Hydrogel Composite Magnetic Scaffolds: Toward Cell-Free In Situ Bone Tissue Engineering

Reconstruction of critical sized bone defects in the oral and maxillofacial region continues to be clinically challenging despite the significant development of osteo-regenerative materials. Among 3D biomaterials, hydrogels and hydrogel composites have been explored for bone regeneration, however, their inferior clinical performance in comparison to autografts is mainly attributed to variable rates of degradation and lack of vascularization. In this study, we report hydrogel composite magnetic scaffolds formed from calcium carbonate, poly(vinyl alcohol) (PVA), and magnetic nanoparticles (MNPs), using PVA as matrix and calcium carbonate particles in vaterite phase as filler, to enhance the cross-linking of matrix and porosity with MNPs that can target and regulate cell signaling pathways to control cell behavior and improve the osteogenic and angiogenic potential. The physical and mechanical properties were evaluated, and cytocompatibility was investigated by culturing human osteoblast-like cells onto the scaffolds. The vaterite phase due to its higher solubility in comparison to calcium phosphates, combined with the freezing-thawing process of PVA, yielded porous scaffolds that exhibited adequate thermal stability, favorable water-absorbing capacity, excellent mineralization ability, and cytocompatibility. An increasing concentration from 1, 3, and 6 wt % MNPs in the scaffolds showed a statistically significant increase in compressive strength and modulus of the dry specimens that exhibited brittle fracture. However, the hydrated specimens were compressible and showed a slight decrease in compressive strength with 6% MNPs, although this value was higher compared to that of the scaffolds with no MNPs.

Dual polymer networks: a new strategy in expanding the repertoire of hydrogels for biomedical applications

Inspired by the double network hydrogel systems we report the formulation of dual networks, which expands the repertoire of this class of materials for potential biomedical applications. The tough dual network hydrogels were designed through sequential interpenetrating polymer formation, applying green chemistry and low-cost methods, devoid of any initiator-activator complexes that may pose risks in biomedical applications. The dual networks were synthesized in two steps, firstly the water soluble poly(vinyl alcohol) was subjected to cryogelation that formed the first network, which was then expanded by intrusion of a dilute solution of sodium alginate and complexed with a solution of calcium chloride under ambient conditions and further freeze-thawed. These hydrogels are flexible, ductile and porous with the ability to absorb and retain fluids as well as possess the versatility to easily incorporate biological molecules/drugs/antibiotics to be applied in tissue matrices or drug delivery systems. The dual network hydrogels can be tailored to have varying mechanical properties, shapes, size, thickness and particularly can be made physically porous if required, to suit the users intended application.

Combinatorial design of calcium meta phosphate poly(vinyl alcohol) bone-like biocomposites

The incidence of degenerative diseases and the ageing population have added to the growing demand for bone grafts. Although autologous bone continues to be the gold standard, limited yield and potential morbidity of the donor site pose considerable challenges. Currently, clinically used synthetic grafts based on calcium phosphates are mechanically brittle and not compliant hence composite scaffolds are expected to be provide viable solutions. In this study we report composites of calcium meta phosphate-poly (vinyl alcohol) with tunable mechanical properties, low swelling and excellent biocompatibility. The elastomeric nature of the composites resist brittle fracture and the scaffolds can be easily shaped to the bone defect by the surgeon. Testing on bone plug shaped specimens of the scaffolds, exhibited superior mechanical properties compared to currently commercially available bone plugs with additional advantages being the ability to increase porosity without compromising properties in compression and degree of swelling, which make these composites promising synthetic alternatives for bone grafts and bone tissue engineering.

Effect of multi-nutrient insufficiency on markers of one carbon metabolism in young women: response to a methionine load

BACKGROUND/OBJECTIVES

Multi-nutrient insufficiencies as a consequence of nutritional and economic factors are common in India and other developing countries. We have examined the impact of multi-nutrient insufficiency on markers of one carbon (1C) metabolism in the blood, and response to a methionine load in clinically healthy young women.

SUBJECTS/METHODS

Young women from Pune, India (n=10) and Cleveland, USA (n=13) were studied. Blood samples were obtained in the basal state and following an oral methionine load (50 mg/kg of body weight in orange juice). Plasma concentrations of vitamin B12, folate and B6 were measured in the basal state. The effect of methionine load on the levels of methionine, total homocysteine, cysteine, glutathione and amino acids was examined.

RESULTS

Indian women were significantly shorter and lighter compared with the American women and had lower plasma concentration of vitamins B12, folate and B6, essential amino acids and glutathione, but higher concentration of total homocysteine. The homocysteine response to methionine load was higher in Indian women. The plasma concentrations of glycine and serine increased in the Indian women after methionine (in juice) load. A significant negative correlation between plasma B6 and homocysteine (r= -0.70), and plasma folate and glycine and serine levels were observed in the Indian group (P<0.05) but not in the American group.

CONCLUSIONS

Multi-nutrient insufficiency in the Indian women caused unique changes in markers of whole body protein and 1C metabolism. These data would be useful in developing nutrient intervention strategies.

In vitro and in vivo optimization of impaction allografting by demineralization and addition of rh-OP-1

Impaction allografting is a bone tissue engineering technique currently used in lower limb reconstruction orthopedic surgery. Our hypothesis was that biological optimization can be achieved by demineralization and addition of osteogenic protein-1 (OP-1) to the allograft. The objective of our in vitro study was to evaluate human mesenchymal stem cell (MSC) proliferation (Alamar Blue assay, titrated thymidine assay, total DNA Hoechst 33258, and scanning electron microscopy) and osteogenic differentiation (alkaline phosphatase assay) in two types of impacted carrier, namely, demineralized bone matrix (DBM) and insoluble collagenous bone matrix (ICBM), with or without OP-1. The objective in vivo was to compare the osteogenic potential of impacted DBM with or without OP-1, with that of impacted fresh frozen allograft (FFA), again with or without OP-1. DBM + OP-1 optimized osteoinduction and significantly improved (p < 0.05) proliferation and differentiation in comparison to the majority of all other graft preparation in vitro. In addition, DBM + OP-1 was significantly superior, with regard to osteogenesis, compared to the impacted FFA alone (p < 0.001), FFA + OP-1 (p = 0.01) and DBM alone (p = 0.02) in vivo. We propose that partial demineralization and addition of OP-1 provides a good method for improving the osteoinductive properties of fresh allograft currently used in the impaction grafting technique.

Tissue engineered intervertebral disc repair in the pig using injectable polymers

The intervertebral disc (IVD) has a central nucleus pulposus (NP) able to resist compressive loads and an outer annulus fibrosus which withstands tension and gives mechanical strength. The tissue engineering of a disc substitute represents a challenge from mechanical and biological (nutrition and transport) points of view. Two hyaluronan-derived polymeric substitute materials, HYAFF 120, an ester and HYADD 3, an amide were injected into the NP of the lumbar spine of female pigs (11.1 +/- 1.0 Kg) in which a nucleotomy had also been performed. Homologous bone marrow stem cells, obtained from the bone marrow three weeks before spinal surgery, were included in the HYADD 3 material (1x 10(6) cells/ml). Two lumbar discs were operated in each animal. Control discs received a nucleotomy only. The animals were killed after 6 weeks and the lumbar spines recovered for histopathological study. Nucleotomy resulted in loss of normal IVD structure with narrowing, fibrous tissue replacement and disruption of the bony end-plates (4/4). By contrast, both HYAFF 120 (4/4) and HYADD 3 (4/4) treatment prevented this change. The injected discs had a central NP-like region which had a close similarity to the normal biconvex structure and contained viable chondrocytes forming matrix like that of normal disc.

In vitro osteoblastic response to 30 vol% hydroxyapatite-polyethylene composite

Hydroxyapatite-reinforced high-density polyethylene (HA-HDPE) composite, as a bone replacement material, has successfully been used clinically as middle ear prostheses and orbital floor implants. The aim of this study was to examine its in vitro biocompatibility in order to develop a further application, that is, as skull reconstruction implants. Human osteoblast cells isolated from femoral heads and crania were used to determine the biological response of the composites. HA-HDPE composites (30 vol %) with two grades of HA filler that had different surface morphologies were selected for this in vitro assessment. The results showed that HA-HDPE composite was bioactive and supported osteoblast attachment, proliferation, and differentiation. The composite with rough-surfaced HA filler demonstrated slightly better cellular response than the composite with smooth-surfaced HA filler. Although osteoblastic cells derived from skull showed an overall slower response compared with those from femoral heads, these in vitro results show that HA-HDPE composite potentially could be used as a skull implant.

A novel ex vivo culture system for studying bone repair

Repair of large bony defects still remains a challenge for surgeons. Hydroxyapatite (HA) is well known for its biocompatibility and osseoconduction properties in the osseous environment. In this study the biofunctionality of a newly developed scaffold comprising of collagen and HA, with variable macropores was examined. The biological response was evaluated using primary human osteoblast cells (HOBs). Cell infiltration, proliferation and differentiation were assessed. The results showed that HOBs were able to migrate from the collagen into the HA pores with greater cell migration and infiltration observed in those scaffolds with larger pores. Furthermore, it was shown that Alkaline Phosphatase, a differentiation marker for HOBs was enhanced as the average macropore size increased. This in vitro model provides a more relevant method of testing the biofunctionality and migration ability of cells at a trauma site following implantation in bone and cartilage.

Enhancing the osteoinductive properties of hydroxyapatite by the addition of human mesenchymal stem cells, and recombinant human osteogenic protein-1 (BMP-7) in vitro

Hydroxyapatite (HA) has been widely used as a bone graft substitute. In this study, we investigated whether the addition of osteogenic protein-1 (OP-1) further enhanced the weak osteoinductive properties of hydroxyapatite when loaded with human mesenchymal stem cells (h-MSCs). Over a 14 day period, cell proliferation in both groups was assessed qualitatively using SEM and quantitatively using alamar blue assay. Cell differentiation was also evaluated by measurement of ALP activity, which was expressed against total DNA. HA/MSC loaded with OP-1 demonstrated a statistically significant increase (p<0.001) in cell proliferation at all time points in comparison to unloaded samples. ALP activity per DNA was also significantly enhanced (p<0.001) in loaded samples when compared to unloaded controls. SEM demonstrated increased cellular attachment and proliferation into HA pores at all time points in the loaded samples. Our study suggests that the osteoinductive potential of HA can be improved in vitro by the combined incorporation of MSCs and OP-1.

The fundamentals of tissue engineering: new scaffolds

The ability to regenerate new bone for skeletal use is a major clinical need. In this study, two novel porous calcium phosphate materials pure HA and biphasic HA/beta-Tricalcium phosphate (HA/beta -TCP) were evaluated as potential scaffolds for cell-seeded bone substitutes using human osteoblast-like cells (HOS) and primary human mesenchymal stem cells (hMSCs). A high rate of proliferation was observed on both scaffolds. A greater increase in alkaline phosphatase (ALP- an indicator of osteoblast differentiation) was observed on HA/beta -TCP compared to HA. This observation indicates that HA/TCP may play a role in inducing osteoblastic differentiation. Although further evaluation is required both materials show potential as innovative synthetic substitutes for tissue engineered scaffolds.

Optimizing HAPEX topography influences osteoblast response

HAPEX (hydroxyapatite-reinforced polyethylene composite) is a second-generation orthopedic biomaterial designed as a bone analog material, which has found clinical success. The use of topography in cell engineering has been shown to affect cell attachment and subsequent response. Thus, by combining bioactivity and enhancing osteoblast response to the implant surface, improved tissue repair and implant life span may be achieved. In this study a primary human osteoblast-like cell model has been used to study the influence of surface topography and chemistry produced by three different production methods. Scanning electron microscopy, fluorescence microscopy, and confocal scanning laser microscopy have been used to study cell adhesion; tritiated thymidine uptake has been used to observe cell proliferation; and the reverse transcriptase-polymerase chain reaction and biochemical methods have been used to study phenotypic expression. Transmission electron microscopy has also been used to look at more long-term morphology. The results show that topography significantly influences cell response, and may be a means of enhancing bone apposition on HAPEX.

Biodegradable microspheres: a new delivery system for growth hormone

A drug delivery system for biologically active agents targeted to specific cells could be used to improve tissue repair in orthopaedics. The system should be controllable and capable of drug release over an extended period of time. Biodegradable, membrane-moderated, monolithic microspheres for the controlled release of growth hormone (GH) were developed and the release of GH was monitored in vitro. Cross-linked gelatin microspheres were used as the vehicle, with the drug dispersed within the gelatin. The amount of GH released from the microspheres was increased following ultrasonication. The release of growth hormone was monitored in phosphate buffered saline and horse serum. Interestingly, a higher level of GH was detected in the phosphate buffered saline than in serum. In addition, both pH and enzyme-induced degradation had an effect on the swelling kinetics of the gelatin microspheres. The release of GH from the microspheres was diffusion controlled, during the time period studied.