Repair of calvarial defects in rats by prefabricated hydroxyapatite cement implants

3D printing of ceramic-based scaffolds for bone tissue engineering: an overview

Currently, one of the most promising strategies in bone tissue engineering focuses on the development of biomimetic scaffolds. Ceramic-based scaffolds with favorable osteogenic ability and mechanical properties are promising candidates for bone repair. Three-dimensional (3D) printing is an additive manufacturing technique, which allows the fabrication of patient-specific scaffolds with high structural complexity and design flexibility, and gains growing attention. This review aims to highlight advances in 3D printing of ceramic-based scaffolds for bone tissue engineering. Technical limitations and practical challenges are emphasized and design considerations are also discussed.

Tenting effect of the elevated sinus membrane over an implant with adjunctive use of a hydroxyapatite-powdered collagen membrane in rabbits

PURPOSE

The aim of this study was to determine the de novo bone formation beneath the Schneiderian membrane supported by an implant and with the adjunctive use of a hydroxyapatite-powdered collagen (HAC) membrane without bone grafting in rabbit sinuses.

MATERIAL AND METHODS

After sinus-floor elevation procedure, an experimentally devised mini-implant (4 mm in length and 3 mm in diameter) was placed in eight rabbits. For the experimental group, an HAC membrane was placed onto the elevated sinus mucosa prior to implant placement. The animals were allowed a healing period of either 4 or 8 weeks. Microcomputed tomography and histologic analyses were performed.

RESULTS

All implants placed at the thin lateral bony wall were histologically osseointegrated. The topography of the newly formed bone appeared to slope gently from the medial side down to the lateral side. The volume of new bone was significantly greater in the experimental group than in the control group at 4 weeks (P < 0.05), but not at 8 weeks. However, none of the samples in the two groups was entirely covered to the apex by bone tissue.

CONCLUSIONS

It can be concluded that using the HAC membrane in combination with placement of an implant resulted in substantial bone formation around the implant, which might have been influenced by the proximity of the axial bony wall.

Structure, properties and animal study of a calcium phosphate/calcium sulfate composite cement

In-vitro and in-vivo studies have been conducted on an in-house-developed tetracalcium phosphate (TTCP)/dicalcium phosphate anhydrous (DCPA)/calcium sulfate hemihydrate (CSH)-derived composite cement. Unlike most commercial calcium-based cement pastes, the investigated cement paste can be directly injected into water and harden without dispersion. The viability value of cells incubated with a conditioned medium of cement extraction is >90% that of Al2O3 control and >80% that of blank medium. Histological examination reveals excellent bonding between host bone and cement without interposition of fibrous tissues. At 12 weeks-post implantation, significant remodeling activities are found and a new bone network is developed within the femoral defect. The 26-week samples show that the newly formed bone becomes more mature, while the interface between residual cement and the new bone appears less identifiable. Image analysis indicates that the resorption rate of the present cement is much higher than that of TTCP or TTCP/DCPA-derived cement under similar implantation conditions.

Setting solution concentration effect on properties of a TTCP/DCPA-derived calcium phosphate cement

The present work was to investigate the effects of concentration of (NH(4))(2)HPO(4) (diammonium hydrogen phosphate) setting solution on properties of a tetracalcium phosphate (TTCP)/dicalcium phosphate anhydrous (DCPA)--derived calcium phosphate cement. Experimental results indicated that working/setting time of the cement paste decreased with increasing (NH(4))(2)HPO(4) concentration of the setting solution. After being immersed in Hanks' solution for 1 day or longer, the XRD intensities of initial TTCP and DCPA phases largely decreased, while apatite phase became dominant. More residual TTCP phase was observed in the 1 day-immersed cement prepared from higher concentration setting solutions. Compressive strength of the cement immersed for 1 day was consistently higher than that immersed for 30 min or 7 days. After being immersed for 1 day, the average CS value reached a maximal value (59 MPa) as (NH(4))(2)HPO(4) concentration was increased to 0.6 M, beyond that the cement strength decreased and maintained in a relatively high range of 47-54 MPa. Cells incubated with conditioned medium of Al(2)O(3) powder and with blank medium exhibited similar average viability values (0.80 and 0.78, respectively). The OD value with extractions of cement decreased with increasing (NH(4))(2)HPO(4) concentration of the setting solution. The average 0.25, 0.5 and 0.6 M--OD values were 0.78, 0.67 and 0.66, respectively. When setting solution concentration was greater than 0.6 M, the OD value sharply declined to 0.47.

Preparation and properties of calcium phosphate cements incorporated gelatin microspheres and calcium sulfate dihydrate as controlled local drug delivery system

To develop high macroporous and degradable bone cements which can be used as the substitute of bone repairing and drug carriers, cross-linked gelatin microspheres (GMs) and calcium sulfate dihydrate (CSD) powder were incorporated into calcium phosphate bone cement (CPC) to induce macropores, adjust drug release and control setting time of α-TCP-liquid mixtures after degradation of GMs and dissolution of CSD. In this study, CSD was introduced into CPC/10GMs composites to offset the prolonged setting time caused by the incorporation of GMs, and gentamicin sulphate (GS) was chosen as the model drug entrapped within the GMs. The effects of CSD amount on the cement properties, drug release ability and final macroporosity after GMs degradation were studied in comparison with CPC/GMs cements. The resulting cements presented reduced setting time and increased compressive strength as the content of CSD below 5 wt%. Sustained release of GS was obtained on at least 21 days, and release rates were found to be chiefly controlled by the GMs degradation rate. After 4 weeks of degradation study, the resulting composite cements appeared macroporous, degradable and suitable compressive strength, suggesting that they have potential as controlled local drug delivery system and for cancellous bone applications.

Brushite-Forming Mg-, Zn- and Sr-Substituted Bone Cements for Clinical Applications

Calcium phosphate cements have been in clinical use for the last 10 years. Their most salient features include good biocompatibility, excellent bioactivity, self-setting characteristics, low setting temperature, adequate stiffness, and easy shaping to accomodate any complicated geometry. They are commonly used in filling bone defects and trauma surgeries as mouldable paste-like bone substitute materials. Substitution of trace elements, such as Mg, Sr and Zn ions, into the structure of calcium phosphates is the subject of widespread investigation nowadays, because of their impending role in the biological process. Subtle differences in composition and structure of these materials may have a profound effect on their in vivo behaviour. Therefore, the main goal of this paper is to provide a simple, but comprehensive overview of the present achievements relating to brushite-forming cements doped with Mg, Zn and Sr, and to identify new developments and trends. In particular, the influence of ionic substitution on the chemical, physical and biological properties of these materials is discussed.

Creation of macroporous calcium phosphate cements as bone substitutes by using genipin-crosslinked gelatin microspheres

Macroporous calcium phosphate cements (CPCs) were developed using genipin-crosslinked gelatin microspheres (GMs) with two weight ratios (2.5 wt% and 5 wt%). The initial setting time of the composite was prolonged by GMs. After GMs/CPCs were soaked in phosphate-buffered saline (PBS) for several weeks, macropores appeared as a result of the degradation of GMs. The presence of GMs accelerated the setting reaction and improved the structure of the composite. The compressive strength increased up to 12 MPa (2.5 wt% GMs/CPCs) and 14 MPa (5 wt% GMs/CPCs) after one week of PBS soaking, then gradually decreased to 9 MPa (2.5 wt% GMs/CPCs) and 7 MPa (5 wt% GMs/CPCs) after three weeks of soaking, and further to 6 MPa (2.5 wt% GMs/CPCs) and 2 MPa (5 wt% GMs/CPCs) after five weeks of soaking. CPCs with 2.5 wt% GMs were the most favorable composite in the tested samples. Cell experiments showed that rat osteoblasts displayed normal morphologies when exposed to the 2.5 wt% GMs/CPCs, and proliferation of the cells was also enhanced. An in vivo study showed that new bone tissue was able to grow into the pores that resulted from GM degradation. This study suggests that the new composite could be a promising candidate for use as a bone substitute under non-compression-loaded circumstances.

Morphology and mechanical behavior of TTCP-derived calcium phosphate cement subcutaneously implanted in rats

A pre-hardened, TTCP-derived CPC was immersed in Hanks' solution as well as subcutaneously implanted into abdomen of rats. The implant-soft tissue interfacial morphology was examined and properties of the CPC were evaluated and compared under in vitro and in vivo conditions. The results indicate that the surface of immersed samples appeared rougher and more porous than that of implanted samples and was covered with a layer of fine apatite crystals. The CPC samples implanted for 4 weeks or longer were surrounded by a layer of fibrous tissue, which was further surrounded by a soft tissue capsule comprising numerous fat cells. The soft tissue capsule had a non-uniform distribution in thickness, which increased most significantly between 4 weeks and 12 weeks after implantation. None of polymorphic cells, osteoblast cells or bone cells adjacent to the implant were observed. The majority of original TTCP powder was transformed into apatite after 1 day of either immersion in Hanks' solution or implantation. The average porosity values of samples immersed in Hanks' solution for 4 weeks or longer were significantly larger than those immersed for 1 day or 1 week. The porosity values of samples implanted for different times were not significantly different. The DTS values of Hanks' solution-immersed samples largely decreased after a few weeks of immersion. The implanted samples maintained their strengths throughout the study.

Porous poly(DL-lactic-co-glycolic acid)/calcium phosphate cement composite for reconstruction of bone defects

Calcium phosphate (Ca-P) cements are injectable, self-setting ceramic pastes generally known for their favorable bone response. Ingrowth of bone and subsequent degradation rates can be enhanced by the inclusion of macropores. Initial porosity can be induced by CO(2) foaming during setting of the cement, whereas secondary porosity can develop after hydrolysis of incorporated poly(DL-lactic- co-glycolic acid) (PLGA) microparticles. In this study, we focused on the biological response to porous PLGA/Ca-P cement composites. Pre-set composite discs of four formulations (4 wt% or 15 wt% PLGA microparticles and low or high CO(2) induced porosity) were implanted subcutaneously and in cranial defects in rats for 12 weeks. Histological analysis of the explanted composites revealed that bone and fibrous tissue ingrowth was facilitated by addition of PLGA microparticles (number average diameter of 66 +/- 25 microm). No adverse tissue reaction was observed in any of the composites. Significant increases in composite density due to bone ingrowth in cranial implants were found in all formulations. The results suggest that the PLGA pores are suitable for bone ingrowth and may be sufficient to enable complete tissue ingrowth without initial CO(2) induced porosity. Finally, bone-like mineralization in subcutaneous implants suggests that, under appropriate conditions and architecture, porous PLGA/Ca-P cement composites can exhibit osteoinductive properties. These PLGA/Ca-P composites are a promising scaffolding material for bone regeneration and bone tissue engineering.

Craniofacial bone tissue engineering

Repair and reconstruction of the craniofacial skeleton represents a significant biomedical burden, with thousands of procedures per-formed annually secondary to injuries and congenital malformations. Given the multitude of current approaches, the need for more effective strategies to repair these bone deficits is apparent. This article explores two major modalities for craniofacial bone tissue engineering: distraction osteogenesis and cellular based therapies. Current understanding of the guiding principles for each of these modalities is elaborated on along with the knowledge gained from clinical and investigative studies. By laying this foundation, future directions for craniofacial distraction and cell-based bone engineering have emerged with great promise for the advancement of clinical practice.

New developments in pediatric plastic surgery research

Pediatric plastic surgery research is a rapidly expanding field. Unique in many ways, researchers in this field stand at the union of multiple scientific specialties, including biomedical engineering, tissue engineering, polymer science, molecular biology, developmental biology, and genetics. The goal of this scientific effort is to translate research advances into improved treatments for children with congenital and acquired defects. Although the last decade has seen a dramatic acceleration in research related to pediatric plastic surgery, the next 10 years will no doubt lead to novel treatment strategies with improved clinical outcomes.