Inflammatory cell response to ultra-thin amorphous and crystalline hydroxyapatite surfaces

Toward a disruptive, minimally invasive small finger joint implant concept: Cellular and molecular interactions with materials in vivo

Osteoarthritis (OA) poses significant therapeutic challenges, particularly OA that affects the hand. Currently available treatment strategies are often limited in terms of their efficacy in managing pain, regulating invasiveness, and restoring joint function. The APRICOTⓇ implant system developed by Aurora Medical Ltd (Chichester, UK) introduces a minimally invasive, bone-conserving approach for treating hand OA (https://apricot-project.eu/). By utilizing polycarbonate urethane (PCU), this implant incorporates a caterpillar track-inspired design to promote the restoration of natural movement to the joint. Surface modifications of PCU have been proposed for the biological fixation of the implant. This study investigated the biocompatibility of PCU alone or in combination with two surface modifications, namely dopamine-carboxymethylcellulose (dCMC) and calcium-phosphate (CaP) coatings. In a rat soft tissue model, native and CaP-coated PCU foils did not increase cellular migration or cytotoxicity at the implant-soft tissue interface after 3 d, showing gene expression of proinflammatory cytokines similar to that in non-implanted sham sites. However, dCMC induced an amplified initial inflammatory response that was characterized by increased chemotaxis and cytotoxicity, as well as pronounced gene activation of proinflammatory macrophages and neoangiogenesis. By 21 d, inflammation subsided in all the groups, allowing for implant encapsulation. In a rat bone model, 6 d and 28 d after release of the periosteum, all implant types were adapted to the bone surface with a surrounding fibrous capsule and no protracted inflammatory response was observed. These findings demonstrated the biocompatibility of native and CaP-coated PCU foils as components of APRICOTⓇ implants. STATEMENT OF SIGNIFICANCE: Hand osteoarthritis treatments require materials that minimize irritation of the delicate finger joints. Differing from existing treatments, the APRICOTⓇ implant leverages polycarbonate urethane (PCU) for minimally invasive joint replacement. This interdisciplinary, preclinical study investigated the biocompatibility of thin polycarbonate urethane (PCU) foils and their surface modifications with calcium-phosphate (CaP) or dopamine-carboxymethylcellulose (dCMC). Cellular and morphological analyses revealed that both native and Ca-P coated PCU elicit transient inflammation, similar to sham sites, and a thin fibrous encapsulation in soft tissues and on bone surfaces. However, dCMC surface modification amplified initial chemotaxis and cytotoxicity, with pronounced activation of proinflammatory and neoangiogenesis genes. Therefore, native and CaP-coated PCU possess sought-for biocompatible properties, crucial for patient safety and performance of APRICOTⓇ implant.

Hydroxyapatite synthesis and characterization from waste animal bones and natural sources for biomedical applications

Hydroxyapatites (HAps) synthesized from waste animal bones have recently gained attention due to their outstanding properties. This is because there is a need to fabricate scaffolds with desirable mechanical strength, ability to withstand high temperatures, and insoluble in solvents such as water, acetone, ethanol, and isopropyl alcohol. This study is an extensive summary of many articles on the routes of synthesis/preparation of HAp, and the optimum processing parameter, and the biomedical application areas, such as: drug administration, dental implants, bone tissue engineering, orthopedic implant coatings, and tissue regeneration/wound healing. A broad catalog of the synthesis methods (and combination methods), temperature/time, shape/size, and the calcium-to-phosphorous (Ca/P) value of diverse waste animal bone sources were reported. The alkaline hydrolysis method is proposed to be suitable for synthesizing HAp from natural sources due to the technique's ability to produce intrinsic HAp. The method is also preferred to the calcination method owing to the phase transformation that takes place at high temperatures during calcinations. However, calcinations aid in removing impurities and germs during heating at high temperatures. When compared to calcination technique, alkaline hydrolysis method results in crystalline HAp; the higher degree of crystallinity is disadvantageous to HAp bioactivity. In addition, the standardization and removal of impurities and contaminants, thorough biocompatibility to ensure clinical safety of the HAp to the human body, and improvement of the mechanical strength and toughness to match specific requirements for the various biomedical applications are the important areas for future studies.

Physicochemical Properties of Inorganic and Hybrid Hydroxyapatite-Based Granules Modified with Citric Acid or Polyethylene Glycol

This study delves into the physicochemical properties of inorganic hydroxyapatite (HAp) and hybrid hydroxyapatite-chitosan (HAp-CTS) granules, also gold-enriched, which can be used as aggregates in biomicroconcrete-type materials. The impact of granules' surface modifications with citric acid (CA) or polyethylene glycol (PEG) was assessed. Citric acid modification induced increased specific surface area and porosity in inorganic granules, contrasting with reduced parameters in hybrid granules. PEG modification resulted in a slight increase in specific surface area for inorganic granules and a substantial rise for hybrid granules with gold nanoparticles. Varied effects on open porosity were observed based on granule type. Microstructural analysis revealed increased roughness for inorganic granules post CA modification, while hybrid granules exhibited smoother surfaces. Novel biomicroconcretes, based on α-tricalcium phosphate (α-TCP) calcium phosphate cement and developed granules as aggregates within, were evaluated for compressive strength. Compressive strength assessments showcased significant enhancement with PEG modification, emphasizing its positive impact. Citric acid modification demonstrated variable effects, depending on granule composition. The incorporation of gold nanoparticles further enriched the multifaceted approach to enhancing calcium phosphate-based biomaterials for potential biomedical applications. This study demonstrates the pivotal role of surface modifications in tailoring the physicochemical properties of granules, paving the way for advanced biomicroconcretes with improved compressive strength for diverse biomedical applications.

Nano-topographical surface engineering for enhancing bioactivity of PEEK implants (in vitro-histomorphometric study)

OBJECTIVES

Dental implants are currently becoming a routine treatment decision in dentistry. Synthetic polyetheretherketone (PEEK) polymer is a prevalent component of dental implantology field. The current study aimed to assess the influence of Nd:YAG laser nano-topographical surface engineering combined with ultraviolet light or platelet rich fibrin on the bioactivity and osseointegration of PEEK implants in laboratory and animal testing model.

MATERIALS AND METHODS

Computer Aided Design-Computer Aided Manufacturing (CAD CAM) discs of PEEK were used to fabricate PEEK discs (8 mm × 3 mm) N = 36 and implant cylinders (3 mm × 6 mm) N = 72. Specimens were exposed to Nd:YAG laser at wavelength 1064 nm, and surface roughness topography/Ra parameter was recorded in nanometer using atomic force microscopy. Laser modified specimens were divided into three groups: Nd:YAG laser engineered surfaces (control), Nd:YAG laser/UV engineered surfaces and Nd:YAG laser/PRF engineered surfaces (N = 12 discs-N = 24 implants). In vitro bioactivity test was performed, and precipitated apatite minerals were assessed with X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). In vivo histomorphometric analysis was performed in rabbits with BIC% calculation.

RESULTS

Ra mean value of PEEK laser engineered surfaces was 125.179 nm. For the studied groups, XRD patterns revealed distinctive peaks of different apatite minerals that were demonstrated by SEM as dispersed surface aggregations. There was a significant increase in the BIC% from control group 56.43 (0.97) to laser/UV surfaces 77.30 (0.78) to laser/PRF 84.80 (1.29) (< 0.0001).

CONCLUSIONS

Successful engineered nano-topographical biomimetic PEEK implant could be achieved by Nd:YAG laser technique associated with improving bioactivity. The combination with UV or PRF could be simple and economic methods to gain more significant improvement of PEEK implant surface bioactivity with superior osteointegration.

Synthesis, Characterization, In Vitro Cytological Responses, and In Vivo Bone Regeneration Effects of Low-Crystalline Nanocarbonated Hydroxyapatite

Hydroxyapatite (HA) has been commonly used as an alternative bone substitute. But it has drawbacks, such as poor degradation and limited osteogenesis. Low-crystalline carbonated hydroxyapatite (L-CHA), which has greater biodegradability than HA, is suggested as one of the main components of bone minerals, but the exact mechanism behind the roles of carbonate substituted in biological behaviors of low-crystalline HA is still a mystery. In this study, L-CHAs with different carbonate contents were prepared, and the effects of the content on the physicochemical properties, in vitro cytological responses, and in vivo bone defects repair effects of L-CHAs were investigated. The results demonstrated that CO₃^2- had successfully entered the lattice structure of L-CHAs with a maximum content of 9.2 wt %. Both low-crystalline undoped HA (L-HA) and L-CHAs were nanocrystalline (20-30 nm) with significantly higher specific surface areas, protein adsorption capacities, and biodegradability compared to high-crystalline HA (H-HA) with submicron crystalline size (200-400 nm). Besides, the amounts of the adsorbed protein and released Ca²⁺ ions increased in a carbonate-content-dependent manner. Compared to L-HA and H-HA, L-CHAs promoted the adhesion and proliferation of bone marrow mesenchymal stem cells and significantly upregulated the levels of alkaline phosphatase (ALP) activity and the expression of osteogenesis-related genes. In addition, L-CHA-9 not only showed a faster biodegradation rate but also effectively promoted bone regeneration when implanted in the critical-sized bone defects of rabbit femora. This study provided evidence for the development of L-CHA as a promising biodegradable and bioactive material with great osteoconductivity and osteogenic capability with respect to conventional HA.

The Cytokine and Bone Protein Expression by Ellagic Acid-Hydroxyapatite in Bone Remodelling Model

Objective

Ellagic acid, a phenolic compound with anti-inflammatory potential, can be used to accelerate the bone healing process and affect human health, while hydroxyapatite is the most commonly used bone graft material. Using a combination of the two materials results in reduced inflammation and increased osteogenesis. This study aimed to determine the effects of combining ellagic acid and hydroxyapatite in bone marker remodelling by analysing the expression of tumour necrosis factor-α (TNF-α), interleukin 10 (IL-10), bone morphogenetic 4 protein (BMP-4), and osteopontin (OPN).

Methods

Thirty Wistar rats were used in the study. A defect was created in each animal's femur using a low-speed diamond bur. In the control group, the bone was then treated with polyethylene glycol (PEG). In one of the other groups, the bone was treated with hydroxyapatite, and in the other, with ellagic acid-hydroxyapatite. The femur was biopsied 7 days after the procedure and again 14 days after the procedure, and an indirect immunohistochemical (IHC) examination was performed for TNF-α, IL-10, BMP-4, and OPN expression.

Results

The ellagic acid-hydroxyapatite decreased TNF-α expression in the bone tissue after 7 days and again after 14 days (p < 0.05). On the other hand, it increased IL-10, BMP-4, and OPN expression (p < 0.05) during the same time periods.

Conclusion

Ellagic acid-hydroxyapatite plays a role in bone marker remodelling by decreasing the expression of TNF-α and increasing the expression of IL-10, BMP-4, and OPN. This hydroxyapatite combination can therefore be recommended for use as bone graft material.

Titanium Implant Surface Effects on Adherent Macrophage Phenotype: A Systematic Review

Immunomodulatory biomaterials have the potential to stimulate an immune response able to promote constructive and functional tissue remodeling responses as opposed to persistent inflammation and scar tissue formation. As such, the controlled activation of macrophages and modulation of their phenotype through implant surface modification has emerged as a key therapeutic strategy.

METHODS

Online databases were searched for in vitro studies between January 1991 and June 2020 which examined the effect of titanium implant surface topography on the adherent macrophage phenotype at either the gene or protein level.

RESULTS

Thirty-nine studies were subsequently included for review. Although there was significant heterogeneity between studies, treatment of titanium surfaces increased the surface roughness or hydrophilicity, and hence increased macrophage attachment but decreased cell spreading. Physical coating of the titanium surface also tended to promote the formation of cell clusters. Titanium and titanium-zirconium alloy with a micro- or nano-scale rough topography combined with a hydrophilic surface chemistry were the most effective surfaces for inducing an anti-inflammatory phenotype in adherent macrophages, as indicated by significant changes in cytokine gene expression and or cytokine secretion profiles.

CONCLUSIONS

The published data support the hypothesis that incorporation of specific topographical and physiochemical surface modifications to titanium can modulate the phenotypic response of adherent macrophages.

Synthetic amorphous calcium phosphates (ACPs): preparation, structure, properties, and biomedical applications

Amorphous calcium phosphates (ACPs) represent a metastable amorphous state of other calcium orthophosphates (abbreviated as CaPO₄) possessing variable compositional but rather identical glass-like physical properties, in which there are neither translational nor orientational long-range orders of the atomic positions. In nature, ACPs of a biological origin are found in the calcified tissues of mammals, some parts of primitive organisms, as well as in the mammalian milk. Manmade ACPs can be synthesized in a laboratory by various methods including wet-chemical precipitation, in which they are the first solid phases, precipitated after a rapid mixing of aqueous solutions containing dissolved ions of Ca²⁺ and PO₄^3- in sufficient amounts. Due to the amorphous nature, all types of synthetic ACPs appear to be thermodynamically unstable and, unless stored in dry conditions or doped by stabilizers, they tend to transform spontaneously to crystalline CaPO₄, mainly to ones with an apatitic structure. This intrinsic metastability of the ACPs is of a great biological relevance. In particular, the initiating role that metastable ACPs play in matrix vesicle biomineralization raises their importance from a mere laboratory curiosity to that of a reasonable key intermediate in skeletal calcifications. In addition, synthetic ACPs appear to be very promising biomaterials both for manufacturing artificial bone grafts and for dental applications. In this review, the current knowledge on the occurrence, structural design, chemical composition, preparation, properties, and biomedical applications of the synthetic ACPs have been summarized.

Biomimetic Calcium Phosphate Coatings for Bioactivation of Titanium Implant Surfaces: Methodological Approach and In Vitro Evaluation of Biocompatibility

Ti6Al4V as a common implant material features good mechanical properties and corrosion resistance. However, untreated, it lacks bioactivity. In contrast, coatings with calcium phosphates (CaP) were shown to improve cell-material interactions in bone tissue engineering. Therefore, this work aimed to investigate how to tailor biomimetic CaP coatings on Ti6Al4V substrates using modified biomimetic calcium phosphate (BCP) coating solutions. Furthermore, the impact of substrate immersion in a 1 M alkaline CaCl2 solution (pH = 10) on subsequent CaP coating formation was examined. CaP coatings were characterized via scanning electron microscopy, x-ray diffraction, energy-dispersive x-ray spectroscopy, and laser-scanning microscope. Biocompatibility of coatings was carried out with primary human osteoblasts analyzing cell morphology, proliferation, collagen type 1, and interleukin 6 and 8 release. Results indicate a successful formation of low crystalline hydroxyapatite (HA) on top of every sample after immersion in each BCP coating solution after 14 days. Furthermore, HA coating promoted cell proliferation and reduced the concentration of interleukins compared to the uncoated surface, assuming increased biocompatibility.

Nanofibrillar cellulose wound dressing supports the growth and characteristics of human mesenchymal stem/stromal cells without cell adhesion coatings

BACKGROUND

In the field of regenerative medicine, delivery of human adipose-derived mesenchymal stem/stromal cells (hASCs) has shown great promise to promote wound healing. However, a hostile environment of the injured tissue has shown considerably to limit the survival rate of the transplanted cells, and thus, to improve the cell survival and retention towards successful cell transplantation, an optimal cell scaffold is required. The objective of this study was to evaluate the potential use of wood-derived nanofibrillar cellulose (NFC) wound dressing as a cell scaffold material for hASCs in order to develop a cell transplantation method free from animal-derived components for wound treatment.

METHODS

Patient-derived hASCs were cultured on NFC wound dressing without cell adhesion coatings. Cell characteristics, including cell viability, morphology, cytoskeletal structure, proliferation potency, and mesenchymal cell and differentiation marker expression, were analyzed using cell viability assays, electron microscopy, immunocytochemistry, and quantitative or reverse transcriptase PCR. Student's t test and one-way ANOVA followed by a Tukey honestly significant difference post hoc test were used to determine statistical significance.

RESULTS

hASCs were able to adhere to NFC dressing and maintained high cell survival without cell adhesion coatings with a cell density-dependent manner for the studied period of 2 weeks. In addition, NFC dressing did not induce any remarkable cytotoxicity towards hASCs or alter the morphology, proliferation potency, filamentous actin structure, the expression of mesenchymal vimentin and extracellular matrix (ECM) proteins collagen I and fibronectin, or the undifferentiated state of hASCs.

CONCLUSIONS

As a result, NFC wound dressing offers a functional cell culture platform for hASCs to be used further for in vivo wound healing studies in the future.

TGF-β mediates thoracic radiation-induced abscopal effects of testis injury in rat

To investigate the thoracic irradiation induced abscopal effect on distal testes and the underlying inflammatory factors, the rats were irradiated on right thorax with fractionated doses. It was found the testes structures were damaged including disorder of spermatogenic cell arrangement and decrease of sperm number. Moreover, the expressions of caspase-3 and caspase-8 in testis tissue were enhanced, and the concentrations of TGF-β and TNF-α in the rat serum were increased. When TM4 cells were treated with the conditioned medium (CS) collected from irradiated rat, the cellular ROS and apoptosis was significantly increased. When the CS was neutralized with anti-TGF-β, its toxic effects were reduced. These results suggest that the thoracic irradiation-induced TGF-β was involved in the above abscopal damage of testes, which reinforces the necessity of new prevention strategy development of radiotherapy in avoiding any abnormal genetic consequence.

Ion-substituted calcium phosphate coatings by physical vapor deposition magnetron sputtering for biomedical applications: A review

Coatings based on ion-substituted calcium phosphate (Ca-P) have attracted great attention in the scientific community over the past decade for the development of biomedical applications. Among such Ca-P based structures, hydroxyapatite (HA) has shown significant influence on cell behaviors including cell proliferation, adhesion, and differentiation. These cell behaviors determine the osseointegration between the implant and host bone and the biocompatibility of implants. This review presents a critical analysis on the physical vapor deposition magnetron sputtering (PVDMS) technique that has been used for ion-substituted Ca-P based coatings on implants materials. The effect of PVDMS processing parameters such as discharge power, bias voltage, deposition time, substrate temperature, and post-heat treatment on the surface properties of ion-substituted Ca-P coatings is elucidated. Moreover, the advantages, short comings and future research directions of Ca-P coatings by PVDMS have been comprehensively analyzed. It is revealed that the topography and surface chemistry of amorphous HA coatings influence the cell behavior, and ion-substituted HA coatings significantly increase cell attachment but may result in a cytotoxic effect that reduces the growth of the cells attached to the coating surface areas. Meanwhile, low-crystalline HA coatings exhibit lower rates of osteogenic cell proliferation as compared to highly crystalline HA coatings developed on Ti based surfaces. PVDMS allows a close reproduction of bioapatite characteristics with high adhesion strength and substitution of therapeutic ions. It can also be used for processing nanostructured Ca-P coatings on polymeric biomaterials and biodegradable metals and alloys with enhanced corrosion resistance and biocompatibility. STATEMENT OF SIGNIFICANCE: Recent studies have utilized the physical vapor deposition magnetron sputtering (PVDMS) for the deposition of Ca-P and ion-substituted Ca-P thin film coatings on orthopedic and dental implants. This review explains the effect of PVDMS processing parameters, such as discharge power, bias voltage, deposition time, substrate temperature, and post-heat treatment, on the surface morphology and crystal structure of ion-substituted Ca-P and ion-substituted Ca-P thin coatings. It is revealed that coating thickness, surface morphology and crystal structure of ion-substituted Ca-P coatings via PVDMS directly affect the biocompatibility and cell responses of such structures. The cell responses determine the osseointegration between the implant and host bone and eventually the success of the implants.

A critical review of multifunctional titanium surfaces: New frontiers for improving osseointegration and host response, avoiding bacteria contamination

Evolution of metal implants progressively shifted the focus from adequate mechanical strength to improved biocompatibility and absence of toxicity and, finally, to fast osseointegration. Recently, new frontiers and challenges of Ti implants have been addressed to improvement of bioactivity, fighting of bacterial infection and biofilm formation, as well as modulation of inflammation. This is closely related to the clinical demand of multifunctional implants able to simultaneously have a number of specific responses with respect to body fluids, cells (osteoblasts, fibroblasts, macrophages) and pathogenic agents (bacteria, viruses). This complex system of multiple biological stimuli and surface responses is a major arena of the current research on biomaterials and biosurfaces. This review covers the strategies explored to this purpose since 2010 in the case of Ti and Ti alloys, considering that the number of related papers doubled about in the last seven years and no review has comprehensively covered this engaging research area yet. The different approaches followed for producing multifunctional Ti-based surfaces involve the use of thick and thin inorganic coatings, chemical surface treatments, and functionalization strategies coupled with organic coatings.

STATEMENT OF SIGNIFICANCE

According to the clinical demand of multifunctional implants able to simultaneously have a number of specific responses with respect to body fluids, cells and pathogenic agents, new frontiers of Ti implants have been addressed to improvement of bioactivity, fighting of bacterial infection and biofilm formation, as well as modulation of inflammation. Literature since 2010 is here reviewed. Several strategies for getting bioactive and antibacterial actions on Ti surfaces have been suggested, but they still need to be optimized with respect to several concerns. A further step will be to combine on the same surface a proven ability of modulation of inflammatory response. The achievement of multifunctional surfaces able to modulate inflammation and to promote osteogenesis is a grand challenge.

Delivery of Mesenchymal Stem Cells from Gelatin-Alginate Hydrogels to Stomach Lumen for Treatment of Gastroparesis

Gastroparesis (GP) is associated with depletion of interstitial cells of Cajal (ICCs) and enteric neurons, which leads to pyloric dysfunction followed by severe nausea, vomiting and delayed gastric emptying. Regenerating these fundamental structures with mesenchymal stem cell (MSC) therapy would be helpful to restore gastric function in GP. MSCs have been successfully used in animal models of other gastrointestinal (GI) diseases, including colitis. However, no study has been performed with these cells on GP animals. In this study, we explored whether mouse MSCs can be delivered from a hydrogel scaffold to the luminal surfaces of mice stomach explants. Mouse MSCs were seeded atop alginate-gelatin, coated with poly-l-lysine. These cell-gel constructs were placed atop stomach explants facing the luminal side. MSCs grew uniformly all across the gel surface within 48 h. When placed atop the lumen of the stomach, MSCs migrated from the gels to the tissues, as confirmed by positive staining with vimentin and N-cadherin. Thus, the feasibility of transplanting a cell-gel construct to deliver stem cells in the stomach wall was successfully shown in a mice stomach explant model, thereby making a significant advance towards envisioning the transplantation of an entire tissue-engineered 'gastric patch' or 'microgels' with cells and growth factors.