC were performed, and their physicochemical properties were characterized, including the swelling ratio, the elastic modulus, the morphology and the porosity. The degradation behavior and mechanism of MTGase in concentration-dependent manner involved in formation hydrogels were identifying in vitro. The cell attachment in vitro and biocompatibility in vivo were also investigated. The results demonstrated that the use of different concentrations of MTGase to crosslink HLC produced products with different degradation times and biocompatibilities. The 50U/g MTGase-prepared MTGH hydrogels had a higher density of crosslinks, which made them more resistant to degradation by collagenase I and collagenase II. However, 40U/g MTGase-prepared MTGH hydrogels were more suitable for cell attachment. In addition, compared with the Collagen Implant I® (SUM) used in animal experiments, the 40U/g MTGase-prepared MTGH hydrogels had a lower toxicity and better biocompatibility. Therefore, 40U/g MTGase crosslinked with HLC should be used to prepare MTGH hydrogels for potential application as soft materials for skin tissue engineering.

Highly Porous β-TCP Block with Triple Pore Structure in Rat Subcutaneous Tissue and Sheep Iliac Critical Bone Defect

Bio-absorbable materials have been strongly needed in bone regenerative surgery. β-TCP ceramics have been widely used as bone tissue scaffold materials, due to their bio-compatibility and bio-degradation. The aims of this study are to estimate blood permeation into different porous β-TCP blocks (75% and 67% in porosity), and to evaluate the behaviors of the 75% porous β-TCP block in rat subcutaneous tissue and sheep iliac bone defect by histological observation and 3-dimensional (3D) imaging analysis by μ-CT. The 75% β-TCP block revealed better performance in blood permeation than the 67% β-TCP in a dish including 3ml of sheep blood at 2 and 10 minutes. Almost area of the 75% β-TCP block turned to red at 10 minutes. In rat subcutaneous tissue, the bulk region of the 75% β-TCP was stained with HE. TRAP-positive multinucleated giant cells appeared on the surface of bulk at 4 weeks. In sheep iliac bone defect (10×15×9 mm3) model, μ-CT showed bone ingrowth into almost pores of the 75% β-TCP block at 2 months, and the block was absorbed and replaced by new bone until 4 months. The block was reduced to one-third in horizontal length and from 10 mm to 4 mm in vertical length at 2 months by 3D images. Body fluid stained by HE was found in the bulk region. We believe the body fluid permeation inside the bulk of the 75% porous β-TCP should contribute to the initial cell adhesion, proliferation and differentiation, and its biodegradation. It was concluded that the super porous β-TCP block with hydrophilic property might be a biological scaffold, harmonized with bone remodeling.

Monodisperse polyethylene glycol diacrylate hydrogel microsphere formation by oxygen-controlled photopolymerization in a microfluidic device.

PEG-based hydrogels have become widely used as drug delivery and tissue scaffolding materials. Common among PEG hydrogel-forming polymers are photopolymerizable acrylates such as polyethylene glycol diacrylate (PEGDA). Microfluidics and microfabrication technologies have recently enabled the miniaturization of PEGDA structures, thus enabling many possible applications for nano- and micro- structured hydrogels. The presence of oxygen, however, dramatically inhibits the photopolymerization of PEGDA, which in turn frustrates hydrogel formation in environments of persistently high oxygen concentration. Using PEGDA that has been emulsified in fluorocarbon oil via microfluidic flow focusing within polydimethylsiloxane (PDMS) devices, we show that polymerization is completely inhibited below critical droplet diameters. By developing an integrated model incorporating reaction kinetics and oxygen diffusion, we demonstrate that the critical droplet diameter is largely determined by the oxygen transport rate, which is dictated by the oxygen saturation concentration of the continuous oil phase. To overcome this fundamental limitation, we present a nitrogen micro-jacketed microfluidic device to reduce oxygen within the droplet, enabling the continuous on-chip photopolymerization of microscale PEGDA particles.

Multiphoton crosslinking for biocompatible 3D printing of type I collagen

Multiphoton fabrication is a powerful technique for three-dimensional (3D) printing of structures at the microscale. Many polymers and proteins have been successfully structured and patterned using this method. Type I collagen comprises a large part of the extracellular matrix for most tissue types and is a widely used cellular scaffold material for tissue engineering. Current methods for creating collagen tissue scaffolds do not allow control of local geometry on a cellular scale. This means the environment experienced by cells may be made up of the native material but unrelated to native cellular-scale structure. In this study, we present a novel method to allow multiphoton crosslinking of type I collagen with flavin mononucleotide photosensitizer. The method detailed allows full 3D printing of crosslinked structures made from unmodified type I collagen and uses only demonstrated biocompatible materials. Resolution of 1 μm for both standing lines and high-aspect ratio gaps between structures is demonstrated and complex 3D structures are fabricated. This study demonstrates a means for 3D printing with one of the most widely used tissue scaffold materials. High-resolution, 3D control of the fabrication of collagen scaffolds will facilitate higher fidelity recreation of the native extracellular environment for engineered tissues.

Customization of mechanical properties and porosity of bone tissue scaffold materials via Layer-by-Layer assembly of polymer-nanocomposite coatings

ABSTRACTThe aim of this preliminary study was to adapt Layer-by-Layer (LbL) assembly to fabricate nanocomposite coatings onto open-cell porous structures, enabling customization of mechanical properties and porosity to obtain materials suitable for bone tissue scaffold applications. LbL assembly is a well-established method for fabricating multilayer films with nanometre scale precision over thickness that is based on electrostatic attractions and involves the adsorption of oppositely charged electrolytes onto a substrate. Using LbL assembly, polymer-nanoclay composite coatings were deposited onto open-cell foam substrates. The elastic modulus of coated specimens in compression was improved from 0.078 MPa to 1.736 MPa. The results suggest that polymer-nanoclay coatings deposited via LbL assembly have the potential to improve mechanical properties of porous substrates and fabricate materials with mechanical properties comparable to that of a cancellous bone tissue upon deposition of a sufficient number of multilayers.

Fabrication of highly porous poly (ɛ-caprolactone) fibers for novel tissue scaffold via water-bath electrospinning

Highly porous fibers were prepared by water-bath electrospinning from pure poly(ɛ-caprolactone) (PCL), and its blends with methoxy poly(ethylene glycol) (MPEG). These fibers were further analyzed by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and gravimetric as well as contact angle measurement. SEM images showed that the fibers diameters as well as pores diameter on the fibers were affected by the weight ratio of MPEG/PCL. DSC and XRD not only revealed suppression of crystallinity of PCL but also indicated the presence of trace amount of MPEG in PCL water-bath collected fibers. The potential use of these hydrophilic porous electrospun fibrous mats as scaffolding materials was evaluated in vitro using mouse osteoblasts (MC3T3-E1) as reference cell lines. Cytotoxicity assessment of the fiber mats indicated that the porous electrospun mat containing trace amount of MPEG was nontoxic to the cell. Cell culture results showed that porous fibrous mats were good in promoting the cell attachment and proliferation. This novel electrospun matrix could be used as potential tissue scaffold material.

New approaches to mapping through-thickness variations in the degradation in poly (lactide-co-glycolide)

Biodegradable poly (lactide-co-glycolide) (PLGA) copolymers have been used for many years for biomedical applications such as soluble sutures, orthopaedic implants and more recently as potential tissue scaffold materials. The rate at which the copolymers degrade can be manipulated from a period of days to months by changing the lactide/glycolic acid ratio. Degradation of PLGA copolymers occurs by hydrolysis of the ester bonds in the polymer backbone. The hydrolysis reaction is autocatalytic and is accelerated by the build up of degradation products in the bulk of the material. As a consequence, material degradation is expected to be non-uniform through the specimen thickness with the material at the centre degrading at a faster rate than at the surface. Despite many studies of PLGA degradation, information on this local variance is sparse as the techniques used to track the process are usually bulk measures. In this study, two new approaches for monitoring degradation have been developed that enable local measurements of degradation to be made throughout the specimen over an extended period of time. Chemical and mechanical variations in the structure of the polymer have been mapped using attenuated total reflectance infrared spectroscopy (ATR-FTIR) and nanoindentation. These have produced comparable results and show that the degradation rate at the centre of the specimens is almost an order of magnitude higher than at the surface.

Axon repair: surgical application at a subcellular scale

Injury to the nervous system is a common occurrence after trauma. Severe cases of injury exact a tremendous personal cost and place a significant healthcare burden on society. Unlike some tissues in the body that exhibit self healing, nerve cells that are injured, particularly those in the brain and spinal cord, are incapable of regenerating circuits by themselves to restore neurological function. In recent years, researchers have begun to explore whether micro/nanoscale tools and materials can be used to address this major challenge in neuromedicine. Efforts in this area have proceeded along two lines. One is the development of new nanoscale tissue scaffold materials to act as conduits and stimulate axon regeneration. The other is the use of novel cellular-scale surgical micro/nanodevices designed to perform surgical microsplicing and the functional repair of severed axons. We discuss results generated by these two approaches and hurdles confronting both strategies.

Resonant ultrasound spectroscopy measurement of Young's modulus, shear modulus and Poisson's ratio as a function of porosity for alumina and hydroxyapatite

Modulus–porosity relationships are critical for engineered bone tissue scaffold materials such as hydroxyapatite (HA), where porosity is essential to biological function. Resonant ultrasound spectroscopy (RUS) measurements revealed that the Young's modulus, E, and shear modulus, G, of both alumina and HA decrease monotonically with increasing volume fraction porosity, P, for 0.06 < P < 0.39 (alumina) and 0.05 < P < 0.51 (HA). Although the elastic moduli of porous materials have been measured by a number of different ultrasonic resonance techniques (of which the RUS technique is one example) and over the last decade the elastic moduli of many solids have been measured by the RUS technique, this study is the first systematic RUS study of porous materials. Comparison of E versus P data for alumina (which has been studied extensively) with literature data from several measurement techniques indicates the RUS technique is effective for modulus–porosity measurements. Another key result is that although the HA specimens included in this study have a unimodal pore size distribution, the details of the decrease in E and G with increasing P agree well with literature data for HA with both unimodal and bimodal pore size distributions. In addition, Poisson's ratio exhibits a local minimum in the porosity range of 0.2 < P < 0.25 for both HA and alumina, which may be related to the pore morphology evolution during sintering.