Bone ingrowth into a porous coated implant predicted by a mechano-regulatory tissue differentiation algorithm

Bone ingrowth into a porous surface is one of the primary methods for fixation of orthopaedic implants. Improved understanding of bone formation and fixation of these devices should improve their performance and longevity. In this study predictions of bone ingrowth into an implant porous coating were investigated using mechano-reculatory models. The mechano-regulatory tissue differentiation algorithm proposed by Lacroix et al., and a modified version that enforces a tissue differentiation pathway by transitioning from differentiation to bone adaptation were investigated. The modified algorithm resulted in nearly the same behavior as the original algorithm when applied to a fracture-healing model. The algorithms were further compared using micromechanical finite element model of a beaded porous scaffold. Predictions of bone and fibrous tissue formation were compared between the two algorithms and to clinically observed phenomena. Under loading conditions corresponding to a press-fit hip stem, the modified algorithm predicted bone ingrowth into approximately 25% of the pore space, which is similar to that reported in experimental studies, while the original algorithm was unstable. When micromotion at the bone-implant interface was simulated, 20 mum of transverse displacement resulted in soft tissue formation at the bone-implant interface and minimal bone ingrowth. In contrast, 10 and 5 mum of micromotion resulted in bone filling 40% of the pore space and a stable interface, again consistent with clinical and experimental observations.     

Tissue engineering by cell transplantation using degradable polymer substrates.

This paper reviews our research in developing novel matrices for cell transplantation using bioresorbable polymers. We focus on applications to liver and cartilage as paradigms for regeneration of metabolic and structural tissue, but review the approach in the context of cell transplantation as a whole. Important engineering issues in the design of successful devices are the surface chemistry and surface microstructure, which influence the ability of the cells to attach, grow, and function normally; the porosity and macroscopic dimensions, which affect the transport of nutrients to the implanted cells; the shape, which may be necessary for proper function in tissues like cartilage; and the choice of implantation site, which may be dictated by the total mass of the implant and which may influence the dimensions of the device by the available vascularity. Studies show that both liver and cartilage cells can be transplanted in small animals using this approach.     

Enhanced growth of animal and human endothelial cells on biodegradable polymers

Biodegradable polymers such as poly(L-lactic acid) (PLLA), poly(glycolic acid) (PGA) and PGA coated with PLLA are being employed for cell transplantation and for in vivo regeneration of vascular tissue. Ingrowth and organization of fibrovascular tissue inside polymer scaffolds lead to the occlusion of the regenerated blood vessel. In order to provide regulatory mechanisms to control the development of an inner capsule, endothelialization of these materials is necessary. To achieve this, we employed a novel ammonia plasma technique to surface modified PLLA substrates. Human endothelial cell (HUVEC) and rabbit microvascular endothelial cell (RbMVEC) growth was studied on modified PLLA and control PLLA. Our studies show that modified PLLA and fibronectin (Fn)-coated modified PLLA exhibited statistically significant improvement in HUVEC and RbMVEC growth (P<0.001) when compared to PLLA and Fn-coated PLLA. Therefore, ammonia plasma treatment gives us the unique capability of modifying prosthetic biomaterials of various constructs with the eventual transplantation of mammalian cells to be used in tissue engineering or as biological implants.     

Effects of pore size in 3-D fibrous matrix on human trophoblast tissue development

The effects of pore size in a 3-D polyethylene terephthalate (PET) nonwoven fibrous matrix on long-term tissue development of human trophoblast ED27 cells were studied. Thermal compression was used to modify the porosity and pore size of the PET matrix. The pore size distributions in PET matrices were quantified using a liquid extrusion method. Cell metabolic activities, estradiol production, and cell proliferation and differentiation were studied for ED27 cells cultured in the thermally compressed PET matrices with known pore structure characteristics. In general, metabolic activities and proliferation rate were higher initially for cultures grown in the low-porosity (LP) PET matrix (porosity of 0.849, average pore size of 30 microm in diameter) than those in the high-porosity (HP) matrix (porosity of 0.896, average pore size of 39 microm in diameter). However, 17beta-estradiol production and cell differentiation activity in the HP matrix surpassed those in the LP matrix after 12 days. The expression levels of cyclin B1 and p27kip1 in cells revealed progressively decreasing proliferation and increasing differentiation activities for cells grown in PET matrices. Also, difference in pore size controlled the cell spatial organization in the PET matrices and contributed to the tissue development in varying degrees of proliferation and differentiation. It was also found that cells grown on the 2-D surface behaved differently in cell cycle progression and did not show increased differentiation activities after growth had stopped and proliferation activities had lowered to a minimal level. The results from this study suggest that the 3-D cell organization guided by the tissue scaffold is important to tissue formation in vitro.     

Investigation of PLLA/PCL Blends and Paclitaxel Release Profiles

Blends of poly (l-lactide) (PLLA) and poly (ε-caprolactone) (PCL) with and without paclitaxel were prepared via solution casting. DSC analysis as well as SEM analysis of the PLLA/PCL blend solution cast films showed that these blends are all phase separated.%PLLA crystallinity was found to increase with increasing PCL content (up till 15 wt.%). The PCL phase is found to homogeneously disperse in the PLLA matrix as spherical domains where the pore diameters of the PCL domains significantly increased with increasing PCL content. The degradation profiles matched with the slower degrading component PCL rather than PLLA and also increasing PCL content of the blends increased the degradation rate relatively. The increased crystallinity of the PLLA phase with increasing PCL contents confirmed that the degradation occurred through PCL phase. Cell proliferation on PLLA/PCL blends showed that all these blends were suitable for the support of cellular growth. Apoptosis assay with the paclitaxel-loaded PLLA/PCL blends showed an increase in cell death throughout 7 days of incubation where the cell death was increased with increasing PCL contents. This was attributed to the faster release of paclitaxel which was at least partially affected by the faster degradation rate at increasing PCL contents. The paclitaxel release was shown to be degradation controlled in the initial stages followed by a faster diffusion-controlled release in the later stages. These polymer blends were found to be very suitable paclitaxel release agents for which the paclitaxel release times can be altered with the composition of the blend and the film thickness.     

Comparison of the hydrolytic degradation and deformation properties of a PLLA-lauric acid based family of biomaterials

Addition of lauric acid to PLLA results in a significantly increased rate of hydrolytic degradation, with the time-to-loss of tensile strength directly related to the concentration of lauric acid. In this study, the hydrolytic degradation profiles of four materials were studied: amorphous PLLA, amorphous PLLA containing 1.8 wt % lauric acid, amorphous PLLA containing 4.5 wt % lauric acid, and pre-crystallized PLLA containing 1.8 wt % lauric acid. Hydrolytic degradation was monitored through mass profiles, molecular weight profiles, crystallinity and the development of mechanical properties and deformation mechanisms (through simultaneous small-angle X-ray scattering and tensile testing), and a "phase diagram" of properties suggested. The key factor in determining the development of properties was found to be the time at which crystallization occurred in relation to the loss of molecular weight, with the two factors most affecting this being the lauric acid content and the pre-degradation annealing treatment.     

A combined strategy to reduce restenosis for vascular tissue engineering applications

Biodegradable polymers including poly(l-lactic acid) (PLLA) have been used to develop cardiovascular prostheses such as vascular grafts and stents. However, implant-associated thrombosis, inflammation, and restenosis are still major obstacles for the utility of these devices. The lack of an endothelial cell (EC) lining (endothelialization) on the implants and the responses of the immune systems toward the implants have been associated with these complications. In our research strategy, we have combined the drug delivery principle with the strategies of tissue engineering, the controlled release of anti-inflammation drugs and enhanced endothelialization, to reduce the implant-associated adverse responses. We first integrated curcumin, an anti-inflammatory drug and anti-smooth muscle cell (SMC) proliferative drug, with PLLA. This curcumin-loaded PLLA material was then modified using adsorptive coating of adhesive proteins such as fibronectin, collagen-I, vitronectin, laminin, and matrigel to improve the endothelial cell (EC) adhesion and proliferation, and ECs were seeded on top of these modified surfaces. Our results showed steady drug release kinetics over the period of 50 days from curcumin-loaded PLLA materials. Additionally, integration of curcumin in PLLA increased the roughness of the scaffold at the nanometric scale using an atomic force microscopic analysis. Moreover, coating with fibronectin on curcumin-loaded PLLA surfaces gave the highest EC adhesion and proliferation compared to other adhesive proteins using PicoGreen DNA assays. The ability of our strategy to release the curcumin for producing anti-inflammation and anti-proliferation responses and to improve EC adhesion and growth after EC seeding suggests this strategy may reduce implant-associated adverse responses and be a better approach for vascular tissue engineering applications.     

Development of biodegradable scaffolds based on magnetically guided assembly of magnetic sugar particles

Biodegradable scaffolds with controlled pore layout and porosity have great significance in tissue engineering for cell penetration, tissue ingrowth, vascularization, and nutrient delivery. Porogen leaching has been commonly used to control pore size, pore structure and porosity in the scaffold. In this paper we focus on the use/development of two magnetically guided porogen assembly methods using magnetic sugar particles (MSPs) for scaffold fabrication. First, a patterning device is utilized to align MSPs following designed templates. Then a magnetic sheet film is fabricated by mixing poly(vinyl alcohol, PVA) and NdFeB powder for steering the MSPs. After poly(l-lactide-co-?-caprolactone) (PLCL) casting and removal of the sugar template, a scaffold with spherical pores is obtained. The surface and the inner structure of the scaffolds are evaluated using light and electron micrographs showing their interconnection of pores, pore wall morphology and porosity. Single layer scaffolds with the size of 8mm in width and 10mm in length were constructed with controllable pore diameters in the ranges of 105-150 μm, 250-300 μm and 425-500 μm.     

Synthesis, solid-state structure, and surface properties of end-capped poly(L-lactide)

End-capped poly(L-lactide) (PLLA) samples with dodecyl or 2-(2-(2-methoxyethoxy)ethoxy)ethyl (MEEE) ester were synthesized by ring-opening polymerization of L-lactide in the presence of zinc dodecanoxide or zinc 2-(2-(2-methoxyethoxy)ethoxy)ethoxide as a catalyst, respectively. On the basis of NMR analysis, it was confirmed that the carboxylic acid chain ends of PLLA molecules were selectively substituted by dodecyl or MEEE ester groups. To evaluate the wettability on the surface of end-capped PLLA films, the advancing contact angle (thetaa) with water was measured. The amorphous PLLA films showed relatively similar thetaa values regardless of the chemical structure of the polymer chain end. In contrast, the thetaa values of semicrystalline films were varied over a wide range, dependent on the chemical structure of the chain end. In addition, the thetaa values of dodecyl ester end-capped PLLA film with low molecular weight increased with an increase in the crystallization temperature. Both the crystallinity and lamellar thickness of dodecyl ester end-capped PLLA films increased with the crystallization temperature. These results suggest that the segregation of the chain ends on the PLLA film surface was strongly affected by the crystallization conditions.     

Cell colonization in degradable 3D porous matrices

Cell colonization is an important in a wide variety of biological processes and applications including vascularization, wound healing, tissue engineering, stem cell differentiation and biosensors. During colonization porous 3D structures are used to support and guide the ingrowth of cells into the matrix. In this review, we summarize our understanding of various factors affecting cell colonization in three-dimensional environment. The structural, biological and degradation properties of the matrix all play key roles during colonization. Further, specific scaffold properties such as porosity, pore size, fiber thickness, topography and scaffold stiffness as well as important cell material interactions such as cell adhesion and mechanotransduction also influence colonization.Key words: colonization, pore size, porosity, topography, mechanotransduction, degradation, matrix turnover     

Enzymatic, alkaline, and autocatalytic degradation of poly(L-lactic acid): effects of biaxial orientation

The hydrolytic degradation of biaxially oriented and de-oriented (melt-crystallized) poly(l-lactic acid) (PLLA) films was investigated in Tris-HCl-buffered solution (pH 8.6) with proteinase K, alkaline solution, and phosphate-buffered solution (pH 7.4) by the use of gravimetry, gel permeation chromatography, differential scanning calorimetry, and scanning electron microscopy. Biaxial orientation disturbed the proteinase K-catalyzed enzymatic degradation of PLLA films and the effects of biaxial orientation overcame those of crystallinity. The former may be due to the fact the enzyme cannot attach to the extended (strained) chains in the amorphous regions of the biaxially oriented PLLA film or cannot catalyze the cleavage of the strained chains. Another probable cause is that the enzyme can act only at the film surface of the biaxially oriented PLLA film, in marked contrast with the case of the de-oriented PLLA films where enzymatic degradation can proceed beneath the spherulitic crystalline residues. The effects of biaxial orientation on the alkaline and autocatalytic degradation of the PLLA films were insignificant for the periods studied here. The crystallinity rather than the biaxial orientation seems to determine the alkaline and autocatalytic degradation rates of the PLLA films. The accumulation of crystalline residues formed as a result of selective cleavage and removal of the amorphous chains was observed for the de-oriented PLLA films, but not for the biaxially oriented PLLA film, when degraded in the presence of proteinase K. This means the facile release of formed crystalline residues from the surface of the biaxially oriented PLLA film during enzymatic degradation, due to the fact that the crystalline regions of the biaxially oriented PLLA film were oriented with their c axis parallel to the film surface.     

Porous scaffolds from high molecular weight polyesters synthesized via enzyme-catalyzed ring-opening polymerization

Several aliphatic polyesters have been synthesized until now using enzyme-catalyzed ring-opening polymerization (ROP) of different lactones, although their molecular weight, hence mechanical strength, was not sufficient enough to fabricate porous scaffolds from them. To achieve this target, 1,5-dioxepan-2-one (DXO) and epsilon-caprolactone (CL) were polymerized in bulk with Lipase CA as catalyst at 60 degrees C, and porous scaffolds were prepared from the polymers obtained thereof using a salt leaching technique. The CL/DXO molar feed ratio was varied from 1.5 to 10, and the reactivity ratios of CL and DXO were determined using the Kelen-Tudos method under such conditions of polymerization. NMR results showed a slightly lower CL/DXO molar ratio in the copolymers than in the feed due to high reactivity of DXO toward Lipase CA catalysis. The crystallinity of the PCL segment of the copolymers was affected by the presence of soft and amorphous DXO domains. The copolymers having high CL content were thermally more stable. The porosity of the scaffolds was in the range 82-88%, and the SEM analysis showed interconnected pores in the scaffolds. Of the two parameters which could affect the mechanical properties, viz., the copolymer composition and the scaffold pore size, the pore size showed a significant effect on the mechanical properties of the scaffolds. The porous scaffolds developed in this way for tissue engineering are free from toxic organometallic catalyst residues, and they are highly suitable for biomedical applications.     

Macromolecular design of aliphatic polyesters with maintained mechanical properties and a rapid, customized degradation profile

An innovative type of triblock copolymer that maintains and even increases the mechanical properties of poly(l-lactide) (PLLA) and poly(ε-caprolactone) (PCL) with a controlled, predictable, and rapid degradation profile has been synthesized. Elastic triblock copolymers were formed from the hydrophobic and crystalline PLLA and PCL with an amorphous and hydrophilic middle block of poly(but-2-ene-1,4-diyl malonate) (PBM). The polymers were subjected to degradation in PBS at 37 °C for up to 91 days. Prior to degradation, ductility of the PLLA-PBM-PLLA was approximately 4 times greater than that of the homopolymer of PLLA, whereas the modulus and tensile stress at break were unchanged. A rapid initial hydrolysis in the amorphous PBM middle block changed the microstructure from triblock to diblock with a significant reduction in ductility and molecular weight. The macromolecular structure of the triblock copolymer of PLLA and PBM generates a more flexible and easier material to handle during implant, with the advantage of a customized degradation profile, demonstrating its potential use in future biomedical applications.     

Osteostimulation scaffolds of stem cells: BMP‐7‐derived peptide‐decorated alginate porous scaffolds promote the aggregation and osteo‐differentiation of human mesenchymal stem cells

The scaffolds for stem cell‐based bone tissue engineering should hold the ability to guide stem cells osteo‐differentiating. Otherwise, stem cells will differentiate into unwanted cell types or will form tumors in vivo. Alginate, a natural polysaccharide with great biocompatibility, was widely used in biomedical applications. However, the limited bioactivity and poor osteogenesis capability of pristine alginate hampered its further application in tissue engineering. In this work, a bone forming peptide‐1 (BFP‐1), derived from bone morphogenetic protein‐7, was grafted to alginate polymer chains to prepare peptide‐decorated alginate porous scaffolds (pep‐APS) for promoting osteo‐differentiation of human mesenchymal stem cells (hMSCs). SEM images of pep‐APS exhibited porous structure with about 90% porosity (pore size 100–300 μm), which was appropriate for hMSCs ingrowth. The adhesion, proliferation and aggregation of hMSCs grown on pep‐APS were enhanced in vitro. Moreover, pep‐APS promoted the alkaline phosphatase (ALP) activity of hMSCs, and the osteo‐related genes expression was obviously up‐regulated. The immunochemical staining and western blot analysis results showed high expression level of OCN and Col1a1 in the hMSCs grown on pep‐APS. This work provided a facile and valid strategy to endow the alginate polymers themselves with specific bioactivity and prepare osteopromoting scaffold with enhanced osteogenesis ability, possessing potential applications in stem cell therapy and regenerative medicine.     

Morphology control in co-continuous poly(L-lactide)/polystyrene blends: a route towards highly structured and interconnected porosity in poly(L-lactide) materials

Poly(L-lactide) is a biodegradable polymer primarily used in biomedical applications. In this paper, both the microstructure and the region of dual-phase continuity are examined for binary and compatibilized poly(L-lactide)/polystyrene blends (PLLA/PS) prepared by melt mixing. The blends are shown to be completely immiscible with an interfacial tension of 6.1 mN/m. The PS-b-PLLA (24,000-b-28,000) diblock copolymer compatibilizer has an asymmetric effect on the blend. It is effective at compatibilizing 50/50 PLLA/PS blends but is only a marginal emulsifier for blends where PLLA is the dominant matrix. Percent continuity, as estimated by solvent extraction/gravimetry and also torque/composition diagrams clearly indicate an onset of the region of dual-phase continuity at 40-45%PS. It is demonstrated that highly percolated blends of the above materials exist from 40 to 75% PS and 40 to 60% PS for the binary and compatibilized blends, respectively. The scale of the microstructure of the continuous morphology is measured using BET and mercury intrusion porosimetry techniques, after extraction of the PS phase. Both the pore size and extent of continuity can be controlled through composition and interfacial modification. Static annealing of the blend after melt mixing can also be used to substantially increase the pore size of the system. Extraction of the PS phase in the blend, carried out after the above preparation protocols, is a route to generating completely interconnected porosity of highly controlled morphologies (pore size, void volume) in poly(L-lactide) materials. In this study, the pore diameter was controlled from 0.9 to 72 microm for a constant void volume of 45-47%, and the void volume was modified from 35 to 74% depending on the blend composition.     

Potential Use of Porous Titanium–Niobium Alloy in Orthopedic Implants: Preparation and Experimental Study of Its Biocompatibility In Vitro

Background

The improvement of bone ingrowth into prosthesis and enhancement of the combination of the range between the bone and prosthesis are important for long-term stability of artificial joints. They are the focus of research on uncemented artificial joints. Porous materials can be of potential use to solve these problems.

Objectives/Purposes

This research aims to observe the characteristics of the new porous Ti-25Nb alloy and its biocompatibility in vitro, and to provide basic experimental evidence for the development of new porous prostheses or bone implants for bone tissue regeneration.

Methods

The Ti-25Nb alloys with different porosities were fabricated using powder metallurgy. The alloys were then evaluated based on several characteristics, such as mechanical properties, purity, pore size, and porosity. To evaluate biocompatibility, the specimens were subjected to methylthiazol tetrazolium (MTT) colorimetric assay, cell adhesion and proliferation assay using acridine staining, scanning electron microscopy, and detection of inflammation factor interleukin-6 (IL-6).

Results

The porous Ti-25Nb alloy with interconnected pores had a pore size of 200 µm to 500 µm, which was favorable for bone ingrowth. The compressive strength of the alloy was similar to that of cortical bone, while with the elastic modulus closer to cancellous bone. MTT assay showed that the alloy had no adverse reaction to rabbit bone marrow mesenchymal stem cells, with a toxicity level of 0 to 1. Cell adhesion and proliferation experiments showed excellent cell growth on the surface and inside the pores of the alloy. According to the IL-6 levels, the alloy did not cause any obvious inflammatory response.

Conclusion

All porous Ti-25Nb alloys showed good biocompatibility regardless of the percentage of porosity. The basic requirement of clinical orthopedic implants was satisfied, which made the alloy a good prospect for biomedical application. The alloy with 70% porosity had the optimum mechanical properties, as well as suitable pore size and porosity, which allowed more bone ingrowth.     

Cell colonization in degradable 3D porous matrices

Cell colonization is an important in a wide variety of biological processes and applications including vascularization, wound healing, tissue engineering, stem cell differentiation, and biosensors. During colonization porous 3D structures are used to support and guide the ingrowth of cells into the matrix. In this review, we summarize our understanding of various factors affecting cell colonization in 3-dimensional environment. The structural, biological, and degradation properties of the matrix all play key roles during colonization. Further, specific scaffold properties such as porosity, pore size, fiber thickness, topography, and scaffold stiffness as well as important cell material interactions such as cell adhesion and mechanotransduction also influence colonization.     

Histomorphometric evaluation of bone ingrowth of porous titanium by a computer-assisted analyzing system]

The objective of this study was to evaluate the bone ingrowth of a new vacuum plasma sprayed titanium surface (vps-ti) in comparison to cs-titanium implants in a g?ttinger minipig model. Fifteen g?ttinger minipigs each received the two implants, vacuum plasma sprayed titanium with a porosity of 50% and a pore size of 200 microm (vps-ti) and an implant with a similar porosity but a different pore size 500 microm (cs-ti), at the proximal femur metaphysis by press-fit technique. The pigs were euthanized at three different postsurgical periods: 4, 8 and 12 weeks. Each femur was harvested and qualitative (macroscopic and microscopic) and quantitative (histomorphometric) histological analysis was done on histological slides. The results indicated that there was a difference in bone ingrowth between the two implants, whereas the bone ingrowth of vps-ti was superior to cs-ti after 4 and 8 weeks healing time. 12 weeks post implantationem no statistiscal difference was evident. The pore size of 200 microm seemed superior to a pore size of 500 microm. Whether or not these effects lead to a better mechanical stability remains unanswered.     

Multi-Scale Modification of Metallic Implants With Pore Gradients,Polyelectrolytes and Their Indirect Monitoring In vivo

Metallic implants, especially titanium implants, are widely used in clinical applications. Tissue in-growth and integration to these implants in the tissues are important parameters for successful clinical outcomes. In order to improve tissue integration, porous metallic implants have being developed. Open porosity of metallic foams is very advantageous, since the pore areas can be functionalized without compromising the mechanical properties of the whole structure. Here we describe such modifications using porous titanium implants based on titanium microbeads. By using inherent physical properties such as hydrophobicity of titanium, it is possible to obtain hydrophobic pore gradients within microbead based metallic implants and at the same time to have a basement membrane mimic based on hydrophilic, natural polymers. 3D pore gradients are formed by synthetic polymers such as Poly-L-lactic acid (PLLA) by freeze-extraction method. 2D nanofibrillar surfaces are formed by using collagen/alginate followed by a crosslinking step with a natural crosslinker (genipin). This nanofibrillar film was built up by layer by layer (LbL) deposition method of the two oppositely charged molecules, collagen and alginate. Finally, an implant where different areas can accommodate different cell types, as this is necessary for many multicellular tissues, can be obtained. By, this way cellular movement in different directions by different cell types can be controlled. Such a system is described for the specific case of trachea regeneration, but it can be modified for other target organs. Analysis of cell migration and the possible methods for creating different pore gradients are elaborated. The next step in the analysis of such implants is their characterization after implantation. However, histological analysis of metallic implants is a long and cumbersome process, thus for monitoring host reaction to metallic implants in vivo an alternative method based on monitoring CGA and different blood proteins is also described. These methods can be used for developing in vitro custom-made migration and colonization tests and also be used for analysis of functionalized metallic implants in vivo without histology.     

Supercritical CO2 Foaming of Thermoplastic Materials Derived from Maize: Proof-of-Concept Use in Mammalian Cell Culture Applications

Background

Foams are high porosity and low density materials. In nature, they are a common architecture. Some of their relevant technological applications include heat and sound insulation, lightweight materials, and tissue engineering scaffolds. Foams derived from natural polymers are particularly attractive for tissue culture due to their biodegradability and bio-compatibility. Here, the foaming potential of an extensive list of materials was assayed, including slabs elaborated from whole flour, the starch component only, or the protein fraction only of maize seeds.

Methodology/Principal Findings

We used supercritical CO₂ to produce foams from thermoplasticized maize derived materials. Polyethylene-glycol, sorbitol/glycerol, or urea/formamide were used as plasticizers. We report expansion ratios, porosities, average pore sizes, pore morphologies, and pore size distributions for these materials. High porosity foams were obtained from zein thermoplasticized with polyethylene glycol, and from starch thermoplasticized with urea/formamide. Zein foams had a higher porosity than starch foams (88% and 85%, respectively) and a narrower and more evenly distributed pore size. Starch foams exhibited a wider span of pore sizes and a larger average pore size than zein (208.84 vs. 55.43 μm², respectively). Proof-of-concept cell culture experiments confirmed that mouse fibroblasts (NIH 3T3) and two different prostate cancer cell lines (22RV1, DU145) attached to and proliferated on zein foams.

Conclusions/Significance

We conducted screening and proof-of-concept experiments on the fabrication of foams from cereal-based bioplastics. We propose that a key indicator of foamability is the strain at break of the materials to be foamed (as calculated from stress vs. strain rate curves). Zein foams exhibit attractive properties (average pore size, pore size distribution, and porosity) for cell culture applications; we were able to establish and sustain mammalian cell cultures on zein foams for extended time periods.