Papers by Author: Larry L. Hench

Abstract: Historically the function of biomaterials has been to replace diseased, damaged and aged tissues. First generation biomaterials, including bio ceramics, were selected to be as inert as possible in order to minimize the thickness of interfacial scar tissue. Bioactive glasses provided an alternative from the 1970’s onward; second generation bioactive bonding of implants with tissues and no interfacial scar tissue. This chapter reviews the discovery that controlled release of biologically active Ca and Si ions from bioactive glasses leads to the up-regulation and activation of seven families of genes in osteoprogenitor cells that give rise to rapid bone regeneration. This finding offers the possibility of creating a new generation of gene activating bioceramics designed specially for tissue engineering and in situ regeneration of tissues.

Abstract: Autogenous bone grafts are considered to be the gold standard in maxillo-facial surgery. However, drawbacks of donor site morbidity and unpredictable rates of resorbtion often limit their use. In vivo tests have shown that 45S5 bioactive glass particles placed in critical size bone defects lead to regeneration of new bone that has the structural characteristics and architecture of mature trabecular bone. In vitro tests using primary osteoblast cultures have shown that the bioactive glass particles release ionic dissolution products that provide genetic stimuli that control osteoblast cell cycles and lead to rapid growth of mineralized bone nodules. These in vitro and in vivo results led to approval of use of bioactive glass particles and monolithic bioactive glass implants for use in maxillo-facial reconstructions after removal of bone cysts and trauma, as described by several case histories.

Abstract: Calcium carbonate (vaterite)-containing poly(lactic acid) (PLA) composites (CCPCs) were prepared for novel biomaterials that are expected to exhibit high bioresorbability and osteoconductivity. CCPC containing 30% vaterite showed bending strengths of 40~50 MPa. 13C CP/MAS-NMR spectrum of CCPC suggested the formation of a bond between Ca2+ ion and COOgroup. The bond may play an important role in the improvement of the mechanical properties. On the surface of CCPC containing 30 % vaterite, ~10-μm-thick hydroxycarbonate apatite (HCA) formed after 1 day of soaking in SBF at 37oC. After 1-week incubation of human osteoblasts (HOBs) on the HCA-coated CCPC, numerous HOBs attached. The adhesion of cells on the composite was greater than that on PLA. After 3-week culture of HOBs on HA-coated CCPC, numerous bone nodules could be seen on the surface. CCPC is believed to be one of the most promising materials for bone repair. A novel CCPC containing polysiloxane was also prepared using aminopropyltriethoxysilane (APTES). Polysiloxane partially assembled in the membrane and a molecular chain of PLA was bonded at the end of an organic chain in APTES through the amide bond formed between carboxy groups in PLA and amino groups in APTES. The composite formed HA on its surface after 3 days of soaking in SBF. The HA layer included Si with Ca and P. The composite coated with silicon-containing HCA had higher cell-proliferation ability than that without HA. The existence of silicon-containing HCA may be apt to stimulate the proliferation.

Abstract: A novel poly(lactic acid) (PLA)/calcium carbonates hybrid membrane containing silica was prepared using aminopropyltriethoxysilane (APTES) for biodegradable bone guided regeneration. Carboxy groups in PLA made a chemical bond with amino groups in APTES, resulting in the formation of the hybrid membrane. The silica-hybridized PLA was an amorphous phase. The membrane formed hydroxycarbonate apatite (HCA) on its surface after 3 d of soaking in simulated body fluid (SBF). After soaking the membrane in SBF, almost no Si was present in SBF. X-ray energy dispersive spectroscopy showed the HCA layer includes Si with Ca and P. A result of osteoblast-like cellular proliferation on the membrane showed no cell-toxicity.

Abstract: The possibility of enhancing mechanical properties by incorporation of polymeric components to sol-gel derived materials is extremely attractive to prepare macroporous scaffolds, leading to materials with potential applications in both hard and soft tissue regeneration. In this work bioactive glass-polyvinyl alcohol hybrids were developed and their mechanical behavior was evaluated. Hybrids were synthesized by adding polyvinyl alcohol to a sol-gel precursor solution, which was then foamed with the addition of a surfactant and vigorous agitation. The foams were cast, aged and dried at 40°C. A cleaning step to decrease the acidic character of the obtained hybrids was undertaken by immersion in a NH4OH solution. The mechanical behavior of the hybrids was evaluated in compression using both stress and strain control tests. Hybrid foams had a high porosity varying from 60-90% and the macropore diameter ranged from 10 to 600 µm. The modal macropore diameter varied with the inorganic phase composition and with the polymer content in the hybrid. The strain at fracture of the as prepared hybrid foams was substantially greater than pure gel-glass foams. The cleaned hybrids presented a slightly higher strength and lower deformation than the as prepared foams.

Abstract: 60CaO-30P2O5-7Na2O-3TiO2 (mol%) glass-ceramic can be strongly joined with a new β-type Ti-29Nb-13Ta-4.6Zr alloy. In the present work apatite-forming ability in simulated body fluid of the glass-ceramic-coated titanium alloy was enhanced by autoclaving in water at 120°C for 1 h; surface of the autoclaved coating was completely covered with apatite after 10 days of soaking. In vivo tests showed that the glass-ceramic-coated titanium alloy after autoclaving in water makes a strong bond to natural bone.

Abstract: Septal cartilage is widely used for the repair of soft tissue defects in the head, neck and nose. Tissue Engineering techniques are being investigated to create cartilage in vitro by seeding appropriate cells on resorbable scaffolds. In this study, human chondrocytes were cultured on macroporous bioactive glass foam scaffolds. The aim was to investigate how Raman spectroscopy could be used as a non-invasive technique to monitor the response of chondrocytes to a 3D scaffold in real time. The spectra were compared to scanning electron microscope (SEM) micrographs and immunohistochemistry results.

Abstract: Hybrid bioactive glass-polyvinyl alcohol foams for use as scaffolds in tissue engineering were developed through the sol-gel route. Hybrids produced by this route present a high acidic character due to the catalysts added during processing and may also contain residual organics after the drying step. Therefore, an additional cleaning step is necessary to produce biocompatible materials. In this study hybrid PVA/bioactive glass foams were cleaned using various procedures and cytotoxicity evaluation was conducted. All the cleaning methods used increased the cell viability levels compared to samples not subjected to a cleaning procedure. The most effective cleaning procedure used was the immersion in NH4OH solution. The cleaning procedure changed the composition and pore structure of the final material.

Abstract: The Classical Least Square (CLS) fitting method was used to analyze the Raman spectra of living cells with the aim of identification of new phenotype-specific spectral markers for osteoblasts. The following chemicals were used for the CLS model: DNA, RNA, serum albumin, chymotrypsin and phosphatidyl choline. In this study we analyzed primary mature osteoblasts as well as two other cell types used as potential sources of osteoblasts: embryonic stem cells and fetal bone cells. The results obtained suggest that the Raman spectra of the cell types can be well approximated with a linear combination of the Raman spectra of the biopolymers used in the CLS model. The relative concentrations of the CLS components varied significantly between cell types, indicating that this analytical method could be used for phenotypic identification of osteoblasts.

Abstract: We present a new bio-photonic method based on Raman spectroscopy able to characterize living cells in in-vitro cultures. The main advantages of this technology are: no labels or other contrast enhancers are required; provides real-time analysis; cells can be maintained in physiological conditions during the measurements; no cell-damage is induced during the measurements; it is rich in information about the biochemical composition of the cell. The results show that this spectroscopic method can be used to study the most important cellular functions involved in cell-biomaterial interactions, such as cell death, differentiation, de-differentiation and mineralization. The method offers the potential for studying cell-bioceramics interaction and reduce the need of animal testing until the final steps of proving efficacy prior to clinical trials.